StarDate

This would be a great day to stand on the Earth-facing side of the Moon. That’s because there’s a full Earth in the sky. Our planet is almost four times the diameter of the Moon, so a full Earth looks much bigger than a full Moon. And Earth reflects an average of about three times more sunlight than the Moon does. Put those numbers together, and a full Earth shines more than 40 times brighter than a full Moon -- a spectacular sight in the lunar sky.

On the other hand, from Earth, we can’t see the Moon at all. That’s because it’s “new” today -- it crosses the line between Earth and the Sun. It appears close to the Sun, so it’s hidden in the Sun’s glare.

The only time we do see the new Moon is during a solar eclipse -- when the Moon passes directly in front of the Sun, blocking all or part of its light.

The Moon crosses the Earth-Sun line about once a month. But the Moon’s orbit around Earth is tilted. Most months, the Moon passes above or below the Sun. Two or three times a year, though, the geometry is just right, creating an eclipse.

The next one is coming up on October 14th, and it’ll be visible across most of North America. The Moon will be farther from Earth than average, though, so it won’t completely cover the Sun’s disk -- a ring of sunlight will encircle the Moon. The next total eclipse will take place in April. It, too, will be visible from North America -- a spectacular sight from Earth and the Moon.
 

Script by Damond Benningfield

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The scorpion has a potent stinger -- a pair of bright stars at the tip of its curving body. They’re low in the southern sky as night falls, with the rest of Scorpius curling to their upper right.

The brighter star in the stinger is known as Lambda Scorpii. It’s the second-brightest star in Scorpius, so it’s hard to miss. Fainter Upsilon Scorpii stands close to its right.

Lambda actually consists of three stars. The main star is more than 10 times as massive as the Sun, so it burns through its nuclear fuel in a hurry. It’ll soon begin to exhaust that supply, so it’ll puff outward. The star will engulf its closer companion, which is only a few million miles away. That may destroy the companion, perhaps sending its core spiraling into the core of the main star. And that may hasten the demise of the main star, which is likely to explode as a supernova.

Upsilon is a single star, but it’s also a stunner. It’s about 10 times the Sun’s mass, and many thousands of times its brilliance.

Although Lambda and Upsilon appear quite close together, they’re dozens of light-years apart. Even so, the stars are related. They were born from the same giant complex of gas and dust. This region has given birth to many massive stars, including Antares, the scorpion’s bright orange heart. But the stars are only loosely bound together, so they’re moving apart -- spreading their brilliance across the galaxy.
 

Script by Damond Benningfield

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Pegasus, the flying horse, is beginning its climb into the evening sky. It clears the eastern horizon by midnight. It’s preceded into the sky by another horse, to its upper right.

Equuleus is far smaller and less prominent than its famous equine cousin. In fact, of all the constellations passed down from the ancient world, it’s by far the smallest.

Unlike most ancient constellations, there’s not much of a story associated with Equuleus. And as it’s drawn in the sky, it’s not even a full horse -- only a head, which is outlined by a lopsided rectangle of four meager stars.

The brightest is Alpha Equulei. It’s actually a pair of stars locked in a tight orbit around each other. Both stars are about twice as massive as the Sun, with one slightly heavier than the other.

That difference in heft has made a big difference in the lives of the two stars. The heavier one has already ended its “normal” lifetime, and is entering one of its final stages -- it’s puffed up like a giant orange balloon.

The smaller star is still in the prime of life. But as the bigger star expands, the surfaces of the two stars may get so close that the stars will begin to swap some of their gas -- a process that may alter the evolution of both stars.

Equuleus is in the east at nightfall. It’s below Delphinus, the dolphin -- another small constellation, but one that’s much easier to pick out.
 

Script by Damond Benningfield

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The globular star cluster Messier 4 has a couple of claims to fame. It’s the closest globular to Earth -- about 7,000 light-years away. And it’s home to the first circumbinary planet ever seen -- a planet that orbits both stars in a binary system. The planet was first reported 30 years ago this month.

Such planets are rare -- astronomers have discovered only about 15 of them.

