StarDate

Last year, volunteers with a project known as Planet Hunters noticed something odd about the light from an otherwise ordinary star in the constellation Cygnus. Looking at observations from the Kepler space telescope, they discovered that the star’s light often flickered — sometimes dimming by almost a quarter. That meant that several objects were passing in front of the star, blocking much of its light.

Astronomers considered several explanations — from the debris from a planetary collision to giant structures built by an alien civilization. They concluded that the most likely explanation was a swarm of comets.

It’s one of the most intriguing results from a host of projects in which the general public helps astronomers study the universe. They’re all a part of Zooniverse — a project that links scientists with the public. Volunteers look at real observations to find things the pros might have missed — or didn’t have time to look for.

Tens of thousands of volunteers have worked on more than a dozen astronomy projects. They’ve looked for erupting black holes, near-Earth asteroids, and gravitational lenses. In some cases, they’ve gone through entire data sets. They scoured an entire set of images from Spitzer Space Telescope, for example, for signs of star formation.

And through Planet Hunters, they’re still sifting through the Kepler observations for signs of planets — and perhaps much more.

More about astronomy technology tomorrow.

Script by Damond Benningfield

It’s been a long time since astronomers studied the universe by looking through the eyepiece of a telescope. Today, they generally operate the telescope from inside a control room and capture the observations with electronic detectors. In the decades to come, though, they may never see the telescope at all — it’ll be operated robotically.

In fact, that’s already happening. Dozens of telescopes around the world are controlled by computers. Astronomers submit lists of targets they want to study, and the computer trains the telescope on the right target at the right time. The computer can also close the dome if the weather turns bad, and shut things down when the night’s work is done.

So far, most robotic telescopes are fairly small. Yet they’re making big contributions to science.

Some, for example, have discovered planets in other star systems. Others have discovered exploding stars, including some of the most powerful ever seen. Some of those telescopes are programmed to turn toward an exploding star when they get an alert from another telescope on the ground or in space.

The largest network of robots is the Las Cumbres Observatory Global Telescope. It consists of 18 individual telescopes at sites around the world, including McDonald Observatory. Among other advantages, the network allows astronomers to track interesting targets around the clock — keeping an unbroken “eye” on the universe.

More about astronomy technology tomorrow.

Script by Damond Benningfield

The spacecraft that’s provided the most extensive look at any of the solar system’s giant planets is setting up its own demise. It’s changing its orbit through a series of rocket firings and encounters with a big moon. Eventually, that’ll lead to the craft’s end.

Cassini entered orbit around Saturn in 2004. It deployed a probe that touched down on the largest moon, Titan. Since then, it’s made dozens of close approaches to Titan and several other moons, snapped tens of thousands of pictures, and observed Saturn’s rings and magnetic field.

The craft is running out of fuel, though, and scientists don’t want to risk it contaminating Titan or Enceladus — two moons that have the basic ingredients for life.

So Cassini is being maneuvered into a new orbit. Several rocket burns over the last few months have been followed by close encounters with Titan. Those approaches use Titan’s gravity to fling the craft out of the plane of the rings and moons, and above Saturn’s poles.

The orbit will be changed again next year, allowing Cassini to pass closer to Saturn than ever — between the planet and the inner edge of its rings. After 22 of these approaches, Cassini will plunge into Saturn’s atmosphere next September — bringing its mission to a close.

Look for Saturn to the lower right of the Moon at first light tomorrow. It looks like a bright golden star. The even brighter planet Mars is about the same distance to the lower right of Saturn.

Script by Damond Benningfield

The Moon, two bright planets, and one bright star form a beautiful quartet in the wee hours of tomorrow morning. They climb into good view by around midnight, and scoot low across the south later on.

The brightest and closest of the Moon’s three companions is Mars, which is to the lower right of the Moon as they hove into view. The little planet currently outshines almost everything else in the night sky, so it’s hard to miss even when the Moon isn’t around.

Mars and Earth are moving closer together, though, which is making Mars a bigger and brighter target. A month from now, the planet will look about twice as bright as it does right now. And that’ll make its orange color stand out even better.

