StarDate

Like other buildings, observatory domes sometimes outlive their usefulness. They may not be big enough for the latest telescopes, for example. Encroaching cities can make it hard for them to see the heavens. Or time may just catch up to them.

Many domes and related buildings have been torn down. Others have been converted to offices or libraries. And still others have been abandoned — left to the elements and the inevitable passage of time.

Several of these buildings are scattered around the country — in Michigan and Nebraska, for example, and in the woods of Indiana. Their domes are rotting away. Their walls are covered with graffiti, their floors with water and trash.

Perhaps the most famous abandoned observatory sits atop a grassy knoll in Cleveland. It was built by the men who founded Warner and Swasey, a machine-making company. They were amateur astronomers who devoted part of their business to building telescopes — including the first big telescope at McDonald Observatory.

They donated an observatory to Case University in 1919, and equipped it with a telescope of their own making. Bigger telescopes were added later. The beautiful building was abandoned in 1982. Its telescopes had been sent elsewhere, and its staff moved into other quarters.

Today, the building is decaying and dangerous — a ghostly presence beneath the stars on Halloween night.

Script by Damond Benningfield

The Skidi Pawnee of Nebraska were avid skywatchers. They used the stars to tell them when to plant corn and conduct other affairs. They worshipped many of the stars as gods. And they even built their dwellings with the stars in mind: The lodges faced the rising Sun, and they included posts that depicted the four stars that held up the sky. And they had a hole in the ceiling, in part, to make sure the residents could see the sky.

And just in case they missed the stars, one Pawnee recorded them on a tanned elk skin about three centuries ago. The skin probably formed part of a medicine bundle, which was used in important rituals. It’s preserved in a museum in Chicago.

The chart is divided into 11 groups of stars, which depict the Skidi Pawnee constellations. The groups aren’t in their correct positions in the sky, so the painting isn’t intended as a sky chart. Instead, it is probably like a catalog — a reminder of the most important stars.

The stars include the Chief Star — known today as Polaris, the Pole Star. All the other stars in the northern sky appear to rotate around it. There’s also the Council of Chiefs — the modern-day Northern Crown; the Seven Brothers, who were the stars of the Pleiades; and the Wolf Star, Sirius, the brightest star in the night sky. And there’s a trail of small stars down the middle — the Path of Departed Spirits. It’s the subtle glow of the Milky Way, lighting the nights on the Great Plains.

Script by Damond Benningfield

One of the prime stars of summer continues to dazzle in the autumn sky. Vega is quite high in the west at nightfall. It’s the brightest member of the Summer Triangle.

Vega is known by many names. One of the most important is HD 172167. That’s its listing in the Henry Draper Catalog. The first volume was published a century ago.

People have been compiling star catalogs for a long time. One of the earliest was done more than 2,000 years ago. It recorded the positions of more than a thousand stars. An early modern catalog was compiled by Johann Bayer, in 1603. In it, Vega is known as Alpha Lyrae — the leading light of the constellation Lyra.

Work on the Henry Draper catalog dates to 1872. That’s when Draper, an amateur astronomer, took the first photograph of the spectrum of a star. It recorded the “fingerprint” of Vega.

When Draper died, Harvard College Observatory took over the job of recording spectra. A first catalog was published in 1890, with a new way of classifying stars.

By 1918, Annie Jump Cannon had led the creation of a new catalog, with 225,000 stars. In it, she reworked the way stars were classified. Both the system and the catalog are still in use today.

Astronomers have compiled many more catalogs since then. The largest was released this year. It consists of observations made by the Gaia spacecraft, which is measuring stellar distances. The catalog lists a record 1.7 billion stars.

Script by Damond Benningfield

We still don’t know if anything has ever lived on Mars. But the evidence that something could have lived there keeps getting stronger. So does the evidence that conditions could still be okay for life today.

There’s little doubt that early Mars was much warmer and wetter than it is now — conditions that were favorable for microscopic life. And a Mars rover recently found evidence of the building blocks of life in three-billion-year-old sediments.

