StarDate

Two well-known star patterns highlight the northern sky this evening. The Big Dipper is low in the north-northwest at nightfall, and in the northeast at first light tomorrow. And W-shaped Cassiopeia is just the opposite – in the northeast at nightfall, and the north-northwest at dawn. As that sequence tells us, both star patterns make a big circle around the sky during the night. They circle the North Star, Polaris – the hub of the sky. All the stars in the northern sky appear to move around Polaris – the result of Earth turning on its axis. For much of the United States, the stars of the Big Dipper and Cassiopeia never set – they’re close enough to Polaris that they never drop below the horizon. So they’re in the sky every day and night of the year, endlessly circling the North Star. Such stars are called circumpolar. The number of such stars from any given location depends on your latitude. From 30 degrees north, anything within 30 degrees of Polaris always remains above the horizon. From 50 degrees north, it’s anything within 50 degrees of Polaris. So as you go farther north, more stars are circumpolar. And if you go all the way to the north pole, all the stars are circumpolar – nothing ever rises or sets. Each star follows the same path across the sky night after night – circling Polaris, the hub of the northern sky. Polaris won’t keep that position; we’ll talk about its successor tomorrow. Script by Damond Benningfield

A thousand spacecraft could head for our closest neighboring planetary system in just a few decades. Don’t book your ticket just yet, though – each craft would weigh about as much as a penny. But working together, they could provide a few sharp pictures of the system, and even look for signs of life. A team of scientists and engineers published the idea earlier this year. The team proposed sending the probes to Proxima Centauri. It’s the closest star outside the solar system – four-and-a-quarter light-years away. And it has two confirmed planets. One of them is about the size and mass of Earth, and it’s in the region that’s most comfortable for life. The probes would be equipped with tough but thin “sails” 13 feet wide. A powerful laser would fire at each probe for eight minutes. The pressure of the light would boost the probes to 20 percent of the speed of light. It would take them 21 years to reach their target. The probes would use lasers to stay in touch with each other, and with Earth. About 300 probes could survive the trip. Their instruments could hunt for evidence of life in the planets’ atmospheres. There’s a lot of work to make it happen – advances in materials, lasers, computers, and even our knowledge of the distance to Proxima Centauri. But the researchers said the current rate of advancement should make such a trip feasible in the decades ahead. Script by Damond Benningfield

The winds on a giant planet more than 200 light-years from Earth are like the Big Bad Wolf: they’ll huff and puff and blow your house down. And if that’s not enough of a problem, the temperature can jump by 500 degrees in just a few hours. The planet orbits the star HD 80606. The star is a lot like the Sun. And it has a distant companion star that’s a near twin. They’re in Ursa Major, the great bear. At dawn, the system stands to the upper right of the Big Dipper, although you need a telescope to see it. The planet is HD 80606 b. It’s about four times the mass of Jupiter, the giant of our own solar system. But it’s about the same size as Jupiter, so it’s much denser. Its orbit is one of the most elongated of any known planet – its distance ranges from just three million miles to 85 million. As the planet approaches the star, it’s like being popped into an oven: The amount of energy it receives when it’s closest to the star is 800 times greater than when it’s farthest. So the planet heats up in a hurry. The approach also stirs up the winds. They blow outward from the point that’s in the middle of the hemisphere that faces the star. They may top out at 11,000 miles per hour – huffin’ and puffin’ all the way around this turbulent planet. Script by Damond Benningfield

The Moon huddles close to the heart of the scorpion this evening – the star Antares. It’s among the 15 brightest star systems in the night sky. If our eyes could see all forms of light, Antares would look perhaps 10 times brighter still. That’s because it emits most of its energy in the infrared – wavelengths that are too long for the human eye to perceive. All stars emit radiation across the electromagnetic spectrum – from radio waves to X-rays. That includes the Sun. But the mix of wavelengths depends on the star’s surface temperature, which we see as its color. Stars like the Sun are yellow-white. Their energy peaks at visible wavelengths – the type of energy our eyes have evolved to see. Stars that are hotter than the Sun look white or blue. But their light peaks beyond those colors – mainly in the ultraviolet – wavelengths that are much too short for us to see. Antares, on the other hand, is thousands of degrees cooler than the Sun, so it looks orange. But it emits most of its light in the infrared. And it produces a lot of it. The star is a supergiant – far bigger than the Sun. At visible wavelengths, it shines about 10,000 times brighter than the Sun. Throw in the infrared and all the other wavelengths, and it could be a hundred thousand times the Sun’s total brightness – one of the true stunners in our part of the galaxy. Tomorrow: A planetary Big Bad Wolf. Script by Damond Benningfield

The first planet ever discovered orbiting a Sun-like star is nothing like anything in our own solar system. But it helped astronomers learn more about the history of the solar system. The planet orbits 51 Pegasi. The star is a little bigger, heavier, and brighter than the Sun. The planet is 51 Pegasi b. It’s about half as heavy as Jupiter, the giant of the solar system. But it’s much closer in – just a few million miles from the star. The planet’s gravity causes the star’s light to “wobble” a bit. Precise measurements of that wobble revealed the planet’s details. Astronomers have since discovered hundreds more planets with the same technique, including many planets that are “hot Jupiters” like 51 Pegasi b. There’s no way for such a massive planet to form so close to its star. So it must have been born much farther out, then migrated to its current location. That realization led to theories that the Sun’s giant planets shifted around when the solar system was young. And that could have nudged the small inner planets, including Earth. It might even have pushed closer planets into the Sun – destroying some of Earth’s planetary siblings. Pegasus is in the east at nightfall. Look for four moderately bright stars that form the Great Square, which is tilted on its side. 51 Pegasi is along the top right side of the tilted square. Under dark skies, it’s barely visible to the eye alone. Script by Damond Benningfield

Pegasus has a bit of an identity crisis. The stars that outline its body – the Great Square – don’t all belong to the flying horse. In fact, the brightest of the four stars officially belongs to Andromeda. The Great Square is in the east at nightfall. Its member stars are all bright enough to see even through moderate light pollution. The square is tilted, so it looks more like a diamond than a square. Its brightest member forms the left point of the diamond – the star Alpheratz. It’s about a hundred light-years from Earth. And it consists of two stars, both of which are a good bit bigger, brighter, and heavier than the Sun. In earlier centuries, Alpheratz was considered a member of both Pegasus and Andromeda – it’s a prominent member of the classical outlines of both constellations. But in the early 20th century, astronomers decided to formalize the constellations. In 1930, they adopted a list of 88 constellations and gave them precise boundaries, like the borders of states or nations. That meant that every star could belong to only one constellation. The way the borders were drawn, Alpheratz stayed with Andromeda. There’s no way to not see the star as part of the Great Square. So unofficially, Alpheratz maintains its dual citizenship: the second-brightest star of Andromeda, and the brightest star of the Great Square of Pegasus. We’ll have more about the flying horse tomorrow. Script by Damond Benningfield

