Globular clusters are the oldest members of the galaxy. They’re tight balls of hundreds of thousands of stars, most of which were born when the universe was no more than a couple of billion years old. Their most-massive stars have long since died. And most of the stars that remain are cool and faint. So a globular tends to be fairly quiet and calm. But that doesn’t mean that things don’t change.

Consider Messier 13. It’s in Hercules, which is high in the east at nightfall. Under dark skies, the cluster is just visible to the unaided eye, looking like a faint, fuzzy star.

The cluster is about 25,000 light-years away, and it contains up to half a million stars. But the stars at the edge of the cluster aren’t held as tightly as those in the middle. So the gravity of the rest of the galaxy can pull some of them away. In fact, astronomers have identified a few dozen stars that appear to be escapees from M13.

But the cluster also can grab stars from the space around it. One especially young star probably became a member of the cluster that way.

And stars inside the cluster can change. Some of them merge, forming bright, blue stars that look much younger. And stars die. M13’s brightest member is dying right now. It’s about as massive as the Sun, but it’s puffed up to dozens of times the Sun’s diameter. Soon, it’ll blow away its outer layers, leaving only its tiny, dead core – one more change in an ancient family of stars.

Script by Damond Benningfield

Three of the four big moons of Jupiter appear to have something in common: oceans of liquid water below their crusts. For Europa, the ocean is considered a slam dunk. The case is also strong for Ganymede. But the case for the third moon, Callisto, is the weakest.

Callisto is about 3,000 miles in diameter – bigger than our own moon. And it’s more heavily cratered than any other large body in the solar system. That indicates that the surface of Callisto is pretty much dead. But things might be different far below the surface.

In the 1990s, the Galileo spacecraft flew near Callisto eight times. Its measurements of the magnetic field around the moon hinted that a salty ocean was sloshing around inside. But those observations also could be produced by an electrically charged layer of Callisto’s thin atmosphere.

In a recent study, though, scientists looked at all of Galileo’s observations, and used computer models to understand them. The work suggested that there is an ocean. It could be dozens of miles deep. But it’s buried beneath an icy crust that could be hundreds of miles thick.

Two spacecraft that are en route to Jupiter will fly close to Callisto many times. Their observations should tell us for sure whether an ocean is sloshing below Callisto’s battered surface.

Jupiter stands below our moon in the early evening twilight. It looks like a bright star.

Script by Damond Benningfield

If stars had trophy cases, Vega’s would be packed. The leading light of Lyra was the first star other than the Sun to have its picture taken, the first to have its spectrum taken, and the first with a published measurement of its distance.

Vega is impressive in many ways. It’s more than twice the size and mass of the Sun, and about 50 times the Sun’s brightness. It’s encircled by a wide belt of dust, produced by collisions between big chunks of ice and rock. In about 12,000 years, it’ll serve as the Pole Star. And in about 200,000 years it’ll become the brightest star in the night sky.

Vega first had its picture taken in 1850. In 1872, an astronomer took a picture of its spectrum, spreading its light into its individual wavelengths. A spectrum reveals a star’s composition, motion, and much more.

In 1838, Russian astronomer Friedrich von Struve published Vega’s parallax – the first publication for any star. He plotted its position when Earth was on opposite sides of the Sun. That revealed a tiny shift against the background of more-distant objects. That shift revealed a distance of about 26 light-years – just one light-year off the modern measurement.

Vega is low in the east-northeast at nightfall and climbs high overhead during the night. It’s the fifth-brightest star in the night sky, so you can’t miss it – a beautiful star with a case full of trophies.

Script by Damond Benningfield

One of the major beauties of the summer sky dangles in the northeast this evening like a piece of cosmic jewelry – the constellation Lyra. Its brightest star is Vega – the fifth-brightest star in the night sky. It sparkles like the diamond stud in an earring. The rest of Lyra hangs to its lower right like the rest of the earring. It forms a parallelogram – a slanted rectangle. Under fairly dark skies, it’s easy to see.