The Curiosity rover is poking around inside Gale Crater. The rover found that the crater was once filled with warm, salty water — some basic necessities for life.

And this year, scientists reported that the rover also found complex organic compounds — some of the building blocks of life. That doesn’t mean the compounds came from living organisms. But it adds more ingredients to the recipe for life. And it increases the odds that if life ever did exist on Mars, evidence of it might not be hard to find.

And an orbiting spacecraft recently found possible liquid water on today’s Mars. Mars Express used radar to scan the ice cap at the south pole. It found evidence of a thin layer of water under the cap. The water could provide a haven for microscopic organisms — perhaps making Mars a friendlier place for life.

The planet is about a third of the way up the southern sky at nightfall, shining like a bright orange star. It sets in the wee hours of the morning.

Script by Damond Benningfield

Stars come in all types, from brilliant to feeble. The brilliant ones are easy to see. But the feeble ones are a challenge just to discover, let alone study. This month marks the 75th anniversary of the discovery of the most feeble star then known.

Georges Van Biesbroeck was an astronomer at Yerkes Observatory in Wisconsin. He specialized in double stars — two stars locked in a mutual orbit around each other. He measured the positions of known double stars, and discovered new ones.

In 1940, he took a photographic plate of a faint red star in the constellation Aquila. Three years later, he was using McDonald Observatory’s 82-inch telescope to take new plates of some nearby stars. He hoped the pictures would reveal companions of some of those stars.

In late October of 1943, one of those plates included the faint star in Aquila. The plate revealed a previously unseen companion close to the main star. The new star moved through space in the same direction as the main star, indicating they were a pair — moving as a single unit.

Known today as Van Biesbroeck’s Star, the companion is one of our closest neighbors — just 19 light-years away. As Van Biesbroeck noted in his discovery paper, though, the star is a bare ember: If you put it in place of the Sun, it would look about as bright as the full Moon.

Van Biesbroeck’s Star remained the low-luminosity champion for years — until an even fainter star was discovered in the 1980s.

Script by Ken Croswell

Sagittarius is disappearing into the evening twilight. Look for the outline of a teapot low in the south and southwest as darkness falls. The teapot is pouring its starry brew toward the horizon.

A giant star cluster lurks near the star that connects the lid and the spout. Through binoculars, NGC 6624 looks like a slightly fuzzy star. A small telescope reveals many of its individual stars.

A recent study says that a middleweight black hole may inhabit the center of the cluster. If so, it’s bigger than the black holes that form from collapsing stars, but smaller than the monsters that live in the hearts of galaxies.

For more than 25 years, a team of astronomers has used a radio telescope in England to monitor a pulsar in the cluster — the collapsed core of a once mighty star. The star is quite near the cluster’s heart. And it spins almost 200 times a second. That rate is like the ticking of a highly accurate clock — it keeps near-perfect time. So if the timing changes, it’s usually the result of something near the pulsar.

In this case, the astronomers determined that changes in the pulsar’s timing were caused by a black hole at least 7500 times the mass of the Sun.

The astronomers say there’s a chance the pulsar orbits a lighter object. And another study found no signature of a black hole in X-rays from the cluster. So it’s still not certain whether a middleweight black hole lives in the heart of NGC 6624.

Script by Damond Benningfield

 

Fifteen years ago as seen from Earth, a star in a distant galaxy suffered a violent death: It was pulled apart by a black hole. As the star was ripped to shreds, it produced an outburst of X-rays. Over the following decade, it slowly cooled and faded.

Astronomers have seen this scenario play out dozens of times. But this one was special. It may have been created by a middleweight black hole — a type that’s rarely seen.

Earlier events were powered by supermassive black holes. They’re millions or billions of times as heavy as the Sun, and they’re found in the hearts of most galaxies.

In October of 2003, though, X-ray telescopes in space noted a brilliant flare in a remote galaxy. The flare came from the galaxy’s edge, not its center. From its brightness, temperature, and the way it faded, astronomers estimated the heft of the disrupting black hole: about 50,000 times the mass of the Sun.

