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StarDate Podcast

StarDate Podcast


StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

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  Astronomy Cast Podcast
by Fraser Cain

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Northern Crown

Sat, May 27, 2017

A pretty little semicircle of stars crowns the sky on spring and summer nights: Corona Borealis, the northern crown. It’s in the east as night falls right now, but stands high overhead a few hours later. In a couple of months, it’ll be overhead at nightfall.

Most of the semicircle isn’t very bright — you need pretty dark skies to see it. It stands out because of the tight pattern, with a fairly bright star at its center: Alphecca, “the bright one.”

Alphecca’s actually a binary — two stars locked in a gravitational embrace. The heavier of them is about three times as massive as the Sun, thousands of degrees hotter, and dozens of times brighter. Its companion is a little smaller, cooler, and fainter than the Sun.

The stars are quite close together — an average of about half the distance between the Sun and its closest planet, Mercury. They orbit each other once every 17 and a half days.

And they’re lined up in such a way that we see the fainter star eclipse the brighter one. When that happens, Alphecca dims by a few percent. That’s not enough for most of us to notice with the eye alone, but it’s an easy catch for astronomical instruments.

Instruments also detect a disk of debris around the stars. It extends billions of miles out into space. The disk consists mainly of small grains of dust — material left over from the formation of Alphecca itself.

Tomorrow, we’ll talk about another pair of stars in Corona Borealis that blew itself up.


Script by Damond Benningfield

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Heading North

Fri, May 26, 2017

While the Moon orbits Earth and Earth orbits the Sun, the Sun isn’t exactly standing still. In fact, it’s racing around the center of the Milky Way galaxy, carrying Earth and the other planets with it.

The solar system inhabits the most luminous part of the Milky Way: its disk, which includes the beautiful spiral arms and most of the galaxy’s stars. It’s shaped like a pancake, except this pancake is enormous: at least a hundred thousand light-years across and a couple of thousand light-years thick.

We’re about 27,000 light-years from the galaxy’s center — nearly halfway to the edge of the disk. And we’re near the midplane of the disk — the line that divides it into northern and southern halves. Estimates vary, but the solar system is probably between 40 and 90 light-years north of the midplane. That’s not very far when compared to the thickness of the disk.

Still, with every passing minute, we’re moving higher. As the Sun orbits the galactic center, it slowly bobs up and down, like a horse on a merry-go-round. And for millions of years, we’ve been moving up. Eventually, we’ll reach a peak altitude and start to head back down. But we’ll never venture beyond the bounds of the Milky Way’s starry disk.

And under dark skies, that disk is visible as the hazy band of light known as the Milky Way. It’s quite low in the sky this evening, but arcs high overhead before dawn tomorrow. It’ll be in better view in the evening sky as we head into summer.


Script by Ken Croswell, Copyright 2017

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Thu, May 25, 2017

Johannes Hevelius saw things that no one else did. Perhaps that was because he had a vivid imagination. Or perhaps it was because he consumed a lot of the famous beer he brewed. But whatever the reason, in the late 17th century he drew 10 new constellations. All of them filled in regions where no constellations had existed before — relatively dark areas of the sky with almost no bright stars.

And seven of those constellations are still with us today. An example is Lynx, which is in the west and northwest at nightfall. Although it’s faint, you can find its location with the help of three bright stars below it: Pollux and Castor, the twins of Gemini, which are almost due west; and even-brighter Capella, the leading light of the charioteer, to their lower right.

Hevelius, who didn’t use a telescope, counted 19 stars in that region, between Capella and the Big Dipper. He linked some of those stars in a zigzag pattern. And showing that he had a sense of humor, he called the new constellation Lynx, after the wild cat. He didn’t pick the name because the pattern looked like a lynx — it was because the viewer needed the eyes of a lynx to see it.

And thanks to light pollution, it’s even harder to see today. To pick it out, you need a nice, dark sky, far from city lights. From the suburbs, you might make out a few stars, especially the brightest one, Alpha Lyncis. It’s an orange giant that’s 200 light-years away — the brightest “spot” of a faint cat.


Script by Damond Benningfield


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Radio Power

Wed, May 24, 2017

A project known as Breakthrough Starshot hopes someday to use a powerful beam of energy to propel a tiny probe to another star. A recent study says that other civilizations might already be doing that, but on a much larger scale — and that we might have seen some of those beams.

