StarDate

Bits of an asteroid appear to confirm what astronomers could see through their telescopes: it’s dark, it’s rich in carbon, and it’s a relic from the early solar system.

A Japanese spacecraft, Hyabusa 2, collected the samples in 2019. It made contact with the asteroid Ryugu, knocking tiny grains off the surface. The craft caught about five grams of that material, which it dropped off at Earth in 2020.

Scientists won’t start taking a thorough look at the samples until this summer. But they’ve done some early analysis, which revealed that the samples match observations of the asteroid made from Earth.

That’s important for several reasons.

Scientifically, asteroids like Ryugu probably are leftovers from the birth of the planets. So studying them tells us more about conditions in the early solar system. In addition, such asteroids could have brought much of the water that fills Earth’s oceans, and some of the chemical compounds necessary for life. So verifying that what astronomers see through the telescope is correct can help us learn about the birth and evolution of our own planet.

On a more practical level, we might someday find an asteroid on a collision course with Earth. Deflecting the asteroid would require a good knowledge of its composition and structure. So learning everything we can from samples of individual asteroids refines the models of all of them — perhaps helping to keep Earth safe from future threats.
 

Script by Damond Benningfield

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Sometime this summer, a few scientists will get little bits of heaven: grains of rock and dirt from an asteroid.

The grains were collected by Hyabusa 2, a Japanese mission. It made contact with the asteroid Ryugu in early 2019. That knocked a little bit of material off the surface. Hyabusa grabbed about five grams of it. The sample-containing capsule landed in Australia in December 2020. And that started a process that will lead to detailed studies of the samples.

The process began when the capsule was recovered. Technicians checked the container to make sure it was undamaged, then stuck a needle in it to pull out any gases for analysis. They transported the container to Japan in a case that protected the samples from vibrations and exposure to the air.

In Japan, the samples were processed in a class-1,000 clean room, where dust and other contamination were scrubbed from the air. And when the sample container was opened, the bits of Ryugu were handled in vacuum chambers or nitrogen-filled cabinets, with special tools made of materials that wouldn’t add earthly contamination. Technicians used microscope-guided tweezers to pluck out each bit of debris that was at least a millimeter across.

Scientists then did a quick analysis of the samples; more about that tomorrow. Now, the samples are being cataloged and sorted before they’re ready for shipment — and a detailed study of asteroid Ryugu.
 

Script by Damond Benningfield

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A meager but reliable meteor shower should be at its best in the hours before sunrise tomorrow. There won’t be any moonlight to interfere with the show, so it’s worth a look.

The Eta Aquarid shower is spawned by Halley’s Comet. As the comet orbits the Sun, it loses grains of rock and dirt. Earth flies through this trail of debris twice a year — in May and October. When it does, some of the comet dust rams into Earth’s atmosphere. The debris is moving at about 150,000 miles per hour, so the particles quickly vaporize. That produces the glowing streaks known as meteors or shooting stars.

The meteors all enter the atmosphere from the direction of the star Eta Aquarii — hence the shower’s name. They can fly across any part of the sky, though, so you don’t have to look toward Aquarius to see them. But the shower is best after Aquarius rises, around 4 a.m.

Eta Aquarids are best viewed from the southern hemisphere. That’s because Aquarius climbs higher across the sky, and it’s in view longer before sunrise.

Here in the United States, the view gets worse as you work toward higher latitudes. From Austin, there are about two and a half hours of good viewing time, with a peak of perhaps a dozen meteors per hour. From Seattle or Milwaukee, though, the viewing window lasts only about one and a half hours, with almost no meteors in view.

Still, occasional bright ones do zip across the sky — bright sparks from a comet.
 

Script by Damond Benningfield

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Evening twilight can be one of the most beautiful times of the day. The light is soft, and the colors of sunset can be intense. But just when twilight ends and night begins depends on which version of twilight you pick.

The version that applies to everyday life is called civil twilight. It begins at sunset and ends when the center of the Sun is six degrees below the horizon — the width of three fingers held at arm’s length. That doesn’t sound like much, but it makes a big difference. By the time civil twilight is over — about 20 to 30 minutes after sunset, depending on the time of year — it’s too dark to drive safely without your headlights.

