Stardate Podcast

The crew of Apollo 15 had a spectacular view. The astronauts landed at the edge of a deep canyon, near the base of some of the tallest mountains on the Moon. For scientists, the site offered a chance to study several eras of lunar geology. Dave Scott, Jim Irwin, and Al Worden headed for the Moon on July 26th, 1971. LAUNCH CONTROL: 4, 3, 2, 1, all engines running. Launch commit. Liftoff! We have liftoff ... They entered lunar orbit 50 years ago today, aboard their command module, Endeavour. APOLLO 15: Hello, Houston, the Endeavour is on station with cargo, and what a fantastic sight. CAPCOM: Beautiful news! Romantic, isn't it? The next day, Scott and Irwin boarded the lunar module, Falcon, and headed for the surface. FALCON: Eight feet, minus one. Contact! Man! Okay, Houston, Falcon is on the plain at Hadley. CAPCOM: Roger roger, Falcon. The site was ringed by the Apennine Mountains, which are almost three miles high. They formed when an asteroid slammed into the Moon four billion years ago. Shockwaves piled up layers of rock. So geologists hoped the base of the mountains might offer samples of the Moon's early crust. The site also offered details on the impact. Falcon landed at the edge of Hadley Rille, a canyon a mile wide and a quarter of a mile deep. It probably formed when a lava tube collapsed. So it offered a chance to study recent volcanic activity — at one of the most spectacular sites on the Moon. More tomorrow.  Script by Damond Benningfield Support McDonald Observatory

Our closest neighbor star is a bare cosmic ember. It's much lighter and smaller than the Sun, and less than one ten-thousandth as bright. Yet the star produces giant explosions that are much more powerful than anything ever seen from the Sun. An outburst two years ago, in fact, was the brightest from any star at some wavelengths. Proxima Centauri is just four-and-quarter light-years away, but it's too faint to see without a telescope. The star is put together a little differently from the Sun. A conveyor-belt effect carries hot gas from the core to the surface, where it cools and falls back toward the core. This motion generates a powerful magnetic field. As the star spins, the lines of magnetic force get tangled. When they cross, they snap, producing massive eruptions. Proxima has produced many such outbursts over the years. But one in May of 2019 beat them all. Astronomers recorded a flare that lasted just seven seconds. At visible wavelengths, though, it was a hundred times brighter than any flare seen from the Sun. And it was even brighter in X-rays and ultraviolet light — the brightest ever seen from any star. Two planets orbit Proxima Centauri. One of them is at a comfortable distance from the star for life. But getting zapped by such powerful radiation is dangerous. So if anything lives on the planet, it most likely would have to be quite different from life on Earth to survive such powerful outbursts.  Script by Damond Benningfield Support McDonald Observatory

Our planet appears to be in one of the safest neighborhoods in the Milky Way Galaxy. We're away from the regions where deadly exploding stars are most common. That's the finding of a study released this year. Researchers in Italy looked at the number of supernovas and gamma-ray bursts over the entire history of the galaxy. A supernova is the death of a star. It fills its region of space with radiation and particles. They can sterilize nearby planets, and be harmful at distances of dozens of light-years. A gamma-ray burst is also an exploding star. But it emits powerful beams from its poles that can zap life thousands of light-years away. The researchers found that early on, the safest region of the Milky Way was its rim, far beyond Earth. There were fewer exploding stars out there. Earth's region, about halfway out to the edge, was a little more dangerous. Over time, though, the “safe” zone moved inward. And over the last half-billion years, we've been at the outer edge of that zone. There have been more supernovas closer to the center, and more gamma-ray bursts out on the rim. In the future, the number of exploding stars in our neighborhood should keep going down — making it even safer. The Milky Way arches across the eastern evening sky now. The center of the galaxy is in the south, above the “spout” of the teapot formed by the stars of Sagittarius. That's the galaxy's danger zone — a neighborhood to avoid.  Script by Damond Benningfield Support McDonald Observatory

Monster black holes were forming when the universe was young — just a few percent of its current age. And that's a problem. Most ideas of how supermassive black holes form can't explain such a rapid birth. But a new idea says the black holes could have had some help: the gravitational pull of dark matter. Supermassive black holes are millions or billions of times as massive as the Sun. They inhabit the cores of most large galaxies, including our own. And they've been seen in galaxies that were forming as little as 800 million years after the Big Bang — 13 billion years ago. One idea says that such monster black holes formed from the collapse of giant clouds of gas and dust. Another says that smaller black holes merged to form the supermassive ones. But neither process could form a giant black hole quickly enough to match what astronomers see. The new idea says these early galaxies formed around clouds of dark matter. Dark matter produces no energy, but we see its gravitational pull on the “normal” matter around it. If there was enough dark matter, it could pull in huge amounts of normal matter in a short time. The combined matter then would collapse to form a supermassive black hole. According to this idea, supermassive black holes would form quickly — even before their home galaxies could fully take shape. So the dark monsters at the hearts of galaxies could have formed under the influence of dark matter.  Script by Damond Benningfield Support McDonald Observatory

The Moon shines big and bright tonight. It climbs into good view by about 11 p.m., and is well up in the southwest at first light tomorrow. And it has a big and bright companion: the planet Jupiter. It looks like a brilliant star to the upper left of the Moon as they rise, and to the right of the Moon at dawn. By that time, the Moon will be about two and a half days past full. So for American skywatchers, the Sun will light up about 93 or 94 percent of the lunar disk. You might think that means the Moon will be 93 or 94 percent as bright as the full Moon. And your eyes might seem to agree — since the Moon looks almost full, it must be almost as bright. This is one of those times that you can't trust your lying eyes, though. The pre-dawn Moon will be only half as bright as a full Moon. By comparison, when the Sun lights up half of the disk, it's only one-sixth as bright as a full Moon. One reason is that the lunar surface reflects sunlight most efficiently when the Moon lines up opposite the Sun — when it's full. The main reason, though, is that when the Moon is full, we don't see many shadows — the central portion of the disk is in direct sunlight. At other times, though, the Sun is at a lower angle. Mountains, the rims of craters, and even big boulders cast shadows that make the surface appear darker. And the farther the Moon is from full, the longer the shadows — and the darker the Moon looks in our sky.  Script by Damond Benningfield Support McDonald Observatory

Jupiter and Saturn are the largest planets in the solar system. Jupiter is about 11 times the diameter of Earth, while Saturn is almost 10 times Earth's diameter. Despite their size, though, they spin faster than any other planets — 10 hours for Jupiter, a bit longer for Saturn. That's compared to 24 hours for Earth. You might wonder why these giants turn so fast. But scientists wonder why they aren't faster. They should have spun a lot faster when they were born, but they slowed down. A study a couple of years ago proposed a solution. Jupiter and Saturn grew so big by gobbling up huge amounts of gas from a disk around the newborn Sun. As the gas fell onto the planets, it caused them to spin faster. Eventually, they should have been spun once every few hours — so fast that they were about to break apart. But some of the gas was directed back outward, forming a disk around each planet. The planets' magnetic fields grabbed onto the gas. That acted like a brake, slowing each planet to a much slower rate than we see today. Their own gravity quickly caused the planets to shrink, which made them spin faster — the same way a skater spins faster by pulling in its arms. That set up the rates we see today — fast or slow. Jupiter and Saturn form a wide triangle with the Moon tonight. As they climb into view in late evening, bright Jupiter is to the left of the Moon, with fainter Saturn to the upper right.  Script by Damond Benningfield Support McDonald Observatory

