StarDate

There’s more than one way to look at the stars. With our eyes alone, we see only a sliver of the spectrum of energy a star radiates into space. But our instruments see the entire spectrum. And as we tune up and down that spectrum, different forms of energy become more prominent.

Consider Adhara, the second-brightest star of Canis Major, the big dog, which is in the southeast by mid-evening.

The constellation’s brightest star is Sirius. It’s the brightest star in the night sky — but only at visible wavelengths.

Adhara is well to Sirius’s lower right, and doesn’t look nearly as impressive. But it’s actually thousands of times brighter than Sirius. It looks fainter because it’s hundreds of light-years farther.

But if you could tune your eyes to the ultraviolet, Adhara would far outshine Sirius. In fact, it would be the brightest star in the night sky.

That’s because Adhara is quite hot, and hot stars produce most of their energy in the ultraviolet. Adhara is also big, so there’s a lot of star to radiate energy into space. The combination makes Adhara a brilliant ultraviolet beacon.

That won’t always be the case, though. In a few million years, the star’s outer layers will puff up. That’ll make the surface much cooler, so Adhara’s ultraviolet light will fade. Instead, the star will blaze in another band — as one of the brightest infrared sources in the sky.

We’ll talk about the big dog’s third-brightest star tomorrow.

Script by Damond Benningfield

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Winter nights sparkle with some of the brightest stars in the sky: Rigel and Betelgeuse in Orion, Aldebaran in Taurus, and Procyon in Canis Minor, to name just a few. Yet it takes only a glance to pick out the brightest of them all: Sirius, the leading light of Canis Major, the big dog. That makes it the top dog. It’s in the southeast by mid-evening, and scoots low across the south during the night.

Sirius looks so bright in part because it is fairly bright — a couple of dozen times brighter than the Sun. But it also shows off because it’s just 8.6 light-years away. Only four other star systems are closer.

By astronomical standards, Sirius is just down the block. By human standards, though, the gap is pretty much incomprehensible — it’s far beyond any ordinary concept of “far away.”

To put it in everyday terms, the distance to Sirius is about 50 trillion miles — a five followed by 13 zeroes. To look at it another way, the farthest that any human has ever journeyed is the Moon. A one-way trip to Sirius would be equivalent to a hundred million round trips to the Moon.

At the speed of the fastest probe we’ve ever launched, it would take more than 150,000 years to get to the top dog. And even if you could streak toward Sirius at the speed of light — a zippy 670 million miles per hour — it would take 8.6 years to get there — hence the star’s distance: 8.6 light-years.

More about Canis Major tomorrow.

Script by Damond Benningfield

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When World War II ended, the U.S. Army was concerned that future enemies might lob high-altitude missiles our way. So it wanted to know if radar could track them. But there weren’t any such missiles at the time, so there was nothing to practice on. So the leader of a Signal Corps team came up with another target: the Moon. His team bounced its first signals off the Moon 75 years ago today.

Project Diana was named for a Moon goddess. It was led by John DeWitt Junior. At age 16, he’d set up the first radio station in Nashville. Before the war, he built a radio telescope. He even tried to detect radio signals reflected from the Moon.

For Project Diana, his team used war-surplus radar equipment, which sent out pulses of radio waves. The receiver couldn’t move much, so the team could look only around moonrise or moonset.

The challenge was to see if the radar beam could pass through a layer of the atmosphere that reflects radio waves. After several days of trying, the team saw and heard the “echo” from the Moon on January 10th, 1946.

Other successful runs followed. The tests revealed that it was possible to “see” missiles with radar. And it established a new field of science. Today, astronomers use the technique to study the planets and moons of the solar system.

One of those targets is Venus, the “morning star,” which is near the Moon in tomorrow’s dawn twilight — two worlds “seen” by the light of radar.

Script by Damond Benningfield

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Early artists from Spain to China were fond of red. They were using a pigment known as red ochre tens of thousands of years ago. American farmers have been fond of it as well — it colors thousands of red barns. And they can all thank the stars for the eye-catching color.

The key ingredient in red ochre is a mineral known as hematite. It’s a combination of iron and oxygen, which are two of the most abundant elements in Earth’s crust.