After civil twilight, there’s nautical twilight. It lasts until the Sun is 12 degrees below the horizon. Although it’s not much of a concern in the era of GPS, by the time nautical twilight ends, it’s dark enough for sailors to use the stars for navigation.

Finally, there’s astronomical twilight, which ends when the Sun is 18 degrees below the horizon. At its beginning, the sky is dark enough to observe brighter stars and galaxies. By its end, all the light of day has drained away, so the night is as dark as it’s going to get. That provides the dark skies needed to observe the faintest objects — distant stars and galaxies that are impossible to study through the glow of twilight.

Of course, the same definitions apply to morning twilight — the end of night and the dawn of a new day.
 

Script by Damond Benningfield

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The Moon and two companions form a wide, skinny triangle in the western twilight this evening. They all drop from view within a couple of hours of sunset, though, so there’s not a lot of time to look for them.

The companions are the star Aldebaran and the planet Mercury. Aldebaran stands to the left of the Moon, with Mercury about the same distance to the lower right of the Moon. Aldebaran and Mercury are equally bright.

Aldebaran and Mercury will remain roughly in step with each other until they disappear in the twilight in a week or two.

Aldebaran is sinking as a result of the annual migration of the stars. It takes Earth about 23 hours and 56 minutes to make one full turn on its axis relative to the background of stars. But our planet moves along its orbit from day to day. That means it takes about four minutes longer each day for the Sun to reach its highest point in the sky. As a result of that difference, the stars rise and set about four minutes earlier each day. So over the seasons, stars arc across the night sky.

Mercury’s motion across the sky is the result of the combined orbital motions of Mercury and Earth. As the planets circle the Sun, our viewing angle to Mercury changes. Right now, that combination means Mercury stays fairly still compared to the background of stars. So like the stars, it’s dropping lower in the sky — soon to disappear in the evening twilight.

Tomorrow: final glimmers.
 

Script by Damond Benningfield

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A faithful hunting dog is following his master into the evening twilight. They’ll both disappear within a few days or weeks, then return to view this summer — in the morning sky.

The master is Orion, the hunter. His constellation is one of the most beautiful of all. It’s also one of the easiest to find. As twilight begins to fade, look for it low in the west, with Orion’s three-star belt parallel to the horizon. Brilliant Betelgeuse is above the belt, with Rigel below it, barely in sight.

Orion is trailed by Canis Major, the big dog. It’s easy to pick out as well because it includes the brightest star in the night sky: Sirius, the Dog Star. It’s to the left of Orion’s Belt.

Not surprisingly, ancient skywatchers paid a lot of attention to Sirius. And they crafted many stories about him and his constellation. In one, the dog was caught in a wild chase with a nasty fox. The fox couldn’t be caught, and the dog couldn’t miss his quarry. To end the never-ending race, Zeus turned both animals to stone, and placed Canis Major in the stars.

In another story, Canis Major was one of Orion’s hunting dogs. He’s chasing Lepus, the rabbit, which is below Orion’s feet. He follows Orion everywhere — including into the evening twilight every spring.

Hunter and hunting dog will begin to vanish over the coming days. Both of them will be out of sight by late May. Orion will return to view in July, with Canis Major following in August.

Script by Damond Benningfield

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The star cluster Messier 13 is impressive. It contains perhaps a half-million stars, all packed into a ball that’s just 150 light-years across. And most of those stars reside near the center of the cluster. That would fill the skies of any planets that are there with brilliant displays — both day and night.

Yet most of the individual stars in the cluster aren’t all that impressive. Almost all of them are less massive than the Sun, which means they’re also fainter than the Sun.

There’s a direct relationship between a star’s mass, its brightness, and how quickly it evolves. Heavy stars burn through their nuclear fuel faster than lightweight stars, so they shine brighter but die faster.

A star as massive as the Sun will live a “normal” lifetime of about 10 billion years. M13 was born about 13 billion years ago, so any stars that were at least as heavy as the Sun have already expired. All that remain are less-massive stars, which live longer but shine less brightly.

