StarDate

Like everyone else, astronomers sometimes have to take some time off to care for family members. Few of them are having to defend against accusations of witchcraft, though.

But that’s what happened to Johannes Kepler. Four hundred years ago today, his mother was arrested — and charged with 49 counts of witchcraft. Kepler moved his family to her village in southern Germany, where he led her defense — and eventually won the case.

Kepler formulated the laws of planetary motion. They provided proof that Earth wasn’t the center of the solar system. Instead, they showed that Earth and the other planets orbited the Sun.

Kepler’s mother was first charged with witchcraft in 1615. She was 68 years old and a widow. And she brewed up herbal remedies that were sometimes accompanied by charms. That made her a good candidate for charges of black magic.

Witnesses said she’d caused them great pain, passed through closed doors, and even turned herself into a cat. She was one of 15 people indicted for witchcraft at the time — and eight of them were executed.

Kepler won her release, and she left town. But when she returned, in 1620, she was arrested again. She was chained to the floor of a cell and threatened with torture if she didn’t confess. She refused.

Kepler used science and common sense to refute the charges. After 14 months in prison, she was acquitted — thanks to the efforts of her son, one of history’s greatest astronomers.

Script by Damond Benningfield

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A strong heart needs strong arteries. And Scorpius has both. The constellation’s “heart” is the star Antares, a bright orange supergiant. And it’s flanked by bright arteries. One is to the upper right of Antares at nightfall, with the other to the lower left.

Over the centuries, both stars have been known as Al Niyat — an Arabic name that means “the arteries.” To help tell them apart, the one to the upper right is also known as Sigma Scorpii, while the other is Tau Scorpii.

Sigma is a system of at least four stars. At least two of them are similar to Antares. They’re much bigger and heavier than the Sun, and many thousands of times brighter.

The two stars are so close together that not even the biggest telescopes can see them as individual stars — their light blurs into a single point. The system’s other two stars are visible. And those stars are impressive as well — though perhaps not as impressive as the tight binary.

Tau Scorpii consists of a single star. But it, too, is a monster — about 15 times the mass of the Sun, and about 20,000 times brighter.

Antares and its arteries all belong to a big family that includes lots of big, heavy stars. Antares and the Al Niyats are all quite young — no more than about 10 million to 15 million years old. And all of them share an impressive fate: Within a few million years, they’ll explode as supernovae — strong endings for the scorpion’s heart and arteries.

Script by Damond Benningfield

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A star in Scorpius likes to blow off steam. It stages big outbursts every decade or so. And the next one could happen any day now.

U Scorpii is a system of two stars that are only a few million miles apart. One of the stars is at the end of its “normal” lifetime, so it’s starting to puff up. The other has already ended its life, so only its hot, dead core remains — a white dwarf.

The white dwarf “steals” gas from its companion. The gas forms a disk around the white dwarf. Some of the gas funnels onto the star’s surface. As it builds up, it gets hotter. Eventually, it gets hot enough to trigger a nuclear explosion. That blasts the built-up gas out into space.

U Scorpii erupts about every 10 years. The most recent outburst came in January of 2010. In a few hours, the system grew about 10,000 times brighter than average. It then faded quickly. Within a few days, though, the white dwarf was already pulling in more gas. But observations over the following years showed that it took about 18 months to fully reestablish the disk of gas around the star.

Astronomers expect to see the next eruption this year. In fact, it’s possible that it’s erupted since we recorded this program. Whenever it happens, astronomers will keep a close eye on U Scorpii — watching it once again blow off some steam.

The system stands above Antares, the scorpion’s bright orange heart, which is in the south as night falls. More about Scorpius tomorrow.

Script by Damond Benningfield

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There aren’t many constellations that really look like what they’re supposed to depict. And there aren’t many whose ancient names are easy to translate without a dictionary. But one that defies both trends is one of the highlights of summer’s evening skies: Scorpius, the scorpion. It’s low in the south as night falls right now.

Under even a moderately dark sky, it’s not hard at all to see the outline of a scorpion. Its “heart” is the bright orange star Antares. The scorpion’s head is formed by a short line of three stars to the upper right of Antares. And its body, tail, and “stinger” curl away to the lower left of Antares.

