StarDate

StarDate

  • Blue Moon

    Folklore doesn’t have to be old to be popular. Consider, for example, the modern definition of Blue Moon: the second full Moon in a calendar month. Although that definition began as a mistake, it became popular more than two decades ago and has ingrained itself in skywatching lexicon.

    And by that definition, there’s a Blue Moon the next couple of nights. There was a full Moon on July first, and there’s another early tomorrow morning — the second full Moon of the month.

    Blue Moon already had several definitions, including the thirteenth full Moon in a calendar year, and the fourth full Moon in a calendar quarter. The phrase could also be taken literally. Under some rare atmospheric conditions — when there’s a layer of ash high in the air, for example — the Moon can actually look blue. And the phrase “once in a blue moon” is unrelated to the Moon itself, and simply means that an event is rare.

    The “second-full-Moon-in-a-month” definition entered the culture in the 1980s, thanks to a mistake in a decades-old magazine article. It was popularized by both Star Date and the game Trivial Pursuit.

    Some have tried to stamp out the definition, but it’s unlikely they’ll succeed. Like Super Moon, which is an unusually close full Moon, and Blood Moon — a reference to the Moon’s red color during an eclipse — Blue Moon is probably here to stay — a fun bit of modern folklore about the night sky.

    Tomorrow: on the wing of the swan.


    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • More Charles Townes

    Back in the 1980s, Charles Townes developed a laser system that helped infrared telescopes get a sharper view of the center of the Milky Way. Other astronomers then used that system to make the first measurement of the mass of the giant black hole at the galaxy’s heart.

    It was a remarkable achievement. And it’s all the more interesting because Townes was one of the fathers of the laser. He developed its predecessor, known as a maser, and he obtained the first patents for the laser itself. He even won the Nobel Prize for those accomplishments.

    Townes was born 100 years ago this week. During his long career, he pursued many interests. He helped develop new applications for radar during World War II. After the war, he studied microwaves and the structure of molecules — work that led to the maser and laser. He provided scientific advice for the Apollo missions to the Moon. Then he turned to astrophysics — an area he pursued until shortly before his death early this year.

    Townes and others turned his inventions and discoveries into tools for exploring the universe. Astronomers use natural masers to probe the composition of other galaxies, and to plot the sizes of black holes. They use lasers to sharpen the view of stars and other objects. And they bounce laser beams off special reflectors on the Moon to study Albert Einstein’s theory of gravity — pursuing the secrets of the universe with beams of light.


    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Last Round

    A dying star has rejuvenated itself in this combined X-ray and optical image. Known as Abell 78, the system consists of a white dwarf -- the dead core of a once sun-like star -- surrounded by a glowing bubble of gas. The star expelled most of its outer layers of gas as it died, forming the spherical bubble. But a thin layer of helium re-ignited, producing one final round of nuclear fusion reactions. The rejuvenated star is particularly hot, so it emits strong, high-speed winds. Those winds have carved an elongated structure within the expanding bubble of gas, creating a cavity. Eventually, the helium fusion will stop and the white dwarf will no longer produce energy. Instead, it will slowly cool over the eons as the surrounding bubble of gas dissipates and vanishes from view. [ESA/XMM-Newton/J.A. Toalá et al.]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Charles Townes

    There’s nothing like a spring day to clear the little gray cells and let the imagination wander. In fact, a spring day in 1951 in Washington, DC, helped lead to the development of the laser.

    Charles Townes was a physicist at Columbia University. He’d been trying to develop powerful beams of radiation, but he wasn’t having any luck. But as Townes recalled last year in this interview from the University of California, after a meeting in DC, it came to him.

    TOWNES: I thought about it and I thought about it, and I sat on a bench in a park. Oh, hey! I got an idea — this is the way to do it. I think it’ll probably work. I went home, and it took me a long time to get it done....

