StarDate

Scientists in China are digging into a rare treasure: bits of the Moon that were brought to Earth last December. The lunar samples could be the youngest ever studied.

The samples were gathered by Chang’e 5. At the same time it was operating, Chang’e 4 was working on the lunar farside — the hemisphere that always faces away from Earth. It didn’t bring back samples, but it did dispatch a rover to study the surroundings.

They’re the most ambitious lunar probes since the 1970s. And China is planning even more-ambitious trips in the years ahead.

Chang’e 4 landed in January 2019, and it’s still going. It used radar to look into the ground below, recording several thick layers. That suggests that its landing site — a crater that’s far south of the equator — is filled with debris from the impacts that formed several other craters. The most recent layer was deposited about 3.6 billion years ago.

Scientists expect the samples from Chang’e 5 to be less than one-and-a-half billion years old — the youngest bits of the Moon yet studied. The samples would help fill in details of the Moon’s recent history.

Future Chinese missions will orbit the Moon, land on it, drive across it, and even fly across it — perhaps leading to a lunar base in the next decade.

For now, look for the Moon teaming up with Venus — the “evening star” — early this evening. They’re low in the sky as night begins to fall, and set a couple of hours later.
 

Script by Damond Benningfield

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If you gaze long enough into a dark, starry sky — a sky that’s not polluted by streetlights or the Moon — it seems like you can see forever. That’s not quite the case, but you can come pretty close — the most distant object that’s easily visible to the unaided eye is two-and-a-half million light-years away.

Messier 31 is a giant galaxy in the constellation Andromeda. It’s high in the east-southeast as night falls, and looks like a skinny smudge of light that’s wider than the Moon.

That smudge is the combined glow of hundreds of billions of stars — a cosmic pinwheel that may be even bigger than our own galaxy, the Milky Way.

We see M31 as it looked far in the past. On average, it takes the galaxy’s light two-and-a-half million years to reach us, so we see it as it looked two-and-a-half million years ago. Many of the stars that contribute to the galaxy’s glow have expired since then — some with titanic explosions that can briefly outshine most of the rest of the galaxy’s stars. We won’t know which ones, though, until their light reaches Earth — perhaps millions of years in the future, or perhaps as early as tonight.

We do know that M31 and the Milky Way are moving closer together, so over the next few billion years M31 will grow larger and brighter. Eventually, it and the Milky Way will merge — and some other galaxy will take Messier 31’s place on the edge of forever.

Tomorrow: bright nights on nearby worlds.
 

Script by Damond Benningfield

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Our star — the Sun — is quite impressive. Its size, mass, and brightness place it among the top 10 percent of all the stars in the galaxy. And it’ll get even more impressive in the future. It’s getting bigger and brighter — all while losing mass.

The Sun shines by “fusing” atoms of hydrogen in its core to make helium. Currently, it fuses almost 700 million tons of hydrogen every second. Not all of the hydrogen is turned into helium, though. Seven-tenths of one percent is converted to energy, which radiates into space, making the Sun shine. Over the Sun’s four-and-a-half-billion-year lifetime, enough matter has been converted to energy to make almost a hundred Earths.

As the helium in the core builds up, the core shrinks. Hydrogen in a layer outside the helium is pulled inward. It gets hotter, revving up the reactions. The hotter core heats the Sun’s outer layers, causing them to expand. So today, the Sun is about 15 percent wider, and 50 percent brighter, than when it was born.

That process will continue. In a billion years or so, the Sun will be so bright and hot that it will boil away Earth’s oceans — turning our planet into a burned-out cinder.

And about five billion years from now, the Sun will begin fusing the helium to make other elements. That will make the Sun much wider than it is today. It might get big enough to engulf anything that remains of Earth — a planet consumed by its impressive star.

Script by Damond Benningfield

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As befits a giant planet, Uranus has a giant entourage of moons — at least 27 of them. Yet the planet is so far away that its moons are tough to see. In fact, most of them weren’t discovered until the last few decades.

William Herschel discovered the first two in 1787 — not long after he discovered the planet itself. Herschel proposed naming them for characters from Shakespeare, and his colleagues agreed. So those first discoveries were named Titania and Oberon, for the queen of the fairies and her husband from “A Midsummer Night’s Dream.”

