StarDate

A cobra slithers across the surface of the Moon. It’s a hundred miles long and up to six miles wide — big enough to see through a small telescope. And it’s almost four billion years old.

The cobra is called Schroter’s Valley, and it’s the biggest valley on the Moon. It begins at a deep hole called the Cobra Head, then twists across a plateau that was thrust upward when a city-sized boulder struck the Moon long ago.

The entire plateau shows signs of ancient volcanic activity. It’s covered by a reddish material that contains lots of tiny glass beads. The beads formed when volcanoes blasted molten rock high above the lunar surface. And narrow, twisting channels carved by flowing lava criss-cross the plateau.

Schroter’s Valley is the largest channel, but it probably formed in a different way from the others. It may represent a fault line that formed when the plateau was created. Giant blocks along this line dropped, leaving a long, wide valley. Lava once spilled from the Cobra Head, then flowed through that valley toward a volcanic plain — the Ocean of Storms.

There are no big volcanoes on the Moon today. But there’s evidence of some activity in the region around Schroter’s Valley — swirls of gas that may escape from below the lunar crust.

And look for the Moon late tonight. It climbs into good view by around 1 o’clock, with a bright companion to the lower right of the Moon: Spica, the brightest star of the constellation Virgo.

Script by Damond Benningfield

The boldest and brightest of all constellations wheels across the south on February nights: Orion. It’s marked by the hunter’s bright belt of three stars, surrounded by a box of four bright stars.

One of the meekest and faintest constellations also wheels across the south on February nights. Caelum, the chisel, is due south a couple of hours after sunset. It sits directly atop the horizon for those at the middle latitudes of the U.S., and a little higher for those farther south.

No matter where you are, though, it’s not much to look at — a few stars that are so faint that you need a dark viewing site to see them at all.

The constellation was first published by Nicolaus Louis de la Caille. The French astronomer visited the southern tip of Africa in the mid-1700s. He made detailed catalogs and maps of the southern stars. When he published his findings, he included 14 new constellations made from those stars. Most of them were named for scientific or artistic instruments.

La Caille named this constellation Caelum Sculptorium — “the engraver’s chisel.” Later, other astronomers shortened the name to just Caelum.

Its brightest star is actually two stars — a binary system about 65 light-years away. The main star is hotter and brighter than the Sun. Its companion is a red dwarf — a cosmic ember that’s not visible without a telescope. But even the bright star is barely visible — a pale dot in a pale constellation chiseled from the southern sky.

Script by Damond Benningfield

This weekend, the rising Sun will shine through the long entryway of an ancient structure in Ireland. Known as the Mound of the Hostages, it was built more than 5,000 years ago. It served as a burial space and as a site for ritual gatherings. And one of the gathering dates probably was Imbolc, a Celtic festival day that celebrated the birth of the year’s new lambs.

Imbolc was one of many worldwide celebrations of a cross-quarter day — a day that comes roughly half way between a solstice and an equinox. In many cultures, these dates represented the beginning of a season, not its mid-point.

The February cross-quarter day was a time to celebrate the returning Sun. The days were noticably longer by then, with the promise of even more sunshine to come. The festivities included bonfires and candles — stand-ins for the Sun on the still-long nights.

The date for Imbolc is usually given as February first. The date of the actual cross-quarter day varies, though, depending on the dates of the solstice and equinox. This year, the moment that’s exactly half way between these points comes on February 4th for those in Ireland, and the 3rd for most of us in the United States.

In ancient times, celebrants may have thought they could foretell the weather by the conditions on Imbolc. A cold, clear day meant more winter, while a warm or cloudy day suggested that spring was at hand. That custom is still observed today — as Groundhog Day.

Script by Damond Benningfield

The biggest member of a belt of planetary flotsam is shining at its best right now. Ceres is the largest object in the asteroid belt — roughly a quarter the diameter of the Moon. And it’s lining up opposite the Sun, so it’s closest to us for the year, at more than 150 million miles. At that range it shines brightest, although not quite bright enough to see with the eye alone.

Ceres accounts for more than a quarter of the mass of the entire asteroid belt — a ring of rocky debris between Mars and Jupiter. The belt contains perhaps a million or more objects that are at least a kilometer in diameter, and countless other smaller ones.

