StarDate

Anything that’s in Earth orbit faces the constant threat of radiation – energy and charged particles from the Sun and beyond. It can cause instruments to glitch or fail, and even destroy a satellite. And it poses a health risk for astronauts.

The threat is greatest in a zone in the southern hemisphere – the South Atlantic Anomaly. It covers several million square miles above South America and South Atlantic Ocean. It’s a weak spot in Earth’s magnetic field that allows intense radiation to penetrate closer to the surface. And it’s getting bigger.

The magnetic field can deflect many of the charged particles that bombard our planet. That protects orbiting satellites and astronauts. It also protects the surface from power blackouts and other effects.

But the field is offset a bit from the center of the planet. It extends a little farther into space in some regions, but dips closer to the surface in others. And the South Atlantic Anomaly is the biggest dip of all. Spacecraft that are passing through the region often have to switch off some of their instruments to protect them from the harsh radiation.

A recent study found that the anomaly has gotten bigger over the past decade – by about half the area of continental Europe. So the space above that part of Earth is getting nastier – a bigger “danger zone” in the southern hemisphere.

We’ll have more about radiation hazards tomorrow.

Script by Damond Benningfield

To the eye alone, the Pleiades cluster looks like a small dipper of about seven stars – a few more if you have nice, dark skies. But when Galileo Galilei looked at it with his first small telescope, he saw a few dozen stars. It was one of the first indications that there’s far more to the universe than meets the eye.

You can share Galileo’s view with a basic pair of binoculars – no telescope required. They’re especially helpful tonight because of the Moon. It passes through the outskirts of the cluster, so it points the way. But the moonlight makes it tougher to see the stars.

The Pleiades is a family of perhaps a couple of thousand stars. The stars were all born together, from the same cloud of gas and dust. That makes the cluster a good laboratory. Since the stars all started with the same mix of elements, any differences among them are the result of their evolution – changes within the stars themselves. That helps astronomers understand how all stars change over the eons.

The cluster probably is a little more than a hundred million years old. That means it’s completed only about half an orbit around the center of the galaxy. During that time, it’s lost many of its original stars. And before it can complete one full orbit from its current location, it’s likely to evaporate – pulled apart by the gravitational tug of the rest of the galaxy.

Tomorrow: a growing “danger zone.”

Script by Damond Benningfield

Stars aren’t always nice to their offspring – especially at the end. As a star dies, it expands. It can get big enough to engulf some of its planets. The Sun, for example, is likely to swallow Mercury and Venus, and might get Earth as well.

A star in Cygnus might have engulfed one of its planets fairly recently. Two others might be doomed as well.

Kepler-56 isa red giant – a dying star that’s much bigger than the Sun. It has three known giant planets. Two of them are quite close in, so they may not survive the star’s final act.

Kepler-56 is rotating much faster than most red giants. And vibrations at the surface reveal that its core and its outer layers are spinning at different rates and angles. There are several possible reasons for this odd behavior. One is the gravitational influence of the close-in planets. Another is that the star might have swallowed a planet early on.

A recent study suggested something else: The star might have swallowed a planet fairly recently. The planet would have been about as massive as Jupiter, the giant of our own solar system. As it plunged in, its orbital momentum spun the star up. So Kepler-56 isn’t being kind to its offspring as its own life comes to an end.

Kepler-56 is in the east-northeast at dawn. It’s half way between Deneb, Cygnus’s brightest star, and even brighter Vega. But Kepler-56 is too faint to see without a telescope.

Script by Damond Benningfield

Things sometimes flash in the night sky. That includes some weird and wonderful astronomical objects. Some of them shine for a few minutes or even seconds, then vanish. So it can be tough to understand just what caused them.

Thousands of these “transients” showed up in a decade-long look at the night sky. And a recent study found a statistical link between some of those transients and both nuclear weapons tests and reports of UFOs.

