StarDate

The brightest star of Pegasus, the flying horse, is a bit difficult to pin down. Depending on how you define the constellation, two stars can claim the title. And one of those two changes brightness, so other stars in Pegasus can outshine it.

The brightest star in the classical connect-the-dots picture of Pegasus is known as Alpheratz. It’s in the Great Square, a pattern of four stars that outlines the horse’s body.

In the 1930s, though, astronomers drew precise boundaries for all the constellations. In this system, Alpheratz is just across the border of Andromeda, where it’s that constellation’s leading light. That leaves Pegasus with a fainter luminary: Enif, from an Arabic name that means “the horse’s nose.”

Enif is a supergiant. It’s perhaps a couple of hundred times wider than the Sun, and thousands of times brighter.

Enif doesn’t shine steadily, though. Instead, its brightness varies by a few percent. The change doesn’t follow any discernible pattern, so no one knows exactly how bright the star will appear on any given night.

And to complicate matters even more, Enif has been seen to flare several times brighter than average for brief periods. Such outbursts might be the result of giant explosions on the surface of the star. Such flares would be brighter than our entire Sun, and blast enormous amounts of particles and energy into space — briefly enhancing the brilliance of the flying horse’s leading light.

Script by Damond Benningfield

Two worlds that are a study in contrasts drop down the western sky early this evening — the Moon and the planet Jupiter. Jupiter is just below the Moon, and looks like a brilliant star.

To the eye alone, the Moon is the biggest, brightest object in the night sky. Compared to Jupiter, though, it’s an astronomical pipsqueak. It’s a ball of rock about 2200 miles in diameter — a bit more than a quarter the size of Earth. It has no atmosphere to speak of, so there’s no weather. And geologically, it’s all but dead, with only an occasional jostle from within.

Jupiter, on the other hand, is the largest body in the solar system other than the Sun — about 40 times the diameter of the Moon. It’s basically a big ball of gas. It’s topped by layers of clouds that are stretched into globe-encircling bands by the planet’s fast rotation.

These clouds form some of the most beautiful and dynamic structures in the solar system — bands and swirls that can look like Impressionist paintings.

And they include the largest storm in the solar system — the Great Red Spot. It’s wider than Earth, and it’s probably been whirling through Jupiter’s atmosphere for more than three centuries. It occasionally swallows other big storms that wander too close, adding their energy to its own — helping sustain this giant storm on a giant planet.

So keep an eye on Jupiter as it drops down the western sky after sunset, not far from the crescent Moon.

Script by Damond Benningfield

A star in Cygnus, the swan, is entering the final stages of life, so it’s starting to puff up like a giant balloon. And that’s trouble for two of its planets. Over the next couple of hundred million years, they’ll be roasted and then engulfed by the dying star.

The system is known as Kepler 56. It’s about halfway between bright Vega, which is high in the east at nightfall, and slightly fainter Deneb, the tail of the swan, to the lower left of Vega.

The star is younger than the Sun, but it’s also heavier, so it’s quickly converted the original hydrogen fuel in its core to helium — a process that will continue in the Sun for several billion years. Today, the core of Kepler 56 is quiet, with nuclear reactions taking place only in a thin shell around the core.

In response to that change, the outer layers are puffing outward, toward two planets. Both worlds are much closer to Kepler 56 than Mercury, the innermost planet in our own solar system, is to the Sun. And both are quite large and puffy — similar to the giants of the solar system.

As Kepler 56 continues to evolve, its outer layers will expand even more. As the star’s surface approaches the planets, their atmospheres will vaporize and stream off into space, leaving only their dense cores. Eventually, those bare chunks of rock and metal will fall into Kepler 56 — and the two planets will vanish from the universe.

Script by Damond Benningfield

Black holes are among the most popular objects in the universe. But they’re also among the most misunderstood. Among many misconceptions, they’re not as voracious as they’re often portrayed.

A black hole is an object with such powerful gravity that nothing can escape from it, including light. Some were born from the collapse of supergiant stars, and are several times as massive as the Sun. Millions of these objects may speckle the Milky Way galaxy.

