StarDate

At the equator of a planet known as HD 189733b, the weather forecast might go something like this: Hazy skies with a chance of showers of molten glass, high temperatures of almost 2,000 degrees, and winds from the west at more than 5,000 miles per hour.

That’s the picture pieced together from more than a decade of observations of the planet — a giant ball of gas just a couple of million miles from its parent star.

It’s one of several astronomical bodies beyond the solar system on which scientists have seen evidence of weather — winds, clouds, or both. Some of these objects are planets. Others are brown dwarfs — objects that are more massive than planets, but not big enough to shine as stars. And at least one is an actual star — a weak stellar ember that’s far fainter and cooler than the Sun.

The weather on HD 189733b was revealed by space telescopes. As the planet passes in front of its star, starlight filters through the planet’s atmosphere. That adds the “fingerprint” of the atmosphere to the starlight. From that, scientists found that a jet stream blows from east to west at the planet’s equator, at more than 5,000 miles per hour. The winds probably are created by the extreme difference in temperature between the planet’s dayside and its nightside.

The atmosphere also contains tiny grains of silicate. Under the heat of the nearby star, they may form liquid droplets that fall from the sky — a rain of molten glass.

Script by Damond Benningfield

Sirius, the brightest star in the night sky, hunkers low in the southwest as night falls — a brilliant beacon that’s less than nine light-years away.

In the crowded confines of a globular cluster, a star as bright as Sirius might not seem so special. The stars are so tightly packed that the night skies of any planet might be filled with hundreds of stars brighter than Sirius — a display unlike any we’ll ever see on Earth.

Not only would those stars look bright enough to touch, but they might be close enough to touch as well.

A globular cluster contains hundreds of thousands of stars packed into a ball-shaped region of space only a few dozen light-years across. That means that individual stars are separated by light-months or even light-days — a fraction of the distance between stars in our region of the galaxy.

Researchers recently suggested that if a civilization developed around the right kind of star, in the right part of a cluster, it would have plenty of time to expand to other star systems. Its telescopes could find habitable planets in those systems, and it would take perhaps only decades to send probes to investigate them. The civilization could then dispatch colonists to settle those worlds.

Each world would move around the cluster — passing more habitable planets, which could be colonized as well. In that way, the civilization could expand throughout the cluster — populating many of the bright stars in the night sky.

Script by Damond Benningfield

Back in 1974, astronomers used the biggest radio telescope on Earth to beam a message to the stars. The message was a simple picture. Among other things, it showed our solar system, the radio telescope, and a stick figure of a human. The astronomers aren’t waiting for a reply, though — their target was the star cluster M13, which is 25,000 light-years away.

M13 is one of about 150 globular clusters in the Milky Way galaxy. It’s a massive stellar “city” — it consists of about 300,000 stars packed into a ball that’s only a few dozen light-years across.

So far, we don’t know whether there are even any planets in M13, much less intelligent life. In fact, only one planet has been found in any globular cluster. Based on the number of planets discovered closer to us, though, it seems likely that M13 does have planets.

And if it does, there’s been plenty of time for life to take hold and flourish. M13 is about 12 billion years old — far older than our own solar system. Indeed, one recent study says that a civilization could easily spread throughout an entire globular cluster; more about that tomorrow. So it’s possible that we might someday hear back from M13 — an ancient city of stars.

M13 climbs into view in the northeast by about 10 or 11 p.m. It’s between the two stars at the top of the Keystone, a lopsided square at the heart of Hercules. Under dark skies, the cluster is just visible to the unaided eye as a hazy smudge of light.

Script by Damond Benningfield

Most stars are born in bunches — great swarms that form from the collapse of a single cloud of gas and dust. The stars tend to stay together for a while, forming clusters. Over time, though, the gravity of the galaxy’s other stars and gas clouds tends to pull a cluster apart, so its stars go their own ways.

Even then, many of the stars can share a common motion through the galaxy — they move at the same speed, and in the same direction. Such associations are known as “moving groups.” And the title star of one of these groups rises into view in late evening at this time of year.

Zeta Herculis is at the top right corner of the Keystone, a pattern of four stars at the center of Hercules.

