StarDate

A few hundred million years after the Big Bang, the universe got a real charge. The light from the first brilliant stars and galaxies ripped apart the hydrogen atoms that filled the cosmos, giving them an electric charge. That ended the cosmic Dark Ages, and began a new era, known as the Epoch of Reionization.

For its first few hundred thousand years, the universe was so hot that protons and electrons couldn’t stick together to make hydrogen atoms. So the hydrogen consisted of bare protons, which have an electric charge.

As the universe expanded, though, it got cooler, allowing the protons and electrons to join. The complete hydrogen atoms had no charge. Since they were neutral, they produced no light. And they had not yet come together in massive numbers to form stars. So the universe was dark.

And it stayed dark for a few hundred million years, until enough of the hydrogen had clumped together to make stars. Many of these early stars were big and hot, so they produced a lot of ultraviolet energy. And so did the first galaxies, which contained many hot stars. The U-V zapped the surrounding hydrogen, breaking the atoms apart — and reionizing the universe.

As more stars and galaxies formed, they zapped ever-larger volumes of space. By perhaps a billion years after the Big Bang, the job was done. Almost all of the hydrogen atoms had been split apart — “re-charging” the universe.

We’ll have more about reionization tomorrow.

Script by Damond Benningfield

Compared to Earth, the Moon is bone dry. There are no lakes, rivers, or puddles anywhere to be found. Even so, there is some water on the Moon. Patches of ice hide inside dark craters at the lunar poles, and bits of ice are mixed with the powdery lunar dirt. And there’s even water mixed in with the mantle — the layer of rock below the Moon’s crust.

A recent study says that most of the water below the surface probably was delivered by rocky asteroids when the Moon was young.

Among other things, the study team compared the chemistry of the water found in moonrocks picked up by Apollo astronauts to the water on Earth and in asteroids and comets. More than 80 percent of the lunar water matches that found in a particular type of asteroid.

The study says these asteroids pounded the Moon from shortly after it formed until it was a couple of hundred million years old. Much of the lunar surface was covered with molten rock at the time. The water in the asteroids mixed with the magma, and was trapped when the Moon began forming a solid crust atop the mantle.

In the billions of years since then, impacts by other asteroids have gouged out deep craters. That blasted some of the trapped water onto the surface — revealing the history of lunar water.

Look for the Moon low in the southwest as darkness falls tonight. Venus, the “evening star,” stands to its lower left, with fainter Saturn close below the Moon.

Tomorrow: giving a “spark” to the universe.

Script by Damond Benningfield

Adventure travelers of the distant future may have some amazing destinations to choose from. They might hike around the volcanoes of Io, one of the moons of Jupiter; on Mars, they could climb the solar system’s tallest mountain; or they could watch giant geysers erupt on Triton, the biggest moon of Neptune.

White-water rafters might have a good location as well: Titan, the largest moon of Saturn. They’ll need a well-insulated wetsuit, though, because the rivers are filled with liquid methane and ethane, which are hundreds of degrees below zero.

Scientists discovered lakes and seas on Titan more than a decade ago. They also found channels that look like riverbeds. But none of the channels appeared to have any liquid in them.

Earlier this year, though, they revealed the discovery of liquid-filled canyons on the big moon. Some of them are miles long, and up to a third-of-a-mile deep.

The liquid in some of the bigger canyons is at the same elevation as the lakes and seas they flow in to. But in some of the smaller canyons, the level is much higher. That means they’d have a quick flow. And if there are any rocks around, they’d also have some choppy sections — perfect spots for a little white-water rafting.

Saturn is in good view this evening. It’s one of two planets to the upper left of the Moon after sunset. The brighter one is Venus, the “evening star.” Fainter Saturn is close to its right.

More about the Moon and planets tomorrow.

Script by Damond Benningfield

Ghosts and goblins and ghouls prowl the streets tonight. And they also prowl the sky. In fact, four stars in the constellation Perseus represent the Gorgons — the mythological sisters whose heads were covered with snakes. One look at them turned the viewer to stone.

The most prominent of these stars really does do something strange. For a couple of hours every three days or so, it fades dramatically. Ancient skywatchers must have found that a bit frightening, because they gave the star a spooky name: Ras Al-gul — “the demon’s head.” Today, it’s known by a shorter version of the name: Algol.

