StarDate

Our galaxy, the Milky Way, is home to hundreds of billions of stars. Some are small, cool, and faint. Others are big, hot, and dazzlingly bright. Yet they all formed in the same basic way: from the collapse of a cloud of gas and dust.

At first, such a cloud is cold and dark. Then something causes it to break into smaller clumps — perhaps the shockwave from a nearby exploding star.

After that initial jolt, the gravity of the gas and dust in each clump causes it to collapse. As the material gets squeezed, it heats up. Eventually, it forms a warm ball surrounded by a wide disk — a stage known as a protostar.

After a million years or so, a protostar that’s up to a few times the mass of the Sun becomes a T Tauri star. It looks like a fully formed star, but it’s much brighter. That’s because it’s still collapsing, so there’s a lot of surface area to radiate energy into space.

At first, that glow comes from the gravitational energy of the star’s collapse. As the star continues to shrink, though, nuclear reactions fire up in its core — first with a heavy form of hydrogen, and then with normal hydrogen.

The T Tauri phase can last for millions of years. It ends when the reactions in the core generate enough energy to counteract the inward pull of gravity, stopping the star’s collapse. The star then enters the main sequence — the stellar equivalent of adulthood. That stage can last for billions of years — the long, long life of a star.
 

Script by Damond Benningfield

 

Some astronomers will be keeping an eye on Orion in the early morning hours over the next few weeks. They’ll be watching a star near Orion’s Belt to see if it gets dimmer. If it does, it could mean that the star is orbited by a planet with a monster set of rings.

The star is known as PDS 110. It’s just above Orion’s Belt as it rises in the wee hours of the morning.

The star is bigger, brighter, and heavier than the Sun. But it’s also a stellar infant — it’s only about 10 million years old, compared to four and a half billion years for the Sun. It’s too faint to see with the unaided eye, because it’s more than a thousand light-years away.

For about a month in both 2008 and 2011, the star got even fainter.

Astronomers considered several explanations for the fade out. And earlier this year, a team proposed that it’s the result of an eclipse by a set of rings around an orbiting planet. The team says the planet orbits the star every 2.2 years. The planet is tilted in such a way that we see its rings cross in front of the star once during each orbit. And the rings may be hundreds of times wider than the rings of Saturn, so it takes weeks for them to pass across the star.

The astronomers say the next eclipse should take place this month — perhaps as early as this weekend. So they’re keeping an eye on PDS 110 in the wee hours before dawn. If it dims as predicted, it’ll confirm that the star is orbited by a planet with a monster set of rings.

Script by Damond Benningfield

The largest moon of the planet Neptune may have lost a twin. In fact, that may be why it orbits Neptune at all.

Triton is about 1700 miles in diameter — a bit smaller than our own moon. It’s one of 14 moons known to orbit Neptune, but the only one of any consequence — it’s about 300 times more massive than all the other moons combined.

Much of the surface of Triton looks like the wrinkled skin of a cantaloupe. It consists of frozen nitrogen atop a layer of water that’s frozen harder than granite. Geysers of nitrogen mixed with dust spew up to several miles high. Winds push the plumes across dozens of miles. The plume material then settles back to the surface, forming dark streaks.

Perhaps the most intriguing thing about Triton is its orbital motion: It orbits in the opposite direction from Neptune’s rotation. That suggests that it wasn’t born with Neptune, but that it was captured by the giant planet’s gravity.

It takes a special set of circumstances for that to happen, though. One possibility is that Triton had a companion. As the pair of them passed close to Neptune, though, the companion was stripped away and shot back into space, while Triton settled into orbit — giving Neptune its biggest moon.

And Neptune stands quite close to our moon tonight. The planet is shining at its brightest for the year. Even so, it’s still too far and too faint to see without a telescope. It looks like a tiny blue disk close to the upper left of the Moon.

Script by Damond Benningfield

 

No matter where you are on Earth, the length of a day is always 24 hours. That’s because our planet has a solid surface, so everything turns at the same rate. But that’s not the case on the giant outer planets. Not only do they not have solid surfaces, they don’t have surfaces at all. Instead, their outermost layers are made of gas. So as these planets turn, different regions can spin at different rates.

