StarDate

Apep was one of the nastier gods of ancient Egypt. He was the god of chaos — a huge snake that lurked in the underworld, fighting the Sun god Re every night.

And he’s the namesake of a star system that could have a nasty future. One of its stars could produce a blowtorch that could destroy any life within hundreds or thousands of light-years.

Officially, the system is known by a catalog number. But in a picture obtained last year, it looks a bit like a coiled snake — a form that helped inspire the nickname.

Apep is about 8,000 light-years away. It consists of three stars. Two of them form a tight pair. The third is well away from them.

The members of the pair probably are Wolf-Rayet stars. These are massive stars that are near the ends of their lives. They’re extremely hot and bright. And they die in violent explosions.

Some of the explosions produce outbursts of gamma rays, the most powerful form of energy. In a few seconds, such an outburst releases more energy than the Sun will produce in its entire lifetime. The beam of gamma rays could incinerate anything close to the star, and severely damage planets at much greater range.

One of the Wolf-Rayet stars is spinning so fast that it’s almost whirling itself apart. It’s producing a “wind” of gas that’s blowing at more than seven million miles per hour. The rotating stream of gas collides with a slower stream from its companion. That produces the coiled-snake appearance — the spooky look of Apep.

Script by Damond Benningfield

Most big, heavy stars die in violent explosions. But some are more violent than others. The most powerful produce cosmic “death rays” — beams of energy that could kill any living thing within thousands of light-years.

A gamma-ray burst may form when the core of a heavy star collapses to form a black hole. Gases around the core form a swirling disk around the black hole. The disk gets so hot that it produces an outburst of gamma rays — the most powerful form of energy.

The gamma rays fire out through the poles of the dying star. These beams are incredibly powerful. They can emit more energy in a few seconds than the Sun will produce in its entire lifetime — about 10 billion years.

The beams of gamma rays are narrow, though, so we have to line up along one of the beams to see them. And our gamma-ray detectors have to be looking at the right time — most bursts last only a matter of seconds.

If we miss the gamma rays, though, we still see some impressive fireworks. The star’s outer layers blast into space as a hypernova — an especially powerful supernova. That part of the outburst can shine brilliantly for months.

Planets that line up close to the beam of gamma rays could be incinerated. And life on planets thousands of light-years away could be destroyed.

Fortunately, no likely future bursters are close enough to Earth to be a concern. But astronomers have identified a star that could produce a gamma-ray burst fairly soon. More about that tomorrow.

 
Script by Damond Benningfield

Most of the time, the planet Venus is the brightest object in the night sky other than the Moon. Once or twice a year, though, it disappears in the Sun’s glare. And that’s what’s happening now. Venus is passing behind the Sun as seen from Earth, so it’s hidden from view.

This alignment is called superior conjunction. It happens about every 19 and a half months. Venus is farthest from Earth at that point — about 160 million miles away. So from our perspective, the planet moves across the sky quite slowly. As a result, it stays close to the Sun for several months — too close for us to see.

Superior conjunction is by the far the longer of Venus’s two vanishing spells. The other occurs at inferior conjunction, when Venus passes between Earth and the Sun. At that point, Venus is only about 25 million miles away — closer than any other planet ever gets. Because of the close range, Venus moves across the sky in a hurry, so it switches from the evening sky to the morning sky in just a few days — hardly enough time to even notice that it’s gone.

But after disappearing from the morning sky, it stays out of sight for much longer. This time, for example, it dropped from view in July. And it won’t return to view in the evening sky until late September or early October, depending on your latitude. Then Venus will begin a long run as the “evening star” — until it vanishes once again, in late May.

Tomorrow: Looking for powerful cosmic “death rays.”

Script by Damond Benningfield

One of the treasures from the tomb of King Tutankhamen is an elaborate pectoral — a piece of jewelry worn on his chest that honored the Sun god. It’s made of gold inlaid with turquoise and other colorful stones. And its centerpiece is a scarab beetle made of golden glass — a symbol of the Sun god, and of the cycle of life.

The glass formed in the Sahara Desert about 29 million years ago. And a recent study says it was the result of an impact by a big space rock.

