StarDate

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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Six years and three days after it left Earth, part of a Japanese spacecraft is headed home. The small capsule holds a few ounces of rock and dirt from an asteroid.

Hayabusa 2 will streak past Earth tomorrow. It’ll release the sample capsule, which will plunge into the atmosphere and parachute to a soft landing in South Australia.

The craft began flying along with the asteroid Ryugu in June of 2018. The asteroid is more than a half mile in diameter, and its orbit occasionally brings it quite close to Earth.

Hayabusa compiled maps of the asteroid, and dropped several small rovers and cameras on its surface. Those observations revealed that the asteroid is quite dark — suggesting it contains a lot of carbon. And they showed that the surface is covered by big rocks and even boulders.

Hayabusa 2 briefly touched the surface and scooped up some samples. Months later, it fired a bullet at the asteroid, then swooped in to grab some of the debris that was blasted into space. Images showed that much of the surface material was quite red. That suggests that Ryugu was once much closer to the Sun than it is now, so it was bombarded by more radiation.

Hayabusa 2 left the asteroid last November. After it releases the 35-pound sample capsule for its return to Earth, the rest of the spacecraft will keep on going. It’ll be targeted to arrive at another asteroid in a decade or so — long after the completion of its original mission.

Script by Damond Benningfield

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If you’re a radio astronomer, it’s hard to get away from it all. The signals from many astronomical objects are faint. And interference from our own technology — from TV stations to cellphones — can drown them out.

But astronomers from South Africa have found a quiet spot in the South Atlantic: Marion Island. It’s 1200 miles from Cape Town, the nearest land, so there’s no radio interference at all.

In 2017, the team set up a small telescope there to study the early universe.

It’s known as PRIzM. And it’s studying an era that began about a hundred million years after the Big Bang. That’s when the first stars and galaxies were being born. Their light caused clouds of hydrogen gas to glow at particular wavelengths. Those wavelengths have been stretched out by the expansion of the universe. So today, they’re around the FM radio band.

Studying that energy can help astronomers understand when the early stars and galaxies were born. It also can tell them how long it took for their energy to fully “charge” the hydrogen left over from the Big Bang.

Keeping the experiment going isn’t easy. A small team lives on the island for shifts of 13 months. A ship drops by just once a year. The island is cold and windy, and about two-thirds of the days are rainy. And there are mice everywhere. So the astronomers protect their gear with steel mesh, scouring pads, and mouse traps — just one more challenge for radio astronomy.

Script by Damond Benningfield

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Pierre Janssen had already traveled the world in the name of astronomy. In 1868 he observed a solar eclipse from India. A year later he studied the planets from atop Mount Etna, in Sicily. And 150 years ago today, he scaled the heights again. To view an eclipse from Algeria, he escaped from Paris in a hot-air balloon.

Pierre Janssen, ca. 1895

He wanted to follow up his work during an eclipse on December 22nd, 1870. But when he needed to leave for Algeria, Paris was under siege by the Prussian army. Prussia’s king was ready to grant him a safe-conduct pass, but Janssen didn’t wait — in part because he was also conducting a secret mission for the government.

There weren’t any balloon pilots in Paris, so Janssen read up on the subject. He flew the balloon himself, carrying three telescopes and some other instruments. He left at dawn on December 2nd and landed beyond enemy lines a few hours later. He then completed his journey to Algiera.

Alas, it was all for naught: The eclipse was blocked by clouds. But Janssen didn’t give up his globetrotting. He watched other major events from Japan, Italy, and Algiera again. And he built an observatory in the French Alps — all to study the Sun.

Script by Damond Benningfield

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Jupiter and Saturn have flirted with each other for months. For almost all of 2020, they’ve been separated by no more than 10 degrees — the width of your fist held at arm’s length. This month, though, the giant planets will outdo themselves. On the 21st, they’ll pass less than half a degree apart. The last time they appeared closer was in 1623.

Jupiter and Saturn pass by each other once every 20 years. It takes that long because the planets are far away from the Sun.

On average, Jupiter is almost half a billion miles from the Sun. At that range, the planet takes almost 12 years to complete a single orbit around the Sun. So as we watch from Earth, that’s also how long it takes for Jupiter to make one lap against the background of stars.

Saturn is almost twice as far from the Sun. Not only does that mean that Saturn has to travel a longer distance around the Sun, but it moves slower than Jupiter does. So it takes Saturn about 30 years to circle the sky.

Put those motions together, and it means the planets get close once every 20 years.

Look for Jupiter and Saturn in the southwest as night falls. Jupiter is the brighter of the two — brighter right now than anything else in the sky at that hour. Saturn is a couple of degrees to the upper left — the width of a finger at arm’s length. Watch as the gap between them closes evening by evening — leading to their magnificent conjunction on the 21st.

Script by Damond Benningfield

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Venus is headed toward a nasty target: a claw of the scorpion. It’ll pass quite close to it in just a few days.

Venus is the brilliant “morning star.” And the scorpion’s claw is the star Zubenelgenubi. It’s directly below Venus at first light tomorrow, but they’ll stand side by side on Friday morning.

Zubenelgenubi is the second-brightest star of Libra, the balance scales. But its name pre-dates Libra’s creation. The name means “the southern claw.” The star represented one of the claws of Scorpius, the next constellation over. But thousands of years ago, it was taken away to form part of the new constellation.

Zubenelgenubi lies just a third of a degree from the ecliptic — the Sun’s path across the sky. So the Sun passes directly in front of the system every year, in early November.

