StarDate

The big dog is best known for the Dog Star, Sirius — the brightest star in the night sky. But many of Canis Major’s bright stars are actually far more impressive than Sirius. They look fainter only because they’re much farther away.

A prime example is Adhara, the constellation’s second-brightest star. Although it looks only a few percent as bright as Sirius, it’s actually thousands of times brighter. But it’s more than 400 light-years farther, which dims its luster.

Adhara is already one of the more impressive stars in the galaxy. It’s 10 times the Sun’s mass, and more than 10 times its diameter. Such heavy stars “burn” through the nuclear fuel in their cores in a hurry, so they produce huge amounts of energy.

Yet Adhara is about to get even more impressive.

It’s at the end of its “normal” lifetime. It’s consumed the original hydrogen fuel in its core, converting it to helium. Now, it’s getting ready to burn the helium to make even heavier elements. As a result, it’ll soon get much bigger, and shine many times brighter. And at the end of its life, the star will get more impressive still: It will explode as a supernova. For a few weeks or months, it’ll outshine billions of normal stars — making Sirius look like a flickering candle by comparison.

Sirius is low in the southeast at nightfall. It’s so bright, though, that it’s easy to find. Adhara perches below it, forming one of the legs of the big dog.

Tomorrow: celebrations of spring.

Script by Damond Benningfield

Chesapeake Bay, on the coast of Maryland and Virginia, is best known for its blue crabs, clams, and other seafood delicacies. It attracts anglers, birdwatchers, and other visitors from around the world — there to enjoy its great natural beauty.

But the bay was born from a cosmic cataclysm. 35 million years ago, a giant asteroid slammed into the surface at 125,000 miles per hour. It blasted out a crater that’s between 25 and 50 miles wide. And it crushed layers of rock up to five miles deep.

Chesapeake is the largest impact crater in the United States, but far from the only one. Geologists have logged almost 30 confirmed craters, and a few more possible ones.

Most of them are so old that they’ve all but vanished. Wind, rain, and the motions of Earth’s crust have washed them away or buried them. But some are still recognizable as craters — especially from the air or space. And a few have left remnants that are easily visible from the ground.

Sierra Madera in Texas, for example, retains part of the crater rim. And a central peak, which formed when rock layers at the center of the impact rebounded, rises almost 800 feet above the crater floor.

The most easily recognizable crater is in Arizona. Meteor Crater formed about 50,000 years ago. Today, the crater still retains its bowl shape. It’s about three-quarters of a mile wide and almost 600 feet deep — the aftermath of a cosmic cataclysm.

Script by Damond Benningfield

The world’s biggest supply of diamonds was created in an instant. An asteroid a few miles in diameter slammed into northern Siberia 35 million years ago. In seconds, the heat and pressure transformed a layer of graphite into diamonds. The deposit could exceed all the other known diamond supplies on the entire planet.

The site is known as Popigai. It’s an impact crater more than 60 miles in diameter. Some of the crater has eroded away or been covered up, but much of it is still visible.

The impact that carved the crater melted hundreds of square miles of rock. And it blasted millions of tons of debris into the sky — some of which landed on other continents.

As the shockwave from the impact raced outward, it heated and squeezed the rocks. At a distance of about seven and a half miles from ground zero, temperatures and pressures were just right to make diamonds. That created a “shell” of diamond-rich rock.

Few if any of the diamonds are gem quality, though. They have a different structure, and most of them are no more than a couple of millimeters across. They’re especially hard, though, so they’d probably be good for industrial uses. That’s not likely to happen soon, though, because Popigai is remote — no towns or roads are anywhere close. And most industrial diamonds are made artificially. So the world’s richest diamond supply is likely to stay right where it is — at the site of a cosmic collision.

More about impact craters tomorrow.

Script by Damond Benningfield

Our home planet is like a target in a shooting gallery. It’s been hit many times by giant space rocks. Each big impact has formed a crater — a bowl-shaped hole in the ground. Most of the craters have been erased by wind, rain, and the motions of Earth’s crust. But scientists have found evidence of almost 200 craters scattered around the world.

The oldest of these craters is in Russia, and dates to about 2.3 billion years ago. The youngest are a group of small craters in Saudi Arabia that could have formed as recently as the late 19th century.