The Moon and Titan, the largest moon of Saturn, have something in common: The best places to get wet are at the poles. The Moon has lots of water ice. And Titan has actual liquid — lakes and seas filled not with water, but with hydrocarbons. On the Moon, the ice is mixed with dirt at the bottoms of deep craters. Sunlight never hits the crater floors, so the ice remains frozen. A recent study suggested there's more than a billion tons of ice around the poles, with most of it near the south pole. Because of that, most lunar exploration over the coming years will be targeted at the south pole. Robotic landers will sniff out and study the ice. And human explorers may use the ice for water, oxygen, and rocket fuel. On Titan, most of the wet stuff is near the north pole — about 95 percent. The largest body of liquid, the Kraken Sea, holds more than all the Great Lakes combined. Differences in climate and landscape account for some of the imbalance between the poles. But one study says the major difference is that the southern landscape is more porous. The liquid ethane and methane can drain away to lower latitudes, where they evaporate — leaving the south pole much drier than the north. And Saturn appears close to our Moon the next couple of nights. Tonight, it's to the left of the Moon as they climb into good view by 10 o'clock, and above the Moon at first light. The giant planet looks like a bright star.  Script by Damond Benningfield Support McDonald Observatory

The galaxy IC 10 is small but busy. It's only a few thousand light-years across — a small fraction of the size of the Milky Way. But pound for pound, it's giving birth to more stars than the Milky Way is. Many of those stars are big, bright, and heavy. At the ends of their short lives, they'll explode. The cores of some of those stars will collapse to form black holes. One system in the galaxy consists of a current black hole and a future one. IC 10 X-1 was the first source of X-rays discovered in the galaxy. The X-rays come from a “wind” of hot gas from the bright star, plus a disk of hot gas around the black hole. Early observations indicated the black hole was about 15 times the mass of the Sun, with its companion about 25 times the Sun's mass. But more recent work has found the masses a little tougher to pin down. The companion appears to be heavy enough to explode as a supernova, leaving behind a second black hole. The blast may send the star and the current black hole racing away from each other. If they stick together, though, in a few billion years they'll merge — forming an especially heavy black hole. IC 10 is in Cassiopeia, which is low in the northeast in early evening and overhead at first light. IC 10 is near the top right point of the “W” that outlines the queen. The galaxy is a couple of million light-years away — quite close as galaxies go. But it's so faint that you need a telescope to see it.  Script by Damond Benningfield Support McDonald Observatory

[Double booms] MISSION CONTROL: Piercing the pre-dawn skies, the space shuttle announces its arrival at the launch site with its signature sound of twin sonic booms, having gone subsonic for the last time. The space shuttle program rolled to a halt 10 years ago today. Atlantis completed the 135th shuttle mission, 30 years after the first. The shuttle had been intended to replace almost all of America's rockets. NASA promised to launch up to a flight a week. But shuttles were harder to maintain than expected. So launches were separated by months, not days. Still, the shuttle was a remarkable machine. Its crews launched and repaired satellites, including Hubble Space Telescope. They conducted experiments. And they built most of the International Space Station. But after the shuttle Columbia was destroyed during re-entry in 2003, NASA decided to ground the fleet after the space station was done. For the final flight, Atlantis carried up spare parts and scientific equipment. Then it headed home. AUDIO: three bells. ISS: Atlantis departing the International Space Station for the last time. It landed at Kennedy Space Center on July 21st, 2011. MISSION CONTROL: Nose-gear touchdown. ... Having fired the imagination of a generation, a ship like no other, its place in history secured, the space shuttle pulls into port for the last time—its voyage at an end.  Script by Damond Benningfield Support McDonald Observatory

Making a mirror for a giant telescope requires a long-term commitment. Back in March, for example, GMT — the Giant Magellan Telescope — began work on the sixth of its mirrors. It'll take about three years to finish the job. GMT will use a total of seven mirrors. They'll work together to act as a single mirror about 80 feet in diameter — far larger than any current telescope. That will allow GMT to see stars and galaxies that are much fainter and farther, greatly expanding our view of the universe. Each mirror is cast in a circular furnace at the University of Arizona. About 20 tons of a special glass is heated to more than 2100 degrees. The furnace rotates, sculpting the molten glass to the proper shape. It takes about three months for the mirror to cool. Technicians then spend more than two years grinding and polishing it. The surface has to be smooth to within a millionth of an inch. Buddy Martin, who leads the process, described that level of accuracy during a March press conference. MARTIN: If the mirror were expanded to the size of North America, 3500 miles in diameter, then the average hill would be two-thirds of an inch tall and the average valley two-thirds of an inch deep. That's how smooth this mirror has to be for it to make the sharpest images that nature will allow. All the mirrors are scheduled to be sent to GMT's mountaintop site, in Chile, late in the decade.  Script by Damond Benningfield Support McDonald Observatory

For most stars, life seems to happen in slow motion — it takes a long time for them to change. One exception appears near the Moon tonight. Over the last 25 years it's gotten a lot brighter, and it's created a “pancake” of gas and dust around itself. Delta Scorpii is close to the lower right of the Moon as night falls. It's the middle star in the “head” of the scorpion. The scorpion's brightest star, Antares, is farther to the lower left of the Moon. Delta Scorpii is about 450 light-years away. It consists of two stars. One of them is about 14 times the mass of the Sun. The other is about two-thirds as heavy. The stars orbit each other once every 11 years. The orbit is stretched out, so most of the time the stars are a long way apart. At their closest, though, they're closer than Earth is to the Sun. By the time of a close approach in 2000, the bigger star had surrounded itself with the pancake — something that hadn't been seen before. The star is big and puffy, and it spins in a hurry. That appears to be throwing gas from its equator, forming the disk. As the smaller star moves inward, it may stir and heat the disk, making the system shine brighter. In fact, it got roughly twice as bright early in this century. The stars made their last close approach 10 years ago this month, so they'll get close again next year. Astronomers will be watching to learn more about this rapidly changing system.  Script by Damond Benningfield Support McDonald Observatory

AUDIO: Godspeed, John Glenn. 10, ... On the morning of February 20th, 1962, John Glenn became an American icon. LAUNCH CONTROL: 3, 2, 1, zero. GLENN: Roger, the clock is operating. We're under way. Glenn became the first American to orbit Earth. He circled the planet three times aboard his tiny capsule, Friendship 7. Then came parades, a reception at the White House, and other honors. Glenn was born 100 years ago today, in Ohio. He was an outgoing athlete in high school, and earned a pilot's license while in college. During World War II, he became a fighter pilot. He flew combat missions during that war and in Korea. Glenn then became a test pilot. And in 1959, he was picked as one of America's first astronauts — the Mercury Seven. During their introduction at a press conference, Glenn emerged as the favorite. GLENN: Well, my wife made a remark the other day, I've been out of this world for a long time, I might as well go on out there. After his flight, NASA didn't want to risk its most popular astronaut, so it grounded him. Glenn turned to politics, and was elected to the U.S. Senate. But he never lost the desire to fly in space again. He convinced NASA to launch him on a space shuttle, in 1998. LAUNCH CONTROL: 3, 2, 1, booster ignition and liftoff of Discovery with a crew of six astronaut heroes and one American legend. Glenn died in 2016, at age 95 — still an American legend. AUDIO: Godspeed, John Glenn.  Script by Damond Benningfield Support McDonald Observatory