Two researchers at Harvard considered the objects known as fast radio bursts. Astronomers have seen about a score of them, all in other galaxies. They’re intense outbursts of radio waves that last only a tiny fraction of a second. They could be powered by exploding stars, collapsing neutron stars, or some other exotic objects.

But the Harvard astronomers wondered if the bursts could have an artificial origin. And they concluded that it’s possible.

Their idea is that a civilization would build a starship propelled by a giant sail. A beam of radio waves would “push” the ship just as the wind pushes sailing vessels here on Earth. Occasionally, the radio beam would sweep past Earth — producing a radio burst.

If the radio beam were powered by solar energy, it would require a collector that’s about twice the diameter of Earth. Building and operating such a system wouldn’t be easy — but it’s within the realm of possibility. And the payoff could be big: it could propel a million-ton ship to a good fraction of the speed of light.

The researchers aren’t saying that fast radio bursts really are produced by other civilizations — only that it’s a possibility worth checking.


Script by Damond Benningfield

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Closing In

Tue, May 23, 2017

[AUDIO: FRB “chirp”] That sound comes from a distant galaxy — perhaps from the corpse of a once-mighty star. It’s one of a couple of dozen outbursts captured from the galaxy — a cosmic puffball that’s three billion light-years away. And it’s helping astronomers understand a new class of objects, known as FRBs — fast radio bursts.

So far, astronomers have discovered only about a score of these objects. They produce intense bursts of radio waves that last only a few thousandths of a second. But until recently, no one could pinpoint the location of even a single burst. Without knowing how far away the bursts are, it’s impossible to know how powerful they are. That means it’s also impossible to know what they are.

But earlier this year, a team of astronomers reported that one FRB has popped off a couple of dozen times in the last few years. That allowed the team to pinpoint the FRB’s location, inside a dwarf galaxy.

Such galaxies give birth to lots of stars. Some of the stars are big and heavy, so they live short, bright lives, then explode. Some of them leave dense corpses that are highly magnetized.

The astronomers say that one of these corpses could produce the outbursts — perhaps as it interacts with the galaxy around it.

This scenario hasn’t been confirmed, though. And so far, there’s no way to know if all FRBs are formed in the same way — there could be several explanations for them. We’ll talk about one of those tomorrow.


Script by Damond Benningfield

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Spying on Supernovae

Mon, May 22, 2017

A project that’s beginning this month will compile dossiers on hundreds of supernovae. That should give astronomers a better picture of the types of stars that explode, how supernovae interact with their surroundings, and how they seed the cosmos with chemical elements.

The Global Supernova Project is a collaboration of about 150 astronomers around the world. It’ll use about 30 telescopes to monitor supernovae after other projects discover them.

The backbone of the project is the Las Cumbres Observatory — a network of 18 telescopes, including one at McDonald Observatory, with mirrors up to two meters in diameter. Because they’re spaced around the globe, they can follow a supernova around the clock.

That’s especially important in the first days after a supernova explodes. Those early moments reveal details about the original star, such as its composition and structure. But the chemical signatures from some of its expelled materials fade quickly, and the radioactive decay of nickel and other elements soon dominates the light from the supernova debris.

This is a follow-up to an earlier project, which ended last month. During its three-year run, it studied more than 400 supernovae. Among other things, it discovered several new classes of supernova.

The new project is expected to see about 600 supernovae, also over a three-year period. Those observations should help astronomers more fully understand these powerful cosmic blasts.


Script by Damond Benningfield

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More Moon and Venus

Sun, May 21, 2017

For the first three decades of the Space Age, Venus was the belle of the ball. Through the 1980s, the United States and the Soviet Union dispatched about 30 missions to the brilliant planet. In fact, Venus was the target of the first successful mission to any planet, and the Soviets landed several craft on its surface.

Since then, though, Venus has been left pretty much alone. A few craft have peeked in when they used Venus to get gravitational “kicks” to other planets. But Venus has been a main target for only a handful of missions.

There are several reasons for the change. One is the success of many of the earlier missions, which answered a lot of questions about the planet.

Another is that it’s tough to build something that can last for very long on the surface of Venus. Because of its hot, dense, toxic atmosphere, nothing has survived for more than about an hour. And it’s hard to explore a world if you only get hour-long peeks.

Some recent work has produced electronics that might be able to survive much longer. In tests, they lasted for weeks in a simulated Venus environment. If those systems can be certified for spaceflight, they might make it possible to get our first long look at the surface — perhaps rekindling the infatuation with the beautiful planet.