    Townes and his students developed that insight into the maser — TOWNES: Maser is microwave amplification by stimulated emission of radiation — a device that creates a beam of microwaves of the same wavelength that all move in step, like soldiers marching in review. Later, Townes and others extended the technique with beams of visible light, creating the laser. His work earned Townes a share of the 1964 Nobel Prize for physics.

    Townes was born 100 years ago today in South Carolina, and passed away earlier this year. During his long career, he helped develop radar bombing systems for the military and probed the workings of molecules. He advised NASA on the science of the Apollo Moon landings, and the Reagan Administration on a missile system. And he used his creations to study the universe. More about that tomorrow.


    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Noctilucent Clouds

    If you live at high northern latitudes, you might see some eerie clouds at this time of year. They show up for a little while in deep twilight, and shine electric blue. And they appear to have a connection to both meteors and our planet’s changing climate.

    Noctilucent clouds were first reported in 1885. That sighting may have been related to the eruption of Krakatoa, a powerful volcano in Indonesia. Tiny grains of ash from the explosion may have drifted to the top of the atmosphere — altitudes of 45 to 50 miles. Molecules of water then latched on to the ash particles, forming ice crystals.

    But recent research suggests that most noctilucent clouds are seeded by tiny grains of space dust. These particles bombard our planet all the time. Many of them are so small that they don’t fall to the ground, but linger in the upper atmosphere. They form the kernels around which cloud particles grow.

    Sightings of noctilucent clouds have become more common in recent years, and the clouds have been seen farther south than ever before — as far down as Utah and Colorado.

    Research says that could be a result of the extra methane we release into the air every year. Some of the methane climbs to high altitudes. Sunlight triggers a series of reactions that breaks the methane apart, leaving two water molecules. That provides more water to freeze around the nuggets of space dust — creating more of these electric-blue clouds in the twilight.


    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Moon, Saturn, Antares

    The gibbous Moon anchors a pretty triangle this evening. The triangle’s other points are the planet Saturn, which is to the right of the Moon, and the star Antares, about the same distance below the Moon.

    Antares is the 15th-brightest star system in the night sky. In the stellar brightness scale, it’s ranked at almost exactly first magnitude.

    Astronomers have been using that scale for many centuries, although they’ve refined it to take advantage of the precise measurements possible with modern instruments.

    Originally, the brightest stars of all were described as first magnitude, the next brightest were second magnitude, and so on. Today, thanks to those precise modern measurements, the brightest stars are actually in negative numbers.

    The scale is logarithmic, so that a difference of five magnitudes equals a hundred-fold difference in brightness. On that scale, a first-magnitude star is roughly two-and-a-half times brighter than one of second magnitude.

    The faintest objects visible to the unaided eye depend on sky conditions, light pollution, and your own eyesight. But under especially dark, clear skies, those with very good eyes can see all the way down to about sixth magnitude — stars that are just one percent as bright as Antares.

    Again, look for first-magnitude Antares below the Moon as night falls, with the slightly brighter planet Saturn to the right of the Moon.

    Tomorrow: electric-blue clouds in the twilight.


    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Moon and Saturn

    The stately planet Saturn accompanies the Moon across the sky tonight. It’s close to the lower left of the Moon at nightfall, and looks like a bright star. As a bonus, the bright orange star Antares is close by as well, farther to Saturn’s lower left.

    Saturn is the sixth planet out from the Sun — more than nine times farther from the Sun than Earth is. It’s also big and bright, which makes it the most distant planet that’s easily visible to the unaided eye. The combination earned Saturn a special place in ancient skylore.

    Saturn takes almost 29-and-a-half years to complete one orbit around the Sun. So as seen from Earth, it takes that long for the planet to complete one full turn against the background of distant stars. That compares to only about two years for Mars, and about 13 years for Jupiter.

    Because of this leisurely progression across the sky, several cultures associated the planet with powerful and stately gods. The ancient Assyrians, for example, named it for a god known as “the oldest of the old.” In Greece, it was named for Cronus, who was the father of Zeus, the king of the gods of Olympus. And the Romans adapted Cronus as Saturn, the god of agriculture.