The study analyzed thousands of nights of observations by the Palomar Sky Survey. From 1949 to 1958, astronomers repeatedly photographed the night sky on glass plates, looking to compile the best map of the heavens to date. Many of the plates revealed transients that were star-like pinpoints of light.

They appeared out of nowhere, then disappeared just as quickly.

The study found that, on average, the number of transients was greater on nights just after above-ground nuclear explosions. And there were more reports of UFOs on nights with more transients.

There are many possible explanations. There could be problems with the original plates, for example. The nukes could’ve created some previously unknown effects in the atmosphere. The study also says the flashes could have been metallic objects far above our planet – perhaps even visitors from other worlds.

But many scientists say we need a much more thorough look at the pictures before we’ll know what caused these flashes in the night sky.

Script by Damond Benningfield

Long-term missions to the Moon and Mars will need a good understanding of the machines, the environment – and the people. Friction among crew members could make a mission much less productive – or even endanger lives.

To minimize the risk, scientists are trying to understand how people get along during long periods of isolation. They’ve conducted test runs in laboratories. They’ve set up habitats on volcanoes and remote islands. They’ve studied research bases in Antarctica. And they’ve sent volunteers into the oceans.

As with space travel, an undersea habitat is isolated and cramped, and the environment can be deadly. So it’s important for the crew to get along.

NASA has conducted quite a few underwater expeditions. For many of them, astronauts spent a few days or weeks in a habitat off the coast of Florida. They conducted experiments both inside and outside the lab. They tested equipment and techniques that might be used in space. And scientists checked out how well they worked as a team.

Recently, the European Space Agency sent 25 volunteers on a two-month trip aboard a submarine. Scientists used questionnaires to check on the volunteers. They also took samples of hair and saliva. The results helped track stress markers, changes in the immune system, and other reactions – better understanding the human factor in long-term missions to other worlds.

Script by Damond Benningfield

If you stepped off a spacecraft onto the surface of Titan, you might experience a little dŽjˆ vu. Saturn’s largest moon has many of the same features as Earth. That includes rivers and seas, clouds, and even rainfall – it’s the only world in the solar system other than Earth with bodies of liquid on its surface.

What wouldn’t seem familiar is the temperature – almost 300 degrees below zero Fahrenheit. In that icebox, water is frozen as hard as granite. So Titan’s rivers and seas and clouds are made of liquid methane and ethane.

Titan is a large world – about half-again the diameter of our moon. And it has the densest atmosphere of any moon in the solar system; the surface pressure is equivalent to a depth of 50 feet in Earth’s oceans.

The methane and ethane are quickly broken apart by sunlight, so the supply in the air has to be renewed. The most likely source is cryo-volcanoes – volcanoes that belch frozen water. Methane mixed with the water would waft into the atmosphere.

The volcanoes could be fed by an ocean of liquid water below the surface – perhaps much more water than in all of Earth’s oceans combined. Both the ocean and the liquid bodies on the surface are possible homes for microscopic life – one more similarity to our own world.

Saturn looks like a bright star near the Moon this evening. Through good binoculars or a small telescope, Titan looks like a tiny star quite near the planet.

Script by Damond Benningfield

The planet Mercury is putting in a decent appearance in the evening sky now. It looks like a bright star low in the west during twilight. And tonight it has a prominent companion: the crescent Moon. In fact, they’ll look like they’re almost touching each other.

Mercury is tough to see because it’s the closest planet to the Sun. Because of that, it never moves far from the Sun in our sky. At best, it’s visible for an hour or two after sunset or before sunrise.

Right now, it’s farthest from the Sun in the evening sky. For a few nights, it won’t set until about an hour and 20 minutes after sunset. As twilight begins to fade, though, it’s so low in the sky that you’ll need a clear horizon to spot it.

The Moon is just a day and a half past “new,” when it crossed between Earth and the Sun. So the Sun illuminates only a tiny fraction of the lunar hemisphere that faces our way. The rest of the disk will be faintly highlighted by earthshine – sunlight reflected from Earth. That will enhance the beauty of this duo in the fading twilight.

