StarDate

When Earth was born, the Sun was fainter than it is today — by about 30 percent. That should have made the young Earth a snowball. But evidence shows that Earth had liquid water on its surface not long after it was formed. That leaves scientists wondering where the extra heat came from.

Some of it might have been provided by the Moon. It was born shortly after Earth itself. A planet as big as Mars slammed into Earth, blasting debris into space. Some of that material quickly coalesced to form one or more moons. Today, only one remains.

The newborn Moon was quite close to Earth — less than one-tenth of its current distance. At that range, its gravitational pull on Earth was much stronger than it is today. That created powerful tides in whatever water stood on the surface — and in the solid planet.

A recent study says those tides would have stretched and compressed rock at and below the surface. That would have generated heat, melting the rocks. That could have boosted the birth of volcanoes, which spewed carbon dioxide and other greenhouse gases into the atmosphere. Combined, that would have warmed the surface by several degrees — accounting for at least some of the heat needed to take up the slack of the weaker Sun.

The Moon is full tonight. It’s the Egg Moon or Grass Moon. And it has a bright companion: Spica, the leading light of Virgo. It rises below the Moon in early evening, and the Moon slides closer to it throughout the night.
 

Script by Damond Benningfield

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The gibbous Moon soars high across the sky tonight. It’s just a day away from “full,” so the Sun lights up almost the entire hemisphere that faces Earth.

The full or nearly full Moon has a big impact on many species of life — especially in the oceans. Reproduction in some corals is determined by the Moon, for example. So are some movements of the giant manta ray, among others. And some fish are more likely to take the bait on a fishing line around full Moon.

A recent study found one more correlation: shark attacks.

Researchers from the University of Florida and LSU looked through records of more than half a century of shark attacks around the world. They plotted them by shark species, geography, and other factors — including the phase of the Moon.

And the only real correlation they found was with lunar phases: more attacks took place when the Moon was at least half full. The trend didn’t vary by species, location, or any other circumstance.

The researchers don’t claim that the Moon is the cause of the attacks. Most attacks take place during the day, when the Moon makes little difference in the amount of light below the surface. The researchers say the peak in attacks could be related to lunar tides, magnetic effects, or some other factor. All they can say for sure is that sharks seem to be more likely to attack when the Moon is high and bright — as it is now.

We’ll have more about the Moon’s influence tomorrow.
 

Script by Damond Benningfield

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The Moon slides by the tail of the lion tonight. Denebola, the star that represents the tail, stands to the left of the Moon as night falls, and to the upper right of the Moon as they set, about an hour before dawn.

Denebola is about 36 light-years away, which makes it a close neighbor. It’s almost twice as big and heavy as the Sun, and about 15 times brighter. And it’s pretty young as stars go — about one-tenth as old as the Sun.

Like a few other stars in its age and size range, Denebola is encircled by a wide disk of dust. Some of the tiny particles that make up the disk probably are left over from the cloud that gave birth to the star. Others may be debris from collisions between larger chunks of material — the size of asteroids or bigger.

No one has detected planets amidst this debris. But astronomers have found gaps in the disk that could have been cleared out by the gravity of orbiting planets. If planets do exist, they probably formed as the dust grains stuck together to form bigger and bigger bodies — the same way our own Earth took shape.

New planet-hunting instruments could someday snap pictures that are sharp enough to actually see planets around Denebola — worlds orbiting the lion’s tail.

Denebola is at the lower left of the triangle of stars that forms the lion’s hindquarters. It’s among the few dozen brightest stars in the night sky, so it’s easy to find even through the glare of the nearby Moon.
 

Script by Damond Benningfield

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Some of the stars may be missing. And one project is trying to find out what happened to them, while also finding more stars that have suddenly vanished or appeared.

VASCO compares large surveys of the sky that were conducted decades apart.

The earliest was compiled at Palomar Observatory in California in the 1950s. The survey was done with photographic plates, which have since been digitized.

More-recent surveys use electronic detectors, which can see fainter objects. So anything that showed up on the Palomar plates should also show up in the later observations.