And Venus is in good view in the early morning sky. It’s the brilliant “morning star.” Tomorrow, it perches quite close to the crescent Moon — a great way to greet the dawn.


Script by Damond Benningfield


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Moon and Venus

Sat, May 20, 2017

There’s no air on the Moon, so there’s no wind or rain to alter the surface. Yet the Moon does have weather — space weather. A steady “rain” of tiny space rocks pounds the surface, breaking up the rocks and forming a powdery dirt known as regolith. And charged particles from the Sun can change the chemistry of the rocks and regolith, turning them darker.

Interactions with the Sun may have other effects as well.

Some recent work, for example, found that big solar storms may induce a sort of “lightning” in regions that receive little sunlight. The solar storms produce lots of particles with an electric charge, which can embed themselves in the regolith. The positively charged particles are entire atoms, so they go deeper than the negatively charged particles, which are lightweight electrons. Like the electric charges within clouds, that can trigger sparks. In this case, the sparks may melt some of the regolith.

Some regions of the Moon may be shielded from solar particles by areas with weak magnetic fields. When the solar wind streams by, the magnetic field may create an electric current that deflects the charged particles. Since these regions are protected, the regolith doesn’t get darkened as much. That creates bright swirls on the surface — regions that haven’t felt the impact of space weather.

Look for the Moon before sunrise tomorrow, with Venus, the “morning star,” to its lower left. More about Venus and the Moon tomorrow.


Script by Damond Benningfield

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Sky Test

Fri, May 19, 2017

It’s time for a little test. This isn’t a test of your knowledge of the universe, though, but of your ability to see it through the glow of outdoor lighting.

To take the test, first find the Big Dipper. It’s high in the north as night falls right now, and it’s upside down, as though the bowl were pouring its contents on the ground below. Then line up the two stars at the outer edge of the bowl, and follow that line to the lower right. The first bright star you come to is Polaris, the North Star.

All of that should be pretty easy. But the next step — the real test — is a bit tougher.

After your eyes adapt to the darkness, look to the upper right of Polaris, toward the tip of the Big Dipper’s handle. Can you see a pattern of stars that outlines a second dipper — the Little Dipper? Polaris is the tip of its handle, with the bowl above it.

One corner of the bowl is marked by Kochab, a star that’s about the same brightness as Polaris. But the other five stars that outline the dipper are fainter. The faintest, in fact, is less than one-tenth as bright as Polaris.

And that’s the test. If you can see the entire outline of the Little Dipper, then congratulations! You have nice, dark skies that will allow you to appreciate the universe in all its glory. If you can’t see anything but Polaris and Kochab, then your skies fail the test. They’re polluted by streetlamps, porch lights, and other sources that overpower the glow of faint stars, meteors, and the Milky Way.

But you can take some steps to return your night sky to its full glory. You can find out how at mcdonaldobservatory.org/darkskies.


Script by Damond Benningfield

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Scorpion’s Claws

Thu, May 18, 2017

All scorpions have claws — except for the scorpion in the sky. As the constellation is configured today, Scorpius has a curving tail; a body, highlighted by bright orange Antares; and a head, marked by a short line of stars. But its claws are gone — and have been for thousands of years.

Yet the stars that represented the claws are still there. And they still bear names related to the scorpion, even though they’re officially in Libra, the balance scales.

Zubeneschamali and Zubenelgenubi are low in the southeast as night falls on May evenings, and skitter higher across the southern sky later on. They’re far above Antares, which climbs into good view by around 11 o’clock.

Their names mean the northern and southern claws. Those names tell us that, when Scorpius was first drawn, thousands of years ago, Zubeneschamali and Zubenelgenubi were part of it.

Later, though, they were assigned to Libra. That’s because the Sun stood in that part of the sky at the September equinox. Day and night are equal then — a time of balance in the heavens. So that region was named for the balance scales.

The Sun no longer appears against the stars of Libra at the equinox, though — and it hasn’t for almost 3,000 years. Instead, it’s a constellation over, near the western edge of Virgo.

Even though Zubeneschamali and Zubenelgenubi no longer officially belong to Scorpius, it’s still quite easy to see them as its claws — leading the scorpion across the sky.


Script by Damond Benningfield


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Matter vs. Antimatter II

Wed, May 17, 2017

Antimatter sounds exotic, and in one way, it is: it’s quite rare. Although a lot of it may have been created in the Big Bang, most of it was cancelled out by interactions with normal matter. As far as anyone can tell, that left only a tiny smattering of antimatter, along with a bit that’s been created since then in various natural reactions.

