StarDate

25 years ago today, space shuttle Atlantis was making history. During the 100th flight of American astronauts, it was about to dock with Mir, a Russian space station.

     ATLANTIS: Houston, Atlantis, we’re stopped at about the 30-foot station-keeping point. FLIGHT DIRECTOR: Good news.

Links between the two space programs had been growing for several years. Another shuttle had flown around Mir earlier in 1995. And astronaut Norm Thagard had launched to Mir aboard a Russian capsule. Atlantis was going to make the first docking with the station. It would pick up Thagard and two cosmonauts, and deliver two other cosmonauts to the station. That set the stage for commander Hoot Gibson to bring the ships together.

     ATLANTIS: Houston, Atlantis, we have capture. CAPCOM: Copy, capture. ATLANTIS: Houston, we think it’s time to open the hatch. We’re gonna proceed if you agree. CAPCOM: Hoot, we concur, you’re “go” to open the shuttle hatch.

And moments later, Gibson and Mir commander Vladimir Dezhurov embraced in the airlock.

Atlantis spent five days docked to the station. The two crews conducted a set of medical tests in a laboratory aboard the shuttle.

In all, shuttles visited Mir 10 times, before the station was plunged to Earth in 2001. And six more astronauts lived there. They conducted experiments and gained experience at living in space for months at a time. And they survived a fire and a collision with a supply ship — making history on a Russian space station.

Script by Damond Benningfield

Support McDonald Observatory

Bright stars have served as more than markers in the sky. They’ve helped many cultures align their temples and other major buildings, and establish their calendars. And one of the most important stellar markers is Spica, the leading light of Virgo.

Research a few years ago said that Spica may have played a role in establishing the first major calendar in Armenia, for example. The calendar began around the year 9,000 BC, when Spica first appeared in the dawn sky, shortly before the summer solstice.

Other research says the star might have been used in the alignment of some monasteries in India. And Spica definitely was used to align temples in ancient Greece.

Perhaps the star’s best-known alignment was with a temple in ancient Egypt. It was built 5200 years ago, dedicated to an early goddess. It lined up with the point on the eastern horizon where Spica rose.

The temple gained greater fame a few thousand years later. A Greek astronomer noticed that the temple no longer aligned with Spica’s rising point. Comparisons with other records confirmed that Spica and all the other stars shift position over time. The shift is caused by precession — a slight “wobble” in Earth’s rotation on its axis. It takes a long time to notice that shift — a change in the alignment of the stars.

And Spica aligns with the Moon tonight. It’s to the lower left of the Moon at nightfall, and closer to the Moon as they set around 1 or 2 in the morning.

Script by Damond Benningfield

Support McDonald Observatory

A scraggly wolf pads low across the southern evening sky at this time of year. Lupus is to the lower right of Scorpius, the scorpion. Unlike Scorpius, though, you need a fairly dark sky to see it.

Even the wolf’s brightest star isn’t all that bright. And it’s so far south that you need to be south of about Dallas to see it at all.

Someday, Alpha Lupi will shine much brighter. That’s because the star is about 10 times the mass of the Sun. Such a heavy star is likely to end its life as a supernova — a titanic explosion. The star’s core will collapse to form a neutron star. Its outer layers will blast into space. For a few weeks or months, it’ll outshine billions of normal stars.

That’s already happened to another star in Lupus. It flared up a millennium ago. At its peak, it was several times brighter than Venus, which right now is the brilliant “morning star.” It was bright enough to see during the day, and at night it was bright enough to read by.

Supernova 1006 was different from the kind of supernova that Alpha Lupi will become, though. It probably formed from the merger of two dead stellar cores known as white dwarfs. Their combined mass was enough to spark a runaway nuclear explosion — like a giant H-bomb. It blasted the two stars to bits. Today, all that remains is a cloud of debris about 65 light-years across. It’s continuing to expand at about one percent of the speed of light — the most interesting feature of a scraggly wolf.

Script by Damond Benningfield

Support McDonald Observatory

Like a chick that’s left the nest, the Sun moves through the galaxy alone. But many of the galaxy’s stars are still in their nests — in great clusters of stars. All the stars in a cluster are members of the same brood — they were all born from the same giant cloud of gas and dust.

Two examples are near the tail of Scorpius, which is low in the south-southeast at nightfall.