VASCO has turned up quite a few objects in the early pictures that don’t show up today. Researchers have ruled out flaws in the original plates and many other possible explanations. They’re left with the idea that these objects have simply vanished.

And that’s hard to explain. Stars change slowly, so most changes in brightness are gradual. Some do change over short periods, but modern surveys should easily see any variable stars that were on the original plates.\

Some stars could vanish — massive stars that collapse to form black holes without blasting away their outer layers. But such events are quite rare, so they can’t account for the missing stars.

Researchers say it’s possible that the disappearing stars were lasers beamed into space by other civilizations. But it’s more likely that they’re seeing an undiscovered natural way that stars might go missing.
 

Script by Damond Benningfield

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A gravitational tug-of-war can really stir things up. A contest between Jupiter and its big moons, for example, has warmed the interiors of the moons. That’s created oceans of liquid water below the surface of some of the moons, and hundreds of volcanoes on another.

A recent study says Earth is being changed by a tug-of-war as well — between the Sun and Moon. Researchers say the back-and-forth could be responsible for the motions of the plates that make up Earth’s crust.

The gravity of the Sun stretches the Moon’s orbit, so it looks like a flattened circle. As a result, the Moon’s distance from Earth varies by almost 30,000 miles.

As the Moon moves back and forth, so does the center of gravity of the Earth-Moon system. Earth and the Moon both orbit that center point. It’s below Earth’s surface, but not at the middle of our planet. And as the Moon’s distance changes, so does the center of gravity.

The researchers say that, combined with other effects, that change is enough to fracture Earth’s crust, forming the plates. It may also contribute heat that helps keep the layers below the crust molten, allowing the plates to move across them.

The idea would fill in some gaps found in other explanations for the crustal plates. But it’s brand new, so it’ll take more work to either confirm it or put it down.

The Moon soars high across the sky tonight, with a prominent star close by: Regulus, the heart of the lion.
 

Script by Damond Benningfield

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When Nicolas Louis de Lacaille journeyed to the Cape of Good Hope in the 18th century, he mapped about 10,000 stars that weren’t visible in European skies. He used some of those stars to create 14 constellations. All but one of them were named for the rage of the day: science.

One of those is Antlia, the air pump. It was named for a device that created a vacuum for scientific experiments.

Antlia passes low across the south this month as viewed from the southern half of the U.S. It’s not much to look at, though. You need pretty dark skies to see even its brightest star.

That’s not to say there’s nothing interesting in the constellation. Among its treasures is a star named S Antliae, about 260 light-years away. It’s actually a pair of stars. But the pair should merge to form a single star.

S Antliae is a contact binary. That means the two stars are so close together that they’re touching each other. In fact, they’re sharing an outer layer of gas.

The main star in the pair is about twice the mass of its companion. It’s wider than its companion as well, so it’s probably contributing most of the shared gas. Over time, it may transfer enough gas to make the companion the heavier star. After that, the process may reverse, with the companion giving gas back.

That exchange is drawing the stars closer together. Eventually, they’ll merge, perhaps with a short but bright display of fireworks — adding a spark to an unremarkable constellation.
 

Script by Damond Benningfield

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Crows aren’t very popular. They’re loud and messy, and they’re generally thought of as devious pests.

According to Greek mythology, though, that wasn’t always the case. Originally, crows had silver-white feathers and beautiful voices. But a crow that misbehaved angered one of the gods, who transformed all crows as part of the punishment.

The story is told in three constellations: Crater, the cup; Hydra, the water snake; and Corvus, which represents the crow itself.

The myth says the god Apollo gave the crow a cup and sent him to fetch some water. As the crow flew toward the nearest spring, though, he saw a fig tree and dropped in for a snack. But the figs were still green, so he had to wait several days for them to ripen.

By then, Apollo was mightily displeased, and the crow knew he would be. So the crow grabbed a snake from the river and flew back to Apollo. He told the god that the snake had blocked his way. But Apollo knew the crow himself was to blame. In anger, he gave crows black feathers and raspy voices. He then flung the crow, cup, and snake into the sky, where they remain today.

