StarDate

Jupiter is like an old friend these days. We see sharp pictures of its clouds and moons all the time. Several spacecraft have flown by or entered orbit, revealing details about Jupiter’s interior, its atmosphere, its radiation belts, and more. The first of those visitors paid a call on Jupiter 50 years ago today. It greatly enhanced our knowledge of the planet, while pioneering the way for more sophisticated missions in the following decades.

Pioneer 10 flew just 81,000 miles from Jupiter on December 3rd, 1973. By then, it had traveled farther than any spacecraft in history.

During an encounter that lasted for several weeks, Pioneer 10 snapped about 500 pictures of Jupiter and some of its moons. They were crude by modern standards, but they were sharper than anything available from telescopes on Earth.

Pioneer also measured Jupiter’s magnetic and gravitational fields, and probed its atmosphere. It found that the planet’s radiation belts were at least 10,000 times as intense as Earth’s. In fact, they knocked out Pioneer’s camera.

The Jupiter encounter was the end of Pioneer 10’s main mission. Yet the craft kept working for another 20 years. It told us about conditions beyond the realm of the planets — more discoveries from a solar-system pioneer.

Jupiter is in the east at nightfall, and looks like a brilliant star — a world we began to really get to know with the visit of Pioneer 10.
 

Script by Damond Benningfield

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Regulus is one of the brightest lights in the night sky. But just how bright depends on how you look at it.

Seen with the eye alone, the heart of the lion has a magnitude of about 1.4. In this scale, the brighter an object, the lower the number. The brightest star in the night sky, Sirius, has a magnitude of minus-1.4. And the faintest stars visible under a dark sky have a magnitude of about six, which is only about a thousandth as bright as Sirius.

Since the stars are all at different distances, that number doesn’t tell you a star’s true brightness. For that, astronomers calculate its absolute magnitude. That’s how bright the star would look at a distance of about 32 light-years. In this scale, Regulus has a magnitude of minus point five. If you lined up Regulus and the Sun at that distance, Regulus would be more than a hundred times brighter.

Even that doesn’t give you the star’s total brightness, because it counts only a star’s visible light. But stars emit many other forms of energy as well. Because Regulus is quite hot, it produces a lot of ultraviolet light. When you add that to the visible light, the star is about 350 times brighter than the Sun. So Regulus is a brilliant beacon any way you look at it.

And you can get a good look at Regulus the next couple of nights. It’s well below the Moon as they climb into good view tonight, about midnight, but much closer to it tomorrow night.
 

Script by Damond Benningfield

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Astronomers who study the material between the stars are ready to “go for the gusto.” They’re planning to launch a telescope aboard a giant balloon. If everything goes as planned, it’ll loop around Antarctica for up to four months, staring deep into the Milky Way and a companion galaxy.

The mission is known as GUSTO. It’ll monitor the sky at far-infrared wavelengths. Water vapor in Earth’s atmosphere absorbs those wavelengths, so the only way to study them is to climb above the atmosphere.

GUSTO will do so with a super-pressure balloon. After launch from McMurdo Station, it’ll climb to about 120,000 feet. It’ll circle around the continent, eventually drifting over the Southern Ocean. Scientists will track it with satellites.

The mission’s goal is to study the ISM — the interstellar medium — the wisps of gas and dust between the stars. Studying this material can help scientists trace the lifecycle of the stars. Stars are born from giant clouds of gas and dust. As they age, they spew out winds of particles that add to the ISM. And when they die, they expel most of their gas back into space, where the cycle starts all over again.

The big challenge for GUSTO may be the weather. The balloon can’t be launched in high winds. A precursor mission in 2012 couldn’t launch until its eighth try. And a second test, the following year, couldn’t get off at all. So GUSTO will need calm winds to soar into the Antarctic sky.
 

Script by Damond Benningfield

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A couple of bright alignments greet early risers tomorrow. The Moon and the twins of Gemini are high in the western sky at dawn. And the planet Venus and the star Spica are in the southeast.

The Moon and Gemini actually climb into good view by about 8:30 or 9 tonight. Pollux, the brighter of the stars that represent the heads of the twins, is quite close to the Moon. Castor, the other twin, is farther to the upper left of the Moon. As the night rolls on, the Moon will widen the gap with Pollux. But they’ll still be quite close at first light.