The brighter one is Messier 7, to the left of the stars that mark the scorpion’s stinger. Under moderately dark skies, it’s visible to the unaided eye as a tight knot of stars. Binoculars reveal more stars, and telescopes reveal still more.

From the types of stars the cluster contains, astronomers deduce that M7 is about 200 million years old — only about five percent the age of the Sun. That youthfulness is one reason the cluster is still together. As a cluster orbits the center of the Milky Way, the combined gravity of the galaxy’s other stars and gas clouds pulls it apart. That sends its stars off on their own.

The other cluster, Messier 6, is above M7. It’s farther away than M7, so it doesn’t look as big or as bright. In fact, you need pretty dark skies to see it without help. With optical aid, the colorful stars of M6 form a pattern that resembles the outline of a butterfly. M6 is also young, so its stars are also still bound together by their own gravity — keeping the nest full for a little while longer.

Script by Damond Benningfield

Support McDonald Observatory

The scorpion packs a mighty sting — the two stars that mark its “stinger” are impressive.

Scorpius is low in the southern sky at nightfall, with its brightest star, Antares, near its middle. The tail curls to the lower left of Antares. It forms a hook, with the barbed stinger at the end.

The brighter of the stinger stars is Lambda Scorpii. It’s actually a system of three stars. Two of them are much more massive than the Sun, and thousands of times brighter. Both of them may be massive enough to end their lives with a bang — a supernova. And that could happen fairly soon. Both stars are nearing the ends of their “normal” lifetimes and are about to enter their final phases. Their explosive demises could happen within just a few million years.

Lambda Scorpii’s third star may be on the other end of the age scale — an infant that hasn’t yet settled into maturity. If that’s the case — and if it survives the supernova blasts — it will outlive its siblings by millions or billions of years.

Upsilon Scorpii forms the stinger’s tip. It’s 570 light-years away — about the same distance as Lambda. It’s probably a single star. It’s about 12,000 times brighter than the Sun. It’s a similar mass to the two older stars of Lambda. And like those stars, it, too, is likely to end its life as a supernova — adding a little more zing to the scorpion’s sting.

We’ll talk about some star clusters that are close to the stinger tomorrow.

Script by Damond Benningfield

Support McDonald Observatory

No matter how unsettled our world gets, there’s one thing you can always count on: the clockwork precision of the heavens. Each star has its own season — a time when it shines at its best. And the Moon glides across the sky with its own predictable rhythm, passing by the same stars each month.

That rhythm is on display in the west as darkness falls the next couple of nights, as the Moon passes Regulus, the heart of the lion. It’s to the left or upper left of the Moon tonight, and to the lower right of the Moon tomorrow night.

The Moon passes closest to Regulus every 27 and a third days. That’s the Moon’s “sidereal” period — its cycle against the background of stars. But each time the two bodies pass, Regulus has moved farther westward in the sky.

That’s because Earth makes one turn on its axis relative to the stars in 23 hours and 56 minutes. Because we’re moving around the Sun, though, it takes a little longer for it to return to the same spot in the sky — 24 hours. Thanks to that difference, the other stars rise and set four minutes earlier each day.

So every star shifts a little farther westward every night. Regulus, for example, first appears in the dawn sky in early September. It stages its best appearances, when it’s in view all or most of the night, in spring. It disappears in the evening sky near the end of July.

And the Moon slips past it roughly every four weeks — a reassuring rhythm in the night sky.

Script by Damond Benningfield

Support McDonald Observatory

Astronomers have discovered thousands of planets in other star systems. You might think they’d have found many of them in clusters — places where hundreds of stars are close together. That’s not the case, though. The clusters are so tightly packed that it’s hard to isolate individual stars and find their planets.

One cluster where planets have been found is M44, the Beehive. It contains a thousand stars, all packed into a region only a few dozen light-years across.

The first planets in the cluster were discovered in 2012. One of them is about half as massive as Jupiter, the giant of our own solar system. It’s quite close to its star, though, so it’s much hotter than Jupiter.

A similar planet was discovered around a second star in the cluster. And another planet was found in the same system a few years later. It’s much heavier than Jupiter. It’s about the same distance out as Jupiter is from the Sun, though, so it’s much cooler than its planetary sibling.

