StarDate

“Alpha Librae” is a perfectly good name for a star. It tells us that it’s in Libra, the balance scales. It also tells us that it’s either the constellation’s brightest star, or that it’s in a special location. In this case, it’s the location — it’s the starting point for a diamond-shaped pattern of stars.

But Alpha Librae doesn’t have nearly the cachet as an older name for the star: Zubenelgenubi. That name comes from an Arabic phrase that means “the southern claw.” At the time the name was bestowed, the star represented the southern claw of Scorpius. Later skywatchers created Libra from Zubenelgenubi and several other stars of the scorpion.

The star itself probably warrants the attention that comes with the name. It consists of at least four stars, which are split into two pairs. The pairs are separated by more than 500 billion miles. That’s far enough apart that we see them as separate pinpoints of light.

That’s not the case with the individual stars in each pair. They’re so close to each other that their light blurs together. When astronomers break down the light from each pair, though, they see the “fingerprints” of two stars — giving the southern claw a total of at least four stars.

Zubenelgenubi huddles close to the Moon late tonight. They’re in the south at first light tomorrow, with Zubenelgenubi close to the right or upper right of the Moon.

We’ll talk about the Moon and the heart of the scorpion tomorrow.
 

Script by Damond Benningfield

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Human beings have touched only one world other than our own — the Moon. But we have eyes and ears throughout the solar system — and even beyond it — with more set to be sent out this year.

Several probes are studying the Sun. Parker Solar Probe has already flown closer to the Sun than any spacecraft in history, and it’s moving closer on each orbit. Eventually, it’ll skim about four million miles above the surface of our star.

One mission is headed to Mercury, the Sun’s closest planet. And one is orbiting Venus, the second planet. Other missions are headed for asteroids, or bringing pieces of an asteroid to Earth. A craft is orbiting Jupiter, the largest planet. And several are well beyond the realm of the planets. Voyagers 1 and 2, in fact, have left the solar system and are exploring interstellar space.

Most of our eyes and ears are at the Moon and Mars. Several orbiters and landers are operating at the Moon, and more are scheduled to head that way soon. That includes Artemis I, a test run of the spacecraft and rocket designed to send American astronauts back to the Moon. On the way, the mission will deploy about 10 small satellites to study the Moon, Sun, asteroids, and more.

About a dozen craft are operating at Mars — in orbit, sitting on the surface, or driving across it. They were dispatched by the United States, Europe, China, India, and the United Arab Emirates — craft sent by one planet to study another.
 

Script by Damond Benningfield

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Like a cruise ship that makes a regular circuit of stops, the Moon has a regular program of ports of call. It passes by the same stars every month, on a schedule that’s easy to predict — no delays for bad weather or virus outbreaks.

And the Moon is paying call on one of those destinations tonight: Spica, the brightest star of the constellation Virgo. Spica is below or to the lower right of the Moon as they climb into good view, after midnight, and closer to the Moon at first light.

The Moon visits the same array of stars because they all line up near the ecliptic — the Sun’s path across the sky. The Moon stays close to the ecliptic as well — it never moves more than a few degrees to either side of it. So during the Moon’s travels, it returns to these same stars over and over.

It visits each star every 27 and a third days. But the Moon’s cycle of phases is a couple of days longer than that, so it’s not at the same phase from one visit to the next. Tonight, for example, the Moon is about 21 days “old” — it’s 21 days into the cycle — and almost two-thirds of its visible hemisphere is in the sunlight. When they last met, the Moon was about two and a half days older, and only about one-third illuminated. And next month it’ll be younger and fuller.

So watch as the Moon cruises past Spica tonight and tomorrow night, then sails toward its next major port of call in a few days: Antares, the bright heart of the scorpion.
 

Script by Damond Benningfield

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A famous before-and-after star system shines at its best on winter nights. Tonight, it’s in the east as night falls, high in the south around midnight, and sets due west a little before dawn.

Procyon is a binary system — it consists of two stars. One of them is big and bright and is nearing the end of its “normal” lifetime. The other is tiny, faint, and dead — the same fate that awaits its brighter companion.