The United States and China both plan to land astronauts on the Moon in the next few years. And scientists from both countries are working on the best landing sites – places that are safe and easy to operate from, but that offer some interesting science. One of China’s possible sites is just north of the equator, near the center of the hemisphere that faces Earth. It offers a range of geologic features, spanning almost all of lunar history. The site is known as Rimae Bode. It’s along the boundary between a smooth volcanic plain – the Sea of Vapors – and a more jumbled region in the lunar highlands. It features ancient lava flows, deep channels, layers of volcanic ash, and material blasted out of a nearby crater. Samples from these regions would help scientists piece together more than four billion years of impacts, volcanic activity, and other events. Planetary scientists are especially interested in the layers of ash, which also contain tiny glass beads. The material might have been blasted from deep below the surface billions of years ago. They would provide details about the Moon’s interior – hard-to-come-by insights into our satellite world. The crescent Moon teams up with the planet Venus in the early evening sky the next couple of nights. Venus is the brilliant “evening star.” But they’re quite low as twilight fades, so there’s not a lot of time to enjoy the view before they set. Script by Damond Benningfield

The roster of constellations includes some weird and wonderful creatures. There’s a dragon, a unicorn, and two centaurs. But perhaps the weirdest of all is Capricornus, the sea-goat – it’s half goat and half fish. It’s associated with the god Pan, who was half goat and half man. The story says that he was about to be attacked by the monster Typhon, so he jumped into the water to escape. At the same time, he tried to transform himself into a fish to speed his getaway. But he botched the spell, and turned his human half into a fish, but kept the half that was a goat. The constellation is low in the southeast as darkness falls at this time of year. Its brightest stars form a wide triangle. None of the sea-goat’s stars is all that bright, though, so you need a fairly dark sky to make them out. The brightest forms the left point of the triangle. It’s known as Deneb Algedi – “the tail of the goat.” It’s actually a system of at least two stars. One is about twice as big and heavy as the Sun, and shines several times brighter. The other is a lot like the Sun. The stars orbit each other about once a day. As they do, each one passes in front of the other for a bit. When the fainter star crosses the brighter one, the system’s overall brightness drops by about a quarter. That’s just enough for a skilled observer to notice with the eye alone – a slight flicker in one of the night sky’s oddest creatures. Script by Damond Benningfield

Young star systems are dangerous places. A planet can be pelted by giant asteroids and comets. It can collide with its siblings, and be kicked out of the system by close encounters with other siblings. It might even be swallowed by its parent star. Astronomers in the U.K. recently found evidence of such encounters in several young stars. The researchers zeroed in on stars in three clusters. All of the clusters are young – from about 40 million to 200 million years old. At that age, their star systems might still be chaotic – planets might be getting blasted or destroyed, and they might still be taking shape. Six stars in the clusters showed especially high amounts of lithium. It’s a common planet-building material. But it’s fragile – stars quickly destroy it. So any lithium in the stars must have been added recently. The most likely source is young, rocky planets. The planets could have been kicked inward by the gravity of other planets, or dragged in by gas and dust around the stars. Over time, the remains churn deep into a star’s interior. But some can linger for a few million years – the remains of dead planets. One of the clusters is Blanco 1. It’s 850 light-years away, in the constellation Sculptor. It climbs into the southeast in mid evening, to the lower left of the bright star Fomalhaut. It’s too faint to see with the eye alone, but it’s a decent target for small telescopes. Script by Damond Benningfield

A planet orbiting a dead star 750 light-years from Earth is a real lemon. The planet is shaped like a lemon – a result of the extreme gravity of its parent star. The system is PSR J2322-2650. The star is a pulsar – the crushed corpse of a once mighty star. It’s heavier than the Sun, but only about as wide as a small city. It spins almost 300 times per second, beaming out “jets” of energy. One of the jets sweeps across Earth, so the star appears to “pulse” on and off. The pulsar is so dense that its surface gravity is about a hundred billion times stronger than Earth’s gravity. And the planet is only about a million miles away – about one percent the distance from Earth to the Sun. At that range, the pulsar’s gravity stretches the planet – making it look like a lemon. The planet is about as massive as Jupiter, the giant of our own solar system. And it has a thick atmosphere made mainly of carbon and helium – a combination that scientists can’t explain. Gamma rays from the pulsar heat the planet’s dayside to 3700 degrees Fahrenheit. So you’d need a lot of lemonade to stay cool on this lemon planet. The system is too faint to see with the eye alone, but it’s easy to pick out its location. It’s low in the southeast by mid-evening, close to the left of Fomalhaut – the only bright star in that region of the sky. We’ll talk about another sight close to Fomalhaut tomorrow. Script by Damond Benningfield

The Sun belongs to a rare class of stars: Class G. Members of this class account for only seven or eight percent of all the stars in the Milky Way Galaxy. A star’s class is determined by its surface temperature, which we see as its color. G stars are in the middle of the temperature scale, so they shine yellow or yellow-white. Most class-G stars are in the prime of life – a span that puts them on the main sequence. They’re steadily “fusing” the hydrogen in their cores to make helium. And most of them will stay in that phase of life for 10 billion years or longer. Most of them are within about 15 percent of the mass of the Sun. Any heavier and they’d get hot enough to move up to class F or higher. Any lighter and they’d be cool enough to move down to class K or M. Main-sequence G stars are only a small fraction of the size, mass, and brightness of the top stars. But the stars in higher classes are even more rare than G stars. So the Sun, which is near the top of its class, shines brighter than about 90 percent of the stars in the Milky Way. Not all G stars are on the main sequence, though. Some are bloated and heavy. Such stars are more massive than the Sun. They’ve burned through the hydrogen in their cores, and are fusing hydrogen in a thin shell around the core. But they’re undergoing a transition, so they won’t stay yellow for long – the short-lived monsters of class G. Script by Damond Benningfield

Under a dark sky, far from city lights, the eye alone can see thousands of stars. They come in a variety of brightnesses and colors. Yet only a few of those pinpoints are like the Sun. Stars are classified based on their surface temperature, which is indicated by their color. Hot stars are blue and white, while cool stars are orange and red. The Sun is in the middle, shining yellow-white, with a surface temperature of about 10,000 degrees Fahrenheit. Those traits mean it’s class “G.” From hottest to coolest, stars are classified with the letters O, B, A, F, G, K, and M. Each class is divided into 10 sub-categories. And each star is given a Roman numeral that indicates its size and its stage in life. The Sun is class G2V. That means it’s toward the hot end of class G, and that it’s on the “main sequence” – it’s in the prime of life, converting the hydrogen in its core to helium. A couple of moderately bright G main-sequence stars are in view by late evening. 51 Pegasi is high in the southeast, while Tau Ceti is just climbing into view far below it, close to the horizon. The brightest class G main-sequence star visible from Earth is Alpha Centauri A. It’s the leading light of a triple star system that’s a bit more than four light-years away – closer than any other stars. It’s so far south, though, that it’s visible from only a tiny sliver of the United States. More about G stars tomorrow. Script by Damond Benningfield

