StarDate

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

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

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

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

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

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

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

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

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

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