StarDate

The long constellation Hydra, the water snake, is beginning its annual crawl across the southern evening sky. As night falls, its head is in the east-southeast, about a third of the way up the sky. The head is outlined by a pentagon of meek stars.

The first star below the head is a bit brighter. In fact, Zeta Hydrae is the third-brightest star in the whole constellation.

The star is only about 400 million years old — less than a tenth the age of the Sun. But it’s nearing the end of its “normal” lifetime. That’s because it’s more than four times as massive as the Sun. Heavier stars live bright but short lives.

One distinction for Zeta Hydrae is that astronomers have a direct measurement of its size. They estimate the sizes of most stars. They measure a star’s temperature, brightness, distance, and other parameters. They then plug the numbers into models of how stars work. The models then calculate the star’s size.

But they used interferometry to get a true measure of the size of Zeta Hydrae. Interferometry uses computers to combine the observations from two or more telescopes. That produces a view that’s as sharp as that of a single giant telescope.

Combined with the star’s distance of about 165 light-years, the technique reveals that Zeta Hydrae is about 18 times the diameter of the Sun. That’s a good match to what the models predict — showing that astronomers have a pretty good grasp of how stars work.

Script by Damond Benningfield

The star Alphard has a barium problem. High levels of the element show up in the star. But the normal explanation for why a star has so much of it doesn’t seem to apply.

Alphard is the brightest star of the constellation Hydra, the water snake. It’s low in the east-southeast as the sky gets good and dark. It’s far to the lower left of Sirius, the brightest star in the night sky.

Alphard is several times as massive as the Sun, dozens of times wider, and hundreds of times brighter. And even though it’s young, it’s already nearing the end of its life.

Astronomers have measured the chemical composition of Alphard’s surface layers. Among other things, they’ve found fairly high levels of barium.

The element is produced slowly — as a by-product of the nuclear reactions that take place in a star’s core. Most stars with high levels of it have “dead” companions — the exposed cores of once-normal stars. As those stars died, they expelled their outer layers of gas. Some of the gas fell onto their companions, “polluting” their surfaces.

Alphard, though, doesn’t appear to have such a companion. Astronomers have looked for any “wiggle” in Alphard’s light as the result of a companion’s gravitational pull. But they’ve come up empty. That suggests that the barium found in Alphard must have been made in the star’s core, then found its way to the surface — creating a minor mystery for astronomers to solve.

More about Hydra tomorrow.

Script by Damond Benningfield

Abu Simbel, in southern Egypt, is a masterpiece of design and construction — times two. The temple was built more than 32 centuries ago to honor Ramses II, one of the greatest of all pharaohs. And it was rebuilt just half a century ago to save it from the Nile. Both projects were guided in part by the rising Sun.

The complex consists of two temples. One honors Ramses himself, while a smaller one honors his Great Royal Wife, Nefertari. The temples were carved into the base of a cliff above the Nile at the southern border of ancient Egypt.

Four giant statues of Ramses guard the entrance to his temple. It consists of several chambers, which reach 185 feet into the cliff. The chamber at the back is the smallest. It houses the seated figures of Ramses and the gods Amon-Re, Re-Horakhte, and Ptah.

Twice each year — on February 22nd and October 22nd — the rays of the rising Sun shine down the long hallway and into the rear chamber. The sunlight illuminates all of the seated figures except Ptah. Since he was a god of the underworld, he was intentionally left in the dark.

When a dam was built along the upper Nile in the last century, the river’s rising waters endangered Abu Simbel. So the complex was cut apart and reassembled a couple of hundred feet higher. The reconstruction maintained the solar alignment. So Ramses and the two forms of the Sun god Re still receive the Sun’s life-giving rays at the same time each year.

Script by Damond Benningfield

One of the most powerful rockets ever built made its first flight 50 years ago today. It was designed to carry cosmonauts to the Moon. Instead, it was a rocket to nowhere. All four of its test flights failed, and the remaining boosters were scrapped.