During their normal lifetimes, stars like those of Procyon “fuse” the hydrogen in their cores to make helium. When all the hydrogen is gone, they begin to fuse the helium to make heavier elements. Eventually, the star can’t continue that process. It expels its outer layers, leaving its hot, dense core — a white dwarf.

That’s what’s happened to the smaller star in the system, Procyon B. When it was born, almost two billion years ago, it was about two-and-a-half times the mass of the Sun. At that weight, it aged in a hurry. It became a white dwarf more than a billion years ago.

The star we see — Procyon A — was born with less mass. So it is spending a much longer span in the prime of life. But it appears to be starting to make the transition from fusing hydrogen to fusing helium. Over tens of millions of years, it’ll puff up to form a red giant. And after spending perhaps hundreds of millions of years in that phase, Procyon A also will become a white dwarf — the burned-out remnant of a once-brilliant star.
 

Script by Damond Benningfield

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The first known visitor from another star may be a fragment of a Pluto-like object thousands of light-years away. It lost most of its mass during its passage near the Sun in 2017, and will continue to fizzle away as it leaves the Sun behind.

‘Oumuamua was discovered in October 2017, a month after its closest approach to the Sun. As it moved away from the Sun, it sped up in a way that scientists couldn’t explain. Its motion resembled that of a comet spewing “jets” of gas into space. But astronomers didn’t see any escaping material, and the object’s composition didn’t match that of any known comets.

Last year, researchers at Arizona State found that ‘Oumuamua most likely is made of frozen nitrogen. That suggests it was knocked off the surface of an object like Pluto, whose surface is coated with nitrogen ice.

The researchers found that ‘Oumuamua could have been blasted out of its home star system — perhaps thousands of light-years away — about 500 million years ago.

As it traveled through the galaxy, cosmic rays blasted away some of its ice. It entered the solar system about 25 years ago. As it approached the Sun, solar energy vaporized more than 90 percent of its nitrogen, which jetted away into space. That whittled ‘Oumuamua down to about 140 feet long by 24 feet wide. The escaping gases gave it an extra “kick,” and also made it tumble end over end — explaining some of the odd behavior of this long-distance visitor.
 

Script by Damond Benningfield

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Pluto is losing its air. It’s going into a sort of hibernation. The atmosphere will freeze onto Pluto’s icy surface. But it’ll come back — in a couple of centuries.

Even at its best, Pluto’s atmosphere is quite thin. It’s made mainly of nitrogen — the same element that makes up most of Earth’s air. And it’s extremely cold — hundreds of degrees below zero.

Pluto was closest to the Sun a couple of decades ago. The Sun warmed the surface, causing some of the frozen nitrogen and other ices to vaporize. Today, though, Pluto is moving away from the Sun. At its most distant, in about a century, it’ll be almost two billion miles farther than when it was closest. That will make it much colder, so nitrogen in the air will freeze onto the surface.

The atmosphere was still in full bloom when the New Horizons spacecraft flew past Pluto in 2015. But it’s begun to thin out since then. Astronomers keep tabs on it by watching as stars pass behind Pluto. Starlight filters through Pluto’s atmosphere as a star disappears and reappears. The way the star dims and brightens reveals details about the atmosphere.

Since 2016, several of these vanishing acts have showed that Pluto’s atmosphere is getting thinner. It’s still there, but it probably won’t be for long. Some studies say it could disappear by the end of this decade — going into a long hibernation.

We’ll talk about a possible chip off a world like Pluto tomorrow.
 

Script by Damond Benningfield

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Uranus was very good to Johann Bode. The planet made him famous, earned him a key job, and gave him a spot in history as the man who named the planet.

Bode was born 275 years ago today, in present-day Germany. He suffered eye problems from childhood onward, so he couldn’t study the universe through a telescope. He could study it with pen and paper, though. He excelled at math, and was especially good at calculating orbits.

For a while, it looked like he was good at forecasting orbits as well. He fleshed out an idea proposed by Johann Titius. It said that the distances of the planets from the Sun followed a simple formula. At the time, it left a gap between Mars and Jupiter, and there was nothing beyond Saturn, the farthest known planet.

