StarDate

Autumn has few bright stars to call its own. In fact, it really has only one major star: Fomalhaut. And not surprisingly, it’s known as the Autumn Star. It’s low in the southeast as night falls now, far to the lower left of the planet Jupiter, which looks like a brilliant star.

If you see Fomalhaut, you’ll notice that there are no other bright stars anywhere around it. That’s a bit misleading, because Fomalhaut appears to have two companion stars. That makes it a triple system. Both companions are faint, though, so you can’t see them with the eye alone.

The brighter of the two is below Fomalhaut, in the same constellation — Piscis Austrinus, the southern fish. The other is above Fomalhaut, in the adjoining constellation Aquarius — an indication of just how spread out the system is. The closer star is about a light-year from Fomalhaut, while the other is about two and a half light-years away.

It’s hard to be sure that such widely separated stars really do form a system. The stars share the same motion through space, they have the same composition, and they’re the same age. That suggests that they were born together, from the same cloud of gas and dust.

Astronomers can’t be certain the stars are bound to each other, though, without plotting their orbits. But it would take millions of years for the stars to complete a single orbit, so there’s no way to confirm that Fomalhaut and its faint companions really are stellar siblings.
 

Script by Damond Benningfield

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A tiny island half way between Africa and South America is sometimes called the Mars of the Atlantic. That’s not just because its landscape looks like an alien world. A 19th-century expedition to the island studied Mars to help refine the scale of the solar system. And since the 1960s, space agencies have built facilities there to watch missions to Earth orbit and beyond.

Ascension Island is a little south of the equator, and covers about 36 square miles.

In 1877, British astronomer David Gill and his wife, Isobel, spent six months there. Mars was lining up opposite the Sun, and was especially close to Earth. By measuring angles between Mars and the Sun, Gill estimated the distance between Earth and the Sun — the key to mapping the entire solar system. His number was just one-tenth of one percent off the present-day value. Today, the site of their observations is known as Mars Bay.

Because Ascension is in the middle of a large expanse of open ocean, it’s a good place for monitoring spacecraft. NASA built a tracking station for its Apollo missions there in the 1960s, and operated it for a quarter of a century. An Air Force runway later served as a backup landing site for space shuttles. And NASA placed a telescope on the island for tracking space debris.

Ascension also hosts stations for tracking GPS satellites and rockets launched from South America — keeping many eyes on space from the Mars of the Atlantic.
 

Script by Damond Benningfield

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The spectrum of radio waves is chopped up like the egg in an egg salad. Different chunks of spectrum are reserved for different uses: radio and TV broadcasts, cell phones, military transmissions, orbiting satellites, and many others.

Several wavelength bands are set aside for radio astronomy — the study of radio waves from the universe. The waves are produced by the remnants of exploded stars, stellar corpses, supermassive black holes, planetary magnetic fields, and many other sources. The radio waves can reveal details about these sources that astronomers can’t learn any other way.

Even with some wavelengths reserved, though, radio astronomy is facing challenges. Devices that broadcast at the surrounding wavelengths often “bleed” into the protected bands, for example. Radio telescopes can pick up the transmissions of cell phones and orbiting satellites. Signals from these sources can overpower anything that comes from beyond Earth. And the problem is only likely to get worse in the years ahead.

Astronomers do what they can to manage the problem. They place their radio telescopes in remote locations. They shield the receivers, and use computers to filter out interference from Earthly sources. They’re even considering placing telescopes on the far side of the Moon, where terrestrial signals would be blocked.

Still, there’s only so much they can do to protect their fragments of the radio spectrum.
 

Script by Damond Benningfield

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We won’t be hearing much from the legion of orbiters, landers, and rovers at Mars right now. That’s because the planet is passing behind the Sun — a passage known as conjunction. And although the Sun isn’t a major source of radio waves, it produces enough to interfere with communications with the Red Planet.

And there’s been a lot of communicating going on. Assuming nothing has happened to them since we recorded this program, there are three working rovers and two stationary landers on the planet. In addition, there are more than a half-dozen craft in orbit around Mars. That’s by far the biggest fleet of working spacecraft ever at any world other than Earth.