The N1 was the Soviet Union’s answer to the American Saturn 5 Moon rocket. But its development was plagued by problems. Soviet leadership didn’t provide enough money, and often meddled in the space program. The agencies that built rockets and spacecraft fought with each other, with their leaders trying to sabotage the others.

So when the first N1 stood on its launchpad in Kazakhstan, it wasn’t ready to fly. But America had already sent three astronauts around the Moon, and was planning to land on the Moon in a few months. So the Soviets didn’t want to fall too far behind.

The first stage of the N1 was powered by 30 engines, which proved to be a problem. When the first model lifted off, on February 21st, 1969, two engines shut down within seconds. Vibrations damaged another engine, which began leaking. Seconds later, another leak developed, filling the engine compartment with propellants, which caught fire. The control system shut down the other engines just 68 seconds after launch. The dead booster hit the ground two minutes later.

Three other test flights failed as well. The N1 was done — and so was the Soviet Union’s effort to send cosmonauts to the Moon.

Script by Damond Benningfield

In late 2011, physicist Rainer Weiss was checking out an instrument in Washington state that he’d helped create. It was one of two sites of LIGO — an observatory designed to “listen” for gravitational waves — tiny ripples in space-time. The project was in its early stages, and Weiss was pondering what it might find.

Weiss got what he asked for, and not just once. As of the end of last year, scientists had reported the discovery of 10 sets of merging black holes. The discoveries confirmed one of the predictions in Albert Einstein’s theory of gravity — and helped earn Weiss a share of the 2017 Nobel Prize in Physics.

Detailed analysis of the waves revealed the distances to the black holes. They also revealed the masses of the black holes, both before and after they merged. The heaviest merged black hole was about 80 times the mass of the Sun.

And scientists could be hearing the “chirp” of merging black holes more often in the future. LIGO is scheduled to return to work this month after an upgrade. It’s also working with a European project, called VIRGO. That should make it possible to detect merging black holes that are farther away. It could also allow the observatories to detect other sources of the waves — more ripples in the universe.

Script by Damond Benningfield

A buzzing insect, a speeding locomotive, and a pair of merging black holes have something in common: They all produce gravitational waves. These “wiggles” in space-time are so puny, though, that only those produced by the black holes are detectable. In fact, by the end of last year, scientists had detected the waves from 10 black-hole mergers.

Those detections were made with LIGO — a pair of observatories in Louisiana and Washington state. And the last few detections were aided by an observatory in Europe.

Gravitational waves are produced by moving objects. They’re incredibly tiny, though, so they’re incredibly hard to find. It takes a massive object moving at extremely high speed to produce waves that are big enough to detect.

Each of LIGO’s detectors consists of mirrors placed at the ends of two vacuum chambers that are more than two miles long. A laser beam is split in two and reflects back and forth off the mirrors.

If a gravitational wave passes by, it compresses one of the arms by about one ten-thousandth the width of a proton. That’s enough to be recorded by sensitive detectors. The event must be “seen” by both LIGO sites to be considered a true detection.

Merging black holes are good targets because they’re small but heavy. And just before they merge, they’re moving at a good fraction of the speed of light. That whips up space-time, producing waves that are just big enough for LIGO to record.

More tomorrow.

Script by Damond Benningfield

When you look into the night sky, all of those little pinpoints of light look pretty much the same. A few are brighter than the others, and a few show some color. But otherwise, there’s little to tell them apart.

From up close, though, it’s a different story. Consider Regulus, the bright heart of Leo, the lion. It rises below the full Moon this evening and follows the Moon across the sky later on.

To the eye alone, Regulus is simply an especially bright star. But telescopes reveal that Regulus is actually two stars — the big, bright one that we can see, plus a tiny stellar corpse known as a white dwarf. And the bright star is quite different from our own Sun; instead of being nice and round, it’s about a third bigger through the equator than through the poles.

That shape is caused by the star’s rotation: It makes one full turn every 16 hours, compared to almost a month for the smaller Sun. That rapid spin may be the result of interactions with its tiny companion.

