StarDate

Betelgeuse gets more interesting by the day. A year ago, the red supergiant star faded dramatically. Two studies reported possible explanations for the big fade. But their conclusions were different.

Betelgeuse marks the shoulder of Orion the hunter. The bright orange star rises due east a couple of hours after sunset, and climbs high across the south during the night.

Betelgeuse is one of the few stars that astronomers can see as more than just a pinpoint of light. One hundred years ago today, in fact, it was the first star other than the Sun to have its size measured. Albert Michelson and Frances Pease came up with a diameter of about 240 million miles. They were off by a fair amount, but only because astronomers thought the star was much closer than it really is.

Beginning in October of last year, Betelgeuse faded dramatically. By February, it had dropped to about a third of its normal brilliance. And this summer, two research teams provided possible reasons.

One team said the star shot out a giant blob of hot gas. As it moved away from Betelgeuse it cooled, forming a cloud of dust. The cloud was dark, and it blocked part of the star from view.

But another team came up with a different mechanism. That team said that a giant “starspot” covered between 50 and 70 percent of the surface. The spot was a magnetic storm similar to a sunspot.

The conflicting results add to the mystery of this brilliant star.

Script by Damond Benningfield

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The Sun and Moon are lining up for one of nature’s most impressive shows early tomorrow: a total solar eclipse. It’ll be visible only along a narrow path in the southern hemisphere.

An eclipse occurs when the new Moon passes directly between Earth and the Sun, blocking the Sun from view. Most months, the geometry isn’t right, so the new Moon passes above or below the Sun. This time, though, everything is in alignment, creating an eclipse.

The eclipse gets under way at 7:34 a.m. Central Time, when the outer portion of the Moon’s shadow first touches Earth. That creates a partial eclipse — the Moon will cover only part of the Sun. The partial eclipse will be visible across most of South America and part of Antarctica.

The total eclipse begins two hours later. It will be visible along a path that begins over the Pacific Ocean, passes over Chile and Argentina, and extends into the Atlantic Ocean. It comes to an end just short of Africa.

At most, the path of totality will be just 56 miles wide. That’s where day turns to night, and the Sun’s faint outer atmosphere surrounds the Moon. The total phase of the eclipse will last only about two minutes.

During most eclipses, people flock to the eclipse path, and cruise lines organize special expeditions. With the coronavirus, though, that’s not the case this year — far fewer people will see it in person. But several web sites will broadcast this impressive light show.

Script by Damond Benningfield

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The first confirmed black hole sits near the center of the Summer Triangle — a pattern of three bright stars that’s in the west on December evenings. Cygnus X-1 was discovered during a short rocket flight in 1964. But strong evidence of its nature was provided by a later mission. Called Uhuru, it was launched 50 years ago today.

The craft was designed to study X-rays. They’re produced by some of the hottest and brightest objects in the universe. But Earth’s atmosphere absorbs X-rays, so we can’t see them from the ground. The only way to study them is from space.

Uhuru was the first X-ray space telescope. It originally was known by a couple of other names. But it was launched by Italy from a platform off the coast of Kenya. In honor of the host country, it was renamed Uhuru — Swahili for “freedom.”

Besides its international pedigree, it had a couple of other distinctions. It was the first science satellite managed by a woman — Marjorie Townsend, an engineer at Goddard Space Flight Center. And its top scientist, Riccardo Giacconi, later won the Nobel Prize for this and other X-ray missions.

Uhuru cataloged four times the number of X-ray sources known before its mission. The list included the remnants of exploded stars, hot binary stars, galaxy clusters, and the disks around black holes. The craft took a close look at several of those targets — including Cygnus X-1, the first confirmed black hole.

Script by Damond Benningfield

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Early risers are in for a treat tomorrow: a close encounter between the crescent Moon and Venus, the “morning star.” They’re in the southeast at dawn.

The two bodies will move even closer during the day. In fact, they’ll get as close as possible: The Moon will occult Venus — it’ll pass directly in front of the planet, blocking it from view. The event will be visible across part of the western United States — but not easily visible.

