StarDate

If you could catch the hot gas that the star Alnilam is blowing into space, in a million years you’d have enough to make two stars as heavy as the Sun. But you wouldn’t be able to tell much difference in Alnilam itself, because it’s one of the monsters of the Milky Way.

Alnilam is the “buckle” in Orion’s Belt, a compact line of three bright stars. It rolls across the south on winter nights.

It’s the most impressive member of the belt. As seen from Earth, it’s the brightest of the three stars, even though it’s hundreds of light-years farther away. And while each of the others consists of more than one star, Alnilam moves through the galaxy alone.

Alnilam is a supergiant. It’s more than 60 times as massive as the Sun, tens of thousands of degrees hotter, and hundreds of thousands of times brighter. Its radiation is so intense, that it blows a dense “wind” of hot gas from its surface. The wind races into space at millions of miles an hour.

Although Alnilam is only a few million years old, it’s nearing the end of its life. It’s probably consumed its original hydrogen fuel. Over the next few million years, it’ll burn through a series of heavier elements forged in its core.

Eventually, though, it won’t be able to sustain that process any longer. Its core will collapse, while its outer layers blast into space as a supernova — briefly outshining the combined light of most of the other stars in the galaxy.
 

Script by Damond Benningfield

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“Tadpoles” swim through the Orion Nebula, a giant stellar nursery more than 1300 light-years from Earth. Like tadpoles, they’re not yet fully mature. Also like tadpoles, not all of them will survive their hostile environment.

The tadpoles are known as protoplanetary disks – proplyds for short. They’re giant “cocoons” of gas and dust. Each one envelops a central star that’s still being born. And some of them may give birth to planets.

The proplyds look like tadpoles because they’re being sculpted by the radiation of nearby stars. The stars are exceptionally hot and bright. They produce a lot of ultraviolet radiation. The UV acts like a blowtorch, blasting the proplyds. The side of a proplyd that faces the stars is hot and bright, so it forms the “head” of the tadpole. The “tail” is formed by gas flowing away from it.

The proplyds are quite young – no more than a couple of million years old. Their central stars are still taking shape. Many of them shoot out “jets” of hot gas from their poles that are billions of miles long.

A disk of cooler gas and dust may surround the infant star. If it survives the blowtorch, the disk may give birth to planets – worlds born from the remains of stellar tadpoles.

The Orion Nebula is visible to the unaided eye. It looks like a wide, fuzzy star in Orion’s Sword. Orion is in the east and southeast at nightfall, with the sword to the right of its three-star belt.
 

Script by Damond Benningfield

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One of the most remarkable sights in the night sky is M42, the Orion Nebula. It looks like a hazy patch of light in Orion’s Sword, which is to the right of his three-star belt in early evening. The nebula is one of the most-distant objects that’s visible to the eye alone – more than 1300 light-years away. It’s also one of the biggest – a couple of dozen light-years across.

What’s really remarkable, though, is the nebula’s identity. It’s a nursery that’s given birth to thousands of stars, with thousands more being born today. And all of that activity has taken place over just a few million years.

M42 contains huge clouds of gas and dust. Clumps of this material collapse to form stars. The most massive stars form a cluster known as the Trapezium. These stars are much bigger, brighter, and heavier than the Sun. They produce a lot of ultraviolet energy. It zaps the gas around them, making it glow.

If you could travel inside M42, you’d see hundreds or thousands of stars. Some would be too bright to look at directly, while others would look like dull embers. Ribbons and curtains of gas would surround you, glowing pink, green, or blue-white. Dark lanes and blobs would run through the background – dense clouds of dust where more stars are taking shape.

You’d also see some objects that look a bit like tadpoles – proplyds – the possible birthplaces of planets. We’ll have more about that tomorrow.
 

Script by Damond Benningfield

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Proxima Centauri b is the closest planet outside our own solar system. So it’s natural to wonder whether it might support life. As with many other exoplanets, the answer is maybe. It has some big plusses, but perhaps some even bigger minuses.

The planet orbits Proxima Centauri, the closest star to our own – a bit more than four light-years away. It’s so faint, though, that it’s not visible without a telescope.