In ancient times, the scorpion was even bigger. Its claws extended far from the head. But more than 2,000 years ago, they were stripped away. Today, they form the constellation Libra, the balance scales. Yet a couple of its stars retain their scorpion names: Zubeneschamali and Zubenelgenubi — the northern and southern claws.

One reason that Scorpius shines so brightly is that it outlines one of the spiral arms of the Milky Way Galaxy. Clouds of gas and dust along the arm are giving birth to new stars. And many of those stars are especially big and bright. That makes the scorpion easy to pick out.

Many cultures have identified these stars as a scorpion. Many others, though, have seen a different but equally understandable pattern — a fishhook, luring prey across the Milky Way.

More about Scorpius tomorrow.

Script by Damond Benningfield

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A Mars rover came to a dark end in June of 2018. A dust storm blanketed all of Mars, blotting out the Sun. The Opportunity rover couldn’t get enough sunlight to power its solar batteries. So after 14 years and 28 miles of roving, it went dark.

The irony is that the dust storm stirred to life because Mars itself was receiving more solar energy than average. The planet was approaching its closest point to the Sun, known as perihelion. And Mars is at perihelion today for the first time since then.

Mars’s orbit around the Sun is lopsided. At its closest, the planet is about 27 million miles closer to the Sun than at its farthest. That means it receives about 40 percent more sunlight. That warms the surface.

As it warms, frozen carbon dioxide atop the polar ice caps begins to vaporize. It rushes into the atmosphere, making it thicker. It also pulls along plumes of dust that can rise high into the sky. Over weeks or even days, the dust can cover a large area. Some years the storms are as big as states or countries. But sometimes, they cover most or all of the planet.

That’s what happened in 2018, in one of the biggest storms yet seen. But such monsters don’t happen on a predictable cycle. They stir up in some years, but not others. And even if there’s a big storm this year, it’s no threat to the only working rover on Mars. Curiosity has a nuclear power source. That allows it to keep going — even when the Sun goes dark.

Script by Damond Benningfield

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If you want to escape the summer heat by plunging into a cool lake or sea, there are only two places in the solar system to do so: Earth, and Titan, the largest moon of Saturn. The big difference is what’s filling those features. On Earth, it’s water. But on Titan, it’s liquid methane and ethane — hydrocarbons that are chilled to hundreds of degrees below zero.

Titan is about half again the size of Earth’s moon. It has a thick atmosphere that’s topped by smog — an orange haze of hydrocarbons. Methane and ethane clouds drift through the sky, sometimes pouring rain on the surface. That fills lakes and seas, and appears to carve riverbeds.

Some of the smaller lakes are surrounded by tall cliffs. Those may have formed at a time when Titan was even colder — so cold that liquid nitrogen flowed across the surface.

A study last year said that some of the nitrogen could have trickled below the surface, forming underground pools. When Titan warmed up, the nitrogen turned to gas. It expanded, blowing sharp-rimmed holes in the surface. The holes later filled with methane and ethane, forming new lakes — perfect places for a really cool plunge.

Saturn is easy to find tonight. The planet looks like a bright star. It’s to the upper right of the Moon as night falls, and leads the Moon across the sky later on. Through a telescope, Titan looks like a tiny star near the planet. The even brighter planet Jupiter is to the right of Saturn.

Script by Damond Benningfield

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A brilliant triangle slides across the south tonight: the Moon and the planets Jupiter and Saturn. Jupiter looks like a brilliant star above the Moon at nightfall. Fainter Saturn stands to the left of the Moon.

The Moon is almost full, so almost the entire hemisphere that faces our way is in sunlight. That reveals the pattern of light and dark that makes up the Moon’s features.

One easy-to-spot feature is at the top right edge of the lunar disk in early evening: Mare Crisium, the Sea of Crises. It’s a small dark circle that’s not connected to any other dark features.

The Sea of Crises is a plain of volcanic rock that fills a big crater. The crater formed almost four billion years ago, when a giant asteroid slammed into the lunar surface. It blasted a hole almost 350 miles across, and several miles deep.

