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StarDate Online - Your guide to the universe

  • Fireworks Factory

    The beautiful spiral galaxy NGC 6946 has been the site of some spectacular fireworks. Over the last century, astronomers have detected 10 exploding stars, known as supernovae, in the galaxy, which is more than any other galaxy. Because of that prolific display, NGC 6946 is also known as the Fireworks galaxy. This image, which combines X-ray (purple) and visible wavelengths, shows massive gas clouds in the galaxy's spiral arms. The gas clouds are nurseries where new stars are born. The most massive of these new stars quickly burn out and explode, adding to the fireworks. [NASA/CXC/MSSL/R.Soria et al; Optical: AURA/Gemini Observatory]

  • Disappearing Star

    NGC 6946 is both beautiful and busy. It’s a spiral galaxy that we see face-on, providing a glorious view of its delicate spiral arms. And over the last century, astronomers have recorded 10 supernova explosions in the galaxy — the most recent just three months ago. That’s earned NGC 6946 a nickname: the Fireworks galaxy.

    The number of firecrackers could have been even higher. But instead of exploding, one of the galaxy’s massive stars simply winked out of existence. That means it might have collapsed to form a black hole.

    For a long time, theory has said that any star born with more than about eight times the mass of the Sun should end its life as a supernova. The titanic blast rips the star’s outer layers to bits, while the core collapses to form a neutron star or a black hole.

    In recent years, though, astronomers have started to suspect that the most-massive stars skip right past the explosion part. They may start to explode, but as the core collapses to form a heavy black hole, its gravity grabs the exploding material and pulls it in.

    An example of that may be the star in NGC 6946. Earlier this year, a team of astronomers reported that, in 2009, the star began getting brighter. But by 2015, it had vanished. There was no explosion, no debris — nothing at all. The team concluded that the star collapsed to form a black hole — depriving the Fireworks galaxy of another bright display.

     

    Script by Damond Benningfield

    StarDate: 
    Wednesday, August 23, 2017
    Teaser: 
    A potential firecracker fizzles out
  • Disappearing Star

    NGC 6946 is both beautiful and busy. It’s a spiral galaxy that we see face-on. Over the last century, astronomers have recorded 10 supernova explosions in the galaxy, with the most recent just three months ago. So NGC 6946 is also called the Fireworks galaxy.

  • Hyperactive Galaxy

    Our home galaxy, the Milky Way, is a giant spiral that contains hundreds of billions of stars. And every now and then, one of its stars explodes as a supernova. The last time astronomers saw that happen was more than 400 years ago, but that may be because we can see only a small portion of our vast galactic home. If we were outside the Milky Way, astronomers estimate, we’d see about two supernova explosions per century.

    We’ve seen supernova explosions in many galaxies beyond our own. But one prolific galaxy puts all the others to shame. It’s a beautiful spiral in the constellation Cepheus known as NGC 6946. During the past hundred years, astronomers have seen a record 10 supernovae in this one galaxy.

    The galaxy owes those fireworks to its impressive star-spawning ways. Its gas and dust are giving birth to large numbers of new stars. The most massive of these stars explode a few million years after their birth, producing the fireworks we see.

    As galaxies go, NGC 6946 is fairly close — about 20 million light-years from Earth. That means these stars actually died 20 million years ago, but it’s taken that long for the light of their explosions to reach us. Astronomers first saw a supernova in this galaxy a hundred years ago, back in 1917. The most recent popped off just a few months ago.

    The supernova count might have gone even higher, but instead of exploding, one massive star collapsed to form a black hole. More about that tomorrow.

     

    Script by Ken Croswell, Copyright 2017

    StarDate: 
    Tuesday, August 22, 2017
    Teaser: 
    A galaxy with lots of fireworks
  • Microscopium

    A faint scientific instrument scoots low across the south at this time of year. Microscopium was one of 12 constellations created by Nicolas Louis de Lacaille in the 18th century. Its stars are quite meager, so you need dark skies and a starchart to pick it out.

  • Brilliant Beads

    Brilliant beads of sunlight, known as Baily's Beads, shine through mountains on the Moon in this photograph of the August 21 eclipse from Madras, Oregon. [NASA/Aubrey Gemignani]

  • Eclipse Day

    Many skywatchers have been planning for this day for years. The Moon will pass directly between Earth and Sun today, creating a total solar eclipse from Oregon to South Carolina. Day will turn to night, and stars and planets will pop into view. And tens of millions of Americans are expected to see the spectacle in person.