To borrow from an advertising campaign, Jupiter is “getting the red out.” Its enormous “eye” – the Great Red Spot – has been shrinking. It’s now just a third as wide as when it was first seen, and it’s getting smaller all the time. The Great Red Spot is one of the most recognizable features in the solar system. But scientists still don’t know that much about it. They don’t know for sure how it formed, why it’s shrinking, or even why it’s red. They have lots of ideas, but no certain answers. The spot was discovered as early as 1831. There were suggestions that it was seen much earlier, but those sightings might have been a different feature. The spot has been tracked on a regular basis since 1878. It’s between two powerful jet streams. They prevent it from wandering to different latitudes. It tops out several miles above the surrounding clouds, and extends at least 150 miles below the clouds. In the late 19th century, the spot was a long oval – about as tall as Earth, but three times as wide. Today, it’s roughly the same size as Earth. And the rate of shrinkage has been increasing. So it’s possible that it could disappear entirely within a few decades. Look for Jupiter close below the Moon at dawn tomorrow. It looks like a brilliant star. The Great Red Spot is visible through a telescope, but whether it’s visible from a particular location depends on the timing. Script by Damond Benningfield

The Moon anchors a prominent triangle in tomorrow’s early-morning sky. The pattern is well up in the east at first light. The stars Pollux and Castor – the twins of Gemini – line up to the upper left of the Moon, with Mars to the upper right. The brilliant planet Jupiter stands well below the triangle. Mars and Pollux are almost exactly the same brightness right now. And they’re the same color: orange. But they achieve that color in different ways. Mars is a planet – a ball of rock and metal that’s smaller than Earth. Its color comes from iron oxide – particles of rust – in the rocks and dust that cover most of its surface. The rust probably formed when iron-rich rocks interacted with liquid water on the surface. But there’s no water on the surface today. So the rocks must have rusted billions of years ago, when Mars was much warmer and wetter than it is today. As the rocks eroded, the Martian winds carried the dust around the globe – enhancing the color of the Red Planet. Pollux, on the other hand, is a star. It completed the prime phase of life, then puffed up to giant proportions – about nine times wider than the Sun. As it expanded, it got cooler. And a star’s color is determined by its surface temperature; cool stars look red or orange. So just by looking at it, we can tell that Pollux is thousands of degrees cooler than the Sun. We’ll talk about the Moon and Jupiter tomorrow. Script by Damond Benningfield

Some of the most imposing features on Mars are its giant volcanoes. The largest is Olympus Mons. It’s more than 13 miles high, and covers an area as big as New Mexico. It’s part of the largest complex of volcanoes on the planet – a region called Tharsis Ridge. The second-largest group is on Elysium Rise. Its largest member is Elysium Mons. It’s the fourth-highest mountain on the planet. It has an elevation of about 10 miles above the Martian equivalent of “sea level,” and it towers about eight miles above the surrounding plains. Like the other major volcanoes, it’s extinct – or at least dormant. It probably hasn’t erupted in hundreds of millions of years. It formed over billions of years, from layers of lava and ash. It’s marred by many craters. Some of them are impact craters, carved by giant space rocks. Others may be volcanic vents, formed by side eruptions of gas or lava. The volcanoes on Mars have grown so big mainly because there are no plate tectonics. Once a pool of magma forces its way to the surface, it just keeps going – the crust above it doesn’t move away. So there’s no “cut-off” valve – the volcano erupts as long as there’s molten rock below to keep feeding it – building some giant mountains on the Red Planet. Mars appears below the Moon in tomorrow’s early morning sky. It looks like a fairly bright orange star. More about the Moon and its companions tomorrow. Script by Damond Benningfield

Little Red Dots might be like Tootsie Roll Pops: colorful on the outside, dark on the inside. They may consist of a glowing cloud of gas and dust encircling a supermassive black hole. And they could be telling us about the birth of the first big black holes in the universe. Little Red Dots were first seen in 2022, by Webb Space Telescope. Since then, it’s discovered hundreds of them. They’re compact but extremely bright. And they’re so far away that we see them when the universe was no more than about one-tenth of its current age. Astronomers have proposed several explanations for them. One is the idea of a black hole surrounded by gas and dust. A recent study looked at a dot that was behind a huge cluster of galaxies. The cluster’s gravity magnified the view of the dot, making it easier to suss out its details. Its heart is a black hole about 50 million times the mass of the Sun. The surrounding cloud is no more than half that mass. As material in the cloud funnels inward, it gets hot, lighting up the rest of the cloud. The gas and dust absorb blue light, so we see only red. Astronomers have pondered the formation of early galaxies for decades. They’ve wondered whether the giant black holes in their hearts formed first, or if the galaxy came first and the black hole formed later. The new finding suggests that, in at least some cases, the black hole came first – born at the heart of a Little Red Dot. Script by Damond Benningfield

In the past decade, astronomers have “heard” almost 400 mergers between black holes. The signals were carried by gravitational waves – tiny ripples in spacetime. They’ve revealed that some of the black holes probably had undergone earlier mergers – making them third-generation black holes. Gravitational waves are produced by the motions of any object. But the waves are extremely weak. So far, the only ones that have been detected were produced by mergers involving black holes or neutron stars – dense, heavy objects that come together in a fraction of a second. The characteristics of the waves reveal the masses of the merging objects. They also reveal how the objects were spinning, and how they were orbiting before the merger. And those details provide hints to the existence of third-generation black holes. One example was discovered in late 2024. A black hole about 20 times the mass of the Sun merged with one about six times the Sun’s mass. Scientists determined that the heavier black hole probably formed from an earlier merger. They even calculated the details of those black holes: about 7 and 13 times the mass of the Sun. Third-generation black holes probably form in places where lots of black holes are jammed close together, such as the hearts of star clusters. That keeps a merged black hole from escaping – setting up the possibility of more mergers ahead. Script by Damond Benningfield

The Moon charges at the Pleiades late tonight. As seen from most of the United States, it will pass especially close to the star cluster – either just skimming its edge or briefly covering some of its stars. The cluster is home to more than a thousand stars of all varieties. The ones that are visible to the eye alone are especially big, hot, and bright. But they’re greatly outnumbered by stars that are much smaller, cooler, and fainter. Many of the stars belong to systems of two stars or more. And the cluster also hosts many “brown dwarfs” – objects that are more massive than planets, but not heavy enough to shine as true stars. Over the decades, there’s been a lively debate about the distance to the cluster. Different telescopes and techniques have provided measurements that vary by many light-years. The best current number puts the distance at about 440 light-years. But that’s the distance to the center of the Pleiades. The cluster actually spans several dozen light-years in all directions. So as you look at the cluster, the light you see from the stars that are closest to Earth headed our way dozens of years earlier than the light from the stars that are farthest – an out-of-sync view of a well-known star cluster. The cluster’s brightest stars form a tiny dipper shape, although it’ll be tough to make out through the moonlight. The cluster will be especially close to the Moon at dawn. Script by Damond Benningfield

The center of the Milky Way Galaxy is packed with treasures: stars, dead stars, gas clouds, and lots of planets. And a new space telescope will spend a lot of its time sorting it all out. That’s one of several big projects for Nancy Grace Roman Space Telescope, NASA’s next big space observatory. The telescope will see the heavens as clearly as Hubble Space Telescope does. But its view will be much wider. And it’ll study the universe mainly in the infrared – wavelengths that are invisible to the human eye. Roman will tackle some of the biggest problems in modern science. As one example, it’ll look away from the center of the Milky Way to study more than a billion other galaxies, and to look for exploding stars. That combination will help us understand how the universe is expanding – a key for deciphering the mystery of dark energy. The telescope’s survey of the center of the galaxy could reveal thousands of new planets. And a special instrument – using a technique proposed by Nancy Roman herself – could provide images of some of those planets. A planet will appear only as a bright dot, with no detail. But breaking down its light will tell us a bit about the planet’s size, temperature, and composition. The center of the Milky Way is in Sagittarius, which is low in the south at nightfall. Its brightest stars outline a teapot. The heart of the galaxy is in the steam above the spout of the teapot. Script by Damond Benningfield

