StarDate

There’s nothing quite like the Double Cluster — two bright star clusters that stand side by side. They’re easily visible to the unaided eye — especially under dark skies, away from the troublesome glow of city lights. The clusters are in the northeast at nightfall, below the “W” outlined by Cassiopeia. They wheel over to the northwest by first light.

The clusters are known individually as NGC 869 and 884. They’re about 7500 light-years away. Combined, they’re about ten thousand times the mass of the Sun. Yet they contain more than 10,000 stars. The Sun is a fairly heavy star, so there are a lot more stars that are “skinnier.” So the clusters have a lot of stars that are small and feeble.

Fortunately for skywatchers, the clusters are young — only about 13 million years old. At that age, they still have quite a few stars that are big, bright, and massive. Those stars are the reason the Double Cluster is easily visible. The stars will burn out and expire fairly soon, though, so the clusters will fade by quite a bit.

Astronomers have recently discovered a wide “halo” of stars around the clusters. It forms long filaments that extend hundreds of light-years into space. Because the clusters are so young, the stars in the halo weren’t pulled out of the clusters. Instead, they probably formed along with them. And they plow through space together — extending the size of the beautiful Double Cluster.
 

Script by Damond Benningfield

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Thanks to a constellation of satellites, your smartphone can tell you exactly where you are — your precise latitude and longitude. It can even tell you which direction you’re facing. And it can do so even in the dark.

In centuries past, though, people had to rely on other sky objects to help them get their nighttime bearings: the stars. And if you’d like to see how it worked, we can help.

As night falls this evening, find the most famous of all star patterns: the Big Dipper. It’s low in the northwest, with the bowl hanging below the handle.

Next, draw a line connecting the stars at the outer edge of the bowl, Merak and Dubhe. Then extend the line to the upper right. Keep going until you reach the first moderately bright star. That’s Polaris, the North Star. Earth’s axis points toward the star, so when you face it, you’re looking due north.

The next step is to hold your fist at arm’s length, and see how many fists you can stack between Polaris and the horizon — the true horizon, not the tops of trees or buildings. Your fist spans about 10 degrees, so if there are three fists between Polaris and the horizon, the star is 30 degrees up. And that reveals your latitude: However far Polaris appears above the horizon corresponds to your latitude north of the equator.

Unfortunately, we can’t help much with longitude. That’s a much more difficult calculation to make — perhaps best accomplished with modern technology.
 

Script by Damond Benningfield

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If people ever build long-term settlements on the Moon, they’ll need a lot of protection from the elements. High on the list of hazards are radiation from the Sun and other sources, and bombardment by small but speedy space rocks. One possible solution is to cover habitats with a thick layer of lunar dirt. Another is to set up camp underground — in lunar caves.

Scientists have found several “pits” in the surface that could be entrances to caves. The one that’s been studied the most is in the Marius Hills, a region in a giant volcanic plain known as the Ocean of Storms. The pit appears to be as wide as a football field, and perhaps deep enough to hold the Empire State Building. It could be an entrance to an empty lava tube that could stretch a long way — plenty of room for living and working.

Scientists have drafted plans for possible robotic missions to explore the pit. One would lower a probe with a crane. Another would fire a “harpoon” into the wall of the pit and lower a probe on a zip line. And still another would lower a ball-shaped probe to roll through the cave — and tell us if it might be a good home for lunar explorers.

The Ocean of Storms is a large dark patch on the upper left quadrant of the lunar disk this evening. And a bright companion stands quite near the Moon, off that same quadrant: the planet Jupiter. It looks like a brilliant star — the second-brightest object in the night sky after the Moon.
 

Script by Damond Benningfield

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Summer’s just about over here in the northern hemisphere. It ends on Wednesday, at the equinox. On the planet Saturn, though, it’s still the middle of summer. And the season won’t end until 2025.

Saturn has seasons for the same reason that Earth does — its axis is tilted. And the tilt is about the same as Earth’s, so the seasonal effects are about the same. Since it’s northern summer, Saturn’s north pole is dipping toward the Sun. That brings more sunlight to the northern hemisphere — and constant sunlight at the pole.