    Saturn will slowly pass by Antares over the coming months, and start to really pull away late next year. After that, it won’t return to the vicinity of the scorpion’s heart until the year 2044.

    We’ll have more about this beautiful evening grouping tomorrow.


    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Future Outbursts

    One of the stars in the binary system V664 Cassiopeia gave some of its gas to its companion. Before long, though, it’ll take some of it back. And that’ll set up a cycle in which the system periodically flares to many times its normal brightness.

    Originally, the system consisted of two stars that probably were a little less massive than the Sun. One of the stars was a bit heavier than the other, though, so it aged more quickly. As it neared the end of its “normal” lifetime, it puffed up to giant proportions.

    The star got so big, in fact, that its outer layers engulfed its companion. The companion most likely swept up some of that hot gas for its own, increasing its own mass to roughly that of the Sun. But it scattered most of the gas, forming a glowing bubble around the system. As V664 Cas moves through space, some of the material in the bubble gets left behind, forming a long streamer.

    Today, the system consists of the heavier star’s hot, dead core — a white dwarf — and the companion, which resembles the Sun. They’re quite close together, and they’re moving even closer. Eventually, the white dwarf will begin to pull gas off the surface of the companion, surrounding itself with a hot disk.

    The transfer of gas will produce outbursts that’ll cause the system to flare to dozens or even thousands of times its normal brightness. So V664 Cas should make a spectacle of itself many times in the coming millennia.


    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Bread Crumbs

    The star system V664 Cassiopeia is leaving "bread crumbs" as it races through the galaxy: a trail of gas and dust that may span several light-years. The system consists of two stars in a very tight orbit. One of the stars recently blew its outer layers into space, and the motion of the companion star kicked the material farther into space, forming a colorful bubble around the system. Some of the material piles up in front of the stars like water in front of a ship. [T.A. Rector (Univ. Alaska Anchorage)/H. Schweiker (WIYN/NOAO/AURA/NSF)]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Bread Crumbs

    V664 Cassiopeia is complicated. It consists of two stars that are so close together they’re almost touching. It’s ramming into clouds of gas and dust like a cosmic fist. And it’s leaving behind a trail of breadcrumbs that may span several light-years.

    The system is in Cassiopeia, the queen, which is low in the north-northeast at nightfall right now. V664 is to the left of the “W” formed by Cassiopeia’s brightest stars, although it’s too faint to see with the eye alone.

    But a telescope sees a remarkable sight — a structure that looks something like a jellyfish squirting across the sky, or perhaps a fist jabbing a pool of water.

    The system consists of a “dead” star known as a white dwarf, plus a second star that resembles the Sun. Not long ago, the white dwarf was also a “normal” star like the Sun. But it puffed up to giant proportions, engulfing its companion.

    As the companion swirled through the star’s outer layers, it stole some of the hot gas for its own, but kicked most of the gas away, forming a colorful bubble around the two stars.

    The system is moving fast, so the bubble piles up material in front of it like water in front of a ship. At the same time, some of the gas in the bubble gets left behind like a trail of breadcrumbs. The system has been leaving that trail for a hundred thousand years, so the trail could stretch across several light-years.

    And V664 Cas is likely to get a lot more interesting. More about that tomorrow.


    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Moon and Spica

    The Moon cycles through its phases about once a month. It starts at new, waxes until it’s full, then wanes until it’s new once more.

    Not only does it changes phases, but it also changes its position in the sky. It creeps into the western evening sky a couple of days after it’s new. When it’s full, it rises at sunset and remains visible all night. And a couple of days before it’s new again, it rises shortly before the Sun, so it’s in the eastern sky at first light.

    If you lived on the side of the Moon that always faces Earth, you’d see our world going through the same cycle of phases that the Moon does. Unlike the Moon, though, Earth’s position in the sky wouldn’t change. Our planet would always appear in the same spot above the horizon, day and night, month after month.