That’s especially true of Neptune, the Sun’s most remote major planet. Overall, the giant world spins once every 16 hours. But the zone around its equator takes 18 hours to make one turn, while the regions around the poles make a turn in only 12 hours.

That creates powerful winds at the boundaries between different regions. They can blow at hundreds of miles per hour — some of the fastest winds in the entire solar system.

The different rotation rates at the surface suggest that different zones inside Neptune turn at different rates as well. But measurements of the planet’s interior aren’t good enough to confirm that possibility.

Neptune is putting in its best showing of the year right now. It rises at sunset and is in view all night, in the constellation Aquarius. It’s brightest for the year, too. It’s so far and faint, though, that you still need a telescope to see it. It’s not far to the lower left of the Moon this evening — a small blue dot shining feebly through the moonlight.

We’ll have more about Neptune tomorrow.

Script by Damond Benningfield

Earth is sometimes called the blue planet, for an obvious reason: most of its surface is covered by water. Earth is really a distant second in the “blue” category, though. At the top of the list is Neptune, the most remote of the Sun’s major planets. The entire planet is blue — and scientists aren’t entirely sure why.

Neptune is one of the giants of the solar system. It’s about four times Earth’s diameter, and about 17 times its mass. It probably has a rocky core surrounded by slushy layers of ices. And those layers are surrounded by an atmosphere of hydrogen and helium gas, which is topped by clouds. The clouds are made of ammonia, water, and other compounds.

One of those compounds is methane, and it’s partially responsible for Neptune’s color, because it absorbs red wavelengths of light.

There’s also a lot of methane in the atmosphere of the planet Uranus. But that world has a greener tint than Neptune does. So some other chemical must be making Neptune look even bluer. And so far, scientists haven’t identified that extra ingredient, so they aren’t sure what makes Neptune the bluest planet in the solar system.

Neptune is putting on its best showing of the year right now. It rises at sunset, is in the sky all night, and shines brightest for the year. Even so, it’s so faint that you need a telescope to see it. And the bright Moon is close by tonight, making it even tougher to find this beautiful planet.

More about Neptune tomorrow.

Script by Damond Benningfield

Solar eclipses are rare and spectacular events. As anyone who saw last month’s eclipse can attest, there’s just nothing else like it. So it’s not surprising that many societies have regarded eclipses as either sacred or scary. They held special ceremonies to celebrate an eclipse or to chase it away. And in some cases, they built special structures to host those ceremonies.

One possible example is near the Pacific coast of Peru. A monument there is like no other in that part of the world: It looks like a small volcano. It’s a cone that’s 50 feet tall, with a crater at its summit.

Researchers say that four total solar eclipses were visible from that spot in a span of just 22 years — from 1521 to 1543. And a recent study says the site was last occupied around that same time.

Archaeologists dug into the structure. They found a buried staircase leading to a small chamber a few feet below the surface. Carbon dating shows that a hearth in that chamber was last used around 1563, give or take half a century. And the cone is easily visible from the nearby mountains, where the people of that area built platforms for recording the motions of the Sun along the horizon.

That culture considered a solar eclipse a good omen. So it’s possible that it built the structure to celebrate one or more of the eclipses. The last ceremony then took place around the time of the final eclipse — a time to celebrate the clockwork motion of the heavens.

Script by Damond Benningfield

A star system in the constellation Cygnus, the swan, just can’t seem to settle down. Every few decades, it flares to thousands of times its normal brightness — possible feeding frenzies by a black hole.

V404 Cygni is about 8,000 light-years away. It was discovered during an outburst in 1989 by X-ray telescopes in space. A little digging through old photographs showed that it had also popped off twice before. And it erupted again in 2015.

These outbursts probably are caused by interactions between the system’s two components: a black hole about a dozen times the mass of the Sun, and a “normal” star that’s less massive than the Sun.

The black hole pulls gas off the surface of the normal star. As the gas funnels toward the black hole, it forms a wide but thin disk.

The gas may build up in the outer regions of the disk, with only a trickle pouring into the black hole. Over a couple of decades or more, though, so much gas builds up that it suddenly floods toward the black hole. It’s heated to millions of degrees, so it shines brightly in X-rays. That high temperature creates “winds” of gas that blow away from the black hole.