The biggest known crater is in South Africa. It’s called the Vredefort crater after a town that’s inside it.

Most of it has been erased as well. Today, all that remains is a partial ring of hills about 45 miles wide. When the crater was blasted out, though, it probably was almost 200 miles wide. It was created when an asteroid a few miles in diameter hit the surface at 45,000 miles per hour. It melted a lot of rock, forming an ocean of magma.

Rock at the center of the crater rebounded from the impact, forming a dome. That’s what remains today — the ring of hills at the crater’s middle.

At first, geologists thought the ring was the remnant of an ancient volcano. But work in the 1990s showed otherwise. Geologists found that rocks there had been subjected to a powerful shock, and rock layers had been flipped — the result of the impact of a giant space rock.

More about impact craters tomorrow.

Script by Damond Benningfield

Mining for gold and other minerals is risky. Miners can never be sure if they’re going to get rich — or go bust.

If astronauts go mining on the Moon, they can’t afford to go bust. They’ll be prospecting for water — the key to survival on the lunar surface. So scientists and engineers are looking at possible ways to extract the most water with the least effort.

The water forms big deposits of ice at the lunar poles. They’re inside craters that never see sunlight. The ice could be melted for drinking water, and split apart to make hydrogen and oxygen for rocket fuel and oxygen to breathe.

NASA’s funding a couple of small studies of innovative ways to process the ice. One approach, for example, would put giant solar mirrors on the rims of the craters, where they’d be in perpetual sunlight. They’d reflect sunlight onto areas with known ice deposits. That would vaporize some of the ice below the surface. The water vapor would be captured as it rose to the surface.

Another study would use a similar approach. The energy would come from rovers on the crater floors. They’d beam microwaves and other forms of energy into the ice, then capture the vapor in tanks as it reached the surface.

Both studies are in their early stages — first steps toward ensuring successful mining on the surface of the Moon.

And the Moon is in the southwest early this evening. It pairs up with Venus, the brilliant “evening star” — a beautiful scene for a winter’s night.

Script by Damond Benningfield

To the eye alone, the unicorn is a bust — there’s just not much to see. Look deeper, though, and the constellation Monoceros offers plenty to see. The list includes a couple of colorful stellar nurseries, which have given birth to thousands of stars.

The Rosette Nebula is named for its resemblance to a red rose. It’s a cloud of gas and dust that’s more than a hundred light-years across. Several young stars inside the nebula are especially hot and bright. They produce ultraviolet energy, which zaps hydrogen gas in the cloud, causing it to glow.

The visible nebula is part of a larger complex of gas and dust, known as the Rosette Molecular Cloud. It’s given birth to about 2500 stars, all within the last few million years.

Another big cloud in Monoceros is giving birth to new stars, too. It consists of several parts. There’s the Snowflake Cluster, which shines brightly. Nearby are the stars of the Christmas Tree Cluster, which — not surprisingly — form the outline of a Christmas tree. And a finger of dark dust extends “above” the tree — the Cone Nebula. It’s a cloud of cold dust that forms a silhouette against the warmer gas around it.

The nebulae should continue to churn out stars for millions of years — providing colorful decorations for the unicorn.

Monoceros is in the southeast as night falls, below and to the lower left of Orion the hunter. You need dark skies to see its stars — and a telescope to see its busy nurseries.

Script by Damond Benningfield

With a name that means “the unicorn,” you might expect the constellation Monoceros to have an interesting story. Unfortunately, though, it doesn’t. It was created mainly to fill in a dark region of the sky near bright Orion the hunter, which is in the southeast in early evening.

The first confirmed record of the constellation is in a 17th-century sky atlas. The atlas was produced by a Dutch mapmaker and astronomer who created a score of constellations in all. Most of them are still in use today — including Monoceros.

The unicorn isn’t much to look at. From a light-polluted city, in fact, you might not see any of its stars at all.

Appropriately enough, though, one of the constellation’s most interesting residents is a black hole — the closest one to Earth yet seen. It’s roughly 3,000 light-years away. It’s nothing to worry about, though — it’s far enough that it’s no threat to Earth.

While there’s not much in the unicorn to see with the eye alone, a telescope reveals quite a few beautiful sights. The list includes star clusters and several nebulae — big clouds of gas and dust.