The planet Venus and the star Spica huddle close the next few evenings. They’re quite low in the west-southwest in early twilight. Venus is the brilliant “evening star.” Tonight, Spica stands close above it. Venus will slide to the left of Spica over the following nights. Venus is named for the Roman goddess of love and beauty. It’s the only major planet in the solar system named for a female character. With a few exceptions, all of the features on its surface are named for women as well – from both mythology and real life. No features were named until the Space Age. Venus is covered by an unbroken blanket of clouds, so we can’t see the surface. Radio telescopes on Earth peered through the clouds in the ’60s, and discovered the first known features. All the other features were mapped by spacecraft in orbit around Venus, which scanned the planet with radar. Today, more than 2,000 features have been named – mountains, craters, canyons, plains, and others. Their names have come from cultures around the world and across the ages. One volcano is named Anuket, for an Egyptian river goddess, while another is named La Shen for a Chinese goddess. Other features are named for Anne Frank, Jane Austen, Pocahontas, and Queen Isabella of Spain, along with other writers, artists, rulers, scientists, and women from many other fields – all commemorated on the planet Venus. Script by Damond Benningfield

If you look carefully at pictures of Saturn, you’ll probably notice something odd about the planet – it looks mashed down, like a beachball that a child is sitting on. The planet is more than 7,000 miles wider through the equator than the poles – only a bit less than the total diameter of Earth. That makes it the “flattest” planet in the solar system. Saturn is the Sun’s second-largest planet, after Jupiter – more than nine times the size of Earth. But it’s much less dense than any other planet. It’s a big ball of hydrogen and helium – the two lightest elements – wrapped around a messy core of rock and metal. Despite its size, Saturn spins in a hurry – its day is less than half as long as a day on Earth. That high-speed rotation pushes material outward at the equator – giving Saturn that “squashed” appearance. That shape affects the planet’s gravity. Saturn’s poles are much closer to the center of the planet than the equator is. And anything at the equator is being pushed outward by the high-speed rotation. The combination means that you’d weigh about a third more at the poles than at the equator – perhaps making you feel more squashed on this giant but squashed planet. Look for Saturn close to the lower right of the Moon as they climb into good view, in mid-evening. It looks like a bright golden star. Tomorrow: famous women on the planet Venus. Script by Damond Benningfield

The world’s top tennis players will spend many hours under the lights over the next two weeks. And thanks to some changes made a couple of years ago, almost all of the light will shine down on them – not into the sky. The U.S. Open is played on 17 tournament courts and five practice courts in Queens, New York. Many of the sessions take place at night. But conventional outdoor lighting directs a lot of light into the sky, producing light pollution. To reduce the glow, the venue replaced its lighting in 2024. The new L-E-D fixtures are shaped and shielded so that almost all of their light shines down onto the courts. The change was certified as “dark-sky friendly” by DarkSky International, a group that’s been encouraging better outdoor lightning for 25 years. Cities, parks, and other places get certified by changing their lighting, and enacting policies designed to keep night skies dark. In all, the group has certified more than 270 sites around the world. And since 2019, it’s certified more than 40 sports venues, most of them in the U.S. – from Texarkana to Waukesha, Wisconsin, and from Seattle to Panama City, Florida. Light pollution does more than just ruin the view of the night sky. It can interfere with the migration of birds, sea turtles, and other animals. It wastes energy and money. And it can hurt people’s health. So reducing light pollution is a winning strategy. Script by Damond Benningfield

The Moon will ply the dark waters of the celestial sea the next few nights – a large region of sky that’s populated by constellations related to water. Tonight, the Moon sails from Aquarius the water bearer into Pisces, the fishes. Pisces is so long that the Moon will remain inside its borders until Monday night. The “sea” consists of six major constellations. Together, they cover almost one-eighth of the entire sky. All of them were created thousands of years ago by cultures around the Mediterranean Sea. The constellations probably were associated with water because the Sun passed across them during the rainy season. Like the open ocean on a moonless night, the entire region is dark – most of its stars are quite faint. The brightest of the lot is Fomalhaut. It’s in Piscis Austrinus, the southern fish. The star climbs into view in the southeast in early evening, and swims across the south during the night. It’s bright on its own, but the lack of other bright lights around it makes it really stand out. Pisces is especially dark. Most of its stars are impossible to see from light-polluted cities, or even the suburbs. And with the almost-full Moon passing through, it’s hard to see any of its stars even from sites that are far away from city lights. So as the Moon moves across the constellation, it looks like it’s floating through an ocean of darkness – the cosmic waters of the celestial sea. Script by Damond Benningfield

A season comes to an end today. It has nothing to do with falling leaves, changing weather, or even big-time sports. Instead, it’s a season of eclipses. It didn’t last long – it started on August 12th, with a total solar eclipse, and it ends tonight, with a partial lunar eclipse. The Moon will be almost completely immersed in Earth’s long shadow, so it’ll turn dark. And at least part of the eclipse will be visible across almost all of North America. An eclipse season is governed by the way in which the Sun and Moon align. Most months, the geometry isn’t right – the Moon and Sun don’t line up the right way, so there are no eclipses at all. But every 173 days, they come into the proper alignment. That produces a solar eclipse at new Moon, and a lunar eclipse at full Moon. They can come in either order, a fortnight apart. And a season lasts for about five weeks – a few days longer than the Moon’s cycle of phases. So if there’s an eclipse near the start of the season, it produces three eclipses. This time, the solar eclipse came a few days after the season began, so we’re limited to two eclipses – including tonight’s. The Moon first dips into Earth’s dark inner shadow at 9:34 p.m. Central Time. The eclipse peaks at 11:13, when the shadow covers 96 percent of the lunar disk. It ends an hour and a half later. Script by Damond Benningfield

The full Moon won’t look quite itself for part of tomorrow night. That’s because it’ll pass through Earth’s long shadow, creating a partial eclipse. At its peak, the shadow will cover all but a sliver of the lunar disk. That will darken the surface, with sunlight that filters through Earth’s atmosphere adding an orange or red tint. Lunar eclipses occur only at full Moon, when the Moon lines up directly opposite the Sun. The Moon’s orbit around Earth is tilted a bit, so most months the Moon passes above or below the shadow. But at least twice a year, the geometry is just right, and the Moon plunges into the shadow. This eclipse is only partial, not total. That means the angle isn’t quite perfect, so the Moon won’t be fully immersed in the shadow. But it’ll be hard to tell much of a difference – the shadow will cover 96 percent of the lunar disk. At least part of the eclipse will be visible from almost the entire United States. It gets started at 8:24 p.m. Central Daylight Time, when Earth’s outer shadow first touches the Moon. It’s so faint that you might not even notice it. But you will notice the partial eclipse, when the Moon enters the dark inner shadow. That starts at 9:34 p.m., peaks at 11:13, and ends at 12:52 a.m. on Friday. More about the eclipse tomorrow. Script by Damond Benningfield