Zeta Herculis actually consists of two stars, which are about 35 light-years from Earth. One of the stars is bigger, brighter, and heavier than the Sun, while the other is less impressive than the Sun.

Decades ago, it was discovered that the system shares its motion through space with several other stars, spread across several constellations. That suggested that the stars were born together, so they were called the Zeta Herculis Moving Group.

Over the years, though, follow-up observations have been unable to confirm whether the stars are all the same age. So the stars of the moving group could be related — or they could just happen to share the same motion through the galaxy.

We’ll talk about a group of stars in Hercules that has stuck together tomorrow.

Script by Damond Benningfield

When you take a picture of your friends or family, it’s a moment frozen in time — you see everyone and everything in the picture as they appeared at the same instant. A shot of the night sky, on the other hand, is like hundreds or thousands of individual snapshots all pasted together. That’s because you’re seeing every star as it appeared at some point in the past — anywhere from a few years to thousands of years ago.

The light from each star races through space at 670 million miles per hour — faster than anything else in the universe. Yet the gulf between stars is vast — trillions of miles to even the closest of them. So even light takes a long time to travel from one star to another.

As night falls this evening, for example, look in the southwest for Sirius, the brightest star in the night sky. The light you see from the star tonight actually began its journey 8.6 years ago. That means the star is 8.6 light-years away.

Orion is off to its right, marked by the hunter’s three-star belt. The constellation’s brightest stars bracket the belt — Betelgeuse above, and Rigel below. Each of these stars is hundreds of light-years away, so we see them as they looked hundreds of years in the past.

Betelgeuse and Rigel are both expected to end their lives with titanic explosions. In fact, it’s possible that one of the stars could have exploded already, and the light from the blast is racing toward us — the light for a future snapshot of the night sky.

Script by Damond Benningfield

Of all the galaxies that adorn the cosmos, the most majestic are the stunning spirals such as our home galaxy, the Milky Way. But astronomers have long thought that the most luminous galaxies in the universe are a less attractive type known as ellipticals, which look like fuzzy footballs. Recently, though, a search turned up a new breed of spiral: mammoth galaxies whose size and brightness rival the greatest ellipticals in the universe.

These “super-spiral” galaxies are extremely rare. In fact, the closest example is more than a billion light-years from Earth. The search identifed 53 of them. Each emits eight to 14 times more visible light than the Milky Way, which itself is brighter than most other galaxies. And the largest of them, in the constellation Hercules, has a disk of stars that’s four times larger than the Milky Way’s.

Now that astronomers have discovered these spectacular galaxies, they’re struggling to understand how they formed. Galaxies grow bigger when they gobble up other galaxies. But such violence can disrupt a galaxy’s delicate spiral arms and transform it into an elliptical. Indeed, that may explain why most of the largest galaxies in the universe are ellipticals rather than spirals. Yet somehow the super spirals managed to do what seemed to be impossible: They grew to enormous proportions while retaining their exquisite beauty.

Tomorrow: Taking a thousand pictures all at once.

Script by Ken Croswell, Copyright 2015

Giant galaxies such as our own Milky Way formed long ago, from collisions between many smaller galaxies. Dozens of dwarf galaxies, which are are similar to those early building blocks, orbit the Milky Way today. And astronomers recently discovered a likely dwarf galaxy that’s crashing into the Milky Way even now, showing us the process of galaxy growth in action.

The dwarf galaxy resides near the head of Hydra, the water snake, the longest constellation in the sky. It zigzags up the southeastern sky this evening, although you need a starchart to pick it out.

Hydra I is just 40,000 light-years from Earth — a fraction of the distance to most of the Milky Way’s other companion galaxies.

Hydra I is anything but bright. While the Milky Way contains hundreds of billions of stars, Hydra I consists of only thousands of stars. But those few stars have a fairly high level of iron — a trait of larger galaxies. That suggests that Hydra I used to be bigger, but the Milky Way’s gravity tore it apart and grabbed most of the smaller galaxy’s stars for itself. In fact, a recent study estimates that Hydra I has lost more than 99.99 percent of its stars to the Milky Way.