So far, astronomers have found only a few dozen good candidates for this class of black holes. They’re important, though, because they could be the “seeds” from which bigger black holes grow. To understand that process, astronomers need to see a lot of these middleweights. But they’re tough to find.

This was the first possible detection made through the disruption of a star. But it suggests that many other middleweight black holes could be sitting quietly — waiting for unlucky stars to point them out.

More tomorrow.

Script by Damond Benningfield

The problem with black holes is that they’re black — they don’t produce any detectable energy at all. So astronomers find and study black holes by observing their effects on the stuff around them. They pull at nearby stars, for example. And they sometimes “feed” on gas and dust, which glows brightly as it spirals toward a black hole.

One of the most spectacular effects is when a black hole rips apart a star. Known as a tidal disruption event, it can be as bright as a supernova. It can shoot out bright “jets” of charged particles. And it can shine for years.

A star has to pass a black hole at just the right distance to be disrupted. If the star goes directly toward the black hole, it can be completely gobbled up, with fewer fireworks. Too far, and it gets away cleanly.

At just the right distance, though, the black hole rips the star into a blazing stream of hot gas. Much of the gas enters orbit around the black hole, blazing brightly before it’s devoured. The rest of it escapes the black hole, forming bright streamers that slowly cool and fade.

In the last decade or two, astronomers have seen perhaps several dozen of these events. Most of them have been produced by supermassive black holes. These monsters sit in the hearts of galaxies. They weigh millions or billions of times the mass of the Sun.

But an event reported this year appeared to be caused by a rare middle-weight black hole. More about that tomorrow.

Script by Damond Benningfield

The planet Uranus is stepping up its game right now. It’s at a point known as opposition — it lines up opposite the Sun. It rises around sunset and is in the sky all night. It’s also closest to us at opposition, so it’s brightest for the year.

Unfortunately, it’s quite close to the Moon. This evening, it’s to the left of the full Moon — known as the Hunter’s Moon. The moonlight makes it tough to spot the faint planet, even with binoculars. It’ll be in better view in a few nights, as the Moon moves away from it.

Uranus hosts a couple of dozen moons of its own. The largest is Titania, which is named for the queen of the fairies in “A Midsummer Night’s Dream.” It’s less than half the diameter of our moon. But it’s about the same distance from Uranus as the Moon is from Earth. And like the Moon, the same hemisphere always faces its planet.

Titania probably has a rocky core, surrounded by layers of rock and ice. Some of its most interesting surface features are tall cliffs and deep canyons. They might have formed long ago, when a layer of liquid water below the surface froze. The freezing water expanded, cracking the layers of ice and rock above it.

Some of the water may have oozed all the way to the surface, repaving the moon. That obliterated any existing impact craters. So today, the surface of Titania is pockmarked by fewer craters than Uranus’s other major moons. That creates a younger face for this intriguing moon.

Script by Damond Benningfield

Most of the planets in the solar system stand more or less upright as they orbit the Sun. That makes them look like spinning gyroscopes. But not Uranus. The seventh planet lies on its side, so compared to the other planets, it moves more like a bowling ball.

That odd configuration probably was the result of a giant impact. Another planet may have struck Uranus, knocking it on its side. And a recent study says the impact could have had other effects.

The study was led by astronomers at Durham University in the UK. They used a supercomputer to simulate different impact scenarios. They found that present-day Uranus was best explained by a glancing impact by a planet about twice as big as Earth. That would have knocked Uranus over, but allowed it to keep most of its atmosphere. Debris from the impact could have created the giant planet’s innermost moons.

The impact also could account for the fact that Uranus is quite cold — colder than Neptune, which is a billion miles farther from the Sun. Rocky debris could have settled inside the planet. The rock would prevent heat from the interior from reaching the top of Uranus’s atmosphere — keeping the planet nice and cold.

And Uranus is putting in its best showing of the year. It lines up opposite the Sun, so it rises around sunset and is in view all night. It’s brightest for the year, too, although you still need binoculars to see it.

We’ll have more about Uranus tomorrow.

Script by Damond Benningfield