When a star becomes a black hole, though, it doesn’t automatically suck up all the planets and other objects around it.

If the Sun were to become a black hole, for example — something that’s not possible, by the way — Earth and the other planets wouldn’t “feel” anything different. Even though the black-hole Sun would be just a few miles in diameter, Earth would continue to orbit at the same speed and distance as it does today. So would Mars and Jupiter and Halley’s Comet.

The point is that while the Sun’s size and energy output would change dramatically, its mass would remain the same, and it’s mass that determines an object’s gravitational pull, not its size.

Objects that got too close to the black hole would be torn apart, and their remains would form a hot disk. As this material spiraled into the black hole, it would get extremely hot, so it would glow brightly. Beyond that close range, though, the rest of the solar system would go on as before — undisturbed by the nearby black hole.

Script by Damond Benningfield

In the movie “Galaxy Quest,” a starship is powered by a sphere of beryllium, one of the lightest chemical elements. That may be strictly Hollywood fantasy, but beryllium is an important component in many spacecraft.

Beryllium comes in several forms, but only one of them is stable. That form is produced between the stars, when cosmic rays zap atoms of heavier elements, splitting the atoms apart.

A tiny bit of beryllium was incorporated into Earth’s crust. And it has a lot of uses. It’s combined with copper or other elements, for example, to make alloys that are especially strong and durable.

Beryllium doesn’t block X-rays or most other forms of radiation, so it’s used in many scientific settings. It forms the pipes that surround the particle beams in the Large Hadron Collider. When the particles in those beams ram together, the radiation and particles they produce pass right through the pipes so they can be recorded by scientific instruments.

Beryllium also frequently finds its way into space. It’s used in some rocket nozzles, and was a key component in the brakes and windshields of the space shuttles.

And because it doesn’t expand or contract much as it changes temperature, it’s also great for the mirrors of space telescopes. All the mirrors aboard Spitzer Space Telescope are made of beryllium, and so are the giant mirrors of the new James Webb Space Telescope — “powering” the continued exploration of the universe.

Script by Damond Benningfield

Oxygen is one of the most important elements on Earth. It makes up about one-fifth of the mass of the atmosphere, nine-tenths of the mass of water, and two-thirds of the mass of the human body. It’s a by-product of plant life, and a necessity for animal life. And it combines with other elements to make everything from water to rocks.

All of the oxygen atoms on Earth — and throughout the universe, for that matter — were made by stars.

When a star is born, it’s made mainly of hydrogen, the simplest chemical element, which was forged in the Big Bang. For most of its life, the star fuses the hydrogen in its core to make helium. At the end of its life, a star as massive as the Sun or heavier fuses the helium to make heavier elements. A star like the Sun makes carbon and oxygen, while heavier stars make even more elements — all the way up to iron.

Over the 14-billion-year history of the universe, stars have made more oxygen than any other element, so it now accounts for about one percent of all the atoms in the universe.

When a star dies, it expels much of its gas into space. Stars like the Sun do so in a fairly gentle process, creating beautiful clouds that eventually dissipate. More massive stars do it more explosively, blasting out debris at a few percent of the speed of light. This mixture of elements can then be incorporated into new stars and planets — and at least in the case of our own Earth, into living organisms as well.

Script by Damond Benningfield

It’s lonely out here in the galactic suburbs. The closest neighbors are light-years away — distances that are truly astounding. The distance to the Sun’s nearest stellar neighbor, Proxima Centauri, is almost 29 million times the Sun’s diameter. At that same scale, if you live in a house that’s 50 feet wide, your nearest neighbor would be more than a quarter-of-a-million miles away — farther than the Moon.

That’s a pretty typical gap between star systems in this part of the galaxy — although not necessarily between individual stars. While the Sun is alone, many other stars have close companions. Proxima Centauri, for example, belongs to a system of three stars.

The space between the stars isn’t completely empty. It contains wisps of hydrogen and helium gas, plus a tiny smattering of heavier elements. On average, there’s about one atom of gas for every cubic centimeter of space.

