StarDate

The bull’s long, V-shaped face stands about a third of the way up the western sky at nightfall. The bright star Aldebaran marks the bull’s eye. But the rest of the face is outlined by the Hyades, a stellar family that’s closer than any other star cluster — about 150 light-years.

The cluster is quite young — probably between 625 million and 750 million years old. By comparison, the Sun is about four and a half billion years old.

The Hyades contains a few hundred stars. They’re all packed into a ball that’s about 65 light-years across. Quite a few other stars are just outside that ball. They probably were born with the cluster, but were pushed away by encounters with other members of the Hyades. They’re no longer bound to the cluster by their gravity. So over time, they’ll drift farther from their stellar birthplace.

The biggest, brightest members of the Hyades have already expired — they were so massive that they guzzled their nuclear fuel in a hurry. The biggest remaining members of the cluster are a bit more than twice as massive as the Sun. They’ve puffed up to giant proportions, and soon will shed their outer layers, leaving only their hot, dead cores.

So as time goes on, the Hyades will be left with fewer and fainter stars. Eventually, all but a few of them will drift away from the cluster. And those that remain will be fairly small and faint, so the bull will lose its bright face.

We’ll have more about the Hyades tomorrow.

Script by Damond Benningfield

Under an especially dark night sky, away from city lights, you might see a few thousand stars. All of them belong to our home galaxy, the Milky Way. But not all of them were born in the Milky Way. It’s likely that some of them were born elsewhere, but the Milky Way swallowed their home galaxies, making the stars its own.

In fact, astronomers recently announced the discovery of 11 streamers of stars in the Milky Way that are remnants of other galaxies. The streams were created when smaller galaxies flew too close to the Milky Way and were captured by its powerful gravity. The Milky Way ripped the galaxies apart, turning the agglomerations of stars into streamers that can span thousands of light-years.

Incorporating the stars of other galaxies has helped the Milky Way grow to giant proportions. Astronomers had already discovered the remains of a couple of dozen small galaxies ingested by the Milky Way. Several other small galaxies are so close to the Milky Way that they’re likely to be pulled in as well.

The new streamers were discovered by the Dark Energy Survey. It uses a giant camera to photograph the entire sky. The goal is to help astronomers understand the cause of dark energy, which is causing the universe to expand faster as it ages. But the survey’s images allow astronomers to study a lot more than just dark energy. In this case, they revealed the new streamers of stars — the remains of small galaxies that are now part of our own.

Script by Damond Benningfield

Every spacecraft that visits one of the planets reveals new details about its target world. Juno, for example, is telling scientists that the interior of Jupiter is quite different from what they expected.

Juno arrived at Jupiter almost two years ago. It’s the ninth spacecraft to visit the planet, and the second to orbit it.

The craft has snapped some great pictures of Jupiter. But its main goal is to study what’s far below the planet’s surface. It’s doing so by measuring Jupiter’s gravitational and magnetic fields. That should help scientists piece together a picture of Jupiter’s insides — especially its core.

Most models of Jupiter say the core is a ball of rock and metal up to about 10 times as heavy as Earth. Other models say there’s no need for a solid core at all. Which model is right can reveal how Jupiter took shape.

But Juno’s early observations say that all the models are off — the core may be bigger and fuzzier than expected. It could be up to a couple of dozen times Earth’s mass. And it could be dissolving in the layer of metallic hydrogen around the core. If so, then the core could take up a third to a half of Jupiter’s diameter, making it far bigger than anticipated.

Each orbit around Jupiter helps Juno provide a sharper picture of the interior of the solar system’s largest planet.

And Jupiter is putting in a good appearance tonight. It rises below the Moon before midnight, and looks like a brilliant star.

Script by Damond Benningfield

Two planets are staging a beautiful conjunction in the dawn sky. Mars and Saturn are in the south at first light, separated by just a couple of degrees — the width of a finger held at arm’s length. Saturn is to the upper left of slightly brighter Mars. They’ll be at their closest tomorrow, but will stay close together for several days as Mars begins to pull away from Saturn.

Saturn and Mars look much alike right now, but that’s an illusion. The two worlds could hardly be more different.