Such occultations aren’t rare. Venus and the Moon both stay close to the ecliptic, which is the Sun’s path across the sky. So they pass close to each other every month. And when the lineup is just right, there’s an occultation.

This one takes place in the afternoon or early evening here in the United States. From much of the country, Venus and the Moon will set before the cover-up begins, or the geometry won’t be quite right. But from parts of the west, everything lines up just right. From San Francisco, for example, Venus will disappear about 1:15 p.m. and stay behind the Moon for an hour.

It’s not an easy thing to see — you need to look carefully to find the Moon in the bright sky. And you need to make sure to not look too close to the Sun. Venus and the Moon are about 25 degrees from it — more than twice the width of your fist at arm’s length.

The Moon is heading toward the Sun, though. It’ll pass in front of it on Monday — creating a total solar eclipse for parts of the southern hemisphere.

Script by Damond Benningfield

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A busy but short-lived meteor shower should be at its peak on Sunday night. It’s one of the year’s best. But it spikes quickly, so there aren’t many meteors before and after the peak. And the shower itself won’t stick around for much longer.

The Geminid shower is named for the constellation Gemini. If you trace the paths of the meteors, they all converge in that region of the sky.

The shower was first recorded in 1862, and it’s been getting “busier” ever since. During its early decades, the numbers peaked at about 15 to 20 meteors per hour. Since then, though, the numbers increased. Today, peak rates are about 150 per hour.

That’s because the path of the debris that causes the meteors is being shifted by the gravity of Jupiter. It’s been pushed enough that Earth now travels through the middle of that path. By the end of the century, though, the stream of debris will stay outside Earth’s orbit, so the Geminids will vanish.

For now, though, look for the meteors beginning as early as 9 or 10 p.m. Many Geminids are especially bright, so the shower is pretty easy to see. And the Moon will be new on the night of the 13th, when the shower’s at its best, so it won’t interfere with the fireworks.

To view the Geminids, find a safe skywatching site away from city lights. Although the meteors appear to “rain” into the sky from Gemini, they can appear anywhere, so you don’t have to look in a particular direction to see them.

Script by Damond Benningfield

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Several stars that are easily visible to the eye alone are destined to explode — some of them quite soon. The list includes Betelgeuse, the bright orange shoulder of Orion; Rigel, the hunter’s blue-white foot; and Antares, the heart of the scorpion.

Another one stands close to the Moon early tomorrow. Spica is the leading light of the constellation Virgo. It’s to the lower right of the Moon at first light.

Spica actually consists of two stars. But most of the system’s light comes from the bigger star. It’s about 20,000 times brighter than the Sun, and tens of thousands of degrees hotter.

The key to its future, though, is its mass — about 11 and a half times the mass of the Sun. When such a heavy star can no longer produce nuclear reactions in its core, the core collapses to make a neutron star or a black hole. The star’s outer layers fall inward, then rebound. They blast into space with tremendous force — creating a supernova.

Spica’s main star is already on that track. It’s beyond its “normal” lifetime, so it’s starting to puff up. Eventually, it’ll swell to a hundred times its current diameter or more. Its companion star is quite close, so it’ll have an effect on the bigger star’s evolution — although no one is quite sure what that might be.

In the end, though, the bigger star is likely to blow itself to bits. And it could happen quite soon on the astronomical time scale — within the next couple of million years.

Script by Damond Benningfield

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In many ways, the galaxy NGC 253 is a lot like our own. Like the Milky Way, it’s a barred spiral. That means its stars form a large disk. It’s accented by bright spiral arms and a long bar of stars in the middle. The galaxy also is about the same mass as ours. And the black hole in its core is comparable to the one at the heart of the Milky Way.

In one way, though, the galaxies are quite different: NGC 253 is giving birth to many more stars.

Most of that activity is taking place in a few dozen clusters in the galaxy’s core. Each of them contains tens of thousands of stars, most of which are quite young. And a few of them are super-clusters, with millions of stars.

The biggest is concealed behind clouds of dust. A study a few years ago said it’s about 14 million times the mass of the Sun. But it’s only a few million years old. So it’s given birth to a lot of stars in a short time — and is still cranking them out today.