As the roster of known planets in other star systems grows, astronomers learn a lot more about planets and stars in general. One key finding is that almost all stars are still infants when their planets form. A planet is born from a disk of gas and dust around the newborn star. Solid particles stick together to form larger and larger bodies. They eventually form a chunk of rock and metal that can be much more massive than Earth. If these embryos are far enough from the star, where conditions are cold, they may sweep up vast amounts of leftover gas to form giant worlds. Observations of infant stars and planets suggest that most planets take shape within 10 million years or so. By then, the star’s radiation and winds have cleared away most of the raw ingredients for making planets. That leaves only the planets and some leftover “building blocks.” The gravity of the giant planets kicks many of the building blocks out of the system. But others remain, forming asteroids and comets. The planetary system isn’t in its final form by then. Gravitational interactions can cause a planet to move toward or away from the star, change the angle of its orbit, or even get kicked out of the system. And the asteroids and comets can pound the young planets – perhaps giving birth to moons. So while planets form quickly, they continue to evolve throughout the lifetime of their star system. Script by Damond Benningfield

Of the thousands of planets that have been discovered in other star systems, only a few orbit stars that are easy to see with the eye alone. Most of the stars are so faint or so far away that they just fade into the firmament. One exception is Hamal, the brightest star of Aries, the ram. It climbs into view, in the east-northeast, by mid-evening. It’s about 66 light-years away, but it’s bright enough that it’s easy to see from all but the most light-polluted cities. Hamal is so bright because it’s completed the “prime” phase of life – a phase known as the “main sequence.” Now it’s in the next phase, as a giant. It’s puffed up to about 15 times the diameter of the Sun, making it much brighter. Hamal has one confirmed planet – Hamal b. It, too, is a big ‘un – it’s almost twice as massive as Jupiter, the giant of our own solar system. But the planet is only a little farther from Hamal than Earth is from the Sun. So every square inch of the surface receives about 10 times more energy than the same-sized patch of Earth. As a result of that bombardment, Hamal b is extremely hot. That makes it highly unlikely to host any form of life – at least not like any life on Earth. And if it ever did have life, it probably perished as Hamal expanded and brightened. So Hamal b isn’t a good place to go hunting for neighbors. We’ll have more about planets in other star systems tomorrow. Script by Damond Benningfield

Jupiter is climbing away from the Sun, moving a little higher into the dawn sky day by day. Right now, it’s quite low in the east as twilight paints the sky. But it’s also quite bright, so if you have a clear horizon, you’ll be able to pick it out. Despite appearances, Jupiter isn’t really close to the Sun at all. It looks close only because of the relative positions of Jupiter and Earth. As seen from Earth, Jupiter passed behind the Sun in late July, so it was hidden in the Sun’s glare for several weeks. But Earth follows a smaller, faster orbit around the Sun. Now, we’re looping around toward Jupiter. We’ll catch up to it and pass it next February. So Jupiter will rise earlier and remain in view longer every day until then. Jupiter repeats this cycle every 13 months. In other words, wherever it appears in the sky now, it’ll be in a similar position 13 months later. But it won’t appear against the same background of stars. It takes Jupiter almost 12 years to orbit the Sun, so it takes that long for it to complete one full circle through the constellations. On average, it shifts eastward by about one constellation per year. So while it’s currently in Cancer, by the next time it graces the dawn sky, next September, it’ll be one constellation over, in Leo. Again, look for Jupiter low in the east during the dawn twilight, and climbing higher into the sky morning by morning. Script by Damond Benningfield

The Sun narrowly skirts by the heart of the lion today and tomorrow – the star Regulus. At their closest, they’ll be separated by just a fraction of a degree. After that, the Sun will slide across Leo for almost four weeks before moving into Virgo. That may surprise those whose astrological sign is Virgo. The Sun is supposed to cross into Virgo tomorrow. That highlights two points: the difference between the “signs” and the constellations, and the Sun’s changing position relative to both. The constellations of the zodiac were drawn thousands of years ago. They were based on connect-the-dots patterns of stars, not formal boundaries. The constellations are different sizes, so the Sun spends different amounts of time crossing each one. On average, though, with 12 months and 12 constellations, the Sun spent a month in each. So astrology divided the zodiac into 12 equal slices. That meant the Sun spent an equal amount of time in each sign, regardless of the size of the constellation itself. But the Sun shifts position relative to the background of the stars. So today, the signs and constellations are out of sync by about a month. And in the early 20th century, astronomers assigned formal borders to the constellations. So the Sun spends from about a week to more than five weeks crossing each constellation. And the way the borders are set up, it actually crosses 13 of them – including Leo. Script by Damond Benningfield

The space around our solar system is cloudy. Astronomers have mapped 15 individual clouds within a few hundred light-years. The clouds are moving in different directions, and they have different mixtures of ingredients. Some of those ingredients were forged by exploding stars. Over the past few years, scientists have used one of those ingredients to trace the solar system’s path through the Local Interstellar Cloud. It’s about 30 light-years across, and we’re close to its edge – perhaps in the transition zone with the next cloud. The scientists have looked at a radioactive form of iron that’s produced when a massive star explodes as a supernova. The explosion scatters the atoms, creating clouds of debris – including iron-rich dust grains. As Earth flies through a cloud, it sweeps up some of the dust, which falls to the surface. The scientists have found the iron in sediments on the bottom of the ocean, and in fresh snow in Antarctica. And recently, they found it in layers of ice deposited 40,000 to 80,000 years ago, also in the Antarctic. Those samples fell to Earth before the others did. And they have lower amounts of the radioactive iron. That could mean that Earth was just entering the Local Cloud during that period. The amount of iron went up as we passed deeper into the cloud. Now, the amount is going down again – perhaps heralding the solar system’s exit from the Local Cloud. Script by Damond Benningfield

All is not well with the universe – or at least our understanding of it. There’s growing evidence, for example, that “dark energy” might not behave the way scientists had thought. And that behavior might control the universe’s fate. Dark energy was discovered three decades ago. It may account for two-thirds of all the matter and energy in the universe. And it appears to cause the universe to expand faster as it ages. So far, no one knows for sure what dark energy really is. One idea is that it’s “constant” – perhaps a property of space itself. As the universe expands, it creates more space, so there’s more dark energy. But no more matter is created. The existing matter spreads out, so the effect of its gravity gets weaker. Dark energy then becomes even more dominant, making the universe expand faster and faster. But some recent studies suggest that dark energy might not be constant – it might change over time. If so, then the universe might not expand forever. One study says the universe could end in 20 billion years. Over the final few billion, gravity would take control, pulling everything into a Big Crunch. All the stars and galaxies would smash together. Finally, everything would merge to form a single black hole. After that, perhaps the universe could rebound in another sort of Big Bang. But that universe would be quite different – a universe that we can’t even begin to understand. Script by Damond Benningfield

