StarDate

A mission known as NeoWise is scanning the solar system for asteroids whose orbits come close to Earth’s — asteroids that could someday endanger our planet. That wasn’t the craft’s original mission, though. Originally known as WISE, it was designed to study the infrared glow of galaxies, gas clouds, and other objects. When it used up its coolant, two of its cameras shut down. But two others still worked, so scientists gave it the new job.

NeoWise isn’t the only scientific spacecraft to get a new mission.

The Kepler space telescope, for example, spent about three years looking for planets around 150,000 target stars in a single patch of sky. But part of its pointing system failed. So scientists came up with a new mission, called K2. It allowed the craft to peer at different patches of sky for a few months at a time — and discover hundreds of new planets.

Deep Impact watched what happened when it fired a small cannonball into Comet Tempel 1. After that, it was renamed Epoxi and sent toward another comet. Along the way, it kept an eye on several stars with known planets — an effort to learn new details about those worlds.

And another mission, Stardust, captured grains of dust from yet another comet. It swung past Earth to drop off the comet dust, then began its new mission. Known as Next, it flew past Comet Tempel 1 — the same one hit by Deep Impact — to see how the comet had changed — a new job for an old spacecraft.

Script by Damond Benningfield

Omega Centauri is an intimate place for stars. The cluster contains millions of stars packed into a ball a few dozen light-years across. On average, the planets in its core are separated by just one-sixth of a light-year. By comparison, the closest star system to the Sun is more than four light-years away. That means the skies of any planet in the cluster would be ablaze with stars.

A recent study, though, found that it’s unlikely that anyone is there to enjoy the view.

The team was led by Stephen Kane of the University of California-Riverside. It used Hubble Space Telescope to study almost a half-million stars in the center of Omega Centauri, which may be the core of a small galaxy that was consumed by the Milky Way.

The researchers calculated the habitable zone of each star — the distance from the star where conditions are best suited for life. They then calculated the interactions between stars.

They found that, on average, each star passes especially close to a neighbor every million years or so. The pull of the passing stars would make the habitable zones unstable — a planet could be pulled out of the zone. So it would be tough for life to form in the core of Omega Centauri — and just as tough for it to survive.

Omega Centauri is bright enough to see with the unaided eye. But you need to be in the southern third of the U.S. to find it. Right now, it’s quite low in the south about 11 p.m. It looks like a fuzzy star.

Script by Damond Benningfield

Centaurus A is the fifth-brightest galaxy in the night sky, so it’s an easy target for telescopes and binoculars. But it’s what they can’t see that makes Centaurus A one of the most interesting galaxies around.

Images of the galaxy show a bright blob of stars with wide, dark dust lanes in front of it. That suggests that Centaurus A is the result of a recent merger between two galaxies. New stars are being born in bunches along the dust lanes.

In 1949, radio astronomers found that the galaxy was one of the “loudest” around. The radio waves come from the galaxy’s core and from “jets” that shoot into space above and below the core. They’re almost two million light-years long.

The radio waves are powered by a black hole that’s probably about 55 million times the mass of the Sun. Gas is funneled toward the black hole, perhaps as a result of the merger. As it spirals toward the black hole, it’s heated to millions of degrees. That rips atoms apart, giving them an electric charge. Powerful magnetic fields around the black hole then fling some of the particles out into space, causing them to emit radio waves.

As seen from the United States, Centaurus A stands almost due south as night falls now. It’s best viewed from south of about Dallas or Albuquerque, where it stands a little higher in the sky. Through binoculars, the galaxy looks like a hazy patch of light. It’s just a few degrees above Omega Centauri, a bright star cluster. More about that tomorrow.

Script by Damond Benningfield

Like a bear that spends part of its time in hibernation, the Sun goes through cycles of more and less activity. It’s at its most active every 11 years, when it produces large numbers of magnetic storms — dark sunspots and bright flares. And it’s least active about half way between peaks. It’s in one of those quiet cycles right now.