Not surprisingly, they’re the biggest of all the planet’s moons. Titania is a thousand miles in diameter, while Oberon is just a bit smaller.

William Lassell discovered the next two moons of Uranus — the third- and fourth-largest — in 1851. And Gerard Kuiper discovered the next one — the fifth-largest — at McDonald Observatory in 1948.

Since then, the moons have come in bunches. The Voyager 2 spacecraft revealed 10 new moons when it flew past the planet in 1986. The rest have been found since then, with Hubble Space Telescope, telescopes on the ground, and through more analysis of the Voyager observations — giving Uranus a mighty entourage.

Uranus itself is in view all night, in the constellation Aries. It’s brightest for the year, too. It’s so far away, though, that you really need binoculars to see the planet — and a telescope to see any of its moons.
 

Script by Damond Benningfield

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If you want to lose a little weight in a hurry, visit the planet Uranus. Its surface gravity is less than 90 percent as strong as Earth’s. So if you weigh 180 pounds here, you’d tip the scales at less than 160 pounds on Uranus — instant weight loss, with no dieting or exercise required.

As with many weight-loss ideas, though, there’s a catch: There’s no “surface” to stand on. The giant planet’s atmosphere gets denser as you descend. Eventually, it merges with the layer below, which consists of hot, dense fluids. So if you dropped into the atmosphere, you’d never hit a solid surface. Instead, you’d be crushed by increasing pressure, vaporized by increasing temperatures, or both.

For planets with no surface, scientists designate a hypothetical one. It’s the depth in the atmosphere where the pressure equals the surface pressure on Earth. That makes it easier to compare planets.

The atmosphere of Uranus consists mainly of hydrogen and helium, with a bit of methane, water vapor, ammonia, and other compounds. The water vapor sometimes forms ribbons of bright clouds. And the methane absorbs red light, giving the planet a blue-green color.

If you have a telescope, that color is especially evident right now. That’s because Uranus is lining up opposite the Sun. It rises at sunset and is in view all night. It’s also closest and brightest for the year — shining like a faint star in the constellation Aries.

More on Uranus tomorrow.
 

Script by Damond Benningfield

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Tornadoes twist around the planet Mercury. They help give it an extremely thin atmosphere — a few traces of hydrogen, oxygen, and other elements.

Mercury is the Sun’s smallest and closest planet. It’s about half again the size of the Moon. And it orbits the Sun at an average distance of about 36 million miles.

Mercury is a dense ball of rock and metal. As it spins on its axis, it generates a magnetic field. The field is only about one percent as strong as Earth’s. But it can interact with the Sun’s magnetic field. Part of that interaction creates twisting columns of magnetic force that resemble tornadoes. They’re up to 500 miles wide.

The magnetic field is stripped away from the inside of a funnel. That allows particles of the solar wind to slam into Mercury. And that can blast atoms from the surface high into the sky — contributing to the planet’s atmosphere. Particles of the solar wind also contribute to the atmosphere, as do particles from passing comets and other sources.

Nothing stays there for long, though. Mercury’s gravity is weak, so particles are easily stripped away. But new ones take their place — maintaining Mercury’s barely-there atmosphere.

Mercury is low in the east-southeast in the dawn twilight now. It looks like a fairly bright star, but it’s so low in the sky that it can be hard to pick out. It’ll be easier tomorrow, though, because the planet will perch close below the crescent Moon.
 

Script by Damond Benningfield

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Fomalhaut, the “autumn star,” rolls low across the south this evening. It’s easy to pick out because it’s the only bright star in that entire region of the sky.

Fomalhaut represents the mouth of Piscis Austrinus, the southern fish — a constellation that dates from antiquity. But today, it’s a bit different from when it was first drawn — it’s lost its tail. Four centuries ago, the stars that formed the tail were split off to make a new constellation: Grus, the crane. From the southern half of the United States, it strides low along the southern horizon, below Fomalhaut.

The crane’s brightest star is Al Nair. The name is a shortened version of an Arabic name that means “the bright one in the fish’s tail.” The star is pretty bright, but it’s also pretty low in the sky, so it’s tough to see if you’re north of about Albuquerque or Atlanta.