    A solar eclipse is the result of a complex ballet involving Earth, the Moon, and the Sun.

    The Moon pirouettes against the background of stars and planets every 27 and a half days. But because the Sun is also moving against that background, it takes a couple of days longer for the Moon to catch up to it.

    While the Moon passes the Sun roughly once a month, most months it doesn’t cause an eclipse. Instead, it usually glides a little above or below the Sun, because its orbit is tilted relative to the Sun’s path across the sky. A solar eclipse occurs only when the new Moon crosses that path. And even then, most eclipses are only partial: the Moon covers only part of the Sun’s disk, which is what most Americans will see today.

    Total eclipses occur an average of about 18 months apart, although the gap can range from a few months to more than two years. The next total eclipse will take place in 2019, visible from parts of South America.

    And there’ll be another eclipse over the U.S. on April 8th of 2024, from Texas to Maine. So if you miss out on today’s show, start planning for the next one — another disappearing act for the Sun.


    Script by Damond Benningfield


     

     

    StarDate: 
    Monday, August 21, 2017
    Teaser: 
    Two chances to see an eclipse
  • Eclipse Day

    The Moon will pass directly between Earth and Sun today, creating a total solar eclipse from Oregon to South Carolina. Day will turn to night, and stars and planets will pop into view. From the rest of the country, the Moon will cover only a portion of the Sun.

  • Anatomy of an Eclipse

    Day will briefly turn to night for parts of the United States on August 21 during a total solar eclipse. The Moon will completely cover the Sun's disk, blocking the sunlight but allowing the Sun's pearly outer atmosphere, the corona, to shine through. This multiple-exposure image shows the entire sequence of an eclipse as the Moon slowly encroaches on the Sun's brilliance, covers the Sun (center), then retreats. While the total eclipse is safe to look at with the eye alone, the Sun is still so bright at all other phases of the eclipse that looking at it without proper protection can result in eye damage. [Rick Fienberg/TravelQuest International/Wilderness Travel]

    More information about the eclipse:

  • Ready for the Eclipse

    For millions of skywatchers in the United States tomorrow, day will briefly turn to night as the Moon passes in front of the Sun, eclipsing its light. The Sun’s outer atmosphere, the corona, will shine silvery-white around the dark Moon. And the stars and planets will shine through the dark as well.

    Regulus, the heart of the lion, will perch closest to the Moon. It’s usually lost from view at this time of year as the Sun crosses Leo’s borders. The planet Mercury will shine brightly a little farther away, with reddish Mars on the other side of the Sun.

    Brilliant Venus and Jupiter will be farther from the Sun, with Sirius, the brightest star in the night sky, low in the southwest.

    You may be tempted to shoot pictures and videos throughout the show. But a total solar eclipse is a once-in-a-lifetime experience, so most veterans say it’s best to simply drink in the spectacle. And it’s one that involves most of your senses — the air will get cooler, and you’ll hear the sounds of birds and other animals preparing for night.

    There are a few safety tips to keep in mind. It’s completely safe to look at the Sun when it’s fully eclipsed, but not at other times; it’s so bright that it can damage your eyes. And highway patrols around the country remind drivers not to stop on busy highways. Instead, find a park or some other safe spot to enjoy the sights and sounds of this amazing lightshow.

    We’ll have more about this skywatching spectacle tomorrow.


    Script by Damond Benningfield


    More information about the eclipse:

     

     

    StarDate: 
    Sunday, August 20, 2017
    Teaser: 
    Getting ready for the big event
  • Ready for the Eclipse

    The Moon will eclipse the Sun tomorrow, briefly turning day to night across part of the United States. It’s completely safe to look at the Sun when it is fully eclipsed, but not at other times; it’s so bright that it can damage your eyes.

  • Eclipse Predictions

    The Great American Eclipse is coming up on Monday. The Moon will briefly cover the Sun, turning day to night across a narrow slice of the United States.

    The timing of the eclipse is known down to the second, and has been for decades. And today, astronomers can predict eclipses far into the future. But making such predictions isn’t easy. It requires a detailed knowledge of the Moon’s orbit around Earth, Earth’s orbit around the Sun, and even the shapes of Earth and the Moon.

    Scientists had been trying to predict eclipses for a long time. Just when they first succeeded is a bit unclear, though.

    There’s no doubt that people have been predicting lunar eclipses for thousands of years. But lunar eclipses are easier to predict. Earth’s shadow is roughly a hundred times wider than the Moon’s, so you don’t need as high a level of precision to get it right.