But Saturn is much farther from the Sun than Earth is — by an average of almost 800 million miles. At that distance, it takes the planet almost 30 years to circle the Sun. When you divide that by four seasons, it means that each season lasts about seven and a half Earth years.

Scientists have watched the changing seasons in detail over the last few decades. They’ve seen changes in color and brightness at the poles and at the equator. They’ve also measured changes in wind speeds.

Giant storms appear on the planet once every 30 years or so. That suggests they’re related to the cycle of seasons. Scientists haven’t confirmed the link, though — a link to the long seasons on Saturn.

The planet is in good view tonight. It’s close to the upper left of the Moon at nightfall, and looks like a bright star. The brighter planet Jupiter is off to the left. More about the Moon and Jupiter tomorrow.
 

Script by Damond Benningfield

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The planet Neptune was discovered 175 years ago this month. Its biggest moon, Triton, was found just 17 days later. But Neptune’s second-biggest moon wasn’t discovered until more than 140 years after that. It’s so small, dark, and close to Neptune that it remained hidden in the planet’s glare.

Proteus is about 250 miles in diameter, and its surface is as dark as charcoal. It has a boxy shape, and it’s been battered by countless space rocks.

Proteus and many of Neptune’s other known moons — there are 14 in all — may have been influenced by Triton. Triton follows a “backward” orbit around Neptune — it orbits in the opposite direction from the planet’s rotation. That suggests it started life elsewhere in the solar system and was captured by Neptune’s gravity.

Triton’s gravity could have caused some of Neptune’s existing moons to ram together and shatter, forming a disk of debris. Other moons may have coalesced from that debris — including Proteus.

Later, another big space rock may have hit Proteus, chipping off a big chunk of the moon. That chunk entered orbit on its own, forming another small moon — a chip off the shoulder of Neptune’s second-largest moon.

Neptune is in the sky all night right now. It’s near the intersection between Pisces and Aquarius. It shines brightest for the year as well. Even so, it’s so far and faint that you need help to find the giant planet with the unruly moons.
 

Script by Damond Benningfield

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Earth’s weather is powered by the Sun, which bathes our planet with energy. But the Sun’s most remote planet powers its own weather. It radiates more than twice as much energy into space as it receives from the Sun. That creates big storms and the fastest winds on any planet in the solar system.

Neptune is the eighth planet from the Sun, and the fourth-largest planet — almost four times wider than Earth. A dollop of methane in its upper atmosphere absorbs red light, making the planet look blue.

Heat generated deep inside Neptune radiates out into the planet’s atmosphere, stirring up some interesting weather.

Over the last three decades, for example, astronomers have seen several giant “dark spots.” The oval features are thousands of miles wide, and they last for years. They appear to be swirling storms that are fairly deep in the atmosphere.

Neptune also produces bands of winds that circle the planet. These jet streams blow at hundreds of miles per hour. The fastest winds yet seen raced along at 1200 miles per hour — about five times faster than anything ever measured on Earth.

The windy planet Neptune is at its best for the year this week. It rises at sunset and is in view all night. It’s low in the southeast as night falls, near the eastern edge of Aquarius. Despite its great size, it’s so far away that you need good binoculars or a telescope to find it.

More about Neptune tomorrow.
 

Script by Damond Benningfield

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To paraphrase a famous saying, the pen is mightier than the telescope — at least sometimes. 175 years ago this month, for example, astronomers discovered the planet Neptune. It wasn’t through weeks of long nights at the telescope. Instead, it took only one night. An astronomer had calculated where the planet should appear, so he told his colleagues just where to look.

The discovery was based on discrepancies in the orbit of Uranus, the seventh planet from the Sun. Two scientists calculated that Uranus was being pulled by the gravity of an unseen planet even farther from the Sun.

French astronomer Urbain Le Verrier and British astronomer John Couch Adams both passed along their calculations to others. Adams didn’t get much support for a search. But Le Verrier did. He sent a letter to the Berlin Observatory. Johann Galle received the letter on September 23rd, 1846, and found the planet that night.