But in most ways, antimatter isn’t exotic at all — it’s just like normal matter. The only difference is its electric charge. A particle of antimatter has the opposite charge from its normal-matter counterpart. So when matter and antimatter meet, they annihilate each other.

In laboratory experiments, physicists have measured the electric charge of the positron, which is the antimatter counterpart of the electron. And they’ve found that its charge is equal and opposite of that of the electron to better than one part in a billion.

Today, physicists are trying to see if the effects of gravity are the same on antimatter as on normal matter. One of those experiments, at the CERN accelerator in Europe, is getting under way this spring. It’s not an easy measurement to make. The experiment must create a charged atom of antimatter, keep it from reacting with normal matter, strip away its electric charge, then drop it to see if it “falls” in the same way as normal matter.

But so far, everything that scientists have found shows that antimatter looks and behaves just like normal matter — as long as you don’t touch it.


Script by Damond Benningfield

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Matter vs. Antimatter

Tue, May 16, 2017

Fictional starships notwithstanding, there’s not much antimatter in the universe. And for us, that’s a good thing. Any time matter and antimatter meet, they cancel each other out in a blaze of energy.

Antimatter is identical to normal matter in almost every way. The only difference is electric charge, which is opposite for the two forms of matter. So there could be a whole galaxy made of antimatter out there and our telescopes wouldn’t see it any differently from a galaxy of normal matter.

Most theories say the Big Bang should have created equal amounts of matter and antimatter. But in the first tiny fraction of a second, something changed that balance. For every billion pairs of matter and antimatter particles, there was one extra particle of matter.

One of the first scientists to consider that imbalance was Andrei Sakharov. The Russian physicist had helped develop the Soviet hydrogen bomb, but turned away from weapons work. In a paper published 50 years ago, he outlined conditions that could create the imbalance.

Sakharov said that protons must decay, but so slowly that it’s almost impossible to detect. Second, he said that the universe must have cooled in a certain way in the moments after the Big Bang. And finally, he said there must be some difference between matter and antimatter.

So far, none of those conditions has been found to account for the imbalance between matter and antimatter, so the subject remains a busy topic of research.


Script by Damond Benningfield

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Mon, May 15, 2017

A banana is a good source of fiber, vitamin C, manganese, and a host of other goodies. It’s also a good source of antimatter. That’s because a banana contains a tiny amount of a radioactive form of potassium. As the element decays, it produces positrons, the antimatter counterpart of electrons. They’re no threat, though — there just aren’t enough of them.

Particles of antimatter have the opposite electric charge from normal matter. An electron, for example, has a negative charge, while a positron has a positive charge. When matter and antimatter meet, they annihilate each other, producing pure energy.

Antimatter appears to be quite rare, but there is some. A tiny fraction of the cosmic rays that strike Earth’s atmosphere, for example, consists of positrons and antiprotons. There’s also evidence that positrons are produced by thunderstorms.

Antimatter is also produced by the decay of radioactive elements, like the potassium in bananas. Antimatter from this type of decay is used in PET scans. And research suggests that antimatter could someday be used to treat tumors.

Of course, the most famous use of antimatter is fictional: as a power source for starships. And it would be the most efficient power source around. The problem, though, is that making the stuff is extraordinarily expensive: trillions of dollars for a single gram. So we’re not likely to go warping around the galaxy in antimatter-powered ships anytime soon.

More about antimatter tomorrow.


Script by Damond Benningfield

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Turning Seasons

Sun, May 14, 2017

Some of the most prominent stars of fall and winter are getting ready to say farewell to the evening sky over the next few weeks. They’re in good view in the west and northwest right now, but it won’t be long before they’ll drop from sight.

As night falls, look almost due west for Procyon, the leading light of Canis Minor, the little dog. For most of us in the United States, it precedes Sirius, the brightest star in the night sky, into the long nights of winter. As they set, though, Sirius goes first. So at nightfall right now, Sirius is already gone from view, but Procyon remains in sight for a couple of hours longer.

Pollux and Castor, the twins of Gemini, stand to the upper right of Procyon. Pollux is the brighter of the two, and shows a slightly orange color. A month from now, the twins will be so low in the sky that they’ll look like a pair of eyes glaring through the fading twilight.