The companion probably began life as the bigger and heavier star. Because of its greater mass, it aged more rapidly, puffing up to giant proportions. As it grew, it began dumping gas on the bright star we see as Regulus. That made Regulus heavier, causing it to spin faster. Regulus eventually took most of the other star’s gas, leaving a small white dwarf — and a star system that’s quite different from most of the others that twinkle through the night sky.

Script by Damond Benningfield

A planetary mismatch highlights the dawn sky right now, but things aren’t quite as they appear.

Venus and Saturn will pass each other over the next three days. Venus is the dazzling “morning star,” so you can’t miss it. It’ll overpower the other planet, Saturn, which looks only about one percent as bright.

That mismatch is an illusion, though. Saturn actually is by far the more impressive of the two planets. It looks more feeble because it’s about 900 million miles farther away.

Saturn is the second-largest planet in the solar system — a ball of gas more than nine times Earth’s diameter. It’s encircled by broad, brilliant rings. They consist of bits of ice, rock, and dust that reflect a lot of sunlight. The rings are so bright, in fact, that when they’re tilted at a steep angle, they just about double Saturn’s brightness.

Venus, on the other hand, is a bit smaller than Earth. It’s the second planet out from the Sun, though, so it receives and reflects a lot of sunlight. And since it’s our closest planetary neighbor, a lot of that light reaches Earth, making the planet shine brightly.

Look for Saturn standing close below Venus tomorrow, by about the width of a finger held at arm’s length. By Tuesday, the two worlds will stand side by side. And by Wednesday, Saturn will be to the upper right of Venus. Saturn will pull away from Venus on the following days, beginning a long climb across the night sky.

Script by Damond Benningfield

The big dog ambles across the southern sky on winter evenings. It’s easy to spot because its brightest star is the Dog Star, Sirius — the brightest star in the entire night sky.

But Canis Major has many stars that are even more impressive than Sirius — stars that look fainter only because they’re much farther away.

An example is Adhara, which represents one of the dog’s hind legs. It’s below Sirius as night falls. To the eye alone, it looks only a fraction as bright as Sirius. But if you could see it from the same distance as Sirius — less than nine light-years — Adhara would look about 200 times brighter than Sirius.

That’s because Adhara is both a good bit bigger than Sirius and a good bit hotter. It’s so hot that it radiates most of its energy as ultraviolet light. When you add up all the forms of energy it produces, Adhara probably is more than 30,000 times brighter than the Sun.

The star is also much heavier than the Sun. That greater heft means the star will live only a fraction as long as the Sun will. In fact, it’s already entering the final stages of life. A series of complex changes in its core will cause it to puff up like a balloon, getting much brighter as it does so.

Eventually, Adhara will explode as a supernova. That will send its outer layers racing through the galaxy at a few percent of the speed of light. Only the star’s dead core will remain — a tiny remnant of a once-mighty star.

Script by Damond Benningfield

It sounds more like bad science fiction than real science: Radiation from an exploding star kills off the biggest shark ever to inhabit the oceans. But a recent study says that could be what happened.

Researchers noted several bits of evidence to support the idea. For one thing, a series of supernova explosions beginning about eight million years ago cleared away gas and dust in our region of the galaxy, forming what’s known as the Local Bubble.

A supernova 2.6 million years ago, about 165 light-years away, created a torrent of cosmic rays — heavy particles formed in the explosion’s aftermath.

In the empty Local Bubble, the cosmic rays traveled to Earth almost unimpeded. And many of those that missed us were reflected back into the bubble by the magnetic field at its edge. The cosmic rays pelted Earth for decades.

At Earth, they rammed into particles in the upper atmosphere. That created showers of other particles, which then hit the surface. The researchers said that large creatures living in shallow coastal waters should have absorbed large doses of these particles, which could have killed them off.

The victims could have included megalodon — a relative of modern sharks that might have reached a length of 60 feet. It became extinct about the time of the possible supernova, as did many other species of life. So if this idea is correct, in the battle of Supernova versus Megalodon, victory went to the exploding star.

Script by Damond Benningfield