StarDate

Venus, the “morning star,” looks down on the Moon at first light tomorrow. It’s one of the most beautiful of all astronomical encounters. But the Moon is headed toward an even more spectacular encounter on Monday, when it crosses in front of the Sun, creating a total solar eclipse. It’ll be visible across a narrow path from Oregon to South Carolina.

But the couple of minutes when the Sun disappears are only part of the eclipse experience. The Moon will partially eclipse the Sun for about an hour and a half before and after totality. In fact, a partial eclipse will be visible across the entire United States, with the Moon covering most of the Sun’s disk across most of the country.

It’s completely safe to look at the total phase of the eclipse — when the Sun is totally covered. But it’s dangerous to look at any other phase. The Sun is so bright that even a sliver of it can damage your eyes.

But there are ways to safely view the partial eclipse. One is to look through special eclipse viewers or a piece of welder’s glass — number 14 or darker.

Another is to poke a hole in a piece of cardboard and let the sunlight shine on the ground or a piece of paper; the hole creates an image of the eclipse. So do the leaves of a tree. If you stand beneath a tree with lots of leaves, but not so many that they block out the sky, you can see hundreds of eclipses projected on the ground — a safe and beautiful way to enjoy an astronomical spectacle.

Script by Damond Benningfield

More information about the eclipse:

The B-57 Canberra has been taking to the skies since the Korean War. Today, only three of the aircraft remain. All three fly research missions for NASA. And on Monday, two of them will be chasing the shadow of the Moon during a total solar eclipse.

The aircraft will conduct experiments for the Southwest Research Institute in Colorado. They’ll look at the Sun’s outer atmosphere, known as the corona. It’s so faint that it’s visible only during a total eclipse. But it’s extremely hot, and astronomers aren’t sure just why.

They’re pretty sure it’s caused by the Sun’s magnetic field. But just how that works is being debated.

One idea says it’s caused by “mini-flares” — a constant series of small explosions near the surface, which transfer energy from the magnetic field to the corona. Another idea says it’s caused by waves that travel through the corona, depositing heat.

The twin Canberras will carry high-speed video cameras to capture detailed images. Those pictures could reveal any waves that might be rippling through the corona. An infrared telescope will map small regions of the corona. And another instrument will capture the light from electrically charged atoms of iron. The iron outlines the magnetic field, which can form loops that are bigger than Earth.

These experiments, along with many others, should provide a better understanding of the Sun’s mysterious corona.

More about the eclipse tomorrow.

Script by Damond Benningfield

More eclipse information

Astronomers have been studying the Sun for so long that you might think they know everything there is to know about it. And they do know quite a bit. It’s a hot ball of gas that’s 865,000 miles wide. It’s powered by nuclear reactions deep in its core. And it’s been shining for billions of years, and will keep going for billions of years more.

Yet there are still some mysteries about the Sun. At the top of the list is what heats its outer atmosphere, the corona. Although it’s quite thin, it’s millions of degrees hotter than the surface of the Sun, and scientists aren’t sure why.

The corona most likely is heated by energy from the Sun’s magnetic field. The field creates dark sunspots, powerful explosions, and outbursts of billions of tons of charged particles. Those events impart some energy to the corona, but not nearly enough to account for its temperature.

Solving the mystery requires more observations of the corona, but they’re hard to get. The Sun’s disk is a million times brighter than the corona, so it overpowers the faint wisps of gas. Satellites can block out the Sun, but they block the inner part of the corona as well.

So the only time scientists get a good look at the corona is during a total solar eclipse — like the one coming up on Monday. As the Moon covers the Sun, the corona will shine around the Moon. So astronomers will probe the corona with telescopes on the ground, in the air, and in space; more about that tomorrow.

Script by Damond Benningfield

For more about the eclipse, visit our special eclipse site

The Moon will pass by several prominent companions over the next week. Tomorrow, the bright star Aldebaran, the eye of the bull, will stand just above the Moon at first light. On Friday and Saturday, the Moon will pass by the planet Venus, the “morning star.” And it’ll end its week of companionship on Monday, when it lines up with the Sun — creating a total solar eclipse.