There’s a lot more stuff packed together in the giant clouds known as nebulae. If they have enough gas and dust, they can give birth to new stars. Even so, by earthly standards a nebula still qualifies as a hard vacuum.

The stars are all following their own orbits around the center of the galaxy, so over time, the distances between them varies. In 10,000 years, for example, Proxima Centauri will no longer be our closest neighbor. Instead, it’ll be Barnard’s Star, at just 3.8 light-years — about half a light-year closer than Proxima Centauri is today.

Script by Damond Benningfield

It’s a long way from Earth to the center of the galaxy. But the exact distance is uncertain — measurements vary by several thousand light-years.

The most accurate method of measuring astronomical distances is called parallax. To understand how it works, hold out a finger and look at it with first one eye, then the other. The finger appears to shift against the background. The angle of the shift reveals how far the finger is from your eyes.

Astronomers determine parallax by looking at an object when Earth is on opposite sides of the Sun. The change in position causes a target to shift a tiny bit compared to the background of more-distant objects.

As the distance increases, though, the angle gets smaller. Eventually, it gets so small that it’s almost impossible to measure. That’s especially true when you’re looking through Earth’s atmosphere, which blurs the view. New technology has sharpened the view, but there’s still a lot of wiggle room in the measurements.

Another technique looks at how certain stars change in brightness. There’s a relationship between the length of each brightness cycle and the star’s true brightness. But clouds of dust between Earth and the center of the galaxy absorb a lot of light, complicating the measurements.

So when you take all the difficulties into account, different studies yield a distance of between about 24,000 and 28,000 light-years away — a long jaunt any way you look at it.

Script by Damond Benningfield

Black widows lurk among the stars. They slowly destroy their companions, ingesting part and sweeping away the remains.

These nasty-sounding objects are pulsars — the spinning corpses of once-mighty stars that blasted themselves apart. All that’s left is their crushed cores, known as neutron stars. Some neutron stars spin, emitting beams of energy that sweep across the cosmos like a lighthouse. From Earth, we see such a beam as on-and-off pulses — hence the name “pulsar.”

Some pulsars have companions — “normal” stars like the Sun, or perhaps the “failed” stars known as brown dwarfs. Radiation from the pulsar heats the companion, causing it to puff up and lose its grip on the hot gas at its surface. Some of the gas is pulled in by the pulsar, causing it to spin faster — up to hundreds of times per second.

But pulling material off the surface of its companion is only half of the story of a black widow.

In some cases, the pulsar’s radiation also erodes the surface of its companion like a blowtorch, with gas streaming away from the pulsar. Over time, the combination of accretion — pulling material into the pulsar — and erosion — blasting stuff away from the pulsar — can completely destroy the companion.

So far, astronomers have caught only a handful of black widows in the process of destroying their companions. But they suspect that many more have already finished the deed — dead stars that have devoured their mates.

Script by Damond Benningfield

The objects known as brown dwarfs are oddballs. They’re heavier than planets, but not heavy enough to trigger the nuclear reactions that would make them shine as true stars. In fact, they’re often described as failed stars.

Yet they share some traits with both stars and planets. Like stars, their surfaces are hot, with temperatures of up to several thousand degrees. But like planets, those surfaces may be topped by layers of clouds and giant storms.

Astronomers have discovered “weather” on the surfaces of several brown dwarfs. They can’t actually see the clouds and storms. But they know they exist because the brown dwarfs get fainter and brighter in different wavelengths as they rotate. The sometimes-dramatic change in brightness indicates that the surface of a brown dwarf consists of layers of clouds with embedded storm systems.

The clouds and storms are quite different from those on Earth, though. The clouds are so hot that they’d be made of small particles of iron or silicon, not water. And the storms might be a lot like Jupiter’s Great Red Spot — cyclones big enough to swallow an entire planet.

Indeed, a stormy brown dwarf might look a lot like Jupiter, with bands of clouds circling all the way around it, and big storms whirling through the clouds. But the brown dwarf would also provide its own inner glow — its heat would make it shine dull red or orange, with the clouds forming dark bands across its stormy surface.

Script by Damond Benningfield