Other stars go through their own magnetic cycles. Two of the best known are Alpha Centauri A and B. They’re just four-and-a-third light-years from Earth. Only their smaller companion, Proxima Centauri, is closer to us.

Star A is a bit bigger and heavier than the Sun. Star B is a little smaller and lighter than the Sun.

X-ray telescopes in space have been watching the system for years. Over the last decade, in fact, Chandra X-Ray Observatory has looked at the system twice a year. Those observations have helped show that both stars have their own magnetic cycles. Star A’s cycle appears to last about 19 years, while B’s is only about eight years.

Chandra also found that any planets around the stars receive relatively low doses of X-rays — good news for any life at Alpha Centauri.

The system is in the constellation Centaurus, which is wheeling quite low across the southern evening sky. To the eye alone, its stars look like a single pinpoint — the third brightest in the night sky. But the system is quite far south. So from the U.S., it’s visible only from Hawaii and far-southern Texas and Florida.

Script by Damond Benningfield

When Apollo astronauts orbited the Moon, they had some quiet time. When they passed behind the Moon, the Moon’s bulk blocked radio chatter from Earth.

That quietness could be good for astronomy in the decades ahead. Radio telescopes on the lunar farside could study the early days of the universe, when the first stars and galaxies were being born.

Astronomers have studied the possibility of placing telescopes on the Moon for decades. Better technology has made it easier to send telescopes into space, though, reducing the need for lunar telescopes.

But one area where the Moon might still have an advantage is studying long radio waves. Earth’s atmosphere blocks some of these waves. And satellites, cell phones, and other technology creates interference.

Astronomers are interested in these waves because they were emitted by the first stars and galaxies, when the universe was less than a billion years old. The expanding universe has stretched them to much longer wavelengths.

Radio telescopes on the Moon could catch these waves. The telescopes would consist of arrays of long antennas spread across many miles. Shielded from terrestrial interference by the Moon, they could provide new insights into the birth of the stars.

Look for the Moon and a bright companion the next couple of mornings. The planet Saturn will be close to the upper left of the Moon at first light tomorrow, and closer to the right of the Moon on Thursday.

Script by Damond Benningfield

The giants of the solar system flank the Moon tonight. Jupiter, the largest planet, rises to the upper right of the Moon late this evening. It looks like a brilliant star. And the second-ranked planet, Saturn, follows them in the wee hours of the morning, well to the lower left of the Moon. It’s not nearly as bright as Jupiter, but there aren’t any other bright stars or planets around it, so it should stand out.

Although both planets are big and heavy, they’re a bit puny compared to some planets found in other star systems. Some of those are many times as massive as Jupiter. Yet none of them is much bigger than Jupiter. It seems that Jupiter is near the “sweet spot” for the sizes of giant planets.

That’s thanks to gravity. A more-massive planet has more stuff, which you’d expect to make it bigger as well. But the extra material also adds to the planet’s gravitational pull, which squeezes it more tightly. That makes it shrink.

And as it shrinks, the planet’s interior gets hotter. At about a dozen times the mass of Jupiter, it gets hot enough that the object is classified as a brown dwarf — an intermediate step between planets and stars. And at about 80 times Jupiter’s mass, the object’s core gets hot enough to ignite nuclear fusion — and shine as a star. Even then, though, it’s not much bigger than Jupiter itself — it’s at the “sweet spot” for big planets, brown dwarfs, and small stars.

More about the Moon and Saturn tomorrow.

Script by Damond Benningfield

Jupiter is named for the king of the gods of ancient Rome. The planet earned the name because it’s one of the brightest objects in the night sky, and because it moves across the sky at a regal pace.

And today, we know just how appropriate the name is. Jupiter is the largest and heaviest of all the planets — more massive than all the other planets put together. And it lords over the largest entourage of known moons. A discovery announced earlier this year, in fact, brought the total to 79.

The new moons were discovered by a team led by Scott Sheppard, who’s been involved in the discoveries of more than half of Jupiter’s moons. The new batch included 10 moons, which were added to a couple of others announced last year.