The process isn’t steady, though. During the outburst in 2015, V404 Cygni’s brightness varied dramatically over just hours or even minutes. One study says that’s because the rush of gas isn’t even. Because of the size of the disk, there are gaps between waves of gas — creating an uneven feeding frenzy for a black hole.

Script by Damond Benningfield

Several stellar time bombs shine in summer’s evening skies. Among the brightest are orange Antares, the heart of Scorpius, which is low in the southwest at nightfall, and Deneb, the tail of the swan, in the east-northeast. Each star will end its life with a titanic explosion known as a supernova.

These and the other future supernovae are all hundreds of light-years away or farther. That’s lucky for Earth, because if they were too close, they could zap our planet — perhaps triggering mass extinctions. Exactly how close is too close is a matter of debate, but it’s probably not more than about 50 light-years.

Supernovae present several threats, including X-rays, which can zap the ozone layer, and cosmic rays, which trigger showers of subatomic particles that pepper the surface. These particles can cause cancer and genetic mutations. And they can trigger thunderstorms, leading to changes in climate.

A supernova 2.6 million years ago may have caused less-dramatic problems. There’s evidence that an unusual number of species disappeared at that time — not enough to classify as a mass extinction, but more than average. That could have been caused by climate changes or other effects, but it also could have been the result of a supernova.

Researchers at the University of Kansas say the supernova was about 150 light-years from Earth — far closer than any current supernova candidate. So we’re probably safe from these big blasts for a long time to come.

Script by Damond Benningfield

A giant doughnut encircles the realm of the planets. Known as the Kuiper Belt, it probably consists of billions of chunks of ice and rock. And one of its first known members was discovered 25 years ago today.

Dave Jewitt and Jane Luu found the object while scanning the sky from Mauna Kea in Hawaii. It was designated 1992 QB1. It took a while longer to confirm its orbit, which placed it well beyond the planets.

Astronomers had suspected that there were objects out there for decades — debris left over from the birth of the solar system. But that region is so far away, and most of its inhabitants are so small, that it took a long time to find any of them.

The discovery of 1992 QB1 confirmed the existence of the Kuiper Belt. And since then, astronomers have found more than a thousand other members. The belt extends billions of miles beyond Neptune, the outermost major planet. And it’s quite thick, with its members following orbits that carry them well above and below the plane of the solar system. So the Kuiper Belt probably should be known as the Kuiper Doughnut.

QB1 wasn’t the first member of the Kuiper Belt to be discovered. That honor goes to Pluto, which was found in 1930. At the time, though, no one had suggested that there were more objects beyond Neptune. That’s one reason why Pluto was designated as a planet. It wasn’t until later that astronomers realized that Pluto is a member of something much bigger: the Kuiper Belt.

Script by Damond Benningfield

Robert Peary and Richard Byrd both claimed they reached the north pole — Byrd by air, and Peary by dogsled. Today, both claims are disputed, although there’s no doubt that both men came close. And they’re just as close to the north pole of the Moon — each has a crater there named in his honor.

In fact, the names of several features at high northern latitudes are related to the Arctic. The most prominent is the Sea of Cold. This dark volcanic plain covers an area as big as the Black Sea here on Earth. It’s far enough from the pole that it’s visible to the unaided eye, near the “top” of the lunar disk.

The craters named for Peary and Byrd are much closer to the pole, and they’re not all that big, so they’re impossible to see without a telescope. Peary said that he reached Earth’s north pole in 1909. And Byrd claimed to have flown over the pole in 1926.

Another far-northern crater is named for Fridtjof Nansen, a Norwegian explorer. In 1895, he pushed farther north than anyone had gone before. And today, his feat is honored on the northern limb of the Moon.

And the Moon is in beautiful view tonight. It’s just past first quarter, so sunlight illuminates more than half of its disk. The Sea of Cold forms a narrow dark streak near the top of the disk. And the Moon is joined by two bright companions. The planet Saturn is close to the lower left of the Moon at nightfall, with the star Antares farther to the lower right of the Moon.

Script by Damond Benningfield