And well to the lower right of Gemini, look for the brightest of the lingering winter lights: Capella, the brightest star of Auriga, the charioteer. The star is distinctly yellow-orange, which adds to its beauty.

All of these bright lights will disappear from view by the end of June. In fact, Capella will already be in view in the morning sky by then, with the others to follow in July and August. They’ll all move back into the evening sky by late fall — continuing the cycle of seasons in the heavens.

Tomorrow: matter versus antimatter.


Script by Damond Benningfield

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More Moon and Saturn

Sat, May 13, 2017

Like bright traffic lights, two solar system objects point the way to an astronomical intersection tonight. It’s the spot where the Sun’s path across the sky meets the galactic equator.

The Moon and the planet Saturn climb into good view by midnight or a little later. Saturn looks like a bright star quite close to the right of the Moon. The astronomical intersection is just below them.

The Sun’s path is known as the ecliptic. The Moon and planets all stay close to that path. Tonight, in fact, Saturn is only about one degree above the ecliptic — less than the width of your finger held at arm’s length. So is the even brighter planet Jupiter, which is high in the south-southwest as Saturn and the Moon climb into view. Connecting the two planets lets you follow the ecliptic across the sky.

The galactic equator is a bit tougher to follow. It outlines the plane of our home galaxy, the Milky Way. It’s easiest to view under a dark sky, when there’s no Moon around. It splits the hazy band of light known as the Milky Way.

From bright cities and suburbs, though, you have to rely on bright stars to track the equator. It stretches to the upper left of the Moon and Saturn, then runs parallel to the body of Cygnus, the swan, and through W-shaped Cassiopeia, low in the north-northeast.

The galactic equator climbs higher in the sky as the night goes on. And it’ll be higher during the evening hours of summer — the hazy outline of our own galactic home.


Script by Damond Benningfield

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Moon and Saturn

Fri, May 12, 2017

One of the moons of Saturn is the Jekyll and Hyde of the solar system, presenting two very different faces to the universe.

Iapetus is about 900 miles in diameter — less than half the size of our own moon. And it’s locked so that one side always faces Saturn, just as the same side of the Moon always faces Earth. That means that the same portion of Iapetus always faces forward as it orbits Saturn. And that may be responsible for its two-faced appearance: The leading hemisphere is almost as dark as charcoal, while the trailing hemisphere is quite bright.

The dark hemisphere is coated with compounds that are rich in carbon, while the bright hemisphere is mostly ice.

The dark material may have been blasted off the surface of another of Saturn’s moons, and swept up by Iapetus. This dark material forms a layer that’s only about a foot thick. But it absorbs energy from the Sun, warming the surface. That caused ices below the coating to vaporize, darkening the surface even more. Some of the vapor then migrated to the opposite side of Iapetus, coating that hemisphere with fresh ice, making it brighter — giving the odd moon a two-faced appearance.

Look for Saturn close to the lower left of our moon as they rise late this evening. Saturn looks like a bright star. The true star Antares, which is about half as bright as Saturn, is a bit farther to the lower right of the Moon. You need a telescope to see Iapetus and Saturn’s other moons.


Script by Damond Benningfield

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Leo’s Triplets

Thu, May 11, 2017

Most of the “star pictures” in the night sky look nothing like their namesakes. But one beautiful exception lunges across the southwestern sky on May evenings: Leo, the lion. It’s high in the sky at nightfall.

Leo consists of two patterns of stars that the brain puts together to make a lion. A backward question mark represents the head and mane. And a triangle of stars to the lower left forms the lion’s hindquarters and tail.

Leo is best known for its bright stars – particularly Regulus, its brilliant heart. But the constellation also contains quite a few bright galaxies. Leading the list are three galaxies that together form the Leo Triplet: M65, M66, and NGC 3628.

NGC 3628 is the most interesting of the three. Like our own Milky Way, it’s a spiral — a pinwheel that spans at least a hundred thousand light-years. We see it edge-on, so it looks like a streak of light with lanes of dark dust running down the middle.

Gravitational encounters with the other galaxies have really pumped up NGC 3628.

They’ve triggered the birth of perhaps millions of new stars near the galaxy’s center. And they’ve pulled out a tail of gas that spans a quarter of a million light-years — enough gas to make half a billion stars as massive as the Sun. In fact, the tail has already given birth to millions of stars in several large clumps.

The Leo Triplet is just one of the wonders in one of the night sky’s most easily recognizable constellations: the lion.