As it turned out, Le Verrier’s calculations were off, so it was a bit of luck that the planet was found. As astronomers tracked it, they refined its orbit. And they named it “Neptune” for the Roman sea god.

And we can tell you just where to find Neptune right now. It lines up opposite the Sun, so it’s in view all night and shines brightest for the year. Even so, you need good binoculars or a telescope to see it. It’s near the border between Pisces and Aquarius, far to the lower left of the brilliant planet Jupiter.

More tomorrow.
 

Script by Damond Benningfield

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Many of the bright stars in the night sky are associated with a particular season — the time of year when they’re best seen during the evening hours. For those of us in the United States, for example, the star Antares is one of the highlights of summer. In fact, it’s been blazing across the evening sky since May. The orange star is quite low in the south-southwest at nightfall. Tonight, it’s almost directly below the Moon.

Antares won’t always highlight the skies of summer, though. In a few thousand years, it’ll become an autumn star. And a few thousand years after that, it’ll move into winter skies, then spring, and finally back to summer.

The change is caused by an effect known as precession. The gravitational pull of the Sun and Moon cause Earth to wobble like a gyroscope that’s running down. As the planet wobbles, so does our view of the stars. They shift position relative to the seasons, so they rise and set later in the year.

It’s not noticeable over a human lifetime, though. It takes about 26,000 years to complete one full wobble, so it takes about a quarter of that — 6500 years — for a star to move from one season to the next. So Antares will remain a summer star for a long time to come.

Again, look for Antares quite close to the Moon tonight. They’ll drop from view in late evening. But they’ll be back tomorrow night, with Antares a good bit farther to the right of the Moon.
 

Script by Damond Benningfield

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When the Spirit and Opportunity rovers landed on Mars in 2004, each carried a couple of treasures from home. One was a DVD bearing the names of four million people who signed up for the trip. The other wasn’t made public until after they landed: pieces of the World Trade Center in New York, which fell in a terrorist attack 20 years ago today.

One of the contractors on the mission was based in Manhattan, just blocks from the Twin Towers. The company was building devices to clean off spots on interesting rocks for the rovers’ instruments to examine. The company wanted to honor the victims of the attack. So a NASA engineer suggested fashioning metal from the fallen buildings to form the shields to protect the devices.

The company obtained some bits of aluminum, which were molded into the proper shape. An American flag was painted on the completed shields.

Spirit and Opportunity discovered that conditions could have been comfortable for life at both of their landing sites in the distant past. Spirit operated for more than six years before it got stuck in a sand dune and went silent. Opportunity ambled on for eight years longer. It covered almost 28 miles before a dust storm blacked out the Sun, depriving it of power.

In the cold, dry conditions on Mars, the expired rovers could remain in good condition for millennia — perhaps allowing future explorers to find precious reminders on Mars of a terrible day on Earth.
 

Script by Damond Benningfield

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Thousands of green peas float through the universe. They weren’t strewn about by the Jolly Green Giant. Instead, they’re small, busy galaxies — little nibbles that are giving birth to new stars.

The galaxies were discovered by volunteers who were looking through pictures of many galaxies. The pictures were snapped as part of an extensive survey of the sky. The volunteers began to see objects that were small, round, and green. In other words, they looked just like green peas.

Astronomers looked at some of these galaxies in detail. They found that the green peas are small and not very massive. They’re generally found in regions with few other galaxies.

But they’re giving birth to vast numbers of stars — the equivalent of about 10 Suns every year. That’s a few times the rate in our home galaxy, the Milky Way. But when you consider that the green peas are only a tiny fraction of the mass of the Milky Way, the numbers are quite impressive.

The high rate of starbirth may be the result of encounters between galaxies. As galaxies swing past each other — or even merge — big clouds of gas and dust smash together, triggering the birth of new stars.

Most of the green peas are fairly close. But they may be like some of the earliest galaxies in the universe, which later merged to form bigger galaxies. So studying these little galaxies may help us learn about conditions when the universe was young — and stuffed with green peas.
 

Script by Damond Benningfield

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