    There are stories that the Chinese were predicting solar eclipses more than 4,000 years ago, but no confirmation. An eclipse in 585 BC that stopped a war supposedly was predicted by Thales, a Greek scientist. Many modern-day scientists doubt that, however.

    The first confirmed prediction was made by Edmond Halley, using the laws of gravity devised by Isaac Newton. Halley forecast that an eclipse would cross England on May 3rd, 1715. And he was right. So the eclipse of 1715 is known as Halley’s Eclipse — honoring the prediction of an astronomical spectacle.

    More about eclipses tomorrow.

     

    Script by Damond Benningfield

    More information about the eclipse:

     

    StarDate: 
    Saturday, August 19, 2017
    Teaser: 
    Predicting a skywatching spectacle
  • More Eclipse

    The Great American Eclipse is coming up on Monday. The Moon will briefly cover the Sun, turning day to night across a narrow slice of the United States. The rest of the country will see a partial eclipse, with the Moon covering only a portion of the Sun’s disk.

  • Safety First!

    The August 21 solar eclipse will be one of nature's grandest spectacles. But it requires special protection for safe viewing, such as special eclipse glasses (shown) or dark welder's glass (No. 14 or darker). Sunshades, exposed photographic film, and other makeshift solutions do NOT provide adequate protection for viewing the partial phases of the eclipse. The only time it's safe to view the eclipse without protection is during totality, when the Moon completely covers the solar disk. [Jay Pasachoff]

  • Eclipse Watching

    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:

    StarDate: 
    Friday, August 18, 2017
    Teaser: 
    Safety tips for a skywatching spectacle
  • Eclipse Watching

    Venus, the “morning star,” looks down on the Moon at first light tomorrow. The Moon is headed toward an even more spectacular encounter on Monday, when it will cross in front of the Sun, creating a total solar eclipse.

  • Chasing a Shadow


    The Sun sets behind a NASA research aircraft, a WB-57F Canberra, at its base near Houston. Two of NASA's three Canberras will chase the Moon's shadow during the August 21 total solar eclipse. They will carry instruments to monitor the Sun's corona, its hot outer atmosphere. They also will study the planet Mercury, which will become visible during the eclipse, and scan the space between the Sun and Mercury for small asteroids, known as Vulcanoids. [NASA/JSC]

    We have much more about eclipse science in the July/August issue of StarDate magazine. Order onlineor by calling 1-800-STARDATE (8 a.m.-4 p.m. Monday-Friday).

     

  • More Eclipse Science

    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

    StarDate: 
    Thursday, August 17, 2017
    Teaser: 
    Chasing a shadow from the sky
  • Moon and Venus

    The “morning star” stands to the lower left of the crescent Moon before dawn tomorrow. Although it looks like a brilliant star, it’s really Venus, our nearest planetary neighbor.

  • Solar Mystery

    Astronomers will pay special attention to the Sun's hot outer atmosphere, the corona, during Monday's solar eclipse. It will form a silvery halo around the intervening Moon. The corona is millions of degrees hotter than the Sun's surface, but astronomers are not yet certain what heats it. They will be watching the eclipse from the ground and from aircraft to try to gather clues about this solar mystery. [Luc Viatour]

    We have much more about eclipse science in the July/August issue of StarDate magazine. Order onlineor by calling 1-800-STARDATE (8 a.m.-4 p.m. Monday-Friday).

     

  • Eclipse Science

    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

    StarDate: 
    Wednesday, August 16, 2017
    Teaser: 
    Studying a solar mystery
  • Solar Corona

    Skywatchers along a narrow path across the U.S. will see a rare sight on Monday: the Sun’s corona, its hot, faint outer atmosphere. It will look like a silvery curtain around the Sun during a solar eclipse, which will be visible from Oregon to South Carolina.

  • Moon on the Move

    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

    StarDate: 
    Tuesday, August 15, 2017
    Teaser: 
    The Moon moves across the sky
  • Moon on the Move

    The Moon will pass several bright objects over the next week. Tomorrow, bright Aldebaran, the eye of the bull, will stand just above the Moon at first light. And on Friday and Saturday, the Moon will pass by the planet Venus, the “morning star.”

  • The Right Path

    The Great American Eclipse is coming up on August 21. This map shows the circumstances of the eclipse across the entire United States. The path of totality, where the Moon will completely cover the Sun, is a shaded strip from Oregon to South Carolina. [NASA/Scientific Visualization Studio]

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