The clusters contain many bright, massive stars, which produce powerful “winds” of charged particles. The winds appear to be blowing away gas and dust in other parts of the galaxy. So the regions that are churning out millions of new stars may prevent the birth of stars elsewhere in this busy galaxy.

NGC 253 is about 12 million light-years away, in Sculptor. The constellation is low in the south at nightfall. Under dark skies, the galaxy is visible through binoculars as a hazy swash of light.

Script by Damond Benningfield

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Most galaxies are members of clusters. They’re bound together by gravity, so they move through the universe as a group. The Milky Way, for example, is one of the two main members of a cluster called the Local Group.

The nearest neighbor cluster is the Sculptor Group. It consists of a dozen or more galaxies. The center of the group is about 12 million light-years away.

The cluster’s dominant member is the Sculptor Galaxy. It’s a lot like the Milky Way, although it’s giving birth to many more stars; more about that tomorrow.

Most of the group’s other galaxies are fairly small and faint. One exception is NGC 247. It’s a beautiful spiral that we see almost edge-on. It’s smaller than the Milky Way, but it contains some bright nurseries — the birthplaces of new stars.

Its most unusual feature is a dark “void” on one side of the galaxy’s core. It looks like a hole has been punched right through the galaxy’s disk. The region contains a few old, faint stars, but almost no young bright ones.

The void could have formed when a blob of dark matter plunged through the disk like a rock through tissue paper. That would’ve scattered stars in the region and blown away the gas and dust for making more — leaving the galaxy with a big hole.

The Sculptor Group is spread across the constellation Sculptor, and the adjoining constellation Cetus. NGC 247 is too faint to see with the eye alone, but it’s an easy target for small telescopes.

Script by Damond Benningfield

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Until about a century ago, the constellations went through many changes. They were created, erased, expanded, contracted, and resculpted. And one constellation that went through most of those steps slides across the southern evening sky at this time of year.

Sculptor was created in the 1750s by Nicolas Louis de la Caille. The French astronomer had traveled to the Cape of Good Hope. He cataloged more than 10,000 stars that were too far south to see from much of the northern hemisphere. From that work, he created 14 constellations.

His original name for Sculptor was Apparatus Sculptoris — the sculptor’s studio. It included a table, a block of granite, tools, and a carved head.

A half-century later, German astronomer Johann Bode made some changes. He rearranged the objects in the studio, then took away half of the constellation to make a new one. It represented a generator used for experiments.

That didn’t catch on, though. The studio was returned to its original configuration. The only change came in the mid-1800s, when the name was shortened to Sculptor.

Like all the other present-day constellations, it was formalized by astronomers in 1930 — blocking any more changes.

Sculptor has no bright stars, so you need to get away from city lights to see any of the constellation. It’s in the south at nightfall, to the lower left of Fomalhaut, the only bright star in that part of the sky.

More about Sculptor tomorrow.

Script by Damond Benningfield

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Regulus, the bright heart of Leo, the lion, shines close to the gibbous Moon the next couple of nights. The star is below the Moon as they climb into view by midnight tonight.

The name “Regulus” means “the little king.” Yet it’s not so much a monarch as a ruling quartet. That’s because Regulus appears to consist of not one star, but four.

Only one of them is bright enough to see with the unaided eye — the one we know as Regulus. But it has a close companion that once shined even brighter.

This companion was heavier than Regulus’s bright star, Regulus A, so it aged more quickly. As it neared the end of its life, it puffed up. Much of the gas in its outer layers poured over onto Regulus A. That made the star bigger and brighter, and made it spin much faster. When the companion’s outer layers were gone, all that was left was its dead core: a white dwarf — a super-dense ball that’s a third as massive as the Sun, but only about the size of Earth.

Regulus has two other companions, but they’re a long way from the bright star — about 4,000 times farther than Earth is from the Sun. They form a widely separated pair. One of the stars is a bit smaller and cooler than the Sun. The other is a bare cosmic ember. From the system’s distance of 78 light-years, you need a telescope to see even the combined light of these two stars — faint companions to the lion’s mighty heart.

Tomorrow: a changing constellation.

Script by Damond Benningfield

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