Lyra represents a lyre – a small harp. In skylore, it was sometimes shown being held by a large bird – an eagle or vulture. In fact, the name “Vega” comes from an Arabic phrase that means “the falling eagle.” But mainly the lyre was associated with the story of Orpheus.

His music was legendary. When he accompanied Jason and the Argonauts, his playing silenced the Sirens – evil creatures who lured sailors to their doom.

Orpheus married Eurydice. But she was bitten by a snake and died. Orpheus begged Hades, the god of the underworld, to let Eurydice return to him. His music was so beautiful that Hades agreed. But there was one condition: Orpheus couldn’t look back until they were outside. But he couldn’t resist – he looked too soon, and Eurydice vanished into the underworld forever.

Orpheus was heart-broken. He roamed aimlessly across the countryside, playing sad but beautiful music on his lyre – an instrument commemorated in the stars.

We’ll have more about Vega tomorrow.

Script by Damond Benningfield

The names of the stars are a cultural mash-up. The names come from Greek, Latin, Arabic, and other cultures. And some names combine words from different languages. Two examples are the stars Tania Borealis and Tania Australis. “Tania” comes from an Arabic phrase that means “the second.” Borealis and Australis come from Latin, and mean northern and southern. Combined, the stars represent the second leap of the gazelle – a bit of skylore from Arabia.

Skywatchers there saw three close pairs of stars as the leaps of a gazelle. All three pairs are at the edge of the modern constellation Ursa Major, the great bear. The “Tanias” are above the stars that form the outer edge of the dipper’s bowl.

Tania Borealis is a single star that’s a good bit bigger, brighter, and heavier than the Sun. It’s at the end of the prime phase of life, so it’s undergoing big changes in its core. That’s causing its outer layers to begin to puff up to giant proportions.

Tania Australis is a binary – two stars bound together by their mutual gravitational pull. One of the stars is similar to the Sun. The other is more than six times the Sun’s mass, and it’s already reached the “giant” phase of life. It’s puffed up to about 75 times the Sun’s diameter, and it shines about a thousand times brighter. So Tania Australis looks a bit more impressive than its northern cousin – the brighter half of the second leap of the gazelle.

Script by Damond Benningfield

A gazelle leaps past the feet of the great bear. In ancient skylore, in fact, it made three leaps – each marked by a pair of stars.

The stars that mark the first jump are known as Alula Borealis and Alula Australis – the northern and southern first leaps. As night falls this evening, they’re high in the northwest. They’re far to the left of the Big Dipper, which has the most prominent stars of the great bear. The “alulas” are close together, so they resemble a pair of eyes.

Alula Australis holds an important distinction in the history of astronomy.

A telescope reveals it’s a “double” star – two stars that are close together. By measuring the motions of the stars, in the late 18th century, astronomer William Herschel showed that they’re bound to each other. That made the system the first confirmed binary – two stars that move through space together, tied by their mutual gravitational pull.

A few decades later, it became the first binary to have its orbit accurately measured. The stars orbit each other once every 60 years, at an average distance of more than 20 times the distance from Earth to the Sun.

In more modern times, astronomers found that both stars are binaries on their own – each has a small, faint companion in a tight orbit. So the first leap of the gazelle consists of at least four stars, leaping through the galaxy as a family.

We’ll talk about the second leap tomorrow.

Script by Damond Benningfield

About 44 lightning bolts flash through the skies of Earth every second. And for a while, it seemed there might be more flashes than that on Venus.

Telescopes on Earth and spacecraft in orbit saw flashes of light in the planet’s clouds, or heard the sounds of lightning in the planet’s radio waves. One estimate said Venus could see several times more lightning bolts than Earth.

But studies in recent years have suggested that lightning on Venus might be quite rare.

Venus has a much thicker atmosphere than Earth does, topped by clouds of sulfuric acid. But there’s very little water vapor in the clouds. And water is a key ingredient for lightning on Earth and other worlds where it’s been confirmed. So that led to some skepticism about claims of lightning on Venus from early on.