Venus and Spica rise into good view by about three hours before sunrise.

Venus is the brilliant “morning star,” so you can’t miss it. Despite the nickname, it’s not really a star at all. Instead, it’s our closest planetary neighbor, which is one reason it shines so brightly.

Spica is a star — the brightest in the constellation Virgo. It stands to the right of Venus, by about the width of three fingers held at arm’s length. It’s one of the brightest stars in the night sky, so you won’t have any trouble spotting it.

By Saturday morning, the Moon will have moved into Cancer, one constellation over from the twins. Venus and Spica will still be close, but Venus will be starting to drop away. It’ll stand a little lower than Spica. The bright planet will continue to move back toward the Sun as Spica climbs higher in the early morning sky.

Tomorrow: Going for the GUSTO!
 

Script by Damond Benningfield

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The letter X has a big reputation. It’s used to designate things that are powerful, scary, mysterious, or all of the above. So we have X-rays and X Men, the X Files and X planes, and in the movies, at least a couple of spies designated triple-X.

The Sun gets into the act, too, with X-class solar flares — eruptions that are powerful, scary, and a bit mysterious.

Solar flares are massive explosions. They occur when the lines of the Sun’s magnetic field tangle up, snap, then reconnect. They generate outbursts of particles and radiation that race into the solar system — and they can have dramatic impacts on Earth.

Scientists use five letters to designate the power of a solar flare. From weakest to strongest, they’re A, B, C, M, and X.

The first three categories are fairly mild. Class M flares can have some impact on Earth, but the really nasty ones are the X-class. The largest can produce as much energy as a billion hydrogen bombs.

They’re often accompanied by massive outbursts of charged particles. They can fry orbiting satellites, disrupt radio broadcasts, and knock out power grids. They can force airlines to reroute flights away from the north pole to avoid dangerous levels of radiation. And they can produce displays of the northern lights in places that seldom see them.

The Sun is getting more active these days, building toward the peak of its magnetic cycle in a couple of years — a lot of X-flares in our future.
 

Script by Damond Benningfield

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The Sun is getting brighter.

Not enough to notice, mind you. In fact, it’ll take more than a hundred thousand human lifetimes to tick up by even one percent. But that gradual change will add up. In a billion years or so, the extra energy should be enough to boil away Earth’s oceans and atmosphere, leaving nothing but a burned-out ball of rock.

The change is the result of changes deep inside the Sun.

Our star shines because its core is a giant nuclear reactor. It “fuses” lightweight hydrogen atoms to make heavier helium atoms — a process that produces enough energy to power the Sun.

As more hydrogen is converted to helium, the core shrinks and gets denser, which makes it hotter. And as the temperature goes up, so does the rate of nuclear reactions. That yields more energy, making the surface of the Sun brighter.

The Sun has already converted a large fraction of its hydrogen to helium. As a result, it beams about 25 percent more energy into space today than when it was born.

A billion years from now, it’ll shine about 10 percent brighter still — bright enough to heat Earth’s surface above the boiling point of water. And a few billion years after that, it’ll shine roughly twice as bright as when it was born.

By then, the Sun will have used up the hydrogen in its core, triggering changes that’ll make it shine hundreds of times brighter — a brilliant flare-up before it fades away for good.

More about the Sun tomorrow.
 

Script by Damond Benningfield

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Giants flank the Moon tonight. They’re among the brightest stars in the night sky, so you can’t miss them, even from a light-polluted city.

As night falls, look to the lower right of the Moon for Aldebaran, the eye of Taurus, the bull. Then look about twice that far to the upper left of the Moon for Capella. It’s the brightest star of Auriga, the charioteer, and the sixth-brightest star in all the night sky.

Aldebaran is a single giant. It’s more than 40 times the diameter of the Sun. It’s also a bit more massive than the Sun. It’s 65 light-years away.

Capella includes two giants. The system is closer than Aldebaran, at just 43 light-years. Both of the giants are about two-and-a-half times the mass of the Sun, and roughly 10 times the Sun’s diameter.