Out of all of those chips of rock, ice, and metal, Ceres is the only one that’s built like a planet. Its gravity was strong enough to pull it into a spherical shape, for example. And it consists of several layers: a rocky core surrounded by an icy mantle, all wrapped in a crust of rock, ice, and salts.

A layer of liquid or frozen water may lie just below the crust. Some of that water appears to be escaping into space, giving Ceres a thin atmosphere. And an orbiting spacecraft found organic materials on the crust — the chemical building blocks for life. The combination means that conditions below the crust could be comfortable for life.

Ceres is passing through the constellation Cancer. Tonight, it’s high above the Moon in early evening. But you need binoculars to spot the little giant of the asteroid belt.

Script by Damond Benningfield

Earth and its planetary siblings were born in a disk of gas and dust around the young Sun. Dust particles in the disk stuck together to form ever larger bodies, which eventually became planets.

One problem with this idea is that Earth is made mostly of rock and iron, and dust grains made of these materials aren’t sticky. So what would make them stick together?

Astronomer Alexander Hubbard at the American Museum of Natural History says the answer may be found in a star in the constellation Orion. In 1936, the newborn star FU Orionis began to erupt there, eventually shining more than a hundred times brighter than it was before. And the star is still bright today. Since then, astronomers have seen a few other infant stars do the same thing.

Hubbard says that if the young Sun behaved that way, the outburst would have melted some of the dust grains near the future Earth, making them sticky. As they stuck together, they would have formed larger bodies. In time, they would have grown big enough to form Earth and the other rocky planets — Mercury, Venus, and Mars.

Orion climbs high across the south tonight. It’s marked by its three-star belt, with bright orange Betelgeuse to its upper left and blue-white Rigel to its lower right. And a giant stellar nursery lurks below the belt — the Orion Nebula. It contains thousands of newborn stars. Some of them are similar to FU Orionis, a young star that may provide new insights into the birth of our own world.

Script by Ken Croswell

The full Moon will experience a whole spectrum of colors tonight. As the second full Moon of the month, it’s known as a Blue Moon. It won’t actually look blue, though. Instead, as seen from most of the United States, it will turn dark orange or red as it undergoes a total eclipse.

The meaning of “blue moon” has undergone several transformations over the years. In recent decades, it’s come to mean the second full Moon in a calendar month. On average, that happens about every 2.7 years. Thanks to the shortness of February, though, this year it’ll happen again in March.

Lunar eclipses are more common, but still rare. There are several per year. Not all of them are total, though, and any eclipse is visible from only a portion of Earth’s surface.

This eclipse gets started in the wee hours of tomorrow morning as seen from the United States. In fact, from the eastern half of the country, the eclipse will be under way as the Moon sets. The western states will see the entire total eclipse, as the Moon both enters and exits Earth’s dark inner shadow.

When the Moon is fully immersed in that shadow, it’ll turn dark orange or red — the result of sunlight filtering through Earth’s atmosphere. The color is more pronounced in photographs than it is to the eye alone.

The Moon will be just past its closest approach to Earth during the eclipse, so it will appear slightly larger than average. That makes this event a Super Blue Lunar Eclipse.

Script by Damond Benningfield

When you watch the Moon move across the sky, you’re actually seeing two separate motions: Earth’s rotation on its axis, and the Moon’s orbital motion around Earth.

The biggest motion is the Moon’s transit from its rising point in the east to its setting point in the west — the result of Earth’s rotation. As our planet spins, everything beyond Earth moves from east to west — the Moon, Sun, stars, and planets.

But the Moon’s other motion, caused by its orbit around Earth, carries the Moon in the opposite direction — eastward against the background of stars. So while the stars all rise about four minutes earlier each day, the Moon rises an average of about 48 minutes later.

This motion is easiest to see when the Moon is near another bright object, as it is tonight — Aldebaran, the orange eye of Taurus, the bull.