A Sun-watching spacecraft has swung close to Venus several times. It’s listened for radio waves like those produced by lightning on Earth. It found them. But they were headed in the wrong direction – toward the ground, not into space, as they are on Earth.

And a Venus orbiter has spent hundreds of hours looking for lightning flashes, but hasn’t seen a thing. In fact, one recent study said some of the flashes seen from Earth might really be meteors burning up in Venus’s atmosphere. So lightning might be rare on our neighboring planet.

Venus is the bright “morning star.” Tomorrow, it’s close to the crescent Moon.

Script by Damond Benningfield

If you ever want to chat with someone on another planet, you better have a lot of patience. It takes a long time for a message from Earth to reach another world, and just as long for the reply to reach Earth.

That’s because radio waves travel at the speed of light. And although light is pretty swift, its speed is limited – 670 million miles per hour. Given the scale of the solar system, that means there’s a long pause between halves of a conversation.

Consider the planets that flank the Moon at dawn tomorrow: brilliant Venus to the lower left of the Moon, and fainter Saturn to the upper right.

Right now, Venus is more than 58 million miles away. At that distance, it would take a radio signal from Earth about five and a quarter minutes to get there – a round-trip time of 10 and a half minutes.

Saturn is about 930 million miles away. So the round-trip travel time is about two hours and 45 minutes.

That’s a big concern for the folks who send probes to these and other planets. Despite what you might see in sci-fi movies and TV shows, there’s no way to have a real-time conversation. So spacecraft are programmed to do much of their work without direct help from Earth. And if they encounter a problem, they shut down most of their systems and place a call for help – then settle in for the long wait to hear from home.

More about the Moon and Venus tomorrow.

Script by Damond Benningfield

A 900-mile-wide, two-toned walnut orbits the planet Saturn. It’s Saturn’s third-largest moon, and definitely the most eye-catching. One hemisphere is as dark as coal, while the other is as bright as sea ice. And a mountain ridge wraps around the equator, making it look like a walnut.

Iapetus was discovered in 1671. And right away, astronomers realized there was something odd about it. It was easy to see when it was on one side of Saturn, but invisible on the other. Today, we know why that’s the case: the planet’s leading hemisphere is 10 to 20 times brighter than the trailing hemisphere.

The leading idea says that long ago, the darker side was pelted by dust and rocks blasted off some smaller moons. The darker material trapped the Sun’s heat, vaporizing ices. The vapor drifted to the other side, where it froze, making that side bright. And that process continues today – making Iapetus the “yin and yang” of moons.

The ridge around the equator is about six miles high. It might have formed long ago when Iapetus rotated much faster than it does today. Or it might be the remains of a ring that collapsed onto the surface – making Iapetus look like a walnut.

Saturn appears quite close to our own Moon at dawn tomorrow. It looks like a bright star to the lower left of the Moon. The much-brighter planet Venus is farther to the lower left. More about this morning lineup tomorrow.

Script by Damond Benningfield

For the most part, black holes come in two varieties: small and jumbo. The small ones are the remnants of dead stars. They range from a few to about a hundred times the mass of the Sun. The jumbos inhabit the hearts of galaxies. They range from about a hundred thousand to several billion times the Sun’s mass. But there just isn’t much in the middle.

In fact, astronomers have logged only a few dozen medium-sized black holes. And many of those are controversial – they’re hard to confirm. Most of them are in other galaxies, so it’s hard to see their influence on the stars and gas around them.

One recent study may have added to the tally. Using observations designed to study dark energy, scientists said they discovered about 300 medium-sized black holes. About 70 of them inhabit the centers of small galaxies. Those black holes are gobbling gas and dust around them, making them brighter and easier to find.

Theory says there should be many more black holes in size “medium.” They may be the remnants of the ultra-massive stars that populated the early universe. Or they may have formed when dense clumps of gas collapsed under their own gravity. Either way, it’s possible that such black holes were the “seeds” from which the jumbo black holes grew.

For now, the search continues for these hard-to-find medium-sized black holes.

Script by Damond Benningfield