Both elements are forged in the hearts of stars. A star “fuses” lighter elements to make heavier ones. For stars like the Sun, that process ends with carbon and oxygen. When such stars die, they expel some of that oxygen into space, where it can be incorporated into new stars and planets.

Heavier stars make elements all the way up to iron. At that point, it takes too much energy to make even heavier elements. So the star explodes as a supernova. That blasts iron and many other elements into the universe.

So the oxygen and iron in Earth’s crust came from long-dead stars. And over the eons, some of those elements have combined to produce red ochre — a pigment that decorates barns and other canvasses the world over.

The remains of one supernova are in Gemini, which is in the east at nightfall. The star exploded thousands of years ago. Today, those remains, known as the Jellyfish Nebula, span dozens of light-years. And they’re expanding by the second — perhaps to provide some red for artists on future planets.

Script by Damond Benningfield

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Many bright, beautiful stars highlight winter nights. The bounty includes Castor and Pollux, the twins of Gemini. But a family of stars at the feet of the twins would put our night sky to shame. It’s a cluster that may contain several thousand stars packed into a fairly small volume of space. And quite a few of those stars are bright. So from a planet inside the cluster, the night sky would sparkle with many stars that are brighter than any in the skies of Earth.

Messier 35 is almost 3,000 light-years away, and it spans a couple of dozen light-years. So as seen from Earth, it covers an area as big as the Moon.

The cluster is about 175 million years old — only a tiny fraction of the age of the Sun. One way astronomers determine that age is by measuring the “weight” of the stars that are still in the prime of life. The lifespan of a star depends on its mass, with the most-massive stars burning out first. Astronomers know how long it takes stars of different masses to expire. So finding the heaviest stars that are still in the prime of life provides a good indication of the cluster’s age — in this case, about 175 million years.

Gemini is in the eastern sky at nightfall. Castor and Pollux are at the left of the constellation, with slightly fainter Castor above its “twin.” The bodies of the twins stretch to the right. M35 is at the feet of the twins, far to the upper right of Castor and Pollux.

Script by Damond Benningfield

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An unexpected visitor dropped in on a Japanese city on January 7th of 1996: a space rock. It blazed across eastern Japan, forming a bright streak in the late-afternoon sky. It also created a sonic boom loud enough to rattle doors and dishes and send residents outside to see what was going on.

At an altitude of about 15 miles, the rock exploded. Some of the debris formed a white cloud in the sky. But small rocky fragments splashed across hundreds of square miles. One of them even punched a hole in the roof of a car-repair business in the city of Tsukuba.

Meteorite hunters fanned out across the countryside to look for those fragments. They found less than two pounds of them. The largest weighed just a few ounces. Together, they were called the Tsukuba meteorite.

Some pieces were found quickly, so scientists began taking a look at them just hours after they fell to Earth.

The scientists concluded that the original rock was a member of the most common class of meteorites. It consisted of small blobs of rock that melted, then cooled and solidified, when the solar system was quite young. Those blobs were cemented together by bits of rock and metal, with a high amount of iron.

The original rock was blasted off the surface of a larger space rock. The chip orbited the Sun for millions of years before it ran into Earth — creating an amazing lightshow over Japan 25 years ago today.

Script by Damond Benningfield

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The Sun is big, bright, and heavy. In fact, compared to the faintest star yet seen, it’s a monster. The star is only as big as Jupiter, the solar system’s largest planet. And it’s only about one ten-thousandth of the Sun’s brightness. So if the star took the Sun’s place, it would look about as bright as a full Moon.

The star is known only by a catalog number, which we’ll shorten to 2MASS J0523. It’s about 40 light-years away, in Lepus, the rabbit.

The star lies along the dividing line between true stars and the failed stars known as brown dwarfs. And the main thing that defines that line is mass.

J0523 is roughly seven percent the mass of the Sun. At that weight, its gravity squeezes its core just enough to sustain nuclear reactions. That releases energy, making the star shine.

Anything below that mass can’t get the job done. Its core doesn’t get hot enough, so the object is a brown dwarf. Gravity does squeeze it enough to produce heat, which shines into space. But the object slowly cools and fades away.

