StarDate

The bright gibbous Moon stages an encounter with one of the brightest stars in northern skies tonight: Spica, the leading light of Virgo. Spica is below the Moon as night falls, and will be even closer to the Moon as they set in the wee hours of the morning.

Spica actually consists of two stars. One of them, Spica A, is more than 10 times as massive as the Sun. At that weight, it probably will end its life in a titanic explosion — a supernova.

But Spica’s fainter star is no slouch, either. Spica B is about seven times as massive as the Sun. And when you add up all wavelengths of light, it’s perhaps 2,000 times brighter. That makes it a one percenter — it’s among the top one percent of the galaxy’s biggest and brightest stars.

Spica B’s demise won’t be nearly as impressive as that of its companion, though. It’s below the weight limit that tips a star into the supernova category. Instead, its fate probably is much like the Sun’s.

As the star ages — a process that’s much faster in heavier stars like Spica B — it’ll puff up to many times its current size. Then it’ll blow its outer layers into space. That will leave only its hot, dense core — a white dwarf. And it’ll be among the galaxy’s biggest.

Of course, that scenario depends on what happens with Spica A. The two stars are quite close together, so interactions between them could alter the fate of either or both — making predictions of their future a bit iffy.

Script by Damond Benningfield

There’s a renewed debate these days about what killed the dinosaurs. Most scientists say it was an asteroid that slammed into the Gulf of Mexico. A few say it was giant volcanoes. And some say it was a combination of the two.

Regardless of whether it was the dinosaur killer, though, there’s no doubt the asteroid impact put on quite a show. It gouged a giant crater, blasted billions of tons of debris into the atmosphere, and created a tsunami that rolled all the way to central Texas.

The crater is known as Chicxulub. It’s centered just off the Yucatan Peninsula. It’s about a hundred miles wide and a dozen miles deep.

A few years ago, researchers drilled into a ring of mountain peaks inside the crater’s rim. The rocks revealed what happened when the miles-wide asteroid hit.

The high temperature and pressure excavated an initial crater about 20 miles deep. For about 10 minutes, the ground around the impact site acted like a fluid, with rocks flowing down the sides of the crater. But with the rock above it gone, the crater floor pushed upward. Granite from deep below the surface flowed up, then out, forming the ring of peaks.

Melted rock formed a thick layer at the bottom of the crater. Some of the rock that was blasted into the air fell into the crater as well.

Nothing survived the impact for hundreds of miles around. Yet life began returning to the site within a few years — new life at a site of mass destruction.

Script by Damond Benningfield

It’s not easy to find impact craters on Earth. Most of these cosmic scars have been erased by wind, rain, and the motions of Earth’s crust. As a result, only a couple of hundred have been cataloged.

But the list is growing in a hurry. In recent months, geologists have confirmed three new craters, and found evidence of a fourth.

One of the discoveries was in Western Australia, a desert region where craters are common. The new one is up to 10 miles in diameter, and it probably formed about 85 million years ago. Researchers confirmed the crater by examining quartz crystals in rocks below the desert floor. The crystals were “shocked” — they’d been smashed by a heavy blow, like that delivered by a space rock slamming into Earth.

A similar effect was seen in samples of black glass at a site in Nicaragua. The site was already a suspected crater — it’s a round hole in the ground with many of the features found in confirmed craters. The rock samples seal the deal. The crater is about eight miles across, and formed less than a million years ago.

Evidence of two craters has been found beneath the glaciers of Greenland. One has been confirmed with multiple lines of evidence. The other is probably a crater, but it’s not possible to get at its rocks to confirm it. Instead, it’s been seen in scans that look through the ice. They show that the possible crater is more than 20 miles in diameter — the possible scar of an ancient collision.

Script by Damond Benningfield

The Little Dipper climbs high across the north on spring nights. It’s anchored on one end by one of the most famous stars in all the night sky: Polaris, the North Star. It’s at the tip of the dipper’s handle.

The other end is anchored by the dipper’s second–brightest star. Kochab marks the top right corner of the dipper’s bowl, and is only a fraction fainter than Polaris.