Look for them climbing into view low in the southeast as the sky gets nice and dark. Corvus is the easiest to find, because its four brightest stars form a pattern that looks like a small sail. The cup is to the crow’s upper right. And the water snake slithers to their right and upper right, stretching almost halfway across the sky.
 

Script by Damond Benningfield

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When a giant radio dish entered service with NASA in 1994, its main job was to track SOHO, a spacecraft that watches the Sun. Today, one of its main jobs is to study the Sun itself. It’s the centerpiece of GAVRT — Goldstone Apple Valley Radio Telescope — a project that’s turned control of the telescope over to students.

The 112-foot dish is in the Mojave Desert. It’s part of NASA’s Deep Space Network, which stays in touch with spacecraft throughout the solar system and beyond.

Network antennas are also used as radio telescopes. And that’s the full-time job of this antenna. It retired from the spacecraft-tracking business years ago. It took over for another antenna that had been used for GAVRT. Today, students around the country, from elementary through high school, help select its targets, move the dish, gather data, and analyze the results.

There are several main projects for GAVRT. One of them is studying the Sun. The observations can help determine how the Sun generates space weather — interactions between the Sun and Earth’s magnetic field. Space weather can knock out satellites, shut down power grids, and cause other problems.

Other projects monitor the radio waves produced by jets of particles shooting away from black holes; study the magnetic field of Jupiter, the solar system’s largest planet; and even listen for radio signals from other civilizations — big science from a “retired” radio dish.
 

Script by Damond Benningfield

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It’s probably not a surprise that supernovas can be dangerous. In fact, the exploding stars have been implicated in one or more mass extinction events here on Earth. It is a bit surprising, though, that supernovas might also be a boon to life. But that’s the finding of a recent study.

A supernova is the violent death of a star. It can briefly outshine an entire galaxy. It produces a lot of ultraviolet and other forms of light that can be deadly. So any supernova that goes off close to Earth could be a big problem. A study in 2020, for example, suggested that one or more supernovas triggered a mass extinction 360 million years ago.

Supernovas also generate huge amounts of cosmic rays — heavy particles that zip through the universe at almost the speed of light. Too many cosmic rays can be bad. But just the right amount could be good for life.

The new study compared the rate of nearby supernovas to cycles of life recorded in ocean sediments. And it found a correlation: More supernovas equals more-abundant life. That could be because the cosmic rays increase the rate of cloud formation and affect global winds. Higher winds stir up the oceans, bringing more nutrients to the surface and boosting the amount of life. That also leads to more organic compounds being stored in ocean sediments, which boosts oxygen production.

The idea is still pretty new, but it hints that life on Earth can benefit from death in the stars.
 

Script by Damond Benningfield

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Astronomers have found several “cows” in the cosmic meadows — including an especially loud one. They’re a powerful form of supernova — the titanic explosion of a star. They’re named for the first one seen, AT2018cow — the Cow.

Only five have been discovered, suggesting that they’re uncommon. But they shine brilliantly at all wavelengths.

The most recent discovery was the brightest of all. A month after the explosion, AT2020mrf was producing 20 times more X-rays than the Cow had a month after it went off. And almost a year after the explosion, it was 200 times brighter than the Cow.

A possible explanation is that we’re seeing parts of the explosion that had never been seen before.

When a supergiant star reaches the end of its life, its core collapses to form a black hole or a neutron star. Its outer layers then blast out into space as a supernova.

Most of the time, the exploding star is surrounded by a cocoon of gas and dust. That blocks our view of what’s happening in the core. In the case of the cows, though, there was little surrounding material. So when they exploded, we could see all the way down to the core — providing the first direct views of the birth of a neutron star or a black hole.

Cow-like events may be kept bright by radiation from a disk of gas around the black hole, or by the magnetic field of the rapidly spinning neutron star. Either way, they help the cows stand out in the cosmic meadows.
 

Script by Damond Benningfield

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