StarDate

For those who are caught in the throes of winter, it’s hard to believe, but it’s true – Earth is snuggling closest to the Sun for the entire year this week. We’ll be at our absolute closest tomorrow, at about 91 and a half million miles – about a million and a half miles closer than average.

That change in distance doesn’t make much difference in the temperature – Earth’s oceans and atmosphere do a good job of distributing heat around the globe.

Instead, the seasons are caused by Earth’s tilt on its axis. At this time of year, the south pole tips toward the Sun, so the southern hemisphere sees longer days. That means there’s more sunlight to warm things up. And the Sun climbs higher in the sky, so its rays fall most directly on the southern hemisphere, making it warmer still.

It’s the reverse of that north of the equator. The north pole tilts away from the Sun, so the days are short and the Sun stays low in the sky.

And the farther north you go, the lower the Sun appears. Just north of the Arctic Circle, in fact, there’s no sunlight at all. Most of the United States sees about 9 or 10 hours of sunlight. But the Sun’s at such a low angle that it doesn’t warm things up much.

That will change over the coming months, though. The Sun is moving slowly northward, so it’ll climb higher in northern skies, and stay in view longer. It’ll peak in a bit less than six months – when Earth is farthest from the Sun.

Script by Damond Benningfield

Few sights in the night sky are more eye-catching than a conjunction between the Moon and Venus. And we get to enjoy such a meeting both tonight and tomorrow night. Venus is the brilliant “evening star.” It’s well above the Moon this evening, but much closer to it tomorrow night.

We’ve explored both worlds in detail. But more missions are being planned – especially to the Moon. Some day, swarms of people and machines might be on the surface or in orbit. Scientists are thinking about ways to time all that activity. So they’re trying to develop a new timekeeping system for the Moon.

You might think that a lunar version of GPS might do the trick. And it could. But time passes at different rates for objects on the surface and in orbit. And neither of those rates matches the passage of time on Earth.

That’s all because of relativity. Clocks in orbit tick a little slower because they’re moving faster than those on the ground. But they tick faster because they don’t feel as strong a gravitational pull. If GPS didn’t account for those effects on Earth, the whole system would become worthless in a few days.

But you can’t use the same numbers at the Moon. The Moon’s gravity is weaker than Earth’s, and orbiting satellites move more slowly. Clocks also have to account for the fact that the Moon is orbiting Earth.

So scientists are working out the details of lunar clocks – perhaps leading to a GPS system for our satellite world.

Script by Damond Benningfield

Two hundred years ago tonight, an Italian astronomer saw something new. He described it this way: “The atmosphere was traversed by a multitude of the luminous bodies known by the name of falling stars.” In other words, he saw a brand-new meteor shower.

The shower is still with us. And it’ll be at its best tomorrow night. It’s known as the Quadrantid shower. Its meteors appear to rain into the atmosphere from the extinct constellation Quadrans Muralis. It represented an instrument that was used to plot the positions of the stars. Today, that part of the sky is in Boštes, the herdsman.

The shower takes place as Earth passes through a trail of debris from an asteroid or dead comet. Bits of rock and dust slam into our atmosphere. They quickly vaporize, forming the streaks of light known as meteors. The Quadrantid shower includes a lot of bigger bits of debris, which form especially bright meteors.

The Quadrantids have the shortest peak of any major meteor shower – only a few hours. During that peak, you might see up to a hundred meteors per hour. Unfortunately for those of us in the United States, the peak is during the daylight hours on Saturday. So the best view should come late tomorrow night.

To see the shower, find a safe skywatching site away from city lights. The meteors can zip across any part of the sky. So bundle up and scan the skies – for a meteor shower that’s marking its bicentennial.

Script by Damond Benningfield

For many, this time of year is a time for reflection – to think about the year that was, and ponder the year to come. So it might be a good time to ponder a reflection in the stars – a giant cloud of gas and dust that’s reflecting the light of some hot young stars.

The stars belong to the Pleiades – a cluster of perhaps a couple of thousand stars. The cluster probably is about a hundred million years old – quite young as stars go.