If you extend the line from the Moon to Mars farther to the lower right, you’ll come to Antares, the bright star at the heart of Scorpius, the celestial scorpion. Antares is only a fraction as bright as Mars right now, but it shows the same orange color. And that’s where the star got its name. The color reminded skywatchers of Mars, so they called the star the “rival of Ares,” the Greek version of Mars.

Finally, look to the lower left of the Moon for the planet Saturn. It’s roughly half-way between the brightness of Mars and Antares, so it, too, is quite easy to pick out.

Mars will back away from Saturn and Antares over the next few weeks, then reverse course and join up with them again in summer.

We’ll have more about this morning lineup tomorrow.

Script by Damond Benningfield

It’ll be decades before humans arrive at Mars. But when they do get there, they can expect a bit of old and a bit of new. Some conditions will feel like home, while others will feel like — well, like another world.

In the “familiar” column are the length of the day — about 40 minutes longer than a day on Earth — and the tilt of the planet’s axis, which creates seasons. And there’s also the Martian atmosphere, which is more like Earth’s atmosphere than that of any other planet.

In the “alien” column are the surface gravity, which is only three-eighths as strong as Earth’s. That means that someone who weighs 150 pounds on Earth would weigh just 57 pounds on Mars. The year is almost twice as long as Earth’s, and the average temperature is almost 140 degrees colder — minus-81 degrees Fahrenheit.

One other alien sight would be in the night sky. Instead of a single big moon, Mars has two smaller ones that move across the sky in a hurry. One of them moves so fast, in fact, that it rises in the west and sets in the east — two and sometimes three times a day.

And look for Mars near our moon late tonight. Mars is well to the lower left of the Moon as they rise, before midnight, and looks like a bright orange star. The golden planet Saturn is to the lower left of Mars, with the orange star Antares below Mars. The whole group will be in especially good view at first light.

We’ll have more about this early morning lineup tomorrow.

Script by Damond Benningfield

The gods of Olympus were a fickle bunch. In some tales, they placed people or animals in the heavens as a reward or a tribute. But in others, being placed in the stars was a punishment, and perhaps a warning that defying the gods wasn’t very smart.

The latter category includes the tale of Corvus the crow.

The story says that the god Apollo gave the crow a cup and sent him to fetch some water. But the crow saw a tree filled with unripe figs. He loitered for a few days while the figs ripened, then gorged himself.

Afterwards, he realized that Apollo would be a bit snippy about the delay. So he filled the cup with water, then grabbed a snake and carried both to Apollo. He told Apollo that the snake had blocked his way, preventing him from filling the cup.

Apollo knew the story was a lie. He became so angry that he cast the crow, the cup, and the snake into the night sky, where they form three constellations. The cup is just out of reach of the crow, so the crow is forever thirsty — giving it a raspy voice for which crows are known.

The constellations are in the southern sky at nightfall. Corvus, in the south-southeast, and the easiest to make out. Four of its stars form a pattern that looks like a sail. The cup stands to its upper right. Under dark skies, you really can see its stars as a cup. And the water snake, which also forms part of another myth, wriggles from below Corvus to far beyond the cup — banished to the stars by the gods.

Script by Damond Benningfield

A few years ago, the light from an exploding star reached Earth. For about a minute, the star was bright enough to see with the unaided eye. What makes that so impressive is that the star was seven-and-a-half billion light-years away. Even more impressive is that the star was many times brighter at other wavelengths — especially in gamma rays, the most powerful form of light. For a few minutes, the star was brighter than the combined light of millions of galaxies.

This “gamma-ray burst” probably happened when the core of a massive star collapsed to form a black hole. Some of the gas in the star’s outer layers was heated to billions of degrees, then blasted into space from the star’s poles. One of these “jets” of gas aimed at Earth, producing the gamma-ray burst.

Because it was so far away, the burst had little effect on our planet. But it’s possible that closer gamma-ray bursts could be harmful.