When Mars passes behind the Sun, though, many of them will take a break. They won’t snap as many pictures, drill as many holes in the rocks, or take as many weather readings as normal. Since engineers won’t be able to talk to their charges if anything goes wrong, they don’t want to take any chances. The probes will have to hold on to most of the observations they do make until Mars begins to pull away from the Sun in a few days.

Mars also is too close to the Sun to see. It’ll technically move into the morning sky at conjunction, on Thursday night. But it won’t become visible in the dawn sky until late November. And it won’t be an easy target until almost Christmas — adding one more light to the holiday nights.

We’ll talk about another challenge to communications tomorrow.
 

Script by Damond Benningfield

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One way astronomers plan to hunt for life on worlds orbiting other stars is to sniff out compounds in a planet’s atmosphere that might have been produced by living organisms. But some recent studies of worlds in our own solar system show just how tough that’ll be.

Last year, a team said it detected phosphine in the atmosphere of Venus. Most of the phosphine on Earth appears to be associated with microscopic organisms. That suggested that the phosphine on Venus could be produced by microbes in the clouds.

But other scientists disagreed with that conclusion. This summer, one team said the phosphine could have been produced by volcanoes — no life required.

Another disagreement concerns methane on Mars. Methane is another compound that, on Earth, is produced mainly by life. On Mars, the Curiosity rover has measured several outbursts of it. But a Mars orbiter has detected almost none. That could mean that any methane at the surface is destroyed as it climbs into the atmosphere, leaving nothing for orbiters to find.

Another team recently reported finding methane in plumes of ice from Enceladus, one of the moons of Saturn. The ice probably comes from an ocean of liquid water below the moon’s crust. So the methane could be produced by organisms living in the ocean. But that detection hasn’t been confirmed, either.

So finding life beyond our own planet isn’t easy — whether it’s on a sister world, or out among the stars.
 

Script by Damond Benningfield

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Our Sun is impressively old — four and a half billion years. That means it’s been around for roughly a third of the lifetime of the universe. But some stars in the galaxy have been around for almost the entire life of the universe. And many of them reside in a star cluster in Pegasus known as Messier 15. It’s one of the oldest clusters in the entire Milky Way — and one of the most tightly packed.

M15 probably was born about 13 billion years ago — roughly a billion years after the Big Bang. Any big, massive stars it contained have long since expired. About all that’s left are stars that are smaller and fainter than the Sun — about half a million of them. The main exceptions are a few stars that have puffed up and gotten brighter at the ends of their long lives.

The cluster spans about 175 light-years. But half of its stars are found in the central 20 light-years. That makes it one of the most densely packed clusters in the galaxy. And it means that if there are any planets in M15’s heart, their night skies are ablaze with hundreds or thousands of stars at least as bright as anything in our skies.

M15 is on the edge of the constellation Pegasus. As night falls, it’s far to the upper right of the flying horse’s most prominent feature — four moderately bright stars known as the Great Square. Through binoculars, the cluster looks like a hazy patch of light — the soft glow of relics from the early universe.
 

Script by Damond Benningfield

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A star that’s barely holding itself together perches to the right of the crescent Moon at dawn tomorrow.

Regulus is the bright heart of Leo, the lion. The star is several times bigger and heavier than the Sun, and hundreds of times brighter. Its most interesting feature, though, is its shape. Instead of a nice, round ball, it’s shaped more like a round jelly doughnut — it’s a third wider through the equator than through the poles.

That odd shape is the result of the star’s rotation. It makes one turn on its axis in less than a day, compared to one turn every 24 days for the smaller Sun. That pushes the gas at the star’s equator outward, making Regulus fat but short. In fact, if the star were spinning just a little bit faster, it would tear itself apart.

Regulus probably had help to reach that dizzying speed.

A dead companion star known as a white dwarf orbits quite close to Regulus. It’s unusually small, suggesting that it somehow lost a good bit of its original mass.