In the mythology of ancient Egypt, the universe began when a great god emerged from the void. He created the air and the divine order of the world. And they gave birth to the land and sky. That’s one of countless creation stories – attempts to explain the birth of the universe. To modern science, the best explanation is the Big Bang, an instant of creation 13.8 billion years ago. Several pieces of evidence support the Big Bang. For one, on the largest scales, galaxies are all racing away from each other. If you trace the motion back in time, everything comes together in a single point. For another, the Big Bang left its “fingerprints” on the universe – an afterglow known as the cosmic microwave background. It was created when the early universe had cooled enough for light to travel freely. As the universe expanded, the afterglow shifted to radio wavelengths, which we see in every direction. One more bit of evidence is the way elements are created. According to the theory, the Big Bang itself created hydrogen and helium, the simplest elements. Later, the first stars “fused” those elements together to make heavier ones. Over time, the percentage of heavy elements has increased as stars make more of them and release them into space. And that’s just what astronomers observe when they look into the universe – a steady build-up of heavier elements, dating to the beginning of time. More tomorrow. Script by Damond Benningfield

The universe consists of everything we can see, plus a whole lot more – all matter and energy, space and time. It was born 13.8 billion years ago, in the Big Bang. It’s been expanding and changing ever since. We don’t know how big it is – it might be infinite. We’re not sure how it will end. And we don’t even know what most of it is made of. Universe comes from a Latin word that means “combined into one.” It’s been described as everything that is, that ever has been, and that ever will be. When the universe was born, it consisted almost entirely of hydrogen and helium, the simplest chemical elements. Some of those elements came together to make the first stars, which clumped together to form galaxies. As the first stars aged, they created heavier elements, which were incorporated into later stars. Some of those elements formed planets, and even the life on Earth. But most of the universe is hidden. About two-thirds of everything in the universe consists of dark energy. We don’t know what it is – only that it’s making the universe expand faster. About a quarter of the universe consists of dark matter. We don’t know what it is, either – perhaps some type of exotic particle. Everything else – all the stars and galaxies and energy that we can see and experience – makes up just five percent of the universe – the bare tip of the cosmic iceberg. More tomorrow. Script by Damond Benningfield

The Artemis II astronauts got to see something that only 24 other people have seen with their own eyes: the far side of the Moon. As they looped behind the Moon, the astronauts could see almost the entire hemisphere that remains hidden from those of us on Earth. The Moon is “locked” so that one hemisphere always faces our planet – a result of the same process that creates ocean tides. We didn’t get our first glimpse of the farside until 1959, when a Soviet probe snapped a picture. The two lunar hemispheres look different. While dark volcanic plains cover about a third of the nearside, they cover just one percent of the farside. The farside is more heavily cratered. And the crust on the farside is thicker. That could be the result of a gentle “splat” by a smaller moon when the Moon was young. The farside often is called the dark side of the Moon – “dark” as in unknown or unseen. It actually receives just as much sunlight as the nearside does. But the nights are darker there. From the nearside, Earth is in view most of the time, brightening the nights. But Earth is never seen from the farside. So the nights are illuminated only by the stars – making the dark side of the Moon a really good spot for stargazing. The crescent Moon is low in the west in early evening. The planet Venus, the “evening star,” is close to its right. And the star Spica is even closer above the Moon. Script by Damond Benningfield

The first of a series of lunar “spy” satellites entered orbit around the Moon 60 years ago today. There wasn’t any secret about it – it was conducted in full public view. But its camera system was adapted from one built for an Air Force spy satellite. Lunar Orbiter 1 was the first American spacecraft to orbit the Moon – a half-dozen earlier attempts had all failed. Its main goal was to snap high-resolution pictures of possible landing sites for Apollo astronauts. But it would also map a good portion of the lunar surface, and take a close-up look at a few spots on the far side. And it would measure the Moon’s gravitational and magnetic fields. Its camera system used two lenses – one for close-ups, the other for wider views. The images were recorded on 65-millimeter film, then processed in an on-board lab. Finally, they were scanned and transmitted to Earth. Eastman Kodak had created the camera system for a spy satellite called SAMOS. But for that craft, the film was dropped back to Earth, where it was grabbed by an airplane as it parachuted toward the surface – something they couldn’t do from a quarter of a million miles away. Lunar Orbiter 1 took more than 200 pictures. They were combined with the images from four successor missions to produce the most comprehensive atlas of the lunar surface to that time. And scientists continue to study the images today. Script by Damond Benningfield

A stellar vanishing act led to a revelation about an iceball far from the Sun: It has a thin atmosphere. It’s the smallest object with a known atmosphere in the entire solar system. The object is 2002 XV93. It’s in the Kuiper Belt – a wide “doughnut” beyond the orbit of Neptune, the Sun’s outermost major planet. The belt contains millions of icy bodies, including Pluto. XV93 is about 300 miles in diameter – just one-fifth as big as Pluto. Astronomers in Japan watched the little iceball in January of 2024. They’d calculated that XV93 would pass in front of a star, hiding the star from view. As they watched the star disappear, it didn’t blink out instantly. Instead, it dimmed a bit before it passed behind XV93. And it took a moment to reach full brightness when it returned to view. That meant that something was partially obscuring the star: an atmosphere. It’s only about one percent as thick as Pluto’s atmosphere, which is a bare wisp. XV93’s gravity is extremely weak, so it can’t hang on to any atmosphere for long. So the gases might vent into space from its interior, which would keep the atmosphere going. Or they might have surrounded the object after it was hit by a small comet. In that case, the atmosphere would start to vanish quickly – eventually leaving XV93 airless. Script by Damond Benningfield

After teaming up with the Sun to produce a solar eclipse today, the Moon will make another skywatching spectacle possible tonight – the Perseid meteor shower. It’s expected to be at its peak tonight. And since the Moon is new, it won’t be around to interfere with the sparklers. The Perseids occur every August, as Earth flies through the orbital path of Comet Swift-Tuttle. The comet is a ball of frozen gases mixed with bits of rock and metal. As it approaches the Sun, some of its gas vaporizes. That releases some of the heavier material, known as comet dust. As Earth zips through this material, some of the dust grains slam into our atmosphere at more than a hundred thousand miles per hour. They vaporize instantly, creating meteors – streaks of light across the sky. Swift-Tuttle returned to the inner solar system a third of a century ago. That was its first appearance since the Civil War, so the Perseids were especially good for a while. With the comet retreating into the outer solar system, though, there’s less comet dust to feed the shower. The meteors enter the atmosphere from the direction of Perseus – hence the name. But they can streak across any part of the sky, so you don’t have to look to a specific region to see them. To view the Perseids, find a safe, dark observing site away from the pesky glare of city lights. Then watch the sky for cosmic sparklers. Script by Damond Benningfield

The top of the world will see a total solar eclipse tomorrow. A partial eclipse will encompass a wider slice of the globe, including Alaska and parts of the northeastern United States. A solar eclipse occurs when the Moon passes directly between Earth and the Sun, blocking the Sun from view. The Sun’s hot but faint outer atmosphere, the corona, looks like silvery tendrils radiating away from the Moon. This eclipse begins when the lunar shadow first touches Earth, over northeastern Russia. The eclipse path then passes near the north pole, slides across parts of Greenland and Iceland, and finally over northern Spain before vanishing over the Mediterranean Sea. At its peak, off the coast of Iceland, totality will last for 2 minutes, 18 seconds. A partial eclipse, where the Moon covers only a portion of the solar disk, will flank that path. In addition to parts of North America, it’ll encompass much of western Europe and western Africa. From far-northern Alaska, the Moon will cover more than half of the Sun’s disk, at about 8:30 a.m. From Anchorage, about a quarter of the Sun will be covered. And from the northeast, the greatest eclipse takes place in northern Maine, shortly before 2 p.m. If you’re in one of those areas, remember to protect your eyes. Watch the eclipse only through special glasses or dark welder’s glass, and never look at the unfiltered Sun. Script by Damond Benningfield