Mars is a ball of rock a bit more than half the diameter of Earth. It has a thin atmosphere, and its surface is coated with orange dust that gives the planet an overall reddish appearance — hence its nickname, the Red Planet.

Saturn is a ball of gas that’s almost 10 times Earth’s diameter. Clouds atop its thick atmosphere give the planet an overall pale golden color. Saturn rotates so fast that it’s a bit flattened, like a squashed beachball.

What really sets Saturn apart, though, is its rings. The main rings span almost the distance between Earth and the Moon. They’re only a few yards thick, but they’re made of particles of ice and dust that reflect a lot of sunlight. So at the right angle, the rings can contribute almost as much light as Saturn itself.

And while Mars has only two small, insignificant moons, Saturn has more than 60, including several that are interesting in their own right — worlds of rock and ice orbiting a solar-system giant.

Script by Damond Benningfield

Finding your way to the other bodies of the solar system is a tough chore. They’re a long way away, they’re relatively small targets, and they’re in constant motion. So it helps to have some navigational beacons to guide you.

One of those beacons is the Sun — the brightest object in the sky. And for many spacecraft, another is Canopus, the second-brightest star in the night sky. It’s a long way from the Sun, so tracking both objects allows a craft to triangulate its position. That provides a precise track of its location in space.

Canopus would make a good navigational beacon for any civilization within a thousand light-years of it. That’s because it’s extremely bright — more than 10 thousand times brighter than the Sun. So even though it’s more than 300 light-years away, it outshines all the other stars except Sirius, which is less than nine light-years away.

Canopus shines so bright because of its size and surface temperature. It’s about 70 times the Sun’s diameter, and its surface is thousands of degrees hotter. The combination makes Canopus one of the most impressive stars in our part of the galaxy.

And Canopus is also a good beacon for skywatchers in the far south of the United States — south of about Dallas or Little Rock. Right now, it stands just above the southern horizon about an hour and a half after sunset. It’s almost directly below Sirius, which is much higher — a lineup of the two brightest stars in the night sky.
 

Script by Damond Benningfield

Sirius, the brightest star in the night sky, arcs across the southwest on March nights. It’s low in the south at nightfall, and wheels westward later on. Not only is it especially bright, it’s also especially twinkly — it shifts from blue to red to white in the blink of an eye.

Sirius is visible from most of Earth’s surface — all but the high Arctic. But the second-brightest star has a more limited range. Canopus is a stunner from the southern hemisphere, but north of the equator it’s tough to see. You have to be south of about San Diego or El Paso to find it. And even then it never climbs more than a few degrees above the horizon.

Canopus itself is quite a bit more impressive than Sirius. It’s far larger and more massive, and about 500 times brighter. But it’s also close to 300 light-years farther, so it can’t quite match Sirius’s luster.

Canopus is at the end of its “normal” lifetime, so it’s quite puffy. If it took the Sun’s place in our own solar system, it would extend all the way out to Mercury. But no one is quite sure whether it’s getting even bigger, or if it’s starting to “deflate” after going through a puffier phase. Either way, Canopus will continue to shine brightly in Earth’s night sky — even if not everyone can see it.

If you’re far enough south, look for Canopus quite low in the south beginning as darkness begins to descend. The star is due south around 9 p.m., almost directly below Sirius.

More about Canopus tomorrow.
 

The Moon cozies up to the star Regulus tonight — the bright heart of Leo, the celestial lion. At their closest as viewed from most of the U.S., they’ll be separated by just a whisker.

We see Regulus as a single point of light. But it appears to consist of at least four stars. One of them is big and bright — the only one visible to the eye alone. A second one is a dead star. It’s so faint, and so close to the bright star, that it wasn’t discovered until this century.

The other members of the system are far away from the bright star — roughly 5,000 times the distance between Earth and the Sun. Astronomers deduce that they’re tied to the bright star because they’re the same distance away from us, and they’re moving at the same speed and in the same direction.

The stars haven’t received a lot of attention, though, so we don’t know a whole lot about them. And what is known has a fairly high level of uncertainty.