Proxima b is one of three possible planets orbiting the star. But it’s the only one in the “habitable zone” – the region around the star that’s thought to be comfortable for life. And the planet is about the same size and mass as Earth. Those are the plusses.

The minuses have to do with the star — a red dwarf. It’s much smaller, cooler, and less massive than the Sun. And most of the time, it produces much less than one percent as much energy as the Sun does.

Sometimes, though, Proxima flares up. It produces explosions of energy and particles that are a thousand times stronger than anything yet seen from the Sun. Proxima b is only about four-and-a-half million miles from the star – just five percent of the distance from Earth to the Sun. So the flares blast the planet with X-rays and charged particles. That could erode the planet’s atmosphere – if it has one – and zap any life on the surface.

So the odds seem to be against finding life on this nearby neighbor – at least for now.
 

Script by Damond Benningfield

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Mercury’s appearances in our sky are like a game of whack-a-mole. First, the planet pops into view in the morning sky, then it ducks into the Sun’s glare, then it pops up in the evening sky, and so on. It never stays in view for long – no more than a few weeks, and often only a few days. So you have to strike fast to catch it.

This is one of its morning pop-up times. Mercury is quite low in the southeast as the dawn twilight gets brighter, so you need a clear horizon to see it. And although it looks like a fairly bright star, it can be hard to spot against the bright sky.

Mercury pops in and out of view so often because it’s the closest planet to the Sun, while Earth is the third planet. As a result, Mercury stays close to the Sun as seen from Earth – it never climbs very high into the sky. And Mercury’s tighter orbit means that it crosses between Earth and the Sun, or behind the Sun, every few months. That carries it from morning to evening and back again in a hurry, leaving little time to catch it.

Mercury is in better view tomorrow because it has some bright companions. It’s close to the upper left of the crescent Moon. Venus, the brilliant “morning star,” is high above the Moon. And Antares, the brightest star of the scorpion, is to the lower right of Venus. And although the Moon will have dropped from view on Wednesday, Mercury will remain in decent view for another week or so.
 

Script by Damond Benningfield

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Bright lights encircle the crescent Moon during the early dawn twilight tomorrow – the star Antares and the planets Venus and Mercury.

Antares appears closer to the Moon than the other two companions. From most of the United States, only a sliver of sky will separate them at first light. For skywatchers in the western part of the country, though, that sliver will disappear as the Moon occults Antares. The Moon will cross between Earth and the star, blocking it from view.

Antares occultations come in groups. They’re tied to an 18.6-year cycle in which the Moon moves farthest north and south across the sky. The current group started last year, and continues into 2028. The next series won’t begin until 2041. But only some of the occultations will be visible from the U.S.

The Moon’s brightest companion is the planet Venus, the “morning star.” Venus is dropping back toward the Sun in our sky, but it’ll take its time. It will remain in view until April. After that, it’ll pass behind the Sun, then hide in the Sun’s glare. It’ll return to view – as the “evening star” – in July.

Mercury is the Moon’s farthest companion tonight. It’s the closest planet to the Sun, so it never moves far from the Sun in our sky. In fact, this is one of its best appearances of the year. It looks like a bright star well to the lower left of the Moon. But it will be much closer to the Moon on Tuesday morning. More about that tomorrow.
 

Script by Damond Benningfield

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The two brightest stars of Gemini — Pollux and Castor — are in pretty good view in the east-northeast not long after the sky gets good and dark. Pollux is the brighter one, with Castor close above it. But Gemini is a big constellation, so it’s a long way over to the third-brightest star, Alhena, which marks a foot of one of the twins. It’s off to the right of the other two, by about twice the width of your fist held at arm’s length.

Alhena consists of two stars. The star we see is about three times the Sun’s mass and diameter. It’s about 125 times brighter than the Sun. And it’s thousands of degrees hotter. That makes it a “class A” star.vb

Astronomers classify stars with the letters O-B-A-F-G-K-M. The classes are based on the surface temperatures of the stars. O stars are the hottest and bluest, while M stars are the coolest and reddest.