There's more than one way to see the stars — or at least the patterns of stars. In western culture, for example, the stars of the Big Dipper and those around it form the great bear, Ursa Major. The dipper outlines his body and tail, while three faint pairs of stars represent his feet. In ancient Arabia, though, those pairs represented the leaps of a gazelle, and they're named accordingly. The first pair is known as Alula Borealis and Alula Australis — the northern and southern halves of the first leap. The second pair is Tania Borealis and Australis — the second leap. And the third pair is known by the name of its brighter star, Talitha — the third leap. The stars in the three pairs are unrelated — they're all at different distances from Earth. They just happen to line up in such a way that they form close pairs as we look toward them. Perhaps the most impressive of all the “leaping” stars is Alula Borealis. It's a red giant — a star that's puffed up at the end of its life. It's about 70 times wider than the Sun, and more than a thousand times brighter — bright enough that it's visible across more than 400 light-years of space. The gazelle leaps across the northwest as night falls. The first leap is well to the lower left of the bowl of the Big Dipper. The second leap is to the lower right of the first, with the final leap farther to its lower right — the leaps of a gazelle in the footprints of the great bear.  Script by Damond Benningfield Support McDonald Observatory

A bright star that follows the Moon this evening shows how tough it is to know what's happening inside a star. Spica is the leading light of Virgo. It's to the lower left of the Moon as night falls. It's one of the brighter stars in the night sky, so astronomers have paid a lot of attention to it over the centuries. And they know a lot about it. For example, they know that it's a binary — two stars locked in a mutual orbit around each other. Astronomers can plot the orbit, which tells them how far apart the stars are. It also gives them the masses of the two stars. The bigger star — Spica A — is about 10 times the mass of the Sun. The other star isn't quite as big, but it's still impressive. Studying the individual wavelengths of light from the stars reveals their composition and temperature. Combined with their masses, that tells us about each star's phase of life. Spica A is going through a transition. It's completing its primary phase of life, the main sequence. That's caused its core to shrink and get hotter, which has made the star bigger and brighter. But astronomers aren't sure exactly where it is in the transition. It could be just finishing it up. On the other hand, it could have finished the transition fairly recently, and is now moving full-on into the next phase of life — puffing up to become a giant. Continued studies might help resolve the question of what's happening inside this big, bright star.  Script by Damond Benningfield Support McDonald Observatory

Pluto shines at its best this week. It lines up opposite the Sun, so it rises near sunset and stays in view all night. It's brightest for the year as well. Don't bother looking for it, though; to be visible to the eye alone, it would have to shine at least a couple of thousand times brighter. But you can spot Pluto's location. It's about half way between the bright planet Saturn, which is low in the east-southeast this evening, and the “teapot” outlined by the stars of Sagittarius, to Saturn's upper right. Pluto is hard to see because it's tiny — only about two-thirds the size of the Moon — and because it's a long way from the Sun — about three billion miles. Its orbit is lopsided, though. So for the next century, Pluto will move even farther from the Sun, heading for a maximum distance of 4.6 billion miles. Pluto's orbit was one reason the little world was dropped from the list of the Sun's major planets. The orbit is more stretched out than any other planet's. It's also more tilted. Finally, Pluto is locked in a “resonance” with Neptune, the farthest of the major planets. Pluto completes two orbits for every three made by Neptune. That suggests that Pluto is being herded along by giant Neptune — just like many other bodies in the outer solar system. The combination spurred Pluto's reclassification — as the Sun's best-known dwarf planet. Tomorrow: looking into the heart of a star.  Script by Damond Benningfield Support McDonald Observatory

An ocean of liquid water might lurk below the icy crust of Pluto. And it might have been around since the little planet was born. Scientists have based those conclusions in part on Pluto's most prominent feature — a heart-shaped basin called Sputnik Planitia. It was discovered by the New Horizons spacecraft, which flew past Pluto six years ago. The basin probably formed billions of years ago, when a giant asteroid hit the young world. The hole gouged by the collision most likely filled with water from the ocean, then was coated with ice when some of the atmosphere froze atop it. New Horizons discovered a jumbled landscape on the other side of Pluto — a region of big ridges and cracks. The area might have been mangled by vibrations from the impact moving all the way through Pluto. But a study suggests that to form such a large area of mangled terrain, Pluto must have had a deep but hidden ocean at the time of the impact. And the only way to keep the ocean from freezing was for Pluto to have formed quickly — in less than 30,000 years. The fast build-up would have made Pluto's interior hot. As the heat worked its way outward, it would have kept the ocean warm and wet. The ocean has undergone many changes over the eons. It's not as deep now, and it's probably slushy. But it appears to still be there — helping make Pluto a dynamic little world. Pluto is at its best for the year this week, and we'll talk about that tomorrow.  Script by Damond Benningfield Support McDonald Observatory

Making a planet is complicated — even a dwarf planet. It involves pushing things together, blasting them apart, and moving them around. And it takes millions of years to finish. Consider Pluto. It's beyond Neptune, the outermost major planet. It's about two-thirds the diameter of the Moon. And it has one big moon of its own, plus four little ones. A spacecraft flew past Pluto in 2015, and a smaller object even farther out in 2019. Scientists pieced together the observations of both bodies to create a possible formation story for Pluto. Pluto began forming more than four and a half billion years ago, in a wide, thin disk around the Sun. Tiny pebbles of ice and rock began sticking together in the outer regions of the disk. They built up into balls a few dozen miles in diameter. Some of those balls gently smushed together to make an even bigger body. As it grew, it swept up more pebbles, plus wisps of gas. A stronger collision blasted debris from the newly forming Pluto into space, making its big moon, Charon. After that, Neptune moved farther from the Sun, into Pluto's region. Its gravity kicked many of the big planetary building blocks farther from the Sun, so Pluto stopped growing. Neptune's gravity also pushed the little world farther from the Sun. And it locked Pluto and Neptune in step. The process was done in about a hundred million years — giving Pluto the basic configuration we see today. More tomorrow.  Script by Damond Benningfield Support McDonald Observatory

The Moon will be busy over the next year or so. The United States plans to launch its first lunar landers since the Apollo missions of the 1970s. Russia and Japan plan to send their own landers. And several tiny satellites will enter orbit or fly past the Moon. The American landers are being built by private companies. They'll carry instruments from NASA, plus other payloads. The first, Peregrine 1, will study how the craft itself affects the lunar surface, and look for evidence of water ice. Both Peregrine and the second lander, Nova-C, will carry special mirrors to reflect laser beams from Earth. The experiments probe the Moon's interior and test theories of gravity. The Russian craft, Luna 25, will land near the south pole. It'll study the Moon's thin “atmosphere” — mainly a few atoms captured from the solar wind. Japan's lander will test the technology for more complex missions in the future. And India and South Korea are preparing lunar missions as well. The U.S. also plans to make the first test flight of a big new rocket. It'll propel about a dozen “cubesats” to the Moon. They'll conduct experiments and check out new technologies. The missions are supposed to launch late this year or early next year — opening a busy new era for the Moon. The Moon is in the west as night falls. The star Regulus stands to its lower left. Venus, the “evening star,” is to the lower right of the Moon, with tiny Mars beside Venus.  Script by Damond Benningfield Support McDonald Observatory

The three big astronomical objects that pass closest to Earth appear close to each other in the western sky early this evening: the Moon and the planets Venus and Mars. Venus is the “evening star,” to the left of the crescent Moon. Mars is only about one-half of one percent as bright as Venus. But it's just a skosh to the left of its brilliant sibling, making it fairly easy to pick out. The trio is quite low in the sky as darkness falls, so the viewing window is short. The Moon is always the closest major object to Earth. It averages less than a quarter of a million miles away. The only bodies that get closer to us are small asteroids. But no asteroid gets closer on a regular basis. Venus is next on the list. At its closest, it cozies about 25 million miles from Earth. It's not that close now, though. It's on the opposite side of the Sun, so it's about 133 million miles away. But it's getting closer. It's looping toward us, and will be closest in about six months, when it passes between Earth and the Sun. Mars can get as close as about 36 million miles. It's about six times that distance now, and moving farther. It'll be farthest in early October, when it will line up behind the Sun. After that, it'll start moving closer again. The Red Planet will be closest in December of next year, so it'll put on a good show in late fall and into the winter.  Script by Damond Benningfield Support McDonald Observatory