Script by Damond Benningfield


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Busy Merger

Wed, May 10, 2017

A galaxy merger can be messy. Stars in the two galaxies are stirred up like chocolate chips mixed into a batch of cookie dough. Some stars are tossed out of the galaxies, while gas clouds slam together to give birth to new stars. And the central black holes of the two galaxies spiral together, setting off their own fireworks when they merge.

Such a merger appears to be underway in a system in Ursa Major, the great bear, which is high in the north on May evenings. The black holes are a few thousand light-years apart, so any merger is still millions of years away. But they reveal something about the individual galaxies in the merger.

The system is known as J1126+2944, for its coordinates in the sky. One of its black holes appears to be hundreds of times more massive than the other. That suggests that this isn’t a merger of equals. Instead, one galaxy may be big and heavy, like our own galaxy, the Milky Way. The other may be a dwarf galaxy, only a fraction the size of its partner.

If so, then its center may contain an intermediate-mass black hole — one that’s perhaps tens of thousands of times the mass of the Sun. So far, there’s evidence of only a handful of these black holes. It’s possible that they’re the “seeds” from which supermassive black holes grow — the monsters that inhabit the hearts of big galaxies. In fact, its merger with the other black hole will make that black hole even bigger — adding to the heft of a monster black hole.


Script by Damond Benningfield

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Doomed Star

Tue, May 9, 2017

A dead star in a distant cluster is facing a fate worse than death: complete annihilation. That’s because the star may orbit just 600,000 miles from a black hole — closer than any other black-hole companion yet seen.

This odd system is known as 47 Tucanae X9. It’s in a globular star cluster in the southern constellation Tucana, the toucan. The cluster is about 15,000 light-years from Earth.

Astronomers have watched X9 for years because it’s one of the brightest sources of X-rays in the cluster. X-rays are an indication that something powerful is going on.

Recent observations with the space-based Chandra X-Ray Observatory suggest that the system consists of a white dwarf and a black hole. A white dwarf is the dead core of a once-normal star. It’s about as big as Earth, but almost as heavy as the Sun.

The recent X-ray observations show that the likely white dwarf orbits the black hole about twice an hour, which tells astronomers that the two are quite close.

They’re so close, in fact, that the black hole appears to be stealing gas from the surface of the white dwarf. This material forms a wide, thin disk around the black hole. As material in the disk spirals toward the black hole, it gets extremely hot, so it emits X-rays.

Over time, the black hole could consume most of the white dwarf, leaving behind an even denser knot of material. On the other hand, it might eat the whole thing — cannibalizing its unlucky companion.


Script by Damond Benningfield

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Moon and Spica

Mon, May 8, 2017

Different stars face different fates. The smallest will shine feebly for trillions of years — many times longer than the current age of the universe — then simply fade away. The heaviest, on the other hand, will blast themselves to bits, briefly shining brighter than billions of normal stars.

A bright star that faces such a violent end is in good view tonight. Spica stands close to the right of the Moon as night falls, with the brilliant planet Jupiter above them.

Spica actually consists of two stars.

The heavier star, Spica A, is about 10 times the mass of the Sun. Such stars burn through their nuclear fuel in a hurry. That makes them extremely bright. But it also means they won’t live long. Spica A, for example, will live a “normal” lifetime of less than 30 million years, compared to about 10 billion years for the Sun. When it can no longer produce nuclear reactions in its core, the core will collapse. The star’s outer layers will fall inward, then rebound violently, blasting the star apart as a supernova.

Its companion, Spica B, is about six times the Sun’s mass. Assuming it’s not destroyed by the nearby supernova, it’ll live more than a hundred million years. At the end of its lifetime, it’ll swell up to many times its current size, just as Spica A will. But it’s not massive enough to explode. Instead, it’ll lose its outer layers in a less-violent process. That’ll leave only its dead core, shining feebly through the long cosmic night.


Script by Damond Benningfield

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Moon and Jupiter

Sun, May 7, 2017

Most of the solar system’s planets are surrounded by radiation belts — zones where charged particles are trapped by the planet’s magnetic field. Earth, for example, is encircled by the Van Allen belts. Spacecraft that pass through these belts need special shielding to protect their electronics.

But the most powerful belts encircle Jupiter, the giant of the solar system. Its magnetic field is far stronger than Earth’s, so it traps more charged particles from the Sun. Other particles come from its volcanic moon Io. These sources create radiation belts that could kill an unprotected person in hours.