Class A stars are toward the top of the temperature scale. And they’re not very common. They account for perhaps one percent of all stars in the galaxy. And Alhena is at the very top of the A stars – one of the hottest – so it shines pure white.

Its companion star has never been seen directly – it’s too faint and too close to see through the glare of the brighter star. But instruments reveal some details. It’s about the same mass as the Sun. It’s probably in the same class as well – class G — the spot for yellow stars like the Sun and the unseen star of Alhena.
 

Script by Damond Benningfield

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Delta Geminorum has one claim to fame. It was just half a degree from Pluto when the little world was discovered, in 1930. Pluto has moved a third of the way around the sky since then. But Delta Gem has stayed put. It’s the seventh-brightest star in Gemini. It connects the body and legs of one of the twins.

The star is also known as Wasat. The name comes from Arabic, and means “middle.” But no one knows what middle is represented.

Delta Gem is a system of at least three stars. Two of them form a tight pair. But the third is far away – more than a hundred times the distance from Earth to the Sun. At that rate, the star takes about 1200 years to orbit the other two.

The system’s main star is a subgiant. That means it’s burned through most of the hydrogen in its core. It’s making the transition to the next phase of life: a giant. It’s already bigger than the Sun, but it’ll get even bigger over the next few million years. It’ll shine hundreds of times brighter than it does now, making it Gemini’s brightest star.

And it’ll get brighter for another reason as well. Today, it’s about 60 light-years away. A million years from now, though, it should pass within about seven light-years of Earth – making it one of the brightest stars in all the night sky.

Delta Gem is low in the east-northeast at nightfall, to the right of Gemini’s current leading light, Pollux. They soar high overhead later on, and remain in view all night.
 

Script by Damond Benningfield

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The night sky is getting brighter. The main culprit is light pollution – the glow of streetlamps, billboards, and many other artificial light sources. But there’s another source of brightness that’s far outside Earth’s atmosphere: satellites.

The number of satellites is, well, skyrocketing. As many satellites have been placed in Earth orbit in the past five years as in the first six decades of the Space Age. And the pace is picking up. Companies are launching thousands of spacecraft every year. Most of them bring Internet access to underserved parts of the world.

That’s becoming a problem for astronomers. The satellites can form bright streaks in their images of the universe, or block their targets from view.

It’s also becoming a problem for casual skywatchers. The satellites reflect a lot of sunlight, casting a “haze” across the night. And when satellites collide or break apart, they produce thousands of bits of debris, all of which add to the glow.

A recent study reported that the congested space around Earth has already brightened the night sky by about 10 percent. And if the projected launch rate comes true, it could make the sky even brighter. Even under dark skies, away from city lights, that could reduce the number of visible stars by almost a third. And it could make it harder to see meteor showers, faint auroras, and the soft glow of the Milky Way – hiding them behind a high curtain of light.
 

Script by Damond Benningfield

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The Quadrantid meteor shower should be at its best tonight. Unfortunately, “best” doesn’t mean great. That’s because the last-quarter Moon gets in the way. It’s in view during the expected peak hours, so its glare will wipe out all but the brightest meteors.

The shower is named for an extinct constellation – the wall quadrant - an instrument that astronomers used for centuries to track the positions of stars. That region of the sky is in Boötes the herdsman, near the handle of the Big Dipper.

The Quadrantids appear to come from a trail of dust left by an asteroid or dead comet. As it orbits the Sun, it sheds bits of rock and dirt. Today, the parent body’s orbit doesn’t cross Earth’s orbit. But it must have in the distant past. That left a trail of debris for Earth to pass through.

As we cross the trail, some of the debris hits the atmosphere at about 90,000 miles per hour. The particles vaporize, forming the streaks of light known as meteors or shooting stars.

The Quadrantids include quite a few “fireballs” – especially bright meteors that can explode. They’re formed by larger bits of debris – the size of pebbles. They can be bright enough to see through the Moon’s glare. And a few fireballs are usually seen for a few nights after the shower’s peak.

Look for the meteors in the wee hours of the morning. You might see up to a few dozen of them – blazing bits of rock and dust high in the sky.
 

Script by Damond Benningfield

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