Mars and Venus are staging an amazing show in the western evening sky. Venus is big and bright — the “evening star.” Mars is just one-half of one percent as bright. But its closeness to Venus will help it stand out. Tonight, it's only about a degree and a half away — the width of a finger held at arm's length. One reason Venus looks so much brighter is that it's covered by clouds. They hide the surface, but they also help protect it. The most common features on Venus are volcanoes and related structures. Impact craters — the scars of collisions with big space rocks — are much less common. Scientists have cataloged fewer than a thousand of them. The largest is only about 175 miles in diameter. That's largely because of Venus's atmosphere. It's extremely dense, and its clouds are made of sulfuric acid. So when a space rock slams into Venus, it's likely to burn up or split apart before it hits the ground. Mars, on the other hand, is a crater-lover's paradise. Scientists have cataloged hundreds of thousands of them that are at least two-thirds of a mile in diameter. The largest is a shallow basin a thousand miles across. Mars's atmosphere is less than one percent as thick as Earth's. So when a big space rock takes aim, there's not much to keep it from hitting. And there's not much to erase impact craters, either. So they just keep adding up — more big holes on the Red Planet. More about Mars and Venus tomorrow.  Script by Damond Benningfield Support McDonald Observatory

Star systems with more stars than you can count on one hand are rare. In fact, you could probably total them all up by yourself if you use your hands and feet. One of those systems is called 65 Ursae Majoris. It consists of six known stars. The two stars at the center of the system orbit each other. All the other stars orbit them. The stars at the center are almost identical — they're almost twice as big and heavy as the Sun. They're so close together that they orbit each other every couple of days. The first two stars out from them are more than twice the Sun's mass. One of them orbits the central pair every 21 months, and the other, once every 118 years. The two most remote members of the system are less well known. One of them takes thousands of years to complete a single orbit. And the other — the one you need an extra hand to tally up — takes hundreds of thousands of years. Astronomers have been watching the stars for only a fraction of that time, though, so they haven't plotted enough of their orbits to know the details. And it could take centuries to figure it all out. 65 Ursae Majoris is in Ursa Major, the great bear. The bear's body and tail are outlined by the Big Dipper, which is in the northwest on July evenings. 65 Ursae Majoris is to the left of the dipper. At a distance of 700 light-years, though, even the combined light of its six stars isn't enough to see without a telescope.  Script by Damond Benningfield Support McDonald Observatory

If you want to hear the sounds of civilization, you're likely to head downtown. If you want the sounds of nature, then you're likely to head for the country. That reflects the strategy in recent months of the world's biggest search for extraterrestrial intelligence. It's been aiming its radio telescopes toward the center of the Milky Way — the galaxy's busy “downtown.” Breakthrough Listen began in 2016. It uses radio telescopes in the United States and Australia to listen for signals from other civilizations. It also uses an optical telescope to look for high-powered lasers. It's scanned hundreds of thousands of stars across a wide range of wavelengths. Most of its observations are still being analyzed. In recent months, it's taken aim at the center of the galaxy. There are a lot more scannable stars in that direction than in any other — stars in the center, and stars across the 27,000 light-years or so between Earth and the galaxy's hub. In addition, the center of the galaxy is considered the best location for a beacon to signal worlds throughout the Milky Way. It could even serve as the hub for a sort of galactic Internet. Early results have found no evidence of powerful beacons. But researchers still have hundreds of hours of recordings to study in their quest to find other civilizations in our galactic home. We'll talk about efforts to find new stars in that region of the sky tomorrow.  Script by Damond Benningfield Support McDonald Observatory

The black hole at the center of the Milky Way Galaxy is an underachiever. It's much fainter than similar black holes in other galaxies. But that hasn't always been the case. Long ago, it might have shined a hundred million times brighter. The black hole is called Sagittarius A-star. It's in the constellation Sagittarius, which is in the southeast as night falls. Some of its stars form the outline of a teapot. Sagittarius A-star is immersed in the “steam” above the spout. The black hole is four million times the mass of the Sun. It's encircled by a faint disk of hot gas. Disks around similar black holes can shine a hundred million times brighter. Those black holes are pulling in a lot of gas and dust. They're heated to millions of degrees, so they shine brightly. Sagittarius A-star is pulling in very little material, though, so it's faint. It does occasionally flare up for a few hours — probably as it gobbles up an asteroid or other bit of debris. And a few hundred years ago, it shined up to a million times brighter than today. Space telescopes have revealed what could have been even bigger outbursts in the past. There was one outburst from the galactic center about 15 million years ago. It could have been caused by the birth of many new stars. But it also could have been a flare-up of the black hole, perhaps as it devoured a star — a brilliant eruption for the Milky Way's black hole. More tomorrow.  Script by Damond Benningfield Support McDonald Observatory

One of the biggest roller coaster rides in the Milky Way Galaxy is a star known as S2. It orbits the black hole at the galaxy's heart. At its closest, it's just 11 billion miles from the black hole. And pulled by the black hole's powerful gravity, it reaches a top speed of almost three percent the speed of light. Perhaps more important for astronomers, the star confirms the existence of the black hole. In this 2010 interview, Andrea Ghez, an astronomer at UCLA, explains.GHEZ: The most definitive proof you can get of a supermassive black hole is to show that things are moving around under the gravitational influence, and from that motion you can show what the mass is directly. There's no question there. It's very much like the planets orbiting the Sun. From those planets' orbits you can get the mass of the Sun and the orbit also tells you a size. Ghez and her colleagues, along with a team led by Reinhard Genzel, have been watching S2 and other stars near the black hole for decades. Their work showed that the black hole is four million times the mass of the Sun. For their work, Ghez and Genzel shared last year's Nobel Prize for Physics. S2 is big, young, and hot. At the peak of its orbit, it's about 170 billion miles from the black hole. After that peak, the star plunges back toward the black hole — continuing its roller-coaster ride through the heart of the galaxy. More tomorrow.  Script by Damond Benningfield Support McDonald Observatory

The downtown of a major city is bold, bright, busy — and crowded. And the same thing applies to galaxies. The downtown of our home galaxy, for example, is packed with millions of stars. Some of them are among the biggest and brightest in the entire Milky Way. And new stars are entering the picture at an impressive rate. The center of the Milky Way is in the constellation Sagittarius. It's in the southeast in early evening, and its stars form the outline of a teapot. The center of the galaxy is in the “steam” of faint stars above the spout of the teapot. Astronomers aren't sure just how far away “downtown” really is. Estimates range from about 23,000 to 30,000 light-years. A study last year came up with a bit less than 26,000. The hub of the galaxy's heart is a black hole about four million times the mass of the Sun. It's encircled by a faint disk of hot gas. Many stars orbit the black hole, including some that come especially close; more about that tomorrow. Several giant star clusters are within a couple of hundred light-years of the black hole. One of them is one of the busiest nurseries in the galaxy, giving birth to many new stars. Another is the densest cluster in the galaxy, with stars packed millions of times more tightly than out here in the suburbs. And yet another contains several stars that are at least a million times brighter than the Sun — brilliant lights for “downtown” Milky Way.  Script by Damond Benningfield Support McDonald Observatory