The cluster began as a giant cloud of gas and dust. The cloud split into smaller clumps, which then collapsed to make stars. Radiation and winds from the newborn stars would have blown away most of the remaining dust and gas, but not all. And for a long time, that’s what astronomers thought they were seeing in the Pleiades. Pictures reveal wisps of blue mingling with the stars – what appeared to be leftover star-making material.

But that’s not the case. The wisps of material belong to a cloud that’s not related to the Pleiades – they just happen to line up in the same direction. Dust grains in the cloud reflect the light of the hot, blue stars in the cluster – reflections from some beautiful stars.

Look for the Pleiades high in the east at nightfall. The cluster looks like a tiny dipper. It stands above the brilliant planet Jupiter and the bright star Aldebaran. But you need to take a long-exposure image to capture the reflection of the Pleiades in the passing cloud.

Script by Damond Benningfield

The Pleiades star cluster is also known as the Seven Sisters. That’s because seven of its stars are fairly easy to pick out. They form a small but prominent dipper.

In Greek mythology, the stars represented the daughters of Atlas, one of the Titans – the ancient gods who reigned before the gods of Olympus. As with many groups of siblings, though, one stands out: Alcyone, the brightest star in the cluster.

It’s actually a lot like its other bright siblings – the standouts in a family of more than a thousand stars. The top stars are all quite impressive – bigger, heavier, hotter, and brighter than the Sun. And as seen from Earth, Alcyone is the most impressive of them all.

Because of its great mass, the star has already moved out of the “prime” phase of life – even though it’s about four and half billion years younger than the Sun.

Alcyone rotates in a hurry – so fast that it bulges outward at the equator. That high speed flings hot gas from the equator into space. And before long, the nuclear furnace at the star’s core will shut down, so Alcyone will expel all the gas in its outer layers. That will leave only the star’s dead core – a white dwarf – the faint ember of a once mighty star.

The Pleiades is in the east at nightfall. It stands above the bright star Aldebaran and the brighter planet Jupiter. The cluster doesn’t set until the wee hours of morning.

More reflections about the Pleiades tomorrow.

Script by Damond Benningfield

The Pleiades star cluster is one of the prettiest sights in the night sky – a group of moderately bright stars that forms a tiny dipper. Depending on your eyesight and your sky conditions, you might see six or seven stars – or perhaps a few more.

But there’s far more to the Pleiades than that. The cluster contains more than a thousand known star systems. More than half of the systems have two or more stars. So the total number of stars may be close to two thousand – or perhaps a few more.

All of the stars were born in a single giant stellar nursery. The first probably were born about a hundred million years ago. The last flared to life millions of years later.

Some of the family members have wandered off – they’re no longer tied to the cluster. The remaining clump of stars spans about 80 light-years. The stars on the outskirts will be pulled away from the cluster by the gravity of the rest of the galaxy’s stars and gas clouds. Stars in the middle of the cluster are more tightly packed, so they’ll stick together longer – perhaps hundreds of millions of years.

This is a great time to look for the Pleiades. The cluster is well up in the east at nightfall. And two bright lights stand below it: the brilliant planet Jupiter and the star Aldebaran, to the right of Jupiter. The name “Aldebaran” means “the follower” – indicating that the bright star follows the Pleiades across the night.

And we’ll follow the Pleiades again tomorrow.

Script by Damond Benningfield

A constellation with connections to both scientific advancement and the horrors of war and revolution scoots low across the southern sky tonight. Fornax is in the southeast at nightfall. It’s not much to look at – its three brightest stars form a faint wedge that aims toward the south. In fact, it’s so feeble and so far south that it wasn’t drawn until the mid-1700s.

Fornax was one of 14 constellations created by French astronomer Nicolas Louis de la Caille, after he mapped southern skies from South Africa. All of the stars of the new constellations are so far south that they were barely visible from Europe – or not visible at all.

La Caille named Fornax for a chemical furnace, in honor of fellow scientist Antoine Lavoisier. Lavoisier had developed accurate descriptions of how things burn and how chemical reactions take place.