Most of the new moons are far from Jupiter, so it takes them a couple of years to orbit the planet. They’re quite small, and they orbit in the opposite direction from the way Jupiter spins on its axis. They probably are fragments of one or more larger moons that were blasted apart by collisions with other moons — adding to the amazing empire of the king of the planets.

And Jupiter is especially easy to find the next couple of nights because it’s quite near our own moon. The planet looks like a brilliant star. It’s to the lower left of the Moon as they climb into good view late this evening, and about the same distance to the upper right of the Moon tomorrow night.

More about the Moon and planets tomorrow.

Script by Damond Benningfield

We got our final look at Hubble Space Telescope 10 years ago this weekend. Astronaut Megan McArthur released it from the robotic arm of space shuttle Atlantis. That completed almost a week of orbital repairs and upgrades.

The crew of Atlantis conducted five spacewalks during Hubble’s final service call. The astronauts installed a new camera and a new spectrograph, which studies the universe at ultraviolet wavelengths. And they repaired two failed instruments.

The astronauts also replaced Hubble’s 18-year-old batteries, and installed six new gyroscopes to keep it pointed in the right direction. And they did additional repairs and upgrades to return it to tip-top shape.

The mission was one of the most complicated in shuttle history. The delicate operations required many months to plan and rehearse. And astronauts and ground crews had to improvise when things didn’t go according to plan. Mission Control praised the astronauts as the shuttle landed.

A decade later, three of the new gyros have failed, and Hubble is showing other signs of its age. Even so, it continues to expand our knowledge of the universe more than a quarter century after its launch.

Script by Damond Benningfield

The eyes of the dragon shine a third of the way up the northeastern sky at nightfall now. Eltanin is the brightest star of Draco, with third-ranked Rastaban just above it. They circle high across the north during the night, and stand in the northwest at first light.

Although Eltanin looks brighter than Rastaban, it’s only because of their different distances. Eltanin is about 150 light-years away, while Rastaban is at 380 light-years. So if you lined them up side by side, Rastaban would shine several times brighter than the dragon’s other eye.

Rastaban is only about 65 million years old, compared to four and a half billion years for the Sun. Yet it’s already passed the end of its “normal” lifetime. That’s because it’s about six times as heavy as the Sun. Such massive stars “burn” through their nuclear fuel at a frantic rate. So Rastaban has already converted the hydrogen in its core to helium. Now, it’s probaby getting ready to ignite the helium to make carbon and oxygen.

That’s caused the star to puff up — it’s about 40 times the diameter of the Sun. That’s the main reason it looks so bright — there’s a lot of surface area to beam light out into space.

Eventually, the nuclear reactions in the core will stop. The star’s outer layers will puff out into space. That will leave only the dead core — a cosmic ember as heavy as the Sun but only as big as Earth — the final stage for one of the dragon’s bright eyes.

Script by Damond Benningfield

The Space Race was all about politics. Both the United States and the Soviet Union were trying to impress the rest of the world with their technological prowess. Without that race, though, we\'d know a lot less about the worlds of the solar system.

Consider Venus, our closest planetary neighbor. The Soviets launched almost a score of successful Venus missions. And 50 years ago this week, two of those craft parachuted through Venus’s atmosphere. They told us a lot about the layers of clouds that blanket Venus, and about the clear skies below them.

Venera 5 entered Venus’s atmosphere on May 16th, 1969, with Venera 6 following it the next day.

Both of them drifted toward the surface for almost an hour. They measured temperatures, pressures, and the sky’s brightness. They also measured the composition of the atmosphere — mostly carbon dioxide, with a little nitrogen, water vapor, and other components.

Venera 5 descended to about 15 miles before it was killed by the intense temperature and pressure — more than 600 degrees at that altitude, with a pressure of about 25 times the surface pressure on Earth. And Venera 6 survived down to about seven miles. They provided a good profile of conditions in Venus’s atmosphere — observations made possible by the Space Race.

And Venus is in view in the dawn sky right now, although it’s getting ready to disappear. It’s the “morning star,” quite low in the east about a half hour before sunrise.

Script by Damond Benningfield