When Uranus was discovered, though, it fit the formula. So the Titius-Bode Law, or just Bode’s Law, gained wide acceptance. And Bode added to his fame by using old observations of Uranus — made before anyone knew they were looking at a planet — to calculate its orbit. The combination helped earn Bode the job as director of Berlin Observatory.

William Herschel, who discovered Uranus, proposed naming it for King George III of England. But Bode proposed Uranus, the father of Saturn. Eventually, it won out.

But Bode’s Law did not. When Neptune was discovered, it didn’t fit the formula at all. So Bode’s Law faded. Bode himself, though, is still remembered for his many contributions to astronomy.
 

Script by Damond Benningfield

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There are plenty of hot topics in modern-day astronomy: exoplanets, black holes, galactic archaeology, and many more. And some of the topics involve not just what we learn about the universe, but how we learn about it. One example is machine learning.

Astronomers are awash in data. Many projects and telescopes generate terabytes of data every week, or even every day. Sorting through all those observations is painstaking work. Some projects rely on volunteers to help them out.

Computers can do the work faster than people, but not always more accurately. They don’t understand what is or isn’t what astronomers are looking for.

Machine learning is changing that. Scientists feed examples of what they want to see to computers, and the machines learn from the repetition. After a while, they learn enough to outperform humans.

In recent years, for example, astronomers have used machine learning to sort through X-ray images to classify types of galaxy clusters and individual galaxies. And they’ve had the computers sift through huge piles of images from TESS, a planet-hunting satellite that also reveals exploding stars, variable stars, and other objects that can change rapidly.

These projects and many others can help astronomers keep up with the torrent of data while learning much more about our changing universe — all with the help of machines.

Tomorrow: counting off the planets of the solar system.
 

Script by Damond Benningfield

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The Moon lines up with the twins of Gemini tonight. Pollux, the brighter of the two, is above the Moon at nightfall. Castor is about the same distance to the upper left of Pollux.

Castor is a family of six stars. Some of them are big and bright, while others are tiny and faint.

As far as we know, Pollux is a single star. But it’s an impressive one. It’s classified as a giant — it’s much bigger and brighter than the Sun. In fact, it’s the closest giant star to the solar system — just 34 light-years away.

Pollux has puffed up because it’s at the end of its normal lifetime. The nuclear reactions in its core have switched over to a new mode. That’s pushed the surrounding layers outward, making Pollux big and bright.

Just because Pollux is a solo star doesn’t mean it’s alone, though — it has at least one planet.

Astronomers at McDonald Observatory found evidence of the planet three decades ago. It was confirmed in 2006.

The planet is about three times the mass of Jupiter, the giant of the solar system. It orbits Pollux once every 19 and a half months.

Scientists called the planet Pollux b. A few years ago, it was assigned a proper name: Thestias. That comes from a Greek name referring to the mother of Pollux. The name hasn’t really caught on yet — it doesn’t show up in scientific papers about the system. But at least it gives science-fiction writers a more lyrical name for the companion of Gemini’s brighter twin.
 

Script by Damond Benningfield

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One of the brightest stars of the summer sky is performing double duty here in the dead of winter — it appears in both early evening and early morning. And from far-northern latitudes, it never sets at all — it’s in the sky every hour of the day, all year ’round.

Deneb is at the tail of Cygnus, the swan. The brilliant star forms one point of the Summer Triangle, which soars high overhead during the summer months.

Deneb remains visible for all or most of the year, though, because it’s quite far north in the sky. It’s about 45 degrees from the North Star, Polaris. From the northern hemisphere, Polaris is always at the same point in the sky, day or night. Its altitude depends on your latitude. From 30 degrees north, it stands 30 degrees above the northern horizon. And from 50 degrees north, it’s 50 degrees above the horizon.

As Earth turns on its axis, any star that’s within that range of Polaris remains in view all night. From Seattle or Duluth, for example, that includes Deneb. At this time of year, the star passes just above the horizon during the night.

For skywatchers south of that range, though, Deneb does disappear — for anywhere from a few minutes to hours. From most of the United States, it’s in the northwest as night falls now and sets a few hours later. But it climbs into view again before dawn — this time in the northeast.

So keep watch for Deneb — a summer star that’s performing double duty on winter nights.
 

Script by Damond Benningfield

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