The star doesn’t really do anything ghoulish, though. Instead, its dimming spells are the result of eclipses.

Algol consists of three stars. Two of them are quite close together, so they orbit each other in a bit less than three days. We see them eclipse each other during each orbit.

One of the stars is a couple of hundred times brighter than the Sun, while the other is much fainter. But the fainter star is also the bigger of the two. So when it passes in front of the brighter star, the system drops to about a third of its normal brightness. Skywatchers in ancient times knew nothing about the cause of the star’s fading act, though — only that it was a ghoulish thing for a star to do.

This “demon” star is low in the northeast as night falls, not far to the lower right of Mirphak, Perseus’s brightest star. It’s a perfect companion for a Halloween night.

Script by Damond Benningfield

If you spend some time gazing into a dark night sky, you’ll notice that the stars are all a bit jumpy. They appear to flicker on and off, shift position, and even change color.

To scientists, this bobbing about is called scintillation. To the rest of us, it’s known as twinkling. It has nothing to do with the stars themselves. Instead, it’s caused by Earth’s dynamic atmosphere.

The stars are so far away that we see them as nothing more than pinpoints. As a star’s narrow beam of light enters the atmosphere, it encounters small pockets of air that are at a different temperature and density from the air around them.

These pockets act as lenses — they bend the rays of starlight. So the light from a star zigs and zags as it passes through the atmosphere, making the star to appear to flicker.

Different colors of light are bent at different angles, so a star can also appear to change color. That’s especially true for the brighter stars, which can swiftly change from red to green to pure white. The effect is most pronounced when a star is close to the horizon, where its light must pass through more atmosphere to reach the viewer’s eye.

And you can see this effect for yourself by looking at the bright stars in view this evening. Fomalhaut, the lonely “autumn star,” is low in the south as night falls, for example. And a bit later, the even brighter star Capella rises into good view in the northeast — twinkling fiercely as it climbs into the sky.

Script by Damond Benningfield

Two planets are slipping past each other in the early evening sky. Venus is the “evening star” — the brightest object in the night sky other than the Moon. Saturn stands to the upper right of Venus this evening, and a bit farther from it on succeeding nights. It’s not nearly as bright, but its proximity to Venus should help you find it.

The appearance of these worlds is an illusion. Saturn is actually the more impressive of the two. It’s the second-largest planet in the solar system — about 10 times Venus’s diameter. It looks fainter only because it’s hundreds of millions of miles farther.

And it’s that distance that allowed Saturn to grow so big.

Venus is the second planet out from the Sun. So it was born in the hottest part of the young solar system. Radiation and a “wind” of charged particles from the Sun cleared much of the planet-building materials from this region. All that was left were chunks of rock and metal. Many of these coalesced to make Venus and the other small inner planets, including Earth.

Saturn was born much farther from the Sun. In that zone of cold and darkness, the rock was supplemented by chunks of ice. That allowed Saturn to build a big, heavy nucleus. As the core took shape, its gravity pulled in vast amounts of hydrogen and helium left over from the birth of the Sun, surrounding Saturn with a thick envelope of gas. So Saturn grew to giant proportions — while Venus stayed nice and small.

Script by Damond Benningfield

Once every few weeks, the star system Z Camelopardalis pops off. It quickly flares to about 50 times its normal brightness, then slowly fades. But at least once in the last couple of thousand years, it probably flared thousands of times brighter than its normal outbursts — like the difference between a flashlight and a searchlight. And today, astronomers can still see the residue of that powerful blast.

The system is in Camelopardalis, the giraffe. The constellation is about a third of the way up the north-northeastern sky at nightfall.

Z Cam consists of two stars. One is a white dwarf — the small, dead corpse of a once-normal star. Its companion is much bigger. The stars are so close that the white dwarf “steals” some of the companion’s gas, forming a hot disk around the white dwarf. Every few weeks, the disk collapses onto the white dwarf, creating a bright outburst.

A few years ago, though, astronomers discovered a shell of gas and dust around Z Cam. It spans several light-years, suggesting it’s been expanding into space for a long time.