Lavoisier used his knowledge to develop gunpowder for the French government. One of his employees later emigrated to the newly formed United States, where he founded the DuPont company. One of his first jobs was developing gunpowder for the American government.

Lavoisier also worked with an agency that collected taxes. After the French Revolution, that wasn’t a popular group of folks. Many of them were guillotined – including Lavoisier.

So the patchwork quilt that forms the constellations tells some interesting tales about our legends and our history – some of them with un-happy endings.

Script by Damond Benningfield

If you’re up early tomorrow, and you have a clear southeastern horizon, you might want to step out into the winter chill for a few seconds – or maybe just look out your kitchen window. The Moon will pass amazingly close to the star Antares, the heart of the scorpion. And an even brighter light will stand not far to the left: the planet Mercury. All three are quite low in the sky during the dawn twilight, and quickly vanish as the sky gets brighter.

The Moon and Antares are visible at some point during most nights of the year. And they can pass high across the sky, so they’re easy to pick out.

Mercury is a little more bashful. It’s the closest planet to the Sun – about a third of Earth’s distance. Because of that, Mercury never moves very far from the Sun in our sky. At best, it’s visible for a little while before sunrise, as it is now, or after sunset.

That makes Mercury a difficult target for skywatchers – and for professional astronomers. They can’t point their telescopes close to the Sun. And Mercury is almost always so low in the sky that it’s seen through a thick layer of air, which muddies the view.

The best views of Mercury have come from three spacecraft that have visited the planet. The third one has passed by Mercury three times, with another visit scheduled for next month. It should enter orbit in November of 2026 – providing the best views yet of this bashful little planet.

Script by Damond Benningfield

Capricornus is one of the constellations of the zodiac, so it’s well known. But it’s small and faint, so it’s not easy to see – especially from light-polluted cities. Right now, though, a bright light points the way. Venus, the “evening star,” is passing quite close to the constellation’s brightest star. The rest of Capricornus spreads out below Venus.

The constellation represents a sea-goat – the body of a goat with the tail of a fish. And there are lots of legends to explain it.

In ancient Babylon, for example, the stars represented a god who had a human torso and the tail of a fish. He came out of the sea to pass along wisdom and knowledge. And in Greece, the stars represented the god Pan, who had the torso of a man and the hindquarters of a goat. The legend says he was threatened by a monster. To escape, he jumped into a river and tried to change himself into a fish. But he botched the job – creating the sea-goat.

The constellation’s brightest star is Delta Capricorni. It’s quite close to the left of Venus, which is well up in the southwest at dusk. Delta actually consists of four stars. The system is about 40 light-years from Earth.

The rest of the sea-goat lines up to their lower right. It forms a wide triangle. The shape is sometimes described as an arrowhead, or the bottom of a bikini bathing suit. No matter how you describe it, though, this is a good time to spot this famous but faint constellation.

Script by Damond Benningfield

O Christmas Tree, O Christmas Tree,

That’s certainly true for the branches of the Christmas Tree star cluster – a family of young stars in the constellation Monoceros, the unicorn. The cluster’s brighter stars form the outline of a Christmas tree. Other stars look like ribbons of lights decorating the tree.

The cluster is about 2500 light-years away. All of its stars are infants – no more than a few million years old.

The most impressive member of the cluster is 15 Monocerotis. It’s a binary – two stars bound by their mutual gravitational pull. One of the stars appears to be about 10 times the mass of the Sun, while the other is more than 30 times the Sun’s mass.

Both stars are tens of thousands of degrees hotter than the Sun. Such stars produce a lot of ultraviolet energy. The U-V zaps giant plumes of hydrogen gas that permeate the cluster, making the gas shine bright pink – forming the branches of the Christmas Tree. Blobs of cold gas and dust create dark silhouettes against that background. New stars are taking shape inside some of those blobs.

The Christmas Tree Cluster climbs into view in the east in early evening. Under dark skies it’s just visible to the eye as a faint smudge of light. A telescope reveals a few of its individual stars and the faint glow of the gas. Long-exposure images reveal the full beauty of this cosmic Christmas tree.

Script by Damond Benningfield