Two more planets were found orbiting a third star a couple of years ago. Both of them are between the size of Earth and Neptune, the Sun’s fourth-largest planet. And both are close in, so they, too, are hot — rare finds in a busy star cluster.

The Beehive is low in the west-northwest as night falls now. It’s a little easier to spot tonight because it’s near the crescent Moon. Binoculars will reveal a swarm of stars close to the lower left of the Moon.

Script by Damond Benningfield

Support McDonald Observatory

The most remote member of the solar system yet seen is a ball of ice nicknamed FarFarOut. Estimates say it’s about 13 billion miles from the Sun — 140 times farther than the distance between Earth and the Sun.

But that’s right next door compared to the farthest objects of all — the members of the Oort Cloud. It could extend about 1,400 times farther than FarFarOut — more than three light-years in every direction. Although no one has seen it, the orbits of many comets suggest they must have come from such a cloud.

The inner part of the cloud begins at about 2,000 times the Earth-Sun distance. It’s shaped like a thick doughnut, and gets thicker near its outer edge.

The outer part of the cloud begins at about 20,000 times the Earth-Sun distance. It forms a shell that encircles the Sun.

The Oort Cloud is populated by perhaps trillions of chunks of ice and rock. They could be leftovers from the birth of the solar system that were kicked out by the gravity of the giant planets.

On the other hand, many of them could have formed around other stars in the cluster that gave birth to the Sun. The stars all exchanged iceballs before they moved apart.

Most estimates put the outer edge of the Oort Cloud at up to a hundred thousand times the Earth-Sun distance. But it could extend twice as far. At that range, the gravity of the rest of the galaxy would pull the objects away from the Sun — and out of the Oort Cloud.

Script by Damond Benningfield

Support McDonald Observatory

The ancients loved creatures that were crosses between humans and something else. One of the favorites of the Greeks, for example, was the centaur. It featured the head and torso of a man combined with the body of a horse. In fact, the list of Greek constellations featured two centaurs. And both of them are still around today. Right now, one of them is dropping from view as darkness falls, while the other is climbing into view.

Centaurus sits low in the south at that hour. From most of the United States, in fact, a good portion of it never climbs above the horizon.

Centaurus represents Chiron, one of the gentlest and most cultured of all centaurs. He was an accomplished teacher. And he was so trusted by the gods that he was godfather to Jason and Achilles. He also served as tutor to Asclepius, the greatest healer.

In the sky, Chiron is part of a larger story. He’s generally shown holding Lupus, the wolf, which is to the left of the centaur. He’s carrying it to be a sacrifice on Ara, the altar, which is below the tail of Scorpius.

There’s no real story associated with the other centaur. But it’s a lot easier to see. Sagittarius is just rising in the southeast at nightfall. It climbs into good view by an hour or so later. Eight of its stars form the outline of a teapot — a pattern that’s easy to pick out. It’s highest in the sky in the wee hours of the morning, and dives toward the southwestern horizon at first light.

Script by Damond Benningfield

Support McDonald Observatory

Stars don’t always play nice. 350 years ago today, for example, an astronomer in France noticed a bright new star in the sky. It wasn’t actually new, though. Instead, it was the result of a dead star ripping apart a companion object.

The “new” star is known by several names, including Nova Vulpecula 1670. It’s in Vulpecula, the fox, quite near the “bill” of Cygnus, the swan. It’s a third of the way up the eastern sky as night falls right now.

When it first appeared, Nova Vulpecula was bright enough to see with the unaided eye. It faded, then flared up twice more over the following couple of years before vanishing entirely.

During the 20th century, astronomers first thought the object was a nova. Such a blast is caused when hot gas stolen from a companion star piles up on a dead star known as a white dwarf. But measurements didn’t seem to match that kind of explosion. So a couple of years ago, astronomers came up with a new explanation: the merger of a white dwarf and a brown dwarf — an object that wasn’t heavy enough to shine as a true star.

The two bodies passed close together, and the gravity of the white dwarf pulled the brown dwarf apart. Some of the gas formed a hot disk that funneled onto the white dwarf. And some formed “jets” that shot out into space from the white dwarf’s poles. That formed a nebula that looks like an hourglass. The nebula is still there, and still growing — the beautiful remnant of a stellar merger.

Script by Damond Benningfield

Support McDonald Observatory