Al Nair is a bit more than 100 light-years away. In other words, we see the star as it looked a bit more than a century ago. If we could see it in real time, though, it’s unlikely that we’d notice any difference — the star probably probably hasn’t changed much over the past century.

Even though we can’t see it, Al Nair is changing — it’s nearing the end of its normal lifetime. That alters the nuclear reactions that take place deep in its core. Those changes will cause the star to get bigger and brighter. But that probably won’t be noticeable from here on Earth for millions of years.
 

Script by Damond Benningfield

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A dead star in the constellation Virgo has taken its planetary system with it. It’s ripped apart the planets, leaving only rubble — chunks of rock and metal and clouds of dust. And even that won’t last long. The bigger pieces of rubble also are being pulled apart, with some of their remains falling onto the star.

The system is a target for the field of necroplanetology — studying dead or dying planets. The name was coined just last year, by astronomers who were studying the system in Virgo.

The star is a white dwarf — the small, hot, dead core of a star that was once much bigger, brighter, and more massive than the Sun. As astronomers studied the star, they found that its surface was “polluted” with iron and other heavy elements. The star’s gravity should pull such elements into its middle. The fact that they’re seen at the surface suggests they’re being added to the star.

Other observations showed that the star’s light dips every few hours — the result of chunks of debris passing in front of the star. The combination means that astronomers are watching as the star gobbles up its dead planets.

Necroplanetologists have discovered other white dwarfs that are pulverizing their planets. And they’ve seen similar behavior from stars that are in the prime of life. So stars aren’t always kind to their planets. They sometimes rip them apart and “eat” the remains — spooky behavior to think about on Halloween.
 

Script by Damond Benningfield

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Even on a dark, moonless night, away from the glow of the city, some regions of the sky look dark and empty. One of those regions is the celestial sea — a connected set of constellations with aquatic themes. It ripples across the south on autumn nights.

Right now, the most prominent member of the sea is Capricornus, the sea goat — but not because of the constellation itself. Instead, the giant planets Jupiter and Saturn are passing across it.

Some of the stars of Capricornus outline a wide triangle, which is in the south at nightfall. Jupiter is at the left point of the triangle, and looks like a brilliant star. Saturn is at the right side of the triangle. Saturn isn’t as bright as Jupiter, but still brighter than the stars around it.

Faint Aquarius is to the left of Capricornus, with Piscis Austrinus, the southern fish, below them. It contains the brightest true star in the entire sea: Fomalhaut, the autumn star.

Pisces, which represents two fish tied together by their tails, stretches from southeast to east. Like Aquarius, it’s especially faint, so you need dark skies to see just about any of its stars. And below it, Cetus, the whale or sea monster, is surfacing into view.

One more watery constellation flows into view later on: Eridanus, the river. It consists of a winding trail of stars that extends all the way to the corner of Orion — a bright constellation that will highlight the bright night sky of winter.
 

Script by Damond Benningfield

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As evening twilight begins to fade, a brilliant point of light pops into view low in the southwest: Venus, the “evening star.” It’s the brightest object in the night sky other than the Moon. And tonight, it stands farthest from the Sun for its current evening appearance. That means there’s a little extra time to enjoy the view before it sets, around 8:30 or 9.

Venus is the second planet from the Sun, while Earth is the third. Since it’s closer in, we never see it for more than a few hours after sunset or before sunrise.

How long we get to see it and how high it stands in the sky vary from one appearance to the next. It depends on the angle of Venus’s path. Right now, it follows a low angle across the sky in early evening. As Venus sets, it slides along the horizon instead of dropping straight down. So it’s not all that high at sunset, and it doesn’t stay in view as long as it would at other times of year.

After today, Venus will begin dropping back toward the Sun as seen from Earth. That’s just an illusion, though. The planet is actually moving closer to Earth. The relative motions of the two worlds make it look like Venus is approaching the Sun. As Venus gets closer, it also will form a bigger target. As a result, it will get a little brighter over the next few weeks.

Venus will cross between Earth and the Sun in January. After that, it will climb into the morning sky, where it will reign for most of the year.
 

Script by Damond Benningfield

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