Aldebaran will stand to the lower left of the Moon as darkness falls. Over the following hours, though, the Moon will creep ever closer to the star. From Kansas City, for example, they’ll be separated by a bit less than six degrees in early evening — about the width of three fingers at arm’s length. But by the time they set, around 3 a.m., they’ll be just two degrees apart — a difference that’s easily visible to any careful skywatcher.

And if you’re in Alaska, the two will get even closer — the Moon will pass in front of Aldebaran, blocking it from view — a disappearing act caused by the Moon’s orbit around Earth.

Script by Damond Benningfield

When a star explodes as a supernova, it’s bad news for any nearby planets. The shockwave blasts the planets to cosmic dust. But that act of cosmic destruction clears the way for new acts of creation: the birth of new planets. And a recent study suggests a way for the second-chance planets to take shape.

A supernova can form when a massive star can no longer produce nuclear reactions in its core. The core collapses, while the outer layers blast into space at up to a few percent of the speed of light. The collapsed core can form a neutron star. It’s up to a couple of times the mass of the Sun, but only a dozen miles or so across.

Astronomers have discovered small, rocky planets around a few neutron stars. There’s no chance that these worlds survived the explosions, so they must have formed afterwards.

One neutron star where astronomers thought they saw a planet is Geminga. It’s in the constellation Gemini, which is in the east at nightfall. The constellation is marked by its two brightest stars, Pollux and Castor — Gemini’s twins.

The possible planet turned out to be a false alarm. But the star is plowing through the galaxy at high speed. It sweeps up grains of dust from interstellar space as it does so.

The recent study says that some of those grains have formed a disk around the star. It contains enough material to make about five Earth-size planets. Over time, some of these grains may merge to form new planets — cosmic birth after cosmic destruction.

Script by Damond Benningfield

Sirius, the Dog Star, is in the southeast this evening. It’s the night sky’s brightest star, so it’s hard to miss. And it’s led into the sky by another bright light — Procyon, the little dog star. It’s to the left of Sirius and a little higher, so it precedes Sirius across the evening sky.

Procyon is among the dozen brightest stars in the night. That’s mainly because it’s just 11 and a half light-years away.

It’s actually a system of two stars. The main star is known as Procyon A. It’s about one and a half times as massive as the Sun, about twice as big, and about seven times as bright.

The star is nearing an important transition point. It’s converted most of the original hydrogen fuel in its core to helium. That’s made the core get smaller and hotter, which in turn has caused its outer layers to puff outward a bit.

Before long, all the hydrogen in the core will be gone, and the star will swell up to giant proportions. It’ll then start converting the helium to carbon and oxygen. Once that process is complete, the nuclear reactions in the core will shut down. Procyon A then will cast its outer layers into space, leaving behind only the dead core — a tiny ember known as a white dwarf.

That’s already happened to the second star in the system, Procyon B. It’s so faint and so close to Procyon A that it’s almost impossible to see, even through a big telescope. But it once was even bigger and brighter than Procyon A. More about that tomorrow.

Script by Damond Benningfield

For many people, one of the most common sights in the night sky is also one of the most confusing. It’s the crescent Moon — a phase in which only a small fraction of the hemisphere that faces Earth is illuminated.

Many folks think the dark portion of the Moon is darkened by Earth’s shadow, but it’s not. The only time the Moon passes through the shadow is during an eclipse. And that happens only during full Moon, when the Moon lines up opposite the Sun.

Instead, the cycle of lunar phases is caused by the Moon’s orbital motion. As the Moon orbits Earth, the angle between Earth, Moon, and Sun changes. That means that sunlight illuminates different fractions of the hemisphere that faces Earth.

The Moon was new on Tuesday, as it passed between Earth and the Sun. The far side of the Moon was facing the Sun then, so the hemisphere that faces Earth was dark.

Today, the Moon has moved away from the Sun, but it still lines up in the Sun’s general direction. At that angle, sunlight illuminates only a few percent of the part of the Moon that faces our way. The rest of the disk is in its own shadow, so it’s nighttime.

If you could stand on the Moon and look toward Earth right now, our planet would be almost full. It’s dozens of times brighter than a full Moon, so it lights up the lunar night. We see that effect as earthshine — a subtle glow across the dark part of the crescent Moon, which is low in the southwest at sunset tonight.

Script by Damond Benningfield