While many Americans were celebrating Independence Day five years ago, a few were celebrating a milestone at another world: All stations on Junocord, we have the tone for burn cutoff on delta-v. Juno, welcome to Jupiter. (cheers) The Juno spacecraft has been orbiting Jupiter ever since. It's provided a peek into the interior of the solar system's biggest planet. And it's given us some impressive looks at Jupiter's busy atmosphere. Juno's main mission was to measure Jupiter's magnetic and gravitational fields. Those readings have shown that Jupiter's interior is like a pat of butter that's just been dropped into a skillet. It's still a little firm in the middle, but the edges are gooey and indistinct. That could mean that another large body hit Jupiter long ago, stirring up its middle. Juno also has taken a look at Jupiter's poles. It found a ring of giant storms encircling each pole. The swirling storms at the north pole resemble a pan of cinnamon rolls just out of the oven. Those at the south pole are more spread out. The craft has also measured the composition of Jupiter's atmosphere, found lightning in the highest clouds, and listened in to radio waves from its northern and southern lights. Juno's mission was supposed to end this summer. But its run has been extended for another four years. And it'll branch out to study Jupiter's rings and moons — perhaps prompting future celebrations of new discoveries.  Script by Damond Benningfield Support McDonald Observatory

Earth's orbit around the Sun is a bit wonky. It's a little stretched out, so our distance from the Sun varies. Over the course of a year, it changes by about three million miles — roughly three percent of the average distance. We're closest to the Sun in January, and farthest in July. In fact, we'll be at our most distant on Monday. One consequence of the changing distance is that Earth moves at different speeds in different parts of its orbit. In January, when the Sun is closest, Earth moves a little faster than average. And now, we're moving a little slower than average. The change in speed affects the length of the seasons. Winter is the shortest season in the northern hemisphere, while summer is the longest. Summer will last almost 94 days — about five days longer than winter. There's also a difference in the length of a day — the time from one local noon to the next. When we're closest to the Sun, a day averages a few minutes less than 24 hours. But now, when we're farther away, a day averages a few minutes more than 24 hours. Unless you go out and plot the Sun's position from day to day, though, it's nothing you're likely to notice. We keep time with mechanical or digital devices. And with Daylight Saving Time, the time on the clock can vary from local solar time by up to a couple of hours. So the rhythm of the Sun doesn't always match the rhythm of daily life — regardless of how far away the Sun is.  Script by Damond Benningfield Support McDonald Observatory

The planet Venus is pushing a little higher into the sky each night. It's the brilliant “evening star,” low in the west-northwest at sunset. It's so bright that it's easily visible even through the twilight, although you do need a clear horizon to spot it. Skywatchers south of about Dallas or Little Rock should also be able to make out a couple of objects near Venus — especially with binoculars. The view will be more challenging north of that line because the array sets at a shallower angle, so it's more obscured by the glow of twilight. One of the companions is Messier 44, the Beehive star cluster. It will appear just to the left of Venus tonight, and just below it tomorrow night. Binoculars will reveal quite a few of the cluster's individual stars. The other companion is the planet Mars. It's to the upper left of Venus. Tonight, it's about six degrees away — roughly the width of three fingers held at arm's length. Mars looks like a humble star, with a slightly orange color. It's dropping toward the Sun now, so it'll disappear from view by early August for the entire country. Venus will pass by it at the end of next week, making its fainter sibling a little easier to pick out. Venus is climbing away from the Sun. It will stand a little higher in the sky each evening over the next few months, and remain in view a little longer. It'll hang around in the evening sky for the rest of the year.  Script by Damond Benningfield Support McDonald Observatory

Fireflies are among the more pleasant features of a summer evening. Children chase them across the yard, and adults just enjoy their beautiful flashes. But our own nightlights could be chasing them away. Recent work has found that artificial lights can interfere with the flashes, which are part of the mating ritual. That means fewer of these twinkling lights for future generations of children to chase. In fact, research is showing that artificial light is a problem for all insects — not to mention professional astronomers and casual skywatchers. A study in Peru, for example, showed that insects were attracted to outdoor LEDs in droves. That made them easier for predators to catch, kept them from catching their own meals, and tired them out. The study did show that LEDs warmed with amber filters attracted fewer insects. For fireflies in North America, though, amber had the opposite result. Scientists studied a species that's common in the eastern U.S. and Canada. They exposed courting fireflies to different colors and intensities of light. And they found that amber light cut down on the “flashiness” of males and the response by females more than any other color. And yet another study looked at fireflies in a forest in Brazil. It found that artificial lights were a bigger threat than habitat destruction or encroaching cities. So for the insect kingdom, it seems, there's no such thing as a good artificial nightlight.  Script by Damond Benningfield Support McDonald Observatory

For the people of the Soviet Union, Soyuz 11 was a novelty. State media provided regular updates on the space mission, which was rare. It even showed TV broadcasts of the three cosmonauts showing off some plants they were growing, and celebrating a birthday with prune paste and presents of an onion and a lemon. Pride in the mission turned to grief, though, when Soyuz 11 returned to Earth. When recovery forces opened the hatch 50 years ago yesterday, all three cosmonauts were dead. Georgi Dobrovolsky, Vladislav Volkov, and Viktor Patsayev had launched on June 6, 1971. They docked with the first space station, Salyut 1. They spent a record three weeks aboard the station. They operated a telescope, observed Earth, and conducted secret experiments for the military. When their work was done, they packed up for home. They separated their Soyuz capsule from the station, then split off their reentry module for the plunge through the atmosphere. No one knew it at the time, but that part of the process went horribly wrong. A valve opened and let the air escape into space. The cabin was too cramped for the cosmonauts to wear spacesuits, so they died in seconds. The automated landing system worked well, though, and Soyuz 11 touched down as expected. Recovery forces quickly reached the capsule, but heard nothing from the crew. When they opened the hatch, they found the cosmonauts dead — a tragic end to a record-breaking stay in space. Script by Damond Benningfield Support McDonald Observatory

Horror movies often inspire sleepless nights. But one that had its American premiere 75 years ago this week inspired something different: a new model of the universe. “Dead of Night” was a British production. In it, an architect is invited to a country house for the weekend. Although he's never met any of the people there, he recognizes them from a series of nightmares, which he recounts. At the end, he murders one of the people. He then awakens and realizes it was all a dream. But he then gets a phone call inviting him to the house — starting the nightmare all over again. Three British physicists — Thomas Gold, Hermann Bondi, and Fred Hoyle — were pondering the beginning and end of the universe. They knew that the universe was expanding, but they didn't agree with the idea that it had a single point of origin. Hoyle even called the theory the “Big Bang” as a term of derision. Instead, they thought the universe had neither a beginning nor an end. After they saw the movie, Gold wondered whether the universe might be similar — constantly “starting over.” So they came up with their own theory of the universe — the Steady State Theory. It said that matter was constantly being created as the universe expanded. That way, the universe would maintain a constant density. And it would just keep going — forever. Observations confirmed the Big Bang, though, leaving the Steady State alone — in the dead of night.  Script by Damond Benningfield Support McDonald Observatory

The brilliant planet Jupiter leads the Moon across the sky late tonight. It's to the upper right of the Moon as they climb into good view, after midnight. Jupiter is the largest planet in the solar system. It's about five times as far from the Sun as Earth is. But it probably hasn't always been at that distance. Models show that it probably moved much closer to the Sun early on, then backed away. Jupiter-sized planets in some other star systems may have moved even more. In fact, it's possible that they switched stars. A recent study looked at a system known as Gliese 3512. It consists of a tiny, feeble star plus a planet at least half as massive as Jupiter. The problem is, there doesn't appear to be a way for such a heavy planet to form around such a little star. The gravity of the star wouldn't allow enough material to come together to make such a world. So researchers suggested another way for a little star to get a big planet: a swap with another star. In the crowded confines of a young star cluster, stars frequently pass close to each other. If a small star flies near a Sun-like star with a Jupiter-like planet, the planet could switch partners — it could leave its parent star behind and be adopted by the smaller star. Gliese 3512 isn't the only system where a small star has a big planet. That suggests that planet exchanges could be common, with planets frequently switching stars inside busy clusters.  Script by Damond Benningfield Support McDonald Observatory