A spacecraft that’s currently orbiting Jupiter has special protection against the radiation. Juno’s computer and much of its other electronics are housed inside a titanium vault. The vault is about as big as the trunk of an SUV, and its walls are almost half an inch thick. And even with that extra level of protection, Juno’s orbit is carefully controlled to keep the craft out of the most dangerous radiation zones.

Juno is measuring Jupiter’s magnetic and gravitational fields. Its readings should help scientists determine how Jupiter is put together. And that will help them learn more about how it generates its magnetic field — creating “dead zones” around the giant planet.

Jupiter is in good view tonight. It stands quite close to the Moon, and looks like a brilliant star. The true star Spica stands below the pair. More about Spica tomorrow.


Script by Damond Benningfield

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Moon and Companions

Sat, May 6, 2017

The Moon swings past a couple of bright companions the next few nights — the planet Jupiter and the star Spica. Jupiter is the solar system’s largest planet, and looks like a brilliant star to the lower left of the Moon as darkness falls tonight. Fainter Spica, the leading light of Virgo, stands below Jupiter.

The gap between Jupiter and Spica will stay about the same for another couple of months. As we get deep into summer, though, Jupiter will start moving toward Spica. And by the start of autumn, it’ll have passed the bright star, and will be leaving it behind at a pretty good clip.

That changing gap is the result of Jupiter’s orbit around the Sun, and our changing viewing angle on the planet.

It takes Jupiter about 12 years to complete one full turn against the background of stars, so it moves slowly across the sky. That means it can linger near a particular star for a good while.

But Jupiter’s position as seen from Earth also depends on Earth’s orbit. We follow a smaller, faster path around the Sun, so we pass by Jupiter once every 13 months or so. In fact, we just passed it last month.

As we pass Jupiter, it appears to stop its normal eastward motion across the sky, and actually move backwards for a while. When Earth gets far enough ahead, though, Jupiter once again resumes its eastward crawl. So the changing gap between Jupiter and Spica is the result of the orbital motions of two planets.

More about Jupiter and the Moon tomorrow.


Script by Damond Benningfield

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Martian Spring

Fri, May 5, 2017

Spring is already halfway through here in the northern hemisphere. But the season is just beginning in the northern hemisphere of Mars. Today is the vernal equinox on the Red Planet. The Sun crosses the planet’s equator from south to north, ushering in spring.

Mars has seasons for the same reason that Earth does: the planet is tilted on its axis. In fact, Mars is tilted at almost the same angle as Earth. So as the planet orbits the Sun, the northern and southern hemispheres take turns receiving more sunlight.

But the Martian seasons are a bit more complicated than those on Earth. That’s because Mars’s orbit is much more lopsided than Earth’s. The planet’s distance from the Sun varies by about 25 million miles, compared to only about three million miles for Earth. So when Mars is closest to the Sun, it receives a lot more energy than when it’s farthest from the Sun.

Right now, Mars is near the middle of that range in distance. As the northern spring progresses, though, Mars will move farther from the Sun. It’ll then start moving closer, and get closest to the Sun near the end of autumn. As a result, northern winters and summers are much more temperate than the southern seasons.

As the distance to the Sun changes, so does Mars’s orbital speed. That means there’s a good difference in the length of the seasons. Northern spring is the longest season. It lasts more than six months, so it’ll continue until the middle of fall here on Earth.


Script by Damond Benningfield

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Thu, May 4, 2017

Most of the matter that passes too close to a black hole will get a one-way trip to oblivion: It’ll vanish into the black hole. But some of that matter may instead get a quick trip back out into space. That’s because many black holes produce jets of charged particles. The biggest of them can span thousands of light-years, and can squirt away at close to the speed of light.

In fact, similar jets are found in other astronomical objects — from infant stars to dead stars.

Scientists still aren’t certain just how these jets form. But the process involves disks of gas and dust and strong magnetic fields. The material in a disk spirals toward the central object — a young star, for example, or a dead star such as a white dwarf, a neutron star, or a black hole.

Friction in the disk heats the material enough to rip atoms apart, creating streamers of charged particles. Magnetic fields then grab some of these particles and shoot them into space from the poles of the central object as narrow high-speed jets.

Those from young stars can stretch across billions of miles. But those from supermassive black holes at the hearts of galaxies can span thousands of light-years. And the black hole’s powerful gravity can accelerate them to much higher speeds — in some cases, just a bit below lightspeed.

As these jets ram into material in the galaxy around the black hole, they produce shockwaves and other dramatic effects — the fate of matter escaping from a black hole.