The companion probably was born much heavier than Regulus. As a result, it aged more rapidly, quickly puffing up to giant proportions. As it did so, it lost the grip on its outer layers. Some of that gas funneled onto the surface of Regulus. That not only transferred hot gas from one star to the other, it also transferred momentum. So as gas poured on to Regulus, the star began spinning faster and faster — almost fast enough to rip itself apart.
 

Script by Damond Benningfield

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A European spacecraft will be getting to know the planet Mercury quite well later in the decade. Today, though, it’s scheduled to get a brief introduction. It will fly past the Sun’s closest planet — the first of six close encounters before it enters orbit in several years.

BepiColombo actually consists of two spacecraft. They’re being carried by a shell that provides electricity and rocket power. They’ll head their separate ways when they begin orbiting Mercury.

The two probes are designed to study Mercury’s composition, structure, and magnetic field. They should tell us whether the planet’s interior is molten or solid. And they’ll tell us more about the little world’s history.

Only two other spacecraft have ever visited Mercury. In part, that’s because it’s a tough planet to snuggle up to. The Sun’s gravity accelerates a spacecraft that heads toward Mercury, so it takes a lot of effort to slow it down. That consists mainly of using the gravity of Mercury and other planets as brakes.

BepiColombo has already flown by Earth once and Venus twice, molding its orbit with each encounter. The passages by Mercury will help even more. But it’ll take a lot of “braking” before BepiColombo can settle into orbit in 2025.

The craft will make some observations of Mercury with each pass. And each brief encounter should add to our knowledge of the smallest planet in the solar system — a world that’s hard to get close to.
 

Script by Damond Benningfield

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The stars have always served as guides for navigation. And in the northern hemisphere, none has been more convenient than the North Star. It always stands due north, every hour of the night — the anchor for the entire sky.

It’s a moving anchor, though. Thanks to a “wobble” in Earth’s rotation, our planet’s axis points to different stars at different eras. Today, it aims at Polaris. But thousands of years ago, it aimed at a star in the coils of Draco, the dragon.

The star is called Thuban — a name that means “the serpent.” It’s near the tail of the dragon’s winding outline.

Thuban served as the North Star at the time the pyramids of Giza were being built in Egypt. Architects used the star to help align the sides of the pyramids. And they achieved a near-perfect alignment with the cardinal directions.

Over the centuries, though, Thuban drifted away from the celestial pole. The gravitational pull of the Sun and Moon cause Earth to wobble like a spinning gyroscope that’s winding down. It takes 26,000 years to make one wobble. Thuban was closest to the pole almost 5,000 years ago. And it’ll resume that position in another 21,000 years — returning the north pole to the clutches of the dragon.

Thuban is in the northwest at nightfall. It’s far to the left of Polaris, at about the same height. While Polaris stays put, though, Thuban will circle below it — a once-and-future North Star looping around the current one.
 

Script by Damond Benningfield

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You might expect the celestial dragon to be a big presence in the night sky. And in one way, it is — it snakes a long way around the sky. In another way, though, it isn’t — none of its stars is especially bright. You need dark skies to make out its twisting body.

There are several legends about the dragon. One says that it belonged to Hera, queen of the gods of ancient Greece.

According to the story, Hera was given a golden apple tree as a wedding gift. She assigned the daughters of Atlas to guard it. But they spent more time eating the apples than protecting them. So she posted a dragon as the new guard. But Heracles — better known by his Roman name, Hercules — was required to snatch some of the apples as one of his 12 labors. To do so, he first killed the dragon with a poisoned arrow. Hera then placed the dragon in the stars.

Three of Draco’s brighter stars have names that mean the dragon or the dragon’s head. The brightest of them all is Eltanin. It’s a red giant — an old, bloated star at the end of its life. It’s much bigger and heavier than the Sun, and hundreds of times brighter. It’s more than 150 light-years away.

Draco is in the north and northwest at nightfall. It wraps around the North Star, Polaris. Eltanin, which is almost as bright as Polaris, stands high overhead, at the top of this twisting path of faint stars.

Another star in Draco served as the North Star long ago. More about that tomorrow.
 

Script by Damond Benningfield

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