The solar system gets the week off to a beautiful start early tomorrow. The Moon will form a wide triangle with the planets Jupiter and Saturn. The trio will climb into view after midnight and stand high in the south at first light. Jupiter is the brighter of the two planets, and stays to the left of the Moon, with Saturn to the right of the Moon. Jupiter and Saturn are the largest planets in the solar system. And not surprisingly, they have the largest collections of moons — almost 80 for Jupiter, and more than 80 for Saturn. Many of those moons have been discovered just in the last couple of decades. That's because most of them are tiny — no more than a few miles in diameter — so they're faint. And they're a long way out from the planets, so astronomers have to search a large area to find them. Some of the little guys probably were asteroids that were captured when they passed close to one of the planets. And some appear to be remnants of larger moons that were blasted to bits by collisions. Instead of Greek and Roman mythology, the names for some of the moons of Saturn have been drawn from other cultures — Gallic, Norse, and Inuit. And some moons of both worlds haven't been named yet. In some cases, that's because astronomers are waiting for confirmation that the moons actually exist. Until then, they're stuck with catalog numbers — waiting for full membership in these giant families of moons. Script by Damond Benningfield Support McDonald Observatory

Other than Earth, there's no place in the solar system that says, “there's life here!” But there are several places that whisper, “there could be life here.” One of those is Titan, the largest moon of Saturn. Its dense atmosphere and its rocky interior are loaded with the chemical building blocks of life. And the moon probably has a global ocean of liquid water below a thick icy crust. If the different layers get together, then Titan would have the basic ingredients for life. Titan is about half again the size of our own moon. It's extremely cold. But its atmosphere is thicker than Earth's. It's topped by an orange “smog” made of organic compounds — the chemistry of life. The atmosphere consists of another organic compound, methane, plus a lot of nitrogen that came from organics. Models of Titan say it has a deep ocean of liquid water buried far below the surface. Impacts by giant space rocks might punch holes in the crust deep enough to allow organics from the surface to reach the ocean. On the other hand, organics might enter the ocean from below — through mineral-rich fountains of hot water like those found on Earth. Either method would provide water, organics, and energy — the basic ingredients for life. Saturn is close to the upper left of our moon as they climb into good view, by midnight. It looks like a bright star. Titan is visible through good binoculars or a telescope, shining like a tiny star next to the giant planet.  Script by Damond Benningfield Support McDonald Observatory

If you like black holes, you might want to check out the core of NGC 6397, a giant ball of stars almost 8,000 light-years away. A recent study says the core could house dozens of black holes. NGC 6397 is a globular cluster. It contains hundreds of thousands of stars. But the stars are ancient — as old as the Milky Way Galaxy. All of the cluster's big, heavy stars expired billions of years ago. When those stars died, they left small but heavy remnants — white dwarfs, neutron stars, or black holes. And in a cluster, such massive objects sink to the middle. Earlier studies had suggested that there's a small, dark mass at the center of NGC 6397 — perhaps a black hole a few hundred times the mass of the Sun. The more recent study used the Hubble and Gaia space telescopes to plot the orbits of stars in the cluster. The way the stars move suggests they're orbiting a large group of stellar remnants, not a heavier single black hole. They total up to about 2,000 times the mass of the Sun. Most of that mass should consist of black holes. They range up to about 40 times the mass of the Sun. Black holes ought to occasionally kick out a normal star, or even merge with each other — stirring things up in this ancient cluster. NGC 6397 is in Ara, the altar. From the U.S., it's visible only from Hawaii and southern Texas and Florida. It's in the south around midnight.  Script by Damond Benningfield Support McDonald Observatory

That's the sound of the winds of Mars, recorded by the Perseverance rover after it landed in February. It's the first direct recording of sounds in the Martian atmosphere. Scientists have been monitoring the Martian winds off and on for decades. Most American landers have included a weather station. Today, there are three working landers with weather stations. Most of the time, the wind is tame, with speeds of only a few miles per hour. But during winter it gets a little friskier. And for the InSight lander, that's too much — the wind can overpower the faint rumblings of marsquakes, which InSight is designed to study. In one way, though, the wind hasn't been strong enough. Scientists were hoping that dust devils might blow the dust from Insight's solar panels. By earlier this year, though, they hadn't. So InSight's workload was cut back — including shutting down its weather station — until Mars moves closer to the Sun, which will provide more life-giving sunlight. Sometimes, the wind stirs up giant dust storms. Some of them can cover most of the planet, driven by winds of 60 miles per hour or stronger. In 2017, such a storm darkened the sky enough to kill the solar-powered Opportunity rover. Perseverance and the other working rover, Curiosity, don't have to worry about that. They use nuclear power — protecting them from the vagaries of the Martian winds.  Script by Damond Benningfield Support McDonald Observatory

If you have a pair of binoculars, this evening is a good time to break them out. They'll provide an excellent view of Mars passing in front of a star cluster known as the Beehive. They're quite low in the western sky as night begins to fall, to the upper left of bright Venus, the “evening star.” The Beehive contains perhaps a thousand stars. They're packed into a loose ball a couple of dozen light-years in diameter. But the cluster is about 600 light-years away, so to the eye alone it looks like a hazy smudge of light. Binoculars reveal a couple of dozen individual stars. The Sun probably was born in a cluster, too. Over time, though, clusters lose many of their stars. They're pulled away by the combined gravity of other stars and gas clouds in the galaxy. So most of a cluster's original stars soon go their own way — just as the Sun did. The Sun was born about four and a half billion years ago. So far, no one knows if any of its birth cluster is still around — it could have disappeared a long time ago. But a study last year suggested that the Sun could have been born in a cluster like the Beehive. Researchers said that such a birthplace would account for some of the traits of the present-day solar system. We may never know just what the Sun's birthplace was like. But scanning the Beehive with binoculars could be like looking into the old homestead — a cluster much like the one that gave birth to the Sun. Script by Damond Benningfield Support McDonald Observatory

If you gaze into the summer night sky in a million years, it'll look a lot different than it does tonight. For one thing, the Sun and all the other stars are moving. The change in position isn't fast enough to notice over a human lifetime, or even many lifetimes, but it adds up. In a million years, many of the stars that are visible now will have moved so far away that they'll be out of sight. At the same time, other stars will have moved into range. Another reason for the change is that some stars may no longer exist — they may blow themselves to bits by then. A leading candidate is Antares, the brightest star of Scorpius. It's close below the Moon at nightfall. It's perhaps a dozen times the mass of the Sun, hundreds of times wider than the Sun, and tens of thousands of times brighter. Antares is only about 15 million years old — a third of a percent of the age of the Sun. Because of its great weight, though, it ages far faster than the Sun does, so it's already nearing the end of its life. Before long — perhaps within the next million years — Antares will no longer be able to produce nuclear reactions in its core. The core will collapse to form an ultra-dense neutron star. The star's outer layers will fall inward, then rebound. They'll blast out into space, forming a brilliant supernova. As the supernova fades, Antares will disappear from view — one more change in the constantly changing night sky. Script by Damond Benningfield Support McDonald Observatory