The shell probably was produced in a much more powerful outburst. Lots of gas from the companion built up on the white dwarf. This material got so hot that it triggered a runaway nuclear explosion, blasting the layer of gas out into space.

The blast was so bright that it might have been visible from Earth. In fact, Chinese astronomers might have recorded it — almost 2100 years ago.

Script by Damond Benningfield

When the Sun disappears during an eclipse, not only does the sky go dark, but the air gets cooler as well. The same thing happens on any world with an atmosphere. And on one world, the atmosphere doesn’t just get cooler. Most of it actually freezes.

Io is one of the largest moons of Jupiter, the biggest planet in the solar system. It takes Io a little less than two days to orbit Jupiter. It’s in eclipse for about two hours of each orbit, as it passes through the shadow of the giant planet.

Astronomers at the Southwest Research Institute studied those eclipses with instruments that are sensitive to heat. And they found that during an eclipse, Io’s atmosphere collapses. About 80 percent of it freezes and collects on the surface as frost. When the eclipse ends, the frost vaporizes and rejoins the atmosphere.

There’s no big “whoosh” when that happens, though, because Io’s atmosphere is only one-billionth as thick as Earth’s.

The atmosphere consists mainly of sulfur dioxide. It’s belched out by hundreds of volcanoes that dot the surface. The volcanoes are so powerful that some of the gas shoots hundreds of miles high. Some of it is captured by Jupiter’s magnetic field and swept out into space, where it forms a ring around the planet. But the volcanoes keep spewing out more sulfur dioxide — renewing Io’s thin atmosphere.

And Jupiter is in great view at dawn tomorrow. It looks like a brilliant star a whisker to the upper right of the crescent Moon.

Script by Damond Benningfield

Cepheus, the king, wheels high across the north on these mid-autumn evenings. It looks like an upside-down child’s drawing of a house. And appropriately enough, it’s a constellation that hosts a king among stars — one of the largest stars in the entire galaxy.

In truth, no one knows for sure which is the Milky Way’s largest star. That’s because the galaxy is so huge that we can see only a small fraction of its stars. Nevertheless, there’s no question that a red star named VV Cephei is one of the biggest around.

VV Cephei was born about twenty times as massive as the Sun. That made it shine hot and blue. As the star aged, though, it puffed up like a balloon, causing its outer layers to cool and turn red. Now, this red supergiant is so large that if it took the Sun’s place in our own solar system, it would swallow Mercury, Venus, Earth, Mars, Jupiter, and maybe even Saturn.

Because VV Cephei is much cooler than the Sun, every square inch of its surface emits much less light than a square inch of the Sun does. But because VV Cephei is so enormous, its surface has a lot of square inches. So the star produces more light in a single hour than the Sun will in an entire year.

VV Cephei is thousands of light-years away, but it’s so powerful that you can still see it with the unaided eye — if the sky is dark and moonless. And this kingly star has the perfect home, in the constellation Cepheus, the king.

Script by Ken Croswell, Copyright 2016

Cepheus, king of the legendary land of Ethiopia, had a problem. His wife, Cassiopeia, had bragged that she was the most beautiful woman of all. The sea nymphs were a bit miffed by that, so they convinced Poseidon to send a monster to avenge the slight. To save his country, Cepheus had his daughter, Andromeda, chained at the shore as a sacrifice. At the last minute, though, she was rescued by Perseus, who turned Cetus to stone by showing it the head of another monster, Medusa.

Most of the major players in that little drama are commemorated in the sky as constellations. And the tales of those constellations were handed down to us in one of the most important books in the history of astronomy.

The Almagest was written almost 2,000 years ago by Claudius Ptolemy, a scientist in the city of Alexandria. The book describes the motions of the Sun, Moon, and planets. It discusses eclipses and the length of the year. And it explains the cosmology of the time — the idea that Earth sat at the hub of a celestial sphere.

The book also includes a star catalog. Part of that catalog is a listing of 48 constellations visible in northern skies. Many of them had been around for millennia. But Ptolemy compiled them into a single convenient source.

All 48 of those constellations are still in use today — including Cepheus. It’s high in the north this evening, and looks like an upside-down version of a child’s drawing of a house.

More about Cepheus tomorrow.

Script by Damond Benningfield