Occasionally, a star in the cluster “steals” gas from a companion, increasing its mass and its brilliance. And when any star nears the end of its life, it gets bigger and brighter for a while. Otherwise, though, M13 is left with old, faint stars that aren’t much to shout about.

Even so, there are enough of those stars to make M13 visible to the unaided eye. Under dark skies, it looks like a faint, fuzzy star in Hercules, which is in view all night.
 

Script by Damond Benningfield

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The sky will get a little dark over parts of South America and the southeastern Pacific Ocean tomorrow afternoon — thanks to a partial solar eclipse. The Moon will cover part of the Sun, blocking its light.

Solar eclipses occur only at new Moon. That’s when the Moon passes between Earth and the Sun. New Moon comes about once a month, but we don’t have solar eclipses that often. That’s because the Moon’s orbit around Earth is tilted a bit. So most months, the Moon passes a little above or below the Sun — and the Sun shines on.

But if new Moon occurs when the Moon is crossing the ecliptic — the Sun’s path across the sky — then, bingo! — an eclipse. If the alignment is just right, it’s a total eclipse — the Moon covers the entire solar disk, and day turns to night. Otherwise, it’s a partial eclipse, with the Moon covering only part of the Sun.

Tomorrow’s eclipse is partial. At its peak, the Moon will cover a little more than half of the Sun. So the sky will grow dark enough for people to notice it, but that’s about all.

The eclipse gets underway at 1:45 p.m. Central Daylight Time, when the shadow of the Moon first touches the Pacific. The shadow then will move northward, covering Chile and Argentina and parts of the adjoining countries. The eclipse reaches its peak at about 3:41, and ends a couple of hours after that.

Those of us in the northern hemisphere are out of luck — we’ll miss the eclipse entirely.
 

Script by Damond Benningfield

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The two brightest points of light in the night sky will almost merge into a single point over the next few mornings. For a couple of days, they’ll be separated by just half a degree — less than the width of a pencil held at arm’s length.

Venus and Jupiter are low in the east at first light. Venus is the brighter of the two — the magnificent “morning star.” It’s about six times brighter than its companion, Jupiter.

The planets are headed in opposite directions right now. Venus is slowly dropping toward the Sun as seen from Earth, so it’s a little lower in the sky each morning — and also a tiny bit fainter. Those changes take a long time to play out, though, so Venus will remain in view in the morning sky until late summer. It’ll pass behind the Sun in October, then climb into the evening sky.

Jupiter, on the other hand, is moving away from the Sun. It stands a little higher in the sky each morning, and shines a little brighter. It’ll reach its peak in late September, when it lines up opposite the Sun and shines all night long.

For now, though, look for Venus and Jupiter beginning shortly before dawn. Tomorrow, they’ll be separated by about a degree and a half. On Saturday, the gap will be just half a degree. It’ll be about the same on Sunday, but the two planets will have switched positions. After that, the brilliant worlds will slide away from each other. But they’ll remain fairly close for several days.
 

Script by Damond Benningfield

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There’s a lot of elbow room out in our region of the Milky Way Galaxy. The nearest star system is four light-years away, and only a few dozen stars are within 15 light-years.

If we were in the middle of a star cluster in Gemini, though, our night skies would be ablaze: Perhaps 2500 stars or more would appear within that 15-light-year range. Many of the stars would outshine any of the ones that are visible in our current skies, so the night would be spectacular.

Messier 35 is in the west at nightfall, at Gemini’s feet — well below its “twins,” the stars Castor and Pollux. Although the cluster is more than 2500 light-years away, under dark skies it’s visible to the unaided eye as a fuzzy blob of light. Binoculars enhance the view, and small telescopes reveal many of the cluster’s individual stars.

M35 is only about 175 million years old. Yet that’s plenty of time for the cluster’s hottest, heaviest stars to have expired. Some may have blasted themselves to bits. Others cast their outer layers into space in a more gentle process, leaving behind their hot, dense cores.

175 million years has also been long enough for many of the cluster’s original stars to have been pulled away by the gravity of the rest of the galaxy. But M35’s remaining stars are bound so strongly by their mutual gravitational pull that they’re likely to stay together for a long time — keeping a crowded stellar neighborhood intact.
 

Script by Damond Benningfield

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