Nancy Roman and Vera Rubin heard it many times: astronomy isn't for girls. Neither of them paid much attention, though. Instead, they kept chasing the stars. They became two of the most accomplished and respected astronomers of their time. And today, they're the namesakes for two major facilities — the first women to receive such an honor. The Nancy Grace Roman Space Telescope is scheduled for launch later this decade. Among other chores, it'll study dark energy and search for planets in other star systems. Roman was born in 1925. In 1960, she became the first chief astronomer for NASA — a post she held for almost two decades. She oversaw development of several space telescopes, and was a driving force in the early years of the Hubble telescope. She also oversaw projects that lofted telescopes on balloons and airplanes. The Vera Rubin Observatory features a giant telescope that's under construction in Chile. When completed, the telescope will snap pictures of the entire sky about every three nights. Comparing images will allow astronomers to study variable stars, discover asteroids, probe dark energy and dark matter, and more. Rubin was born in 1928 and became a leader in studying galaxies. Her observations of the motions of spiral galaxies helped confirm the existence of dark matter. Roman and Rubin also were strong advocates for women in science, helping many women — and girls — understand that astronomy is for them. Script by Damond Benningfield Support McDonald Observatory

Alpha Sextantis is moving south. The star crossed the celestial equator less than a century ago. It’ll continue moving southward for millennia. The star is fairly impressive. It’s about three times as massive as the Sun, and more than a hundred times brighter. That makes it visible to the naked eye even though it’s about 280 light-years away. Perhaps the most notable thing about Alpha Sextantis, though, is its location: It’s only a quarter of a degree south of the celestial equator — the projection of Earth’s equator on the sky. In 1923, the star crossed the equator from north to south. The star wasn’t responsible for the shift, though. Instead, the equator is moving. That’s because the pull of the Sun and Moon cause Earth to wobble like a spinning gyroscope. It takes about 26,000 years to make one full wobble. During that time, we have different pole stars. The stars also drift across the seasons. And the equator moves north and south across the sky, so the stars move north and south as well. Alpha Sextantis will continue moving southward for thousands of years. Then it’ll reverse course. It’ll cross the equator around the year 18,000 — returning once again to the northern half of the sky. Alpha Sextantis is in the constellation Sextans, the sextant. It’s in the southeast as night falls. Under dark skies, Alpha Sextantis is just visible. It’s to the lower right of Regulus, the bright heart of the lion. Script by Damond Benningfield Support McDonald Observatory

Early 1771 was a busy time for Charles Messier. The French astronomer was most interested in discovering comets. To make the process faster, he compiled a list of objects that resembled comets: galaxies, gas clouds, and star clusters. He could ignore the objects on the list, reducing the number of false alarms. And 250 years ago, he recorded four of them. Two of them are clusters in the constellation Puppis: Messier 46 and 47. They stand side by side — so close together that they’re in the same field of view through binoculars. M47 is the brighter of the two. It’s about 1600 light-years away, and consists of several hundred stars. The cluster is still pretty young, so some of its more massive stars haven’t yet had time to burn out. They’re especially bright, and they shine blue-white, so they overpower most of the rest of the cluster. A couple of massive stars are at the ends of their normal lifetimes. They’ve gotten bigger and cooler, so they look red or orange. M46 is fainter than M47 in part because it’s about three times as far as M47. But it’s also because the cluster is about three times as old. Its heaviest and most vigorous stars have already expired, leaving it with fewer standouts to draw attention. The clusters are in the south as night falls. They’re not far to the upper left of Sirius, the brightest star in the night sky. Messier 46 stands close to the left of its brighter neighbor. Script by Damond Benningfield Support McDonald Observatory

One of the closest stars in the constellation Puppis has a tight family of big planets. All three of them are between 10 and 20 times as massive as Earth. That makes them comparable to Neptune, one of the giants of our own solar system. And all three are much closer to their star than Earth is to the Sun. HD 69830 is about 40 light-years away. The star is a bit smaller and lighter than the Sun, and less than two-thirds as bright. So unless you have really sharp eyes and really dark skies, you need binoculars to pick it out. Astronomers discovered its planets 15 years ago. The closest planet is just eight million miles away from the star — less than a tenth of the distance from Earth to the Sun. It’s the smallest of the planets as well. The farthest planet is about twice as heavy. And it’s still only a little more than half the Earth-Sun distance. That puts the planet near the inner edge of the star’s “habitable zone” — the region that’s most comfortable for life. And there’s been plenty of time for life to take hold there. Estimates of the star’s age range up to about 10 billion years — twice the age of the Sun. So if life exists there, it could have been around since long before the birth of our own planet. Puppis is low in the south at nightfall on these early April evenings. HD 69830 is at its northeastern corner. That puts it well to the left of Sirius, the brightest star in the night sky. Script by Damond Benningfield Support McDonald Observatory

Zeta Puppis is one of the most impressive stars in the galaxy. It’s big, hot, heavy, and bright. Unfortunately, though, astronomers aren’t sure just how big, hot, heavy, and bright it really is. That’s because they can’t agree on how far away it is. Estimates range from roughly a thousand to two thousand light-years. Zeta Puppis is the brightest star of the constellation Puppis. It represents the poop deck — the elevated deck at the stern of the Argo, the boat that carried Jason and the Argonauts. The constellation is due south as night falls, just above the horizon. Zeta Puppis is a class “O” star — the hottest and brightest of all stars. Its details vary depending on its distance. In general, though, it’s a few dozen times the mass of the Sun, and up to a couple of dozen times the Sun’s diameter. And it’s probably at least half a million times the Sun’s total brightness. The star is moving through space in a hurry — far faster than any of the stars around it. That suggests that it’s a “runaway” — a star that got the boot. It could have had a companion star that exploded as a supernova, for example. Zeta Puppis is quite young — only a few million years old. Because of its great bulk, though, it will live only a few million years longer. When its time is up, its core will collapse to form a neutron star or a black hole. And its outer layers will explode as a supernova — a brilliant ending for a brilliant star. Script by Damond Benningfield Support McDonald Observatory

The Argo survived many adventures. In the tale of Jason and the Argonauts, it escaped some terrible storms, the Clashing Rocks, a bombardment of huge stones, and other hazards. But it couldn’t survive the whims of astronomers. They split the Argo apart — turning the largest of all constellations into three smaller ones. The original constellation was known as Argo Navis — the ship Argo. It was created about 3,000 years ago. According to Greek mythology, it was placed in the heavens by Poseidon, the god of the sea. Its demise began in the mid-1700s. In a sky atlas, French astronomer Nicolas Louis de Lacaille split it into three constellations: Puppis, the poop deck — the raised deck at the back of the ship; Vela, the sail; and Carina, the keel. Lacaille said the constellation was too big and contained too many bright stars to track. Although other astronomers began using the new constellations, many still used Argo Navis as well. It came to its end in 1930, when astronomers adopted 88 official constellations. So the stellar Argo met its fate not on the high seas, but on a list compiled by astronomers. Puppis is the largest of the surviving bits of the Argo. It sits atop the southern horizon as night falls. It’s to the lower left of Sirius, the brightest star in the night sky. Vela follows it a little later. But from most of the U.S., Carina stays below the horizon and out of sight. We’ll have more about Puppis tomorrow. Script by Damond Benningfield Support McDonald Observatory

From the late 1600s through the early 1800s, European astronomers went on a constellation binge. They drew dozens of new ones, usually in areas of the sky with few bright stars. Many of their creations are still in use. But many others have vanished. Johannes Hevelius, for example, drew a few constellations in the late 1600s. One was the northern fly. It was adapted from an earlier constellation, the bee. Another was Cerberus — a three-headed snake in the hands of Hercules. Both of those defunct constellations are low in the west at nightfall, well below the bright star Aldebaran. German astronomer Johann Bode drew seven new constellations in an 1801 atlas. One honored the electric generator, while another honored the creation of the printing press more than three centuries earlier. Its stars were later absorbed into Puppis, the poop deck, which is in the south at nightfall. None of Bode’s creations is still around. But one of them gave its name to the Quadrantid meteor shower. Another German, Father Maximilian Hell, drew the constellation George’s Harp in the 1700s. It honored King George III of England, the patron of astronomer William Herschel. Most of the new creations quickly fell out of use. And in 1930, astronomers adopted a list of official constellations, which dropped many of the creations of the previous three centuries. We’ll talk about the largest obsolete constellation tomorrow. Script by Damond Benningfield Support McDonald Observatory