Hydra I is so modest that it might be a star cluster instead of a galaxy. Either way — a disintegrating galaxy or a disintegrating star cluster — Hydra I demonstrates how the Milky Way grew into a cosmic colossus that rules an empire of dozens of lesser galaxies.

Script by Ken Croswell, Copyright 2015

Big telescopes are usually better than small ones, but the little guys can still make some big discoveries. Astronomers recently proved that point by detecting dozens of ghostly galaxies with an array of telephoto lenses, each of which is just 16 inches across. Named Dragonfly and located in New Mexico, the array of small telescopes captures a large swath of sky with just one exposure.

Astronomers aimed it at the Coma cluster, a huge gathering of galaxies about 340 million light-years from Earth. It’s in the constellation Coma Berenices.

The images revealed 47 large but ghostly galaxies. Many are as big as the Milky Way, but they emit roughly a thousandth as much light, because they have few stars, and the stars are spread out from one another.

These ultra-diffuse galaxies must have lots of dark matter, which exerts a gravitational force but emits no detectable energy. Without dark matter to hold them together, these galaxies would get torn apart by the other galaxies in the Coma cluster.

No one knows how these odd galaxies formed. Perhaps they were on their way to becoming brilliant galaxies like the Milky Way when some of their stars exploded and blew gas out into intergalactic space. Gas is the raw material for stars, so the loss of gas would have shut down the process of starbirth.

Whatever the case, their discovery demonstrates that even in the twenty-first century, small telescopes can still play a big role in astronomy.

Script by Ken Croswell, Copyright 2015

The Coma galaxy cluster is one of the biggest and brightest around. It contains thousands of galaxies, including quite a few that are far more impressive than our own galaxy, the Milky Way. Even so, most of what makes up the cluster is invisible.

The cluster is in the constellation Coma Berenices, which is in the east at nightfall. It’s well above brilliant Arcturus, which is low above the horizon. You need a telescope, though, to see the galaxies.

So far, no telescope can show us the bulk of the cluster’s mass. That’s because it consists of dark matter. This form of matter produces no detectable energy, but reveals itself through its gravitational pull on the visible matter around it. In fact, dark matter was discovered through its influence on the Coma galaxies.

In 1933, astronomer Fritz Zwicky measured the motions of the cluster’s galaxies. He found that all the visible galaxies couldn’t account for those motions — something else was tugging at them. He called it “dark matter” — but it took decades for other astronomers to accept his discovery.

Today, we know that dark matter accounts for about 85 percent of all the matter in the universe. Even now, though, its true nature is unknown. It’s probably a type of particle that interacts with normal matter only through gravity. But no one has yet seen such a particle — leaving our knowledge of the bright Coma cluster a bit in the dark.

More about dark matter and the Coma cluster tomorrow.

Script by Damond Benningfield

A sprinkling of faint stars stands high in the east as night falls this evening, well above brilliant Arcturus, the brightest star in that part of the sky. Those strands of stars are the main feature of Coma Berenices, a constellation that was first drawn just a few centuries ago.

The constellation represents Queen Berenice II of Egypt. The legend says that when her husband was about to head into battle, she offered her beautiful golden hair to the gods in exchange for his safety. When he returned home, she cut her hair and placed it in a temple; the gods then placed it in the stars.

The brightest of those stars looks a lot like the Sun. Beta Coma is about the same size, mass, and brightness as the Sun. It’s also about the same color — fittingly enough, bright gold, which shows up in binoculars or a telescope.

Long-term observations reveal that Beta Coma goes through a 16-and-a-half-year magnetic cycle — half again the length of the solar cycle. During that cycle, the star probably goes through periods of high and low magnetic activity. During active times, more of the dark storms known as “starspots” probably speckle its surface — the result of lines of magnetic force getting twisted and stretched. When they snap, they produce powerful outbursts known as flares — eruptions that are the equivalent of millions or billions of nuclear bombs.

Coma’s real claim to fame isn’t stars, though — it’s a cluster of galaxies. More about that tomorrow.

Script by Damond Benningfield