Scientists have debated the origin of Libyan Desert Glass for decades. Some studies have suggested it formed when a space rock exploded above the surface. The resulting heat melted the desert sand, creating slabs of glass that were blasted across many square miles.

But the new study, by researchers in Australia, says the meteoroid made it all the way to the ground.

The impact melted the sand, just as an airburst would have. An impact, though, created more powerful shock waves, which rippled through the melted glass. That converted grains of zircon to a mineral known as reidite. Over time, that mineral reverted to zircon. But it left a “fingerprint” in the zircon, which the researchers discovered.

At least a couple of big space rocks are known to have exploded in the atmosphere in the last century-plus, supporting the idea of an airburst over the Sahara. The new research, though, suggests that such outbursts might be less common — and less of a threat to life — and to desert sands.

Script by Damond Benningfield

After cozying up to the solar system’s biggest planet a couple of nights ago, the Moon sets its sights on the second-biggest planet tonight. Saturn looks like a bright star to the left of the Moon as darkness falls. It’ll stand even closer above the Moon as they set in the wee hours of the morning.

The Moon can appear close to both worlds because all three bodies follow roughly the same path across the sky. It’s known as the ecliptic. Technically, it marks the Sun’s path. But the Sun’s major planets all stay within a few degrees of the ecliptic, and so does the Moon. So the Moon passes close to Jupiter and Saturn every month.

Saturn’s orbit is tilted by about two and a half degrees. That means the planet never appears farther from the ecliptic than roughly the width of your finger held at arm’s length. The Moon’s orbit is tilted by about five degrees. So some months, the Moon passes above Saturn, and some months it passes below.

Occasionally, though, their paths precisely overlap. When that happens, the Moon passes in front of Saturn, briefly blocking the planet from view.

Such an event is known as an occultation. And the next one is coming up in November. It won’t be visible from the United States, though. Instead, it’ll highlight the skies of Australia, New Zealand, and some islands in the Southern Ocean — a disappearing act made possible by the clockwork precision of the solar system.

Tomorrow: A fiery birth for an ancient Sun god.

Script by Damond Benningfield

The Perseid meteor shower will be at its best the next few nights. This “rain” of space dust has put on some good shows over the decades. Unfortunately, though, this year’s probably won’t be one of them. The gibbous Moon will overpower all but the brightest of the “shooting stars.”

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 heavier rock and metal. As it approaches the Sun, some of its gas vaporizes. In turn, that releases some of the heavier material. The bits of debris are known as comet dust.

When Earth flies through this material, some of the dust grains slam into our atmosphere at tens of thousands of miles per hour. They vaporize instantly, creating meteors — streaks of light across the night sky.

Swift-Tuttle returned to the inner solar system a quarter of a century ago. That was its first appearance since the Civil War, so the Perseid showers 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 shower should peak on Monday night. Its meteors enter the atmosphere from the direction of the constellation Perseus — hence the name. But they can appear anywhere in the sky, so you don’t have to look at a specific region to see them.

To view the Perseids, find a safe, dark observing site away from city lights. Then watch the sky for cosmic sparklers.

Script by Damond Benningfield

There are two features in the solar system that just about anyone will recognize. One is the rings of Saturn. The other is the baleful “eye” of Jupiter: the Great Red Spot.

Recent work suggests that both are temporary. Saturn’s rings could disappear in as little as a hundred million years. And the Great Red Spot could be gone in decades.

Astronomers have kept an eye on the Great Red Spot — the solar system’s largest storm — for a couple of centuries. And they might have seen it as early as the 1600s. At its peak, it was more than twice as wide as Earth.

In the last few decades, though, it’s been shrinking. Today, it’s only about half its earlier diameter. And in the last couple of years, it’s started to show some odd behavior. Friction with a band of clouds below the spot has started pulling out blade-shaped streamers of clouds. The streamers wrap around the spot, and they can stretch for thousands of miles.

It’s possible that that’s just part of a normal cycle. But it’s also possible that the streamers could drain away this giant storm — marking the beginning of the end for one of the solar system’s best-known features.