The full Moon has a follower tonight: Spica, the leading light of Virgo. It’s below the Moon as it climbs into good view by 9 or 10 p.m., and closer to the lower left of the Moon at first light tomorrow. Spica is an amazing system. It consists of two stars, not one. But they’re only a few million miles apart — much, much closer than Earth is to the Sun. In fact, they’re so close together that not even the biggest telescopes can see them as individual stars — they form a single pinpoint of light. At such a tight separation, the gravity of each star distorts the shape of the other. So instead of balls, both stars are shaped like eggs, with the skinny end of each one pointed toward its companion. The stars bombard each other with radiation and with winds of charged particles. Where the winds ram into each other, they create X-rays. All of that makes the companion-facing side of each star a good bit hotter and brighter than the rest of the star. Things will get even brighter before too long. The bigger star is at the end of its normal lifetime. It’s so massive that it’s puffing up to become a supergiant. And at the end of that phase of life, it’s likely to explode as a supernova. It will leave behind a small, ultra-dense core: a neutron star. And the blast should send the smaller companion star careening through the galaxy — the runaway survivor of an amazing star system. Tomorrow: obsolete constellations. Script by Damond Benningfield Support McDonald Observatory

One of the biggest families of stars yet discovered rotates down the northwestern evening sky at this time of year. It’s one of the two most populous star systems yet found. AR Cassiopeia consists of seven stars. They’re split into three pairs, with a third star tied to one of the duos. But they’re not exactly a close family — the pairs are trillions of miles apart. The most impressive member of the family is identified as star Aa. It’s about six times the mass of the Sun, and five times the Sun’s diameter. It’s paired with star Ab, which is also more impressive than the Sun. Star B orbits them once every 545 years. The members of the other two pairs are a little smaller. And they’re way off on their own. It takes each pair several hundred thousand years to complete a mutual orbit with the central trio. That’s really about the only way for such a busy star system to remain stable. If you pack a bunch of stars close together, gravitational interactions among them kick some of them out. So the systems need to be widely spread. And it’s best if they form smaller groupings, like the stars of AR Cassiopeia — one of only two septuple star systems yet discovered. The system is in Cassiopeia the queen, which is in the northwest at nightfall. Some of its stars form a big letter W, which is tilted on its side right now. AR Cas is below the bottom point of the W. Under dark skies, it’s barely visible to the unaided eye. Script by Damond Benningfield Support McDonald Observatory

When Galileo looked at the heavens through his early telescopes, he saw many cosmic wonders. One of the most astounding was the planet Venus, which went through a cycle of phases just like the Moon’s. Venus shows phases because its orbit is inside Earth’s orbit around the Sun. Venus is “new” when it crosses between Earth and the Sun, so its nightside faces our way. It’s “full” when it passes behind the Sun, so its dayside faces our way. And in fact, Venus is passing behind the Sun today — a point called superior conjunction. But although Venus is full, it’s also hidden in the Sun’s intense glare. It won’t return to view for weeks, when it will appear as the “evening star.” By then, a telescope will show Venus in its gibbous phase — it’ll be daylight across most of the planet’s Earth-facing hemisphere. But Venus will be near its greatest distance from Earth then, so it won’t shine at its brightest. Instead, the planet is brightest when it’s in its crescent phase. Although most of the hemisphere visible from Earth then is dark, the planet is especially close, so it looks bigger. And at closer range, more of the planet’s reflected sunlight reaches Earth — making the brilliant planet even brighter. Look for Venus to reappear late next month and climb into better view in the evening sky in May. And if you have a telescope, keep an eye on the planet as it continues its cycle of phases throughout the year. Script by Damond Benningfield Support McDonald Observatory

Teams of scientists are digging into the Moon again. They’re nowhere near the lunar surface, though. Instead, they’re opening up samples collected by Apollo astronauts that have never been studied. The astronauts brought back more than 840 pounds of rocks and dirt. Most of those samples have been studied in some way. But a few were held back. Scientists wanted to wait for new instruments and techniques. They started digging in to a few of those samples in late 2019. And they’ll do a few more over the coming months and years. The first of the new samples is a core tube collected by astronaut Gene Cernan during Apollo 17, the final Apollo mission. Cernan drilled down about two and a half feet, filling the tube with layers of material that had piled up over millions of years. The core was split into two parts. Scientists opened the lower half first. The new studies have several goals. One is just to learn more about the Moon itself — about how its surface changed over millions of years, for example. Another is to help set goals for new sample-gathering missions in the years ahead. And a third is to evaluate how well the sample storage systems have worked over the past half-century — helping to get ready to dig in to the Moon once again. Look for the Moon in the east at nightfall, and arcing high across the southern half of the sky during the night. Regulus, the bright heart of Leo, is just a few degrees away. Script by Damond Benningfield Support McDonald Observatory

A brilliant visitor to the inner solar system zipped by Earth in March of 1996. Comet Hyakutake was closest to us 25 years ago tomorrow — less than 10 million miles away. That was the closest passage by a comet in two centuries. The comet had been discovered just two months earlier by an amateur astronomer in Japan. It quickly became visible to the naked eye. And by the time of its closest approach, its tail spanned more than a third of the sky. It was moving so fast, though, that it faded from sight in just a few weeks. The comet itself wasn’t much — a ball of ice and rock less than three miles in diameter. As it approached the Sun, though, solar energy vaporized some of the ice at its surface. That surrounded the comet with a cloud of gas, as well as dust and pebbles that were also released into space. The Sun’s radiation and the solar wind “blew” that material outward, forming a tail. Later observations showed that the tail spanned about 360 million miles — four times the distance from Earth to the Sun. Hyakutake came from deep space — far beyond the orbit of Pluto. It hadn’t visited the inner solar system in 17,000 years. While it was here, it got a gravitational “boost” from the giant outer planets. That hurled it even farther from the Sun. As a result, the comet won’t visit the inner solar system again for another 70,000 years. Tomorrow: Digging in to a scientific treasure box. Script by Damond Benningfield Support McDonald Observatory

The Sun isn’t quite steady. It goes through an 11-year cycle of magnetic activity. When the cycle is at its peak, there are lots of sunspots and other powerful events. But no two cycles are alike. The most recent cycle, for example, was weak. And over the centuries, both weak and strong cycles tend to come in clumps. One of the weakest “clumps” of the last millennium was the Spoerer Minimum. It may have lasted more than a century, and been the “quietest” of all the Sun’s known quiet periods. It’s named for German astronomer Gustav Spoerer, who discovered it. It could have started as early as 1415, and lasted until about 1540, although the exact dates are uncertain. In part, that’s because no one was counting sunspots at the time. Instead, scientists deduce what was happening on the Sun by looking at tree rings and ice cores. When the Sun is quiet, it allows more cosmic rays to enter the solar system. They interact with Earth’s atmosphere to make radioactive forms of carbon and other elements. Trees take up some of the carbon, and some of the other elements are trapped in the ice. So measuring those elements reveals how active the Sun has been over the ages. The intensity of the solar cycle appears to have a small effect on Earth’s climate. During the Spoerer Minimum, there’s evidence that the planet was cooler than average. So studying the solar cycle can help us understand more about conditions right here on Earth. Script by Damond Benningfield Support McDonald Observatory