A star like J0523 trades brilliance for longevity. The star is expected to remain in the prime of life for more than 10 trillion years — a thousand times longer than the Sun.

Lepus is low in the southeast at nightfall, to the lower right of bright Orion. Although J0523 is close to the constellation’s brightest star, you need a powerful telescope to see this faint nightlight.

Script by Damond Benningfield

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You don’t need big telescopes or special instruments to learn about the universe. Sometimes, you can learn a great deal with not much more than your eyes alone.

2200 years ago, for example, the Greek astronomer Hipparchus learned that the stars change position relative to the Sun from year to year. He did so by measuring the position of Spica, the brightest star of Virgo. Spica is in good view at dawn tomorrow, to the lower left of the last-quarter Moon.

During a lunar eclipse, Hipparchus measured the angle from Spica to the middle of the Moon. And from that, he calculated Spica’s position relative to the Sun. He found that the star had moved about two degrees since another eclipse 150 years earlier — about the width of a finger held at arm’s length. He realized that the entire celestial sphere — the background of fixed stars — rotated with respect to the Sun.

That rotation is known as the precession of the equinoxes. It’s caused not by the stars, but by Earth. Our planet “wobbles” on its axis like a spinning gyroscope that’s running down. As it wobbles, the stars appear to shift position relative to the Sun. It takes about 26,000 years to complete one full wobble and have the stars return to their starting positions.

The precession of the equinoxes was an important discovery because it showed that the heavens can change — a discovery made with some simple tools and the nimble mind of Hipparchus.

Script by Damond Benningfield

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Nailing down the distance to a star isn’t easy. New observations can show that earlier ones had it all wrong.

That seems to be the case with Bellatrix, the third-brightest star of Orion. It’s to the upper left of Orion’s three-star belt during the evening.

For a long time, astronomers thought Bellatrix and the stars of the belt were members of the same family. Like the stars of the belt, Bellatrix is big, bright, and heavy. It’s eight or nine times the mass of the Sun, and thousands of times the Sun’s brightness.

But measurements made more than a decade ago by a space telescope contradict that idea. While the stars of the belt are all more than a thousand light-years from Earth, Bellatrix is only about 250 light-years away. So there’s no way it could belong to the same family as the stars of the belt.

The star’s fate depends in part on its distance.

Its mass is thought to be about eight-and-a-half times the mass of the Sun. That puts it right along a dividing line. A star at that mass or heavier may explode as a supernova; much below that line and it’ll have a less spectacular demise.

If Bellatrix were a little farther than 250 light-years, that would make it a little heavier, which would make it more likely to blow up. At less than 250 light-years, though, it would be less massive — and less likely to explode. So even a slight change in its distance could make a big difference in the fate of this impressive star.

Script by Damond Benningfield

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When spring arrives in March, the Sun will stand near the fish outlined by the constellation Pisces. That hasn’t always been the Sun’s home for the start of spring, though. About 6500 years ago, it appeared just above the head of Orion the hunter.

Orion is best known for his sparkling belt and sword. The tiny triangle of stars that marks his head doesn’t look nearly as impressive. Yet the stars themselves really are standouts.

The brightest of the three is Lambda Orionis. It’s actually a pair of stars locked in a tight orbit. Both stars are many times bigger, hotter, and brighter than the Sun. In fact, the system’s leading light is a member of the hottest class of stars. It’s tens of thousands of degrees hotter than the Sun, and more than 160,000 times brighter. That makes it easily visible across more than a thousand light-years of space.

The other stars in Orion’s head are Phi-1 and Phi-2 Orionis. They represent the hunter’s cheeks. Although they share a name, they aren’t related — they’re hundreds of light-years apart. But they do have something in common: Both are much more impressive than the Sun.

Orion is low in the eastern sky at nightfall. Look for his belt — a short line of three bright stars — extending almost straight up from the horizon. The bright orange star Betelgeuse is to the left of the belt. The faint triangle that makes up Orion’s head is above Betelgeuse.

Tomorrow: a deadly blast.

Script by Damond Benningfield

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