Script by Damond Benningfield

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Moon and Regulus

Wed, May 3, 2017

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 ranks as the 21st brightest star in the night. On the astronomical scale, it has a visual 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 from Earth, though, 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 10 parsecs — about 32 light-years.

In this scale, Regulus has a magnitude of point five. So 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, for example, it produces a lot of ultraviolet energy. 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 brilliant Regulus tonight, standing just a whisker away from the Moon.

Script by Damond Benningfield


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Tue, May 2, 2017

At first glance, the largest resident of the asteroid belt looks kind of dull. Its brownish surface is pockmarked by thousands of impact craters, much like the Moon and many other bodies — a world of little interest.

But a more detailed look reveals some remarkable features. There’s a mountain made of ice, for example, along with deposits of salts that may have bubbled up from an ocean below the surface.

Ceres is about 600 miles across — a quarter the diameter of the Moon. And it contains more than a quarter of all the material in the asteroid belt — a ring of debris between the orbits of Mars and Jupiter.

The Dawn spacecraft has been orbiting Ceres for more than two years. Its observations have supported the idea that there’s a lot of water in Ceres. Much of it is mixed with a layer of rock below the crust. But some could form a subsurface ocean.

Some of that water could have bubbled to the surface just four million years ago, inside a wide crater. The water quickly evaporated. But it left behind mineral deposits that are almost pure white — the brightest features on the entire world.

Water also may have formed the largest mountain on Ceres. It’s two-and-a-half miles tall, and its slopes are bright and smooth. An impact by an asteroid may have cracked the crust halfway around Ceres, allowing a mixture of water, ice, and minerals to push up from below on the opposite hemisphere. That built a mountain of ice on this intriguing little world.


Script by Damond Benningfield

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Asteroid Belt

Mon, May 1, 2017

The realm of the planets is neatly divided into two regions. There’s the region close to the Sun, which contains the small, rocky planets: Mercury, Venus, Earth, and Mars. And there’s the region far from the Sun, with the giant planets Jupiter, Saturn, Uranus, and Neptune.

The two regions are separated by a “dotted line”: the countless bits of rubble that make up the asteroid belt.

When the first asteroids were discovered, more than two centuries ago, many astronomers thought they were the remains of an exploded planet.

It turns out, though, that nearby Jupiter prevented the asteroids from clumping together to make a planet. Its powerful gravity stirred things up so much that when asteroids hit each other, instead of sticking together, they blasted each other apart. Much of the debris from these collisions escaped the asteroid belt. That depleted the supply of planet-making materials. Instead of a planet, the leftovers formed a wide, thin ring around the Sun.

Hundreds of thousands of asteroids have been found so far, with tens of millions more likely awaiting discovery. They don’t add up to much, though — only a few percent of the mass of the Moon.

And despite what you see in the movies, the asteroid belt is mostly empty space. The average distance between asteroids is a million miles or more. In fact, many spacecraft have flown through the asteroid belt with no trouble at all — unmolested by the debris from a planet that never was.


Script by Damond Benningfield

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The Most Beautiful

Sun, Apr 30, 2017

Russian astronomer Friedrich Wilhelm von Struve discovered and catalogued thousands of binary stars — pairs of stars that are gravitationally bound to each other. But a system that he first saw in 1829 was so striking that he gave it a special name: Pulcherrima — “the most beautiful.” The name honors the contrasting colors of the two stars. One looks pale orange, while the other looks blue-white or even green.

The system is also known by an even older name: Izar, “the girdle,” because it represents the middle of Bo?tes, the herdsman. Regardless of what you call it, most skywatchers agree with Struve: Seen through a telescope, the pair is quite a beauty.

The orange star is a giant. It’s burned through its original hydrogen fuel and is nearing the end of its life. As a result, it’s puffed up to many times the diameter of the Sun. That “puffiness” caused the star’s outer layers to cool, which is why it looks orange.

Its companion is much hotter, so it shines almost pure white. It looks blue or green only when it’s compared to its orange companion. It’s less massive than the companion, so it has a lot longer to go before it reaches its own “giant” phase of life.

Bo?tes is in the east as night falls. Look for its brightest star, brilliant yellow-orange Arcturus. Izar is the first noticeable star to the left of Arcturus. To the unaided eye, it looks like a single point of light. But a telescope reveals the true beauty of this colorful duo.


Script by Damond Benningfield

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