    Earth’s place in the sky would depend on your location on the lunar disk. If you were at the middle, Earth would stand straight overhead. But if you were near one of the poles, Earth would stand low above the horizon.

    And if you lived on the lunar farside, you’d never see Earth at all — it would remain forever hidden on the other side of the Moon.

    And the Moon itself isn’t hidden tonight. It’s near first quarter, so sunlight illuminates almost half of the lunar disk. It’s in the south as darkness falls, and sets a few hours later. Spica, the brightest star of Virgo, stands close to the left of the Moon — a bright companion to our always-on-the-move satellite world.


    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Emptiness

    Space is mostly empty, but some parts of the universe are emptier than others. During the 1970s, astronomers began to discover vast reaches of space that contain almost no galaxies at all.

    We don’t live in one of those “voids” ourselves. Instead, we live in a galaxy that’s part of a group of several dozen galaxies. This group and several others make up an even bigger collection of galaxies. When you map them out, they form a long string known as a filament. Most other galaxies belong to similar structures. Between these glowing filaments, though, there’s mostly empty space.

    These voids typically measure about 300 million light-years across. That’s an enormous distance — every star and galaxy you can see with the unaided eye is much, much closer to us than that.

    One of the greatest astronomers of the 20th century didn’t believe such things existed. Edwin Hubble, who discovered that the universe is expanding, thought that space was much more uniform. He reached that conclusion by counting galaxies in different directions. But Hubble didn’t know how far most of the galaxies were. When astronomers measured the distances and plotted the galaxies on a map, they discovered that the galaxies fell along filaments, with vast voids between them.

    Astronomers are fortunate that we’re not in one of these voids, because there’d be few nearby galaxies for them to study. Instead, they have a plethora of them to examine, adding to our understanding of the cosmos.


    Script by Ken Croswell, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Blowing Bubbles

    Giant bubbles of hot gas erupt from the core of the Milky Way galaxy in this artist's concept. The galaxy's thin disk is shown edge-on, with the bubbles billowing thousands of light-years into intergalactic space. Known as Fermi bubbles for their discovery by the Fermi space telescope, they may have been created by eruptions in a disk of gas close to the galaxy's central black hole. The bubbles are visible only to space telescopes that are sensitive to gamma rays and X-rays. [NASA/GSFC]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Fermi Bubbles

    Hot gas is exploding out of the center of the galaxy. It forms giant bubbles that extend more than 30,000 light-years above and below the galaxy’s hub. The bubbles emit gamma rays — the most powerful form of energy. Fermi Gamma-ray Space Telescope has traced these expanding bubbles, which have been named Fermi bubbles in its honor. The observations have revealed how fast the gas is moving. In turn, that reveals when the outflow began.

    The astronomers used Hubble Space Telescope to observe a distant quasar that’s behind the bubbles. As the quasar’s light passes through the Fermi bubbles, atoms of gas absorb some of the energy. These observations indicate that the gas is rushing out of the Milky Way’s central regions in all directions — at about two million miles per hour.

    That speed reveals that the outflow started about two-and-a-half million to four million years ago. So that’s when something happened to trigger the eruption. One possibility is that a cloud of gas fell toward the supermassive black hole at the Milky Way’s center. The gas got extremely hot as it did so, creating enough radiation to blow surrounding gas far out into space.

    Astronomers are analyzing more than 20 other quasars whose radiation passes through the Fermi bubbles. Since each quasar probes a different line of sight, the observations should yield the velocities of gas throughout the bubbles — perhaps settling the question of their origin.


    Script by Ken Croswell, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Stinger

    The celestial scorpion has a potent stinger — a pair of bright stars at the tip of its curving body. They’re low above the southern horizon as night falls, with the rest of Scorpius curling to their upper right.

    The brighter star in the stinger is known as Lambda Scorpii. It’s the second-brightest star in Scorpius, so it’s hard to miss. Fainter Upsilon Scorpii stands close to its right.

    Lambda actually consists of three stars. The system’s main star is more than