Over the centuries, eclipses have helped astronomers learn a lot about the Sun and the universe. During an eclipse in 1868, for example, French and British astronomers discovered a new element in the Sun’s atmosphere. It was named “helium” for Helios, an ancient Greek Sun god. Later observations revealed that it’s the second-most-abundant element in the universe, after hydrogen.

Perhaps the most famous eclipse discovery came in 1919.

Just a few years earlier, Albert Einstein had published his theory of gravity, known as general relativity. Among other things, it predicted that the gravity of a massive object like the Sun would “warp” the space around it.

To test that idea, British astronomer Arthur Eddington led an expedition to an island off the coast of Africa. His team photographed the eclipse, as well as stars that appeared near the Sun in the darkened sky. The apparent positions of those stars were shifted a tiny bit by the Sun’s gravity — confirming general relativity, and turning Einstein into an international celebrity.

More about this year’s eclipse tomorrow.

Script by Damond Benningfield

Visit our special eclipse web site

https://stardate.org/nightsky/2017-solar-eclipse

Check your tires and your gas gauge and get ready to hit the road for nature’s most spectacular sky show: a total solar eclipse. It takes place a week from today, and will cover a narrow slice of the United States, from Oregon to South Carolina. And be sure to allow plenty of time to get there — millions of Americans are expected to travel to the eclipse path. That should make it the most-viewed solar eclipse in history.

A solar eclipse occurs when the new Moon passes directly between Earth and the Sun, covering the Sun’s disk. Day briefly turns to night, and the Sun’s corona — its hot but faint outer atmosphere — encircles the intervening Moon.

The Moon’s shadow covers a narrow path. For this eclipse, the maximum width will be about 70 miles, over Illinois and Kentucky. That’s where the eclipse will last longest — two minutes and 41 seconds.

About 12 million people live along that path. But almost 90 million live within a couple of hundred miles of that region. So millions of people may travel to see it. In towns near the centerline of the eclipse, where totality lasts longest, the population could triple.

So if you’re among the travelers, eclipse veterans and state highway patrols recommend that you plan your route in advance, leave plenty of time to get there, and check the weather forecast — you don’t want clouds to spoil the most spectacular of all skywatching events.

We’ll have more about the eclipse tomorrow.

Script by Damond Benningfield
 

For more details, visit our special eclipse pages
 

A dying star in Sagittarius isn’t going quietly. A couple of decades ago, it was “reborn” with an intense outburst of energy. It’s faded from view since then, but it’s starting to return.

Sakurai’s object long ago used up the hydrogen fuel in its core, triggering a series of changes. Those changes culminated when the star expelled its outer layers of gas into space, forming a glowing bubble. That left only its hot core, made of carbon and oxygen topped by thin shells of hydrogen and helium. The core was cooling off to form a white dwarf — the final phase of life for stars that are similar to the Sun.

In the 1990s, though, Sakurai’s object flared up — it grew more than 10,000 times brighter. That’s because it was going through a phase called a “final flash”: There was enough helium to ignite a new series of nuclear reactions at the star’s surface.

The new reactions produced a strong “wind” of gas. As this material surrounded the star, it cooled and clumped together to form a cloud of dust. That blocked the star’s light, so it vanished from view.

Today, though, the dust is getting thinner. That’s allowed astronomers to start watching it again. In fact, they’ve seen that it seems to be blowing giant bubbles into space from above its poles — a final act for a dying star.

Although we can’t see the star, we can see its location. It’s above the “teapot” formed by the brightest stars of Sagittarius, which is low in the south at nightfall.

Script by Damond Benningfield

The black hole at the heart of the Milky Way galaxy is one of the quietest around. It’s not pulling in much material, so there’s nothing to heat up and produce light. Every once in a while, though, the black hole pulls apart an unlucky star, creating a powerful display of fireworks — including some “cannonballs” as big as planets.

The black hole is called Sagittarius A-star. It’s about 27,000 light-years away. It’s above the spout of the teapot formed by the bright stars of Sagittarius, which is low in the south at nightfall.

The black hole is about four million times the mass of the Sun — rather small for a galactic hub. It’s encircled by a thin disk of gas and dust, which emits a trickle of energy.