Hubble’s Variable Nebula, for example, consists of a young star that’s embedded in a cocoon of material. The star lights up that cloud, making it glow. It’s possible that the cocoon is hiding a young planetary system — new worlds that haven’t fully taken shape.

Monoceros also contains a couple of beautiful stellar nurseries, and we’ll talk about those tomorrow.

Script by Damond Benningfield

If Nicolas Louis de Lacaille were naming constellations today, he might call them the spectrometer, seismometer, or even DNA sequencer. Since Lacaille was working in the 1750s, though, he went with names for the scientific instruments of his own time. So today, we have constellations named for the telescope, the compass, and the microscope.

Another is Fornax, the furnace. It’s named for a piece of lab equipment used by chemists. Like Lacaille’s other constellations, it’s south of the celestial equator. So from the United States, it’s best seen from the southern states. Right now, it stands low above the southern horizon as night falls.

Lacaille was a French astronomer. He went on his constellation-naming spree after spending two years at the Cape of Good Hope in South Africa. He cataloged 10,000 southern stars. And he used some of those stars to create 14 constellations.

Most of them are small and faint, like Fornax. Its brightest star is only fourth magnitude — too faint to see from light-polluted cities.

The star is known as Alpha Fornacis. It’s about 45 light-years away. It actually consists of two stars. The main star is bigger, brighter, and heavier than the Sun. Its companion is less massive than the Sun. But it shines bright blue, which is rare for such a lightweight star. That suggests it got “revved up” by swallowing gas from a possible third star in the system — or by merging with the star — heating up the furnace.

Script by Damond Benningfield

The Sun is a giant presence in our sky. So you might think that astronomers don’t need big telescopes to study it. You would be wrong. To learn the details about how the Sun works, astronomers need to see the details on its surface. The bigger the telescope, the more detail.

The world’s largest Sun-watching telescope is scheduled to begin science operations this year. The Daniel K. Inouye Solar Telescope is named for a former U.S. senator from Hawaii. It’s atop Haleakala, a 10,000-foot mountain on Maui. Appropriately enough, Haleakala means “house of the Sun.”

The telescope's main mirror is more than 13 feet in diameter. The telescope will use a technique known as adaptive optics to eliminate the blurring effect of Earth’s atmosphere. The combination will show details that are less than 15 miles across.

Scientists will study what’s happening on the Sun now, and what happens over a period of years.

The short-term observations will allow them to probe the Sun’s magnetic field, which produces sunspots, flares, and other features. That’ll help them understand the dynamo that powers the magnetic field. And it’ll help them understand and predict space weather — interactions between Sun and Earth.

The Sun goes through an 11-year magnetic cycle. And no two cycles are alike. So long-term studies will tell us more about what’s happening inside the Sun over many decades — studies made with a giant telescope atop the house of the Sun.

Script by Damond Benningfield

William Herschel was one of the top astronomers of his day. He discovered that the ice caps on Mars change with the seasons. He was the first to suggest that the Milky Way is shaped like a disk. And he was the first person to find a planet: In 1781, he discovered Uranus, the seventh planet from the Sun. So when Herschel suggested that the Sun was inhabited, other astronomers paid attention.

Herschel presented his views on the Sun to Britain’s Royal Society in 1795 — 225 years ago.

At the time, many scientists thought that all the planets were inhabited. And many considered the Sun to be a planet as well. So Herschel’s idea didn’t seem off base.

He suggested that the Sun was surrounded by a hot, glowing atmosphere. Dark sunspots were “holes” in that layer that provided a view of the solid Sun below. That realm was inhabited by, as Herschel put it, “beings whose organs are adapted to the peculiar circumstances of that vast globe.”

Some scientists were skeptical of that picture. They wondered how anyone could survive below the Sun’s bright, hot atmosphere. So a few years later, Herschel suggested there was a layer of dark clouds below the bright atmosphere — thick enough to protect the Sun’s inhabitants.

It wasn’t until the 20th century that scientists finally worked out the details about the Sun. It’s a giant ball of gas that shines by fusing together hydrogen atoms in its core to make helium — with no “Solarians” in sight.

Script by Damond Benningfield