Two other planets are close by. Saturn is to the upper right of Mercury and the Moon, and looks like a fairly bright star. Venus is heaving into view below them. It’s much brighter than Mercury, but much lower, making it tougher to pick out. But Venus will climb higher over the coming weeks – blazing as the “evening star.”

More about the Moon and Saturn tomorrow.

Script by Damond Benningfield

Car wrecks aren’t all alike, so there’s a wide range in the results.

The same principle may apply to the bodies of the early solar system, when the planets were taking shape. In fact, a recent study says the modern appearance of the planet Mercury could be explained by a glancing blow between two bodies of similar size.

Mercury is an oddball among the rocky planets of the inner solar system. Its metallic core accounts for about 70 percent of its mass – a far higher ratio than for Earth or the other planets. And the core is surrounded by a fairly thin mantle – a layer of lighter-weight rocks.

Some simulations have suggested that was the result of a giant impact – a massive collision between bodies of much different sizes. Such impacts were common in the early solar system; one of them might have led to the creation of the Moon.

But the recent study suggested something else. It found that a glancing blow between Mercury and a similar-sized planet could have stripped away much of Mercury’s mantle. But the research doesn’t tell us what happened to the other planet, or the debris from the impact. So scientists will ponder the possible collision a little longer to understand the planet Mercury.

Mercury is peeking into view in the early evening. It looks like a bright star, but it’s quite low in the west during twilight, so it can be hard to spot. The Moon will join it tomorrow night; more about that tomorrow.

Script by Damond Benningfield

There’s nothing like a merger to stir things up. That applies not only to companies and families, but to galaxies as well. One example is Messier 61. A recent merger with a smaller galaxy has brought its central black hole to life, triggered the birth of thousands of new stars. It also kicked out a ribbon of stars that’s as long as the galaxy itself.

Messier 61 is a lot like our home galaxy, the Milky Way. It’s about the same size and mass, and it looks about the same – a beautiful spiral with a long bar of stars across its middle.

But a close look shows big differences. M61 is giving birth to stars at a much faster rate than the Milky Way. It’s produced more supernovas – the explosive deaths of young, massive stars. The supermassive black hole in its heart is “feeding” much more voraciously. And last year, astronomers discovered a “streamer” of stars behind M61. The streamer is a hundred thousand light-years long, and ten thousand wide.

The likely cause of all that activity is a merger with a smaller galaxy. The encounter squeezed big clouds of gas, triggering the starbirth. It provided fresh material for the black hole. And it pulled out stars in the galaxies to form the long tail – stirring things up in a beautiful spiral galaxy.

Script by Damond Benningfield

A celestial grandfather strolls low across the south on winter evenings. He’s represented by two stars. In the western world, they’re part of the constellation Columba, the dove. But in ancient China they were known as the Grandfather.

The stars are Alpha and Epsilon Columbae. Coincidentally, they’re about the same distance from Earth – about 280 light-years. And both are much bigger and brighter than the Sun. But there’s a big difference in their ages, so the stars aren’t related.

Alpha – the First Star of Grandfather – is the brighter of the two – the brightest member of Columba. It’s less than a hundred million years old – about two percent the age of the Sun. But it won’t be around much longer. It’s about four and a half times the mass of the Sun. Heavier stars age more quickly. In the next 150 million years or so, Alpha will move out of the “prime” phase of life and into the next phase, as a giant.

Epsilon has already reached that phase. It’s not as massive as Alpha, but it’s about one and a half billion years older – a third the age of the Sun. It’s puffed up to many times the size of the Sun, so it shines much brighter. Before long, though, it will cast off its outer layers, leaving only its hot, dead core – and Grandfather will be down to a single star.

Columba is low in the south-southeast at nightfall. Alpha and Epsilon are close together, near the center of the constellation.

Script by Damond Benningfield