The Moon and planets also stay close to the ecliptic as they move across the background of stars. So the Moon occasionally passes in front of Zubenelgenubi as well, blocking it from view.

The planets can pass in front of it as well. But planets cover a much smaller portion of the sky than the Moon does, so it takes a perfect alignment for them to hide Zubenelgenubi. The last planet to do so was Venus, in 1947.

Venus won’t cover the star this time around, but it won’t miss by much. At their closest, on Friday, they’ll be separated by about a degree and a half — about the width of your finger held at arm’s length.

Script by Damond Benningfield

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The full Moon will fade a bit in the wee hours of tomorrow morning. The effect isn’t especially obvious, but it should be noticeable.

The reason is an eclipse. But it’s a penumbral eclipse, which means the Moon will pass through the faint outer ring of Earth’s shadow. None of the Moon will go completely dark, as it does during a partial or total eclipse. Instead, most of the lunar disk will take on a dusky appearance — as though it were covered by a thin layer of clouds.

Eclipses occur in cycles. Each eclipse in a cycle is separated by 18 years and 11 days. The last eclipse in this cycle, for example, took place on November 20th of 2002. And the next one comes on December 11th of 2038.

A cycle begins with a series of penumbral eclipses. The Moon then moves deeper into the shadow of Earth, eventually creating a set of total eclipses. It then moves back out of the shadow, ending with more penumbral events. The current cycle is in that phase, so all the remaining eclipses are penumbral, with the last one in 2291.

Tonight’s eclipse gets underway at 1:32 a.m. Central Time, when the shadow first touches the Moon. It’ll be at its peak at 3:44 a.m., when the penumbra will cover about two-thirds of the lunar disk. The eclipse will end at 5:53, when the Moon exits the penumbra. As a bonus, the Moon has a bright companion all night: Aldebaran, the eye of Taurus, the bull.

Script by Damond Benningfield

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The Moon arcs high across the sky tonight. It rises in the east-southeast a little before sunset, and sets in the west-northwest a little before sunrise.

The Moon’s rising and setting points move north and south along the horizon. And there’s a big swing between the northernmost and southernmost points every month. Yet the extremes for any given month reflect only a part of the lunar cycle. Over a period of 18.6 years, the northernmost and southernmost setting points vary by quite a bit.

Many cultures have paid attention to that cycle. They’ve even built structures to mark it.

One example is the Newark Earthworks in central Ohio. It consists of several giant geometric figures — an octagon, a circle, an ellipse, and a square. They were built a couple of thousand years ago by the Hopewell culture.

The Hopewell lived in small villages. But they built large earthworks for ceremonial events across the region.

The Newark site covered four and a half square miles. Its figures were built to a high level of precision. And the circle and octagon were linked. Scientists studied those figures. And they found many alignments to key moonrise and moonset points. The odds of such alignments being random were one in a million.

The scientists also found alignments between the two figures and nearby hilltops, and between other figures on the site. Together, they suggest that the site was a giant observatory for watching the Moon — 2,000 years ago.

Script by Damond Benningfield

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Two beautiful spiral galaxies in the constellation Cetus are getting each other all stirred up. The galaxies are about half a million light-years apart — not very far on the galactic scale. At that distance, the gravity of each galaxy tugs heavily at the other. That has warped at least one of the galaxies, and triggered the birth of many new stars in both of them.

Messier 77 and NGC 1055 are about 50 million light-years from Earth. Both are giant spirals like our home galaxy, the Milky Way. NGC 1055 is about the same size as the Milky Way, while M77 appears to be a good bit bigger.

We see M77 almost face-on, so we have a good view of its spiral arms and the wide bar of stars in its middle. On the other hand, we see NGC 1055 almost edge-on. We don’t see its middle as clearly, but we have a good view of waves that ripple across its disk.

The waves probably were created by the interaction between the two galaxies. That interaction has compressed giant clouds of gas and dust. The clouds have collapsed and given birth to new stars. Many stellar nurseries are visible in both galaxies — the birthplaces of millions of new stars.

The galaxies are in Cetus, the whale or sea monster. Cetus is in the southeast as night falls, to the right and lower right of the almost-full Moon.

Script by Damond Benningfield

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Not many stars have entire clusters named after them. One that does is Alpha Persei, the brightest star of Perseus, the hero. It’s a massive young star that’s nearing the end of its life. And it’s surrounded by a family of hundreds of other stars — the Alpha Persei Cluster.

Alpha Persei — also known as Mirfak — is the dominant member of the cluster. It’s at least eight times the mass of the Sun, about 70 times the Sun’s diameter, and 5,000 times the Sun’s brightness. That brilliance makes it easy to spot even though it’s more than 500 light-years away.

Several other big, bright stars are within a few light-years of Alpha Persei. And hundreds of smaller stars lie within a few dozen light-years. The stars are members of the cluster — a family of stars that was born from a single giant cloud of gas and dust.

Estimates of just when that took place vary, but the cluster’s maximum age appears to be about a hundred million years. At that age, Alpha Persei has already passed the end of its “normal” lifetime. Now, it’s about ready to expire. But just how it will do so isn’t clear. The star’s mass puts it near a dividing line. A star above that line explodes as a supernova. A star below the line dies a bit more quietly, leaving behind a small, hot ember known as a white dwarf.

Look for Alpha Persei in the northeast at nightfall. It’s far to the left of the Moon, and well above the brighter star Capella.

Script by Damond Benningfield

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