Kochab is about 130 light-years from Earth. It’s completed its “normal” lifetime, so it’s undergoing a series of changes in its core. Those changes are causing its outer layers to puff up, making the star bigger and brighter. It’s about 40 times wider than the Sun and 130 times brighter. And it’s probably about 1.4 times the Sun’s mass.

Kochab has at least one planet. It’s much heavier than Jupiter, the giant of our own solar system. That means the planet is basically a big ball of gas. It’s much closer to Kochab than Jupiter is to the Sun, though, so the planet’s atmosphere is much hotter than Jupiter’s.

As Kochab continues to age, it’ll get bigger and brighter still, then expel its outer layers into space. That process is likely to strip away some of the planet’s atmosphere — leaving the dead star with a much-reduced companion.

Kochab is high in the north-northeast as night falls, to the upper right of Polaris. It stands directly above Polaris around midnight, and to its upper left at first light, as the Little Dipper wheels around the North Star.

Script by Damond Benningfield

The first-quarter Moon huddles close to the heart of the lion tonight. Regulus, the brightest star of Leo, stands to the left of the Moon at nightfall, and even closer to the Moon at first light tomorrow. The star will stand to the right of the Moon tomorrow night.

Today, the Moon is about a quarter of a million miles from Earth. But that hasn’t always been the case. When the Moon was born, not long after Earth was, it was only a fraction of its current distance. And in the remote future, it’ll be much farther.

That’s thanks to the tides. The Moon’s gravity tugs at the oceans, creating “bulges” in the water. These bulges follow the Moon across the sky. As they slosh into the land, the bulges slow Earth’s rotation by a tiny amount.

To keep the books balanced on the overall motion of the Earth-Moon system, the Moon must move a little faster in its orbit. That causes it to move farther from Earth — by about an inch and a half per year.

Over tens of billions of years, things would reach a point where the same side of Earth would always face the Moon, just as the same side of the Moon always faces Earth. The Moon would stop moving away then, and the system would stay locked.

The evolution of the Sun complicates that picture, though. In a couple of billion years, the Sun will be so bright that it’ll boil away Earth’s oceans. No oceans, no tides — locking Earth and the Moon in a closer configuration.

Script by Damond Benningfield

Rocks are portals to the past. They tell us how and when they formed, and what the air and oceans were like at the time. They preserve evidence of ancient life. They can even tell us if they were exposed to radiation. The decay of uranium, for example, can bore thin “tunnels” in the rock. And one team of scientists wants to look for traces of something else: dark matter.

Dark matter appears to account for about 85 percent of all the matter in the universe. Yet so far, it’s never been detected. We know it’s there only because it exerts a gravitational pull on the visible matter around it. It appears to keep the galaxies in clusters from flying away from each other, for example.

The leading theory says that dark matter consists of some new type of subatomic particle, which should pass through Earth in torrents. But extensive efforts to catch them haven’t yielded even a single confirmed particle.

A team from Sweden and the U.S. has suggested looking for signs of dark matter in ancient rocks. The idea is that dark matter particles could have left “tracks” in the rocks — no more than a few millionths of an inch long.

One group tried to find such tracks a quarter century ago, but saw no trace of them. The new group wants to use the more-sensitive microscope technology that’s available today. The scientists would examine bits of rock drilled from deep below the surface — rocks that might contain evidence of dark matter.

Script by Damond Benningfield

Most stars move through the galaxy with at least one stellar companion. These siblings are bound to each other by their gravitational pull. But just how close they are varies by quite a bit. Some stars are so close that they’re actually touching. Others are separated by billions of miles.

An example of such a distant binary is Izar, the second-brightest star of Bootes, the herdsman. The constellation is half way up the eastern sky at nightfall. Its leading light is yellow-orange Arcturus, one of the brightest stars in the night sky. Izar is to the left of Arcturus, and is easy to pick out.

Izar consists of two known stars. The more prominent one is at the end of its lifetime, so it’s puffing up to enormous proportions. That’s made it especially bright — 500 times brighter than the Sun. It’ll get even bigger and brighter over the next few million years. Eventually, it’ll expel its outer layers of gas into space, surrounding itself with a colorful bubble.