A total solar eclipse is coming up on Wednesday. The Moon will cover the Sun, turning day to night across a narrow slice of the globe. Parts of Alaska and the northeastern United States will see a partial eclipse. The timing of the eclipse is known down to the second, and has been for decades; astronomers can predict eclipses far into the future. But making such predictions isn’t easy. It requires a detailed knowledge of the Moon’s orbit around Earth, Earth’s orbit around the Sun, and even the shapes of Earth and the Moon. Just when the first prediction was made is unclear. There’s no doubt that people have been predicting lunar eclipses for thousands of years. But they’re easier to forecast. Earth’s shadow is roughly 35 times wider than the Moon’s, so you don’t need to be quite as precise to get it right. There are stories that the Chinese were predicting solar eclipses more than 4,000 years ago, but no confirmation. An eclipse in 585 BC that stopped a war supposedly was predicted by a Greek scientist. But many present-day scientists doubt that. The first confirmed prediction was made by Edmond Halley, using the laws of gravity recently devised by Isaac Newton. Halley forecast that an eclipse would cross England on May 3rd, 1715. And he was right. So the event is known as Halley’s Eclipse – honoring the prediction of an astronomical spectacle. Script by Damond Benningfield

The Moon forms a nice triangle with the twins of Gemini at dawn tomorrow – the stars Castor and Pollux. Castor is to the left of the Moon, with brighter Pollux about the same distance to the lower left. Castor consists of six known stars. We haven’t found planets orbiting any of them. Pollux is a single star. And it has one likely planet – a giant that’s much heavier than any of the planets in our own solar system. The planet was discovered 20 years ago, by astronomers at McDonald Observatory. They’d seen evidence of the star earlier, but they couldn’t confirm it. The planet is known as Pollux b. It also has a formal name – Thestias – a variation of the name of Pollux’s mother in Greek mythology. The planet is almost three times the mass of Jupiter, the Sun’s largest planet. It’s farther from Pollux than Earth is from the Sun. But that’s much too close for the planet to be habitable. That’s because Pollux has passed beyond the prime phase of life. It’s puffed up to about nine times the Sun’s diameter, so it’s much brighter than the Sun. That extra energy makes Thestias much too hot to have liquid water at its surface – a key ingredient for life. The temperature could have been more comfortable in the past. The planet itself probably is a big ball of gas – not a good place to live. But if it has any moons, it’s possible that they could have offered better environments for life. Script by Damond Benningfield

The terms that describe the phases of the Moon can be a little confusing. Take tomorrow morning, for example. From most of the United States, the Sun will light up one-quarter of the lunar hemisphere that faces Earth. You might think that would make it a “quarter” Moon – but no. A “quarter Moon” doesn’t describe the Moon’s appearance – it describes the position in its month-long cycle of phases. The cycle begins when the Moon is new. The Moon crosses the line between Earth and the Sun then, so it’s hidden in the Sun’s glare. A bit more than a week after that, the Moon is a quarter of the way through the cycle – it’s at first quarter. It lines up at a right angle to the Earth-Sun line, so the Sun lights up half of the visible disk. A week later comes full Moon. And a week after that comes last quarter – three-quarters of the way through the cycle. Once again, half of the lunar disk is illuminated – but it’s the opposite half from the first-quarter Moon. Then the Moon rolls back around to new – starting a new cycle. The next cycle starts on Wednesday. And this time it brings a rare treat – a total solar eclipse. In the meantime, look for the Moon passing through Taurus tomorrow. Aldebaran, the bull’s bright eye, is to the right of the Moon. Elnath, the tip of one of its horns, is closer to the lower left of the Moon. As a bonus, Mars is below them, and the Moon will pass close to it on Sunday. Script by Damond Benningfield

The Dog Star is just beginning to emerge from the Sun’s glare in the dawn sky. By tradition, that means we’re just getting into the Dog Days of summer. Sirius is the brightest star in the night sky. It’s climbing into view in the morning glow of the brightest star in all the sky – the Sun. Sirius is quite low in the east-southeast shortly before sunrise. It’s best seen from the southern tier of states, although it’ll pull into better view from the northern states over the coming days and weeks. Sirius is also the leading light of the constellation Canis Major, the big dog, so it’s known as the Dog Star. And that’s where we get the name for this part of summer – the Dog Days. Sirius makes its closest approach to the Sun during summer, disappearing for a few weeks in the Sun’s glare. In ancient times, it returned to view in the morning by early July – just as the weather was reaching its hottest. At the time, it seemed logical to associate the bright star with the sweltering weather. So the people of ancient Greece and Rome named that stifling time of year in the star’s honor. Thanks to an effect known as precession, the stars shift position with respect to the Sun over the centuries. So Sirius now returns to view a few weeks later than it did thousands of years ago. So the heat is already in full force at northern latitudes – the Dog Days of summer. Script by Damond Benningfield

NGC 6397 seems like a pretty ordinary globular star cluster. It’s not especially big or bright, and nothing about its stars is going to strike anyone as odd. Yet it’s been an important astronomical laboratory. Among other things, it’s helped astronomers determine the age of the galaxy, and the minimum “weight” of a star. NGC 6397 is in the constellation Ara, the altar. It’s below the tail of Scorpius, the scorpion. That puts it so far south that it’s visible only from the southernmost United States. Hubble Space Telescope has monitored the cluster for decades. It contains several hundred thousand stars, packed into a ball only a few dozen light-years across. The Milky Way contains about 150 of these clusters, which are the galaxy’s oldest inhabitants. Over the decades, Hubble has monitored many of the cluster’s stars. The observations helped astronomers lock down the minimum mass for an object to shine as a true star – about eight percent the mass of the Sun. Another set of observations helped measure the cluster’s distance – just 7800 light-years – one of the closest of all globulars. That number is important for determining the cluster’s age – 13.4 billion years. That means that NGC 6397 – and its home galaxy, the Milky Way – took shape when the universe was just 400 million years old. Script by Damond Benningfield

The gods of ancient Greece weren’t great parents. One of the ancient gods known as the Titans, for example, swallowed his newborn children. Eventually, though, the kiddos escaped and overthrew him. Their victory is commemorated in the stars, as the altar where they swore allegiance to each other. It’s the constellation Ara, and it’s below the tail of the scorpion. In the story, Cronus was the king of the Titans. He’d come to power by defeating his own father. A prophecy said that one of his children would defeat him. To prevent that, he swallowed each of his first five children. But his wife, Rhea, got tired of that plan. When the last child was born, she hustled him away to an island and gave Cronus a rock wrapped in a blanket. That child was Zeus. When he grew up, he returned home and forced his dad to cough up his brothers and sisters. They pledged to defeat the Titans, and won a 10-year war. Zeus became the king of the new gods and ruler of the sky. To celebrate the victory, he placed the altar among the stars. The altar is so far south that most of it’s visible only from far-southern parts of the United States – places like Florida, South Texas, and especially Hawaii. Ara is one of the smaller constellations, with only a couple of moderately bright stars. But it does have some good deep-sky objects, and we’ll talk about one of them tomorrow. Script by Damond Benningfield