A star becomes a giant when it uses up the original hydrogen fuel in its core. The core shrinks and gets hotter, starting a new round of nuclear reactions. The hotter core pushes outward on the star’s outer layers. That causes the star to puff up to many times its original size, making it much brighter. Aldebaran, for example, is more than 400 times the Sun’s total brightness, while each of Capella’s giants is about 75 times the Sun’s brightness.

Eventually, each star will cast its outer layers into space, leaving only its small, hot core.

The Sun faces the same fate — beginning in several billion years.

More about the future of the Sun tomorrow.
 

Script by Damond Benningfield

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 A stellar “cannonball” is racing across the constellation Cassiopeia at more than two million miles per hour. And it’s leaving a long trail behind it.

The cannonball is a pulsar — the spinning, superdense corpse of an exploded star. The explosion was a supernova. When the original star’s core could no longer produce energy, it collapsed. That formed a neutron star — an object more massive than the Sun, but only the size of a city. It spins about nine times per second, sending out “pulses” of radio waves.

The explosion that created the neutron star probably was a little off center. That gave the star a big kick, sending it careening away from the site of the explosion.

Astronomers discovered the star in 2019. Using radio and X-ray telescopes, they’ve since found a trail behind it that’s trillions of miles long. It has some bends and kinks, suggesting that the star is passing through thick clouds of gas.

Astronomers also found a “bow shock” in front of the star — gas and dust that’s being “squeezed” by the speedy cannonball, like water ahead of a fast boat. The star should be moving fast enough to escape the galaxy — and blast through the gulf between galaxies on its own.

Cassiopeia the queen is high in the northeast at nightfall. It looks like a sideways letter W. The cannonball star is near the top right point of the W. But it’s much too faint to see without the right kind of telescope.
 

Script by Damond Benningfield

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For a star like the Sun, which travels through the galaxy alone, the future is pretty certain. But for stars with close companions, the future is tougher to see. Interactions between the two stars change their evolution, blurring the view through the astronomer’s crystal ball.

Consider Capella, one of the brightest stars in the night sky. The yellow star is in the northeast at nightfall, and soars high overhead later on.

Capella consists of two stars. Each is bigger, brighter, and heavier than the Sun.

The stars are only about 10 percent the age of the Sun. But because of their greater heft, they’ve aged much more quickly. Both stars have completed their “normal” lifetimes. Now, thanks to changes in their cores, their outer layers are puffing outward — especially the heavier star’s.

The stars are close together — only about two-thirds the distance from Earth to the Sun. So as the stars puff up, their surfaces will get closer and closer to each other. Eventually, the heavier star will begin to dump gas on the companion. It’ll also generate strong “winds” that’ll surround both stars in a cloud of gas.

That’s likely to alter the evolution of the smaller star. As it adds mass, its own reactions will crank up. The two stars also may spiral closer together — and could even merge. That could create a bigger star, or it could trigger an explosion. For now, though, just how it plays out remains hard to predict.
 

Script by Damond Benningfield

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Jupiter is the third-brightest object in the night sky — only the Moon and Venus outshine it. If our eyes were sensitive to infrared light, Jupiter would look even brighter. That’s because it radiates about twice as much energy into space as it receives from the Sun — all in the infrared.

Scientists still aren’t sure what powers Jupiter’s internal heat. But they have some ideas.

Some of the heat may be left over from Jupiter’s birth. Current models say that when Jupiter was young, its internal temperature was about twice what it is now. Over the eons, much of that heat flowed into space, making Jupiter cooler and smaller.

Some of the heat may come from that contraction. Gravity squeezes the planet, making it shrink. Today, Jupiter is shrinking by about one millimeter per year, making it hotter.

And yet another idea says that a “rain” of liquid helium plunges through Jupiter’s interior. At greater depths, it’s heated. The droplets vaporize, releasing their heat into the surroundings. Some of that heat then rises through Jupiter’s outer layers and flows into space — helping Jupiter glow brightly in the infrared.

Look for Jupiter near the gibbous Moon tonight. The solar system’s largest planet looks like a brilliant star. It’s to the lower left of the Moon at nightfall. The Moon will slide closer to Jupiter during the night. They’ll be at their closest as they set, a couple of hours before dawn.
 

Script by Damond Benningfield

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