If the star’s companion was close by, those changes might affect it as well. Instead, though, the star is about 17 billion miles away — almost 200 times farther than Earth is from the Sun. At that range, it’ll feel little effect from its dying companion. Its surface will get a little hotter, and it will pull in a little of the dying star’s gas. Otherwise, though, it’ll continue shining on its own, until it begins its own death throes — sometime in the distant future.

Script by Damond Benningfield

The Sun’s magnetic field sometimes “snaps” like a breaking rubber band. That produces a huge explosion, known as a solar flare. And it’s sometimes accompanied by an outburst of charged particles, which are potential trouble for Earth.

Different layers of gas within the Sun rotate at different speeds. That causes the lines of the Sun’s magnetic field to get all tangled up. That produces the dark magnetic storms known as sunspots.

The lines don’t stay tangled, though. They snap, releasing tremendous amounts of energy — in some cases, the equivalent of millions of H-bombs. Such a flare can zap Earth with X-rays and other radiation. That heats the outer atmosphere, causing it to expand. It can also disrupt some types of radio transmissions, and force airlines to reroute flights that receive little protection from Earth’s magnetic field.

Many flares are accompanied by big clouds of charged particles. They can damage orbiting satellites and knock out power grids on Earth. In fact, there’s concern that an especially big flare could cause blackouts that would last for months.

The most powerful flare ever seen was also the first one ever seen, in 1859. It caused telegraph operators to get electric shocks, and even started fires. A flare in 1972 might have set off some magnetic mines. And in 2017, a flare knocked out some communications during hurricanes in the Caribbean. So “snaps” on the Sun could snap off technology here on Earth.

Script by Damond Benningfield

The crescent Moon anchors a pretty lineup of stars and planets this evening. One of the stars will be so close to the Moon that it will look like they could reach out and touch each other.

The more prominent of the Moon’s companions are the planet Mars and the star Beta Tauri, also known as El Nath. Mars looks like a fairly bright orange star to the upper right of the Moon. El Nath is a little farther to the right of Mars. It’s about the same brightness as Mars right now.

El Nath is much bigger and heavier than the Sun, and hundreds of times brighter. Its claim to fame, though, is its position in the sky. It’s the closest bright star to the point that’s opposite the center of the Milky Way galaxy. So when we look in that direction, we’re looking into the sparse outer regions of the galaxy’s disk.

The Moon’s closest companion is Zeta Tauri. It’s only about a third as bright as Mars and El Nath. But it’s right next to the Moon, which helps it stand out.

Zeta Tauri consists of two stars. The main one is about 11 times the mass of the Sun. At that great heft, it’s likely to end its life as a supernova — a titanic explosion that’ll blow it to bits.

The other star is about the same mass as the Sun. It’s so close to the main star, though, that astronomers can’t see it through the glare. So they can’t tell whether it’s a “normal” star like the Sun, or a stellar corpse — perhaps the remnant of another supernova that exploded long ago.

Script by Damond Benningfield

Aldebaran, the bull’s bright eye, puts in one final good evening showing tonight. It’s close below the Moon after sunset. It’s so low in the sky that it would be hard to spot on its own. But its proximity to the Moon will help it stand out.

Aldebaran is at the end of its “normal” lifetime, so it’s undergoing a series of changes. Those changes cause its outer layers to puff up, making Aldebaran much brighter.

It’s all building up to the star’s final stage of life: a white dwarf — a stellar corpse more than half as massive as the Sun but no bigger than Earth.

The star will reach that point when its core can no longer produce nuclear reactions. The core will be a ball of carbon and oxygen. It’ll be squeezed so tightly that a teaspoon of its matter would weigh tons.

As it reaches that point, Aldebaran’s outer layers will puff away into space, exposing the dying core. Thanks to the final smattering of nuclear reactions around the core, it’ll be extremely hot.

As the reactions die out, the star will lose most of that heat and quickly start to fade away. The dead core will still be quite hot, but faint. It’ll then slowly radiate the rest of its heat into space — eventually leaving a black dwarf. That’ll take some time, though. In fact, the universe hasn’t been around long enough for even a single white dwarf to completely cool off. So the eye of the bull will shine — albeit faintly — for a long time to come.

Script by Damond Benningfield