One thing astronomers are pretty sure of is that the stars form a binary — they’re tied to each other by their gravitational pull. Even so, they’re not close — they’re separated by about 600 times the Earth-Sun distance.

The brighter of the two stars, known as Regulus B, is a little less massive than the Sun, and only about half as bright. The other, Regulus C, is perhaps a third of the Sun’s mass. That makes it only a few percent as bright as the Sun — a feeble companion to the lion’s brilliant heart.

Script by Damond Benningfield

In the 1969 novel “The Andromeda Strain,” microbes from beyond Earth attach themselves to an orbiting satellite. When the satellite returns to Earth, the microbes kill several people and threaten everyone on the planet. A special team of scientists is called in to save the day.

Real scientists are pondering similar scenarios. They’re looking at how to protect Earth from possible microbes from Mars and other worlds — and to protect those worlds from Earthly germs. Many of those scientists are meeting in Houston this week to discuss their work.

NASA already takes steps to protect other worlds from contamination. When the Cassini mission to Saturn was ending, for example, the craft was destroyed by having it plunge into Saturn’s atmosphere. That kept it from accidentally hitting some of Saturn’s moons, which could be homes for microscopic life. And some possible landing sites for the Curiosity Mars rover were ruled out because they were spots where microbes might be found — or where microbes carried from Earth might survive.

The concerns will grow bigger as robotic probes bring samples of Mars to Earth — and, perhaps, as people travel to the Red Planet. Humans carry a lot of “bugs,” so they could easily contaminate Mars, making it difficult to find Martian life. And they could bring back Martian germs. So explorers will have to be examined carefully to make sure they don’t bring home a real-life “Andromeda Strain.”

Script by Damond Benningfield

A supermassive black hole appears to be “blowing out the candles” in its home galaxy. It’s producing a strong wind that’s blowing away the gas around it, shutting down the birth of new stars.

A team led by Shelley Wright of the University of California-San Diego used telescopes on the ground and in space to study a galaxy known as 3c 298. It’s more than nine billion light-years away. That means we see the galaxy as it looked more than nine billion years ago, when the universe was just a third of its present age. And the galaxy is merging with a smaller galaxy.

The heart of 3c 298 contains a black hole that’s a few billion times the mass of the Sun. The black hole is surrounded by a disk of gas that’s spiraling into the black hole. As it gets close, the gas is heated to extreme temperatures, so the disk shines brilliantly. That creates a quasar — one of the brightest objects in the universe.

Observations of 3c 298 show that huge amounts of gas are moving away from the quasar — enough to make thousands of Sun-sized stars every year. The gas appears to be pushed by jets of particles that are shooting out from the poles of the black hole. The jets create strong winds that blow through the entire galaxy. At least for a while, this “feedback” from the black hole will limit the number of stars that are born in the heart of this young, busy galaxy.

Script by Damond Benningfield

Eighteenth-century astronomer William Herschel described the star system known as Beta Monocerotis as “one of the most beautiful sights in the heavens.” It’s one of the hidden beauties of Monoceros, the unicorn. The constellation is well up in the southeastern sky in early evening, between two bright stars: the “little dog” star Procyon, and Betelgeuse, the orange shoulder of Orion.

There’s not much to see in Monoceros with the eye alone. But telescopes reveal a bounty of beautiful sights. And Beta Monocerotis straddles both domains. It’s faintly visible to the unaided eye as one of the unicorn’s two brightest stars. But to see the same beauty that Herschel did, you need a telescope. That view reveals three stars, not one, all with a lovely blue-white color.

The color comes from the temperatures of the stars — their surfaces are many thousands of degrees hotter than the Sun’s. And all three stars also are much more massive than the Sun. That great heft revs up the nuclear reactions in their cores, which is what makes their surfaces so hot. It also makes the stars extremely bright — up to about 3200 times as bright as the Sun. That makes them visible across 700 light-years of space.

The two faintest members of the system probably form a wide binary, with the brightest of the three stars orbiting around them. Combined, they make Beta Monocerotis a beautiful skywatching sight — a vision in blue on a chilly winter’s night.

Script by Damond Benningfield