Some research, for example, suggested that a burst that reached Earth more than 1200 years ago could have damaged our planet’s ozone layer, allowing harmful energy from the Sun and other stars to reach the surface.

And a burst 450 million years ago is one possible cause of a mass extinction that killed 80 percent of the life on Earth.

Today, no stars that are likely to produce gamma-ray bursts are close enough to Earth to cause a problem. Still, it’s possible that such a deadly outburst could hit our planet in the distant future.

Script by Damond Benningfield

The birth of a black hole can be a violent event.

The nuclear reactions in the core of a massive star come to an end, so the core collapses to form the black hole. Gas in the star’s outer layers falls toward the black hole, where some of it is heated to billions of degrees. Some of that gas forms a swirling disk around the black hole, but some punches through the star’s poles, creating a brilliant flash of energy.

If the poles happen to aim toward Earth, then space telescopes can see the flash as a gamma-ray burst — the most powerful type of outburst in the universe. In a few seconds or minutes, it can radiate more energy than the Sun will produce in its entire 10-billion-year lifetime. And the gamma-ray burst is followed by a supernova, as the star’s outer layers blast out into space.

That’s the leading explanation for gamma-ray bursts that last for two seconds or longer. Some of them appear to be powered by stars that are about as big as the Sun, but many times more massive. These outbursts last up to a few minutes — the time it takes their stars’ outer layers to collapse, then explode into space.

Other gamma-ray bursts can last for hours. These also appear to be powered by heavy stars, but the stars are also many times bigger than the Sun. It takes a long time for their outer layers to collapse and explode, so the jets last a lot longer — and so does the gamma-ray burst — the possible birth of a black hole.

More tomorrow.

Script by Damond Benningfield

Last September, the universe jiggled. An observatory detected gravitational waves from the merger of two black holes more than a billion light-years away. It was the first direct detection of gravitational waves, which were predicted by Albert Einstein.

Just four-tenths of a second after the waves rippled past Earth, a space telescope detected a flash from the same region of the sky. It lasted for less than a second, but it emitted more energy than the Sun will produce in its entire lifetime.

That flash was known as a gamma-ray burst. Space telescopes see about one such outburst per day. They’re the most powerful events in the universe. And they fall into two classes. One lasts for a few seconds to a few hours — probably triggered by the death of a massive star; more about that tomorrow.

The other class lasts no more than two seconds, and that’s the class that was seen last year. Theory says these bursts occur in the merger of two stellar “corpses” — a neutron star and a black hole. The black hole takes a bite out of the neutron star, producing a brief but brilliant outburst.

But the gravitational waves from last year’s event show that it was the merger of two black holes. That could mean that the waves and the gamma rays came from different events that just happened to show up at the same time and place. But it also could mean that the merger disrupted a disk of material around the black holes — producing a brief but brilliant outburst.

Script by Damond Benningfield

LAUNCH CONTROL: 2, 1, zero, and lift-off of the space shuttle Atlantis and the gamma-ray observatory, seeking out the explosive forces of the universe. [:10]

Twenty-five years ago this month, NASA launched its second Great Observatory — a space telescope sensitive to gamma rays, the most powerful form of electromagnetic energy. Compton Gamma Ray Observatory was designed to study some of the most energetic objects in the universe, including exploding stars and the super-hot disks of gas around black holes.

One of its key goals was to help astronomers understand the nature of gamma-ray bursts — brilliant outbursts that typically last from a fraction of a second up to a few minutes.

The first of these eruptions were discovered in the 1960s. But it took astronomers a while to begin to understand their nature.

They all appear to come from far beyond our own galaxy. That means they must be incredibly bright. In fact, a gamma-ray burst can emit more energy in a few seconds than our Sun will produce in its entire 10-billion-year lifetime.

Compton observatory discovered more than 2600 of these outbursts. And it helped astronomers realize that they fall into two major categories — outbursts that last no more than two seconds, and those that last longer than two seconds.

That may sound like a minor distinction, but it’s not. The two types appear to be produced by completely different types of events. More about that tomorrow.

Script by Damond Benningfield