Later, magma bubbled up through cracks in the crater floor. As the magma cooled and hardened it formed a vast plain that bulges upward in the middle. Dense rock from the lunar mantle pushes up below that bulge, so the Moon’s gravitational pull is a little stronger there than in surrounding areas.

In 1976, a Soviet robotic lander brought back 170 grams of dirt from the Sea of Crises. The composition wasn’t what had been expected. That may be because the probe landed atop a ribbon of material blasted out of a nearby crater. So the only sample from the Sea of Crises may have come from deep below this prominent lunar feature.

Script by Damond Benningfield

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If cockroaches ever find their way into habitats on the Moon, they’re likely to thrive. In a study a half century ago, roaches that were fed lunar dirt grew a bit faster than those that weren’t.

Before the first Apollo astronauts landed on the Moon, some scientists were concerned they might bring back dangerous microscopic organisms. The odds were low because the lunar surface is bombarded by deadly radiation. But the risk was deemed high enough to take some precautions. The astronauts from the first three missions spent three weeks in quarantine, for example. Samples weren’t sent to researchers until some had been examined for microbes. And several types of Earth life were exposed to the samples.

The results of that study were published 50 years ago today. Researchers ground up a few grams of the rock and dirt from Apollo 11, the first lunar landing mission. They mixed it in with the water that was holding fish, shrimp, and oysters. And they fed it to birds, flies, and cockroaches.

Scientists kept an eye on the subjects, along with control groups, for four weeks. None of the animals exposed to the samples were any worse off than the ones in the other groups. The roaches actually did a little better with lunar dirt than without, although the difference wasn’t much.

The tests confirmed that the lunar surface is lifeless. That allowed scientists to get on with studying the samples — a safe treasure from the surface of the Moon.

Script by Damond Benningfield

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If there just aren’t enough hours in the day for you, think of this: Earth’s day is longer now than it used to be. A recent study found that 70 million years ago, it was a half-hour shorter than it is now. And as you go even farther into the past, the day gets even shorter.

That’s because the tides act like a brake. As they race around the planet, they slosh against the land and the seafloor. That exerts a “push” against the solid planet, causing it to spin a little slower. At the same time, the tides are causing Earth and the Moon to move farther apart — by an inch and a half per year.

Researchers recently used lasers to count the growth rings in the fossils of a type of clam. The study showed that near the end of the reign of the dinosaurs, Earth rotated 372 times a year. In other words, a year consisted of 372 days. The length of a year hasn’t changed, so that means the length of a day has — it’s gotten a half hour longer.

Earlier studies, which used ancient coral and other fossils to look even farther into the past, extend that trend. 620 million years ago, for example, the year consisted of about 400 days. And 1.3 billion years ago, it was about 546 days. If that’s correct, then the length of a day then was just 16 hours.

And the process goes on. As the tides continue their ceaseless action, they’ll slow Earth down even more — adding some extra time to get things done.

Script by Damond Benningfield

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Stars are funny things. Despite what you might expect, the biggest stars are among the coolest — at least on the outside. On the inside, they’re the hottest.

An example is Antares, the brightest star of the scorpion. It’s close below the Moon at nightfall.

It’s a bit harder to see its color when the Moon is around, but Antares shines bright orange. That tells us that its surface is fairly cool — more than 4,000 degrees cooler than the surface of the Sun.

But Antares is many times the Sun’s mass. That classifies it as a supergiant. The powerful gravity of such a heavy star squeezes its core tightly. And that jacks up the core’s temperature. So the heart of Antares is tens of millions of degrees hotter than the heart of the Sun.

The heat on the inside is the reason the star’s outside is so cool. The hot core produces radiation that pushes on the star’s outer layers of gas. That causes them to puff outward. As they expand, they get less dense. And as the density of the gas drops, so does its temperature.

A cooler gas emits less overall energy than a hotter gas. So each square foot of Antares emits much less energy than the same area of the Sun. But the surface area of Antares is several hundred thousand times greater than the Sun’s. So overall, Antares shines perhaps 75,000 times brighter than the Sun.

Again, look for bright Antares keeping pace with the Moon throughout the night.

Tomorrow: the shorter days of yesteryear.

Script by Damond Benningfield

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