When the black hole grabs a star, though, it produces some major pyrotechnics. It rips the star to shreds, producing a torrent of energy. Some of the material enters the disk before it plunges into the black hole. But some of it, accelerated by the black hole’s powerful gravity, shoots back out into space.

Earlier this year, a study said that some of that hot gas coalesces to form blobs as big as planets. They’ve moving so fast that they’ll eventually leave the galaxy behind.

A few of these blobs could be passing through our galactic neighborhood. Right now, there’s no way to tell them apart from planets drifting through space on their own. But future telescopes might be able to track down these blobs from the Milky Way’s dark heart.

Script by Damond Benningfield

Sagittarius marks the center of our home galaxy, the Milky Way. So the constellation is packed with stars, star clouds, and star clusters. But one of the clusters doesn’t belong to the Milky Way at all — at least not yet. It’s in a small, puffy galaxy on the far edge of the Milky Way’s disk.

Messier 54 is a globular cluster. It’s a ball-shaped region a few dozen light-years across, packed with hundreds of thousands of stars.

Native globulars are among the Milky Way’s oldest residents — they were born with the galaxy itself, more than 10 billion years ago. But a few of these clusters are interlopers — they were born in other galaxies, then were absorbed when their galaxies were consumed by the Milky Way.

For a long time, astronomers thought that M54 was a charter member of the Milky Way — one of its early globular clusters. A couple of decades ago, though, they found that it’s near the center of a newly discovered galaxy, the Sagittarius Dwarf, so it’s outside the Milky Way’s disk. But the Milky Way is pulling in the smaller galaxy, and eventually will incorporate all of its stars. So M54 will become a member of the Milky Way — one of its newest — and oldest — residents.

Sagittarius scoots low across the south on summer nights. Its brightest stars form the outline of a teapot, with clouds of stars rising from its spout like steam. M54 is at the lower left corner of the teapot, although you need a telescope to pick it out.

Script by Damond Benningfield

One of the problems with planets in other star systems is that they don’t just walk up to you and tell you their life stories. But a mammoth telescope that’s being developed now should help with the introductions. When it’s completed in the next decade, it will allow astronomers to actually see planets around nearby stars. They won’t see any details, only points of light near the stars. But the view will be good enough to learn if the planets have atmospheres, and whether the atmospheres show any evidence of life.

GMT — the Giant Magellan Telescope — will be built in in the Andes Mountains of Chile. It’s being developed by a consortium that includes the University of Texas at Austin. When it’s completed in the next decade, its main mirror will span 80 feet — more than twice the size of anything in operation today.

That mirror will collect several times more light than any current telescope, allowing it to view objects that are fainter and farther away. And it’ll see them more clearly than even Hubble Space Telescope.

In addition to studying exoplanets, astronomers will use GMT to look for the first stars in the universe. The stars flared to life soon after the Big Bang. They probably were quite heavy, so they would have burned out and exploded in a hurry. They seeded the universe with the first heavy elements — the elements that make up planets and people. And they triggered the birth of more stars — lighting up the universe.

Script by Damond Benningfield

When it comes to seeing deep into the universe, size matters. A big telescope gathers more light than a small one, allowing it to see objects that are fainter and farther away. And astronomers are working on a handful of giant telescopes that are scheduled to come on line in the next decade. Their main mirrors, which gather starlight, will be big enough to hold a tennis court. That will allow them to see back to shortly after the Big Bang.

The first of these new behemoths is GMT — the Giant Magellan Telescope. Its main mirror will consist of seven segments, each of which is as big as the largest single telescope mirrors in use today. Each segment will have a slightly different curvature, allowing them to work together as a single mirror.

Combined, they’ll span about 80 feet, allowing GMT to gather several times more light than any telescope in operation today.

The telescope will use a technique known as adaptive optics to sharpen its view of the heavens. This technique uses a set of smaller mirrors to compensate for the blurring effects of Earth’s atmosphere.

GMT is being built atop an 8,000-foot mountain in the Atacama Desert of Chile. The air is clear and steady, with few clouds to spoil the view. And the site is remote, so the skies are nice and dark.

Among other things, GMT will allow astronomers to study planets in other star systems and look back to the beginnings of the universe. More about that tomorrow.

Script by Damond Benningfield