It’s probably hard to make such a planet, and for it to hang around. The gravity of the stars in a binary should keep the planet-building materials close to them stirred up, preventing the birth of planets. And their gravity could easily kick a planet that does form out of the system.

The one in M4 is especially hard to explain. It orbits two dead stars -- a neutron star and a white dwarf. The neutron star is the corpse of a supernova -- a star that blasted itself to bits. The white dwarf died in a gentler process, but one that isn’t very kind to planets. So the planet either survived a double cataclysm, or it was born later, from the debris of the stellar deaths. Either way, it’s ancient: perhaps 12 billion years old -- almost as old as M4 itself.

Messier 4 stands due south as the sky gets dark now. It’s close to the right of Antares, the bright orange star at the heart of the scorpion. Through binoculars, it looks like a fuzzy star. But it’s really the combined glow of a hundred thousand stars -- and at least one planet.
 

Script by Damond Benningfield

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The Moon poses near the face of the bull early tomorrow. The face is outlined by the bright stars of the Hyades star cluster -- with one exception. The brightest star is Aldebaran, the bull’s eye. It moves through the galaxy on its own.

Aldebaran is 65 light-years away -- less than half the distance to the Hyades. It’s more than six billion years old -- a couple of billion years older than the Sun. It’s well beyond the prime of life, so it’s puffed up to become a giant. That’s made it especially bright, and caused its surface to shine a vivid orange.

The Hyades includes several giants as well. They’re the brightest lights in the bull’s V-shaped face. But they’re only one-tenth of Aldebaran’s age. They’ve become giants at a younger age because they’re more massive than Aldebaran. Heavier stars burn through their nuclear fuel much faster than lighter stars, so they reach the ends of their lives in a hurry.

One of those stars, Epsilon Tauri, represents the bull’s other eye. It’s more than twice as massive as Aldebaran. It’s still puffing up, though, so over millions of years, it’ll get much bigger and brighter -- giving the bull two impressive eyes.

Look for the face of the bull to the right of the Moon before and during dawn. Aldebaran is separated from the Moon by about the width of your fist held at arm’s length, with the Hyades above and to the right of Aldebaran -- and twice as far away.
 

Script by Damond Benningfield

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A likely gas cloud is getting stretched out and pulled apart by the supermassive black hole at the heart of the Milky Way Galaxy. Astronomers have been watching it for a couple of decades. And it’s gotten a lot longer and thinner over that time. That could mean it’s doomed.

The black hole is called Sagittarius A-star. It’s in the constellation Sagittarius, which is in the southeast at nightfall. Its brightest stars form the outline of a teapot. The black hole is immersed in the “steam” above the spout of the teapot.

Sagittarius A-star is more than four million times the mass of the Sun. Its gravity pulls in anything that gets too close. As the material falls toward the black hole, it’s heated to millions of degrees, so it emits copious amounts of X-rays. Big bursts of X-rays flare up about once a day as the black hole swallows clumps of material.

One object that may meet that fate is called X7 -- a cloud that astronomers have been watching for 20 years. It’s about 50 times as massive as Earth.

Today, it’s more than twice as long as when astronomers first saw it. It’s moving toward the black hole, and will pass closest in 2036. It’ll be stretched out even more, forming long strands and small clumps. Some of those clumps may be pulled into the black hole -- ending with big bursts of X-rays just before they disappear forever.
 

Script by Damond Benningfield

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The universe is full of surprises. One example: Astronomers have found several young stars close to the supermassive black hole at the heart of the Milky Way Galaxy. And one of those stars is still in the process of being born.

The stars are surprising because the space around the black hole is messy. The black hole’s powerful gravity stirs up everything around it. A disk of hot gas swirls around the black hole. It emits X-rays, which can blast away the raw material for making stars. And powerful magnetic fields thread through the space near the black hole, mixing things up even more.

That doesn’t sound like a great spot for young stars. Yet astronomers have found several of them. The youngest, X3a, appears to be only a few tens of thousands of years old. In fact, it’s not even a fully mature star -- it’s the youngest of infants.