And Jupiter is especially easy to find this evening. It looks like a brilliant star, quite close to the lower right of the Moon. As a bonus, the bright orange star Antares — the heart of the scorpion — is a little farther along the same line, completing a beautiful lineup in the evening sky.

Script by Damond Benningfield

A planet that’s as solid as a bowling ball is peeking into view in the early dawn sky the next few days. It’s low in the east-northeast as twilight begins to paint the sky. It looks like a fairly bright star, but it’s so low that you need a clear horizon to spot it.

Mercury is the closest planet to the Sun. It’s also the Sun’s littlest planet. It’s about half again the diameter of the Moon. And like the Moon, its surface is pockmarked by craters — the scars of countless collisions with space rocks over the last four and a half billion years.

On the inside, though, Mercury is built a lot like Earth. And a recent study revealed just how much.

Scientists carefully studied readings made by Messenger, a craft that orbited Mercury for four years. It monitored Mercury’s magnetic field. And scientists tracked Messenger’s orbit around Mercury, which revealed the planet’s gravitational field.

When combined, those observations allowed scientists to map the planet’s interior. They found that Mercury has a solid inner core made of iron, surrounded by an outer core of molten metal. The inner core spans more than a third of the planet’s total diameter. By comparison, Earth’s inner core accounts for only about one-fifth of our planet’s diameter.

That massive core means that Mercury is the planetary equivalent of a bowling ball — a heavy, dense little world spinning in its lane around the Sun.

Tomorrow: a giant planet that may be losing its “eye.”

Script by Damond Benningfield

Deneb — the brightest star of Cygnus, the swan — stands high in the eastern sky during the evenings at this time of year. It forms the northernmost point of the big, bright Summer Triangle, so it’s easy to pick out.

Deneb’s brilliance makes it a popular target for casual skywatchers, but not necessarily for the pros.

They already know some basics about Deneb: It’s a blue supergiant that’s perhaps 2500 light-years away, for example. And it’s going through some changes. They should cause the star to get even bigger, and to change colors from blue to orange. But a lot of questions remain.

It’s hard to get answers because there just isn’t a lot of time available to study an individual star.

Most of the observing time on the world’s biggest telescopes is devoted to objects that are faint and far away — things like distant galaxies and quasars.

And when astronomers do look at a bright star, it’s often as part of a study of a group of similar objects — blue supergiants, for example, or stars that pulse in the same way that Deneb does.

To study a star in detail, astronomers tend to use smaller telescopes. A study about Deneb a few years ago, for example, used more than 300 nights of observations made with a one-meter telescope, which is pretty small by modern standards.

Studies like these have answered some of the questions about Deneb. But as is often the case, they’ve raised a lot more — questions that may take some time to answer.

Script by Damond Benningfield

You might think that astronomers would know just about all there is to know about one of the biggest, brightest stars in our section of the galaxy. That’s not quite the case, though. The star still presents a lot of mysteries.

Deneb is the brightest star in Cygnus, the swan. It’s high in the east-northeast at nightfall, at the northernmost point of the wide Summer Triangle.

Astronomers do know quite a bit about Deneb. They know that it’s about 15 to 20 times as massive as the Sun, and more than a hundred times wider. They know that it’s hotter than the Sun, too. They’ve seen that it pulses in and out a bit, but in an odd way — like a heart in which each chamber cycles to its own beat. And they know that it’s a good ways off, although the exact distance is still a little uncertain.

But there are a lot of things that astronomers don’t know about Deneb.

They don’t know exactly what’s happening in its core, for example. They’re pretty sure that it’s converted its original hydrogen fuel to helium, but they don’t know if it’s burning the helium yet.

They also aren’t sure what’s around the core. It could be a layer of gas made of heavier atoms, which rises and falls like the boiling water in a tea kettle.

And they’re not even sure how fast Deneb turns. Most stars of its class rotate slowly, but Deneb appears to turn faster.

In a way, the questions highlight how modern astronomy works, and we’ll explain how next time — on Star Date.

Script by Damond Benningfield