The formal name for a planet almost 50 light-years from Earth is Kua’Kua – a Costa Rican name that means “butterfly.” But there’s nothing beautiful or delicate about this world. Its surface is a desolate landscape of volcanic rock. The planet is in the system LHS 3844. Its star is a cool, faint ember known as a red dwarf. Kua’Kua – LHS 3844 b – is a super-Earth. It’s bigger and heavier than Earth, and it’s made of rock and metal. The planet is only about half a million miles from the star, and the same hemisphere always faces the star. So the dayside sizzles at more than 1300 degrees Fahrenheit. Every 11 hours, the planet passes behind the star as seen from Earth. Astronomers have watched several passages with Webb Space Telescope. Watching before and after a passage revealed the combined make-up of the star and planet. But when the planet disappeared, that left only the star in view. Comparing the readings revealed details about the surface of the planet. In fact, it’s the first “exoplanet” for which we have such a close look. The surface appears to be made of dark volcanic rock that could have been deposited recently, making it fairly smooth and unbroken. But the surface also could be much older. In that case, a constant pounding by radiation and meteorites could have pulverized the surface. Either way, Kua’Kua is not a good place to go hunting for butterflies. Script by Damond Benningfield

The dawn twilight has a bright visitor the next few mornings – the planet Mercury. It’s farthest from the Sun for its current morning appearance. It looks like a bright star, but it’s so low in the sky that it’s tough to find. Mercury holds an important spot in the history of astronomy and physics. It provided some of the first confirmation of General Relativity – Albert Einstein’s theory of gravity. Mercury’s orbit around the Sun is lopsided, so the planet’s distance from the Sun varies. For a long time, astronomers had seen that the orbit’s closest point shifted a tiny bit over time. Isaac Newton’s laws of gravity explained most of the difference. But there was still a tiny amount that couldn’t be accounted for. Einstein’s theory of gravity held that massive bodies warp the space around them. Since Mercury is the Sun’s closest planet, its orbit is influenced by that “warpage” more strongly than any other planet’s. In fact, general relativity accounted precisely for the shift in the orbit. So Mercury’s orbit provided some of the first evidence to support general relativity – a new way of thinking about gravity. Look for Mercury quite low in the eastern sky during the waxing twilight. It’ll shine a little brighter each day over the next few mornings. But it’ll also drop a little closer to the Sun, so you’ll need a clear horizon to spot it. Tomorrow: catching waves. Script by Damond Benningfield

The Sun is getting bigger, hotter, and brighter. The change isn’t enough to notice during a human lifetime – or even a thousand lifetimes. It plays out over hundreds of millions of years. And it’s all the result of changes deep inside our star. Like all stars in the prime phase of life, the Sun is “fusing” atoms of hydrogen in its core to make helium. That generates the energy that makes the Sun shine. As the amount of helium builds up, the core gets denser, so gravity squeezes it more tightly. That speeds up the fusion reactions, making the core even hotter. Radiation from the hotter core pushes on the Sun’s outer layers, making the Sun bigger. It also makes its surface hotter. The combination of bigger and hotter makes the Sun brighter. So over its four-and-a-half-billion-year lifetime, our star has grown about 15 percent wider, and perhaps 40 percent brighter. That should mean that the young Earth would have been an iceball. But studies suggest the atmosphere was much thicker when Earth was young. The atmosphere also contained much more carbon dioxide and other greenhouse gases. They trapped more heat, keeping Earth from freezing over. The Sun’s bigger-hotter-brighter trend will continue. In perhaps a billion to two billion years, it’ll be so hot and bright that Earth’s air and oceans will boil away. That will reduce our planet to a bare cinder. Script by Damond Benningfield

Eta Aquilae is big, bright, and unsteady. Over a bit more than seven days, the star pulses in and out like a beating heart. That causes its brightness to change. How it changes makes the star a good “standard candle” – a type of object that astronomers use to measure the scale of the universe. Eta Aquilae is a Cepheid variable – the first one ever discovered. Such stars brighten and fade in a predictable way. By timing the cycle, astronomers can determine the star’s true brightness. Comparing that to how bright the star looks allows them to calculate the star’s distance. Cepheids are bright enough to see hundreds of millions of light-years away – in galaxies beyond the Milky Way. To go even farther, astronomers rely on another type of standard candle: the exploding stars known as Type Ia supernovas. Like the Cepheids, the way they brighten and fade reveals their true brightness. Some of them appear in galaxies with Cepheids, where we already know their distance. That provides a way to calibrate all of the supernovas, which can be seen from billions of light-years away. Of course, it’s all a little more complicated than that. There are different classes of Cepheids, for example. So astronomers have to understand all the details – making sure that a standard candle really is a good distance marker. Eta Aquilae is high above the Moon in early evening, near Altair, its constellation’s brightest star. Script by Damond Benningfield

Saturn feels like it has a big region of the early morning sky practically to itself right now. The giant planet climbs into good view after midnight, and stands high in the south at first light. It looks like a bright golden star. You have to scan a long way in every direction to find another planet or star that rivals it. Saturn is traveling through Pisces, skimming along the border with Cetus. That region of the sky is well below the Milky Way – the hazy band of light that outlines the disk of the Milky Way Galaxy. When we look at the Milky Way, we’re looking into the most heavily populated part of the galaxy. So not only are there a lot more stars in and around that band, there are a lot more bright stars. At the same time, Saturn’s location is a quarter of the way around the sky from the center of the galaxy, which is in Sagittarius. Again, that means we’re looking into more thinly settled parts of the galaxy. It’s like looking toward the suburbs of a major city instead of its busy downtown – there’s just a lot less to see. Saturn is so far from the Sun that it takes the planet about 30 years to make one full circle against the starry background. So the planet will stay in this dimly settled region of the sky for a couple of years – making it especially easy to find as you look into the darkness. Tomorrow: bright “mile markers” for measuring the scale of the universe. Script by Damond Benningfield

Gliese 710 isn’t much to look at. It’s smaller and lighter than the Sun, and just one-tenth as bright. So from its current distance of 62 light-years, it’s much too faint to see with the eye alone. But come back in about 1.3 million years and it’ll be a different story. The star will shine about three times brighter than Sirius, the night’s current brightest star. All the stars are on the move. Like the Sun, they’re orbiting the center of the Milky Way Galaxy. Each star follows its own path, so its direction and speed are a little different from all the other stars. Some stars are moving toward us, while others are moving away. Gliese 710 is moving toward the Sun at more than a quarter of a billion miles per year. Studies have shown that it’ll pass just one-sixth of a light-year away – just four percent the distance to the current closest neighbor. That’s closer than any other star will approach the Sun over the next several million years. Gliese 710 will pass through the Oort Cloud – a huge shell of rocky, icy bodies that surrounds the Sun. That will push many of those objects toward the Sun. Some of them could slam into Earth – some un-neighborly gifts from a close neighbor. Gliese 710 is in Serpens, the serpent. The star is about half way up the south-southeastern sky at nightfall. You need a telescope to see it – for now. Script by Damond Benningfield