X3a is about 15 times the mass of the Sun, so it’s a really big infant. It’s in a clump of gas and dust. The clump may have come from the outer edge of a wide ring of gas and dust around the black hole. As X3a has taken shape, the clump has fallen closer to the black hole. Now, it’s just a couple of light-years out -- surprising activity at the heart of the Milky Way.

The black hole is in Sagittarius, which is in the southeast at nightfall. The constellation looks like a teapot. The black hole is hidden in the “steam” rising from the spout of the teapot.

More tomorrow.
 

Script by Damond Benningfield

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The Moon and the planet Jupiter will be quite chummy the next couple of mornings. Jupiter will stand close to the Moon at dawn tomorrow, and a little farther on Wednesday.

Jupiter looks like a brilliant star. But it’s really a planet -- the solar system’s largest -- about 11 times wider than Earth.

That’s a popular size for objects throughout the galaxy, including planets, brown dwarfs, and even stars -- objects that can be many times heavier than Jupiter.

Jupiter and many of the planets in other star systems are big balls of gas with solid or semi-solid cores. Because they’re so heavy, gravity squeezes them tightly. But it can squeeze only so much. The gases and solids reach a point where they can’t be squeezed any tighter. That point depends on the mass of the planet -- a heavier planet has stronger gravity, so it can squeeze itself to a higher density. The balance point is at about the size of Jupiter.

The same thing happens with brown dwarfs -- objects that are more massive than planets, but not massive enough to shine as stars. They’re held up in part by heat from their cores, which pushes outward against the surrounding gas.

And something similar happens with lightweight stars. Gravity is balanced by the radiation from nuclear reactions in the star’s core. So a star that’s up to a couple of hundred times Jupiter’s mass isn’t much bigger -- a one-size-fits-all pattern for heavy planets and lightweight stars.
 

Script by Damond Benningfield

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Aquila, the eagle, spreads its wings across the evening sky. It’s well up in the east as the sky gets dark. Its brightest star, Altair, is at the bottom right point of the wide-spread Summer Triangle. Altair represents the eagle’s breast, with the wings above and below.

A pair of stars at one of the wingtips faces an uncertain future. Early studies said the two stars will ram together and explode as a supernova -- in 700 million years. But more recent work says they won’t.

Henize 2-428 consists of two white dwarfs -- the dead cores of once-normal stars. They probably started out as fairly massive stars. As the main star aged, it dumped most of its gas onto its companion. As that star aged, it began dumping gas as well, forming a cloud around both stars. The gas was kicked out into space, forming a colorful nebula around the pair.

Today, the stars are so close that they orbit each other once every four hours. As they orbit, they radiate gravitational waves, causing them to spiral even closer -- and eventually merge.

The early work said the combined mass of the two stars would exceed the weight limit for white dwarfs. As a result, they’d blast themselves to bits as a supernova.

But the more recent work said the stars are less massive than originally thought. If that’s true, then their merger will be much less spectacular. Henize 2-428 will survive -- as a heavy stellar “corpse” floating through the galaxy unnoticed.
 

Script by Damond Benningfield

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[Audio: winds of Mars] That’s the sigh of the winds of Mars blowing across the Perseverance rover. Some day, those winds could be an important power source for human explorers. According to a recent study, at some locations, a single wind turbine could power an entire Mars habitat. And it could supplement solar power just about anywhere.

There are several options for powering a human base on Mars. A nuclear generator could provide power 24 hours a day, and wouldn’t be influenced by the weather. But shipping the nuclear materials to Mars has some safety risks. A second option is solar power. But, over the course of a year, the Sun is in good position only about 40 percent of the time. So it would need good batteries to store up enough energy for the frigid Martian nights.

The new study found that solar and wind could combine to provide power 60 to 90 percent of the time at most locations. And at some spots, wind could carry the entire load. Wind power would be most efficient at night and during winter, when there’s less sunlight and stronger winds. Wind would also be better during dust storms, and near the poles -- opening more of Mars for exploration.

Look for Mars in the west at nightfall, to the upper left of Venus, the “evening star.” Tonight, Mars is close to the right of the star Regulus, the heart of Leo. Mars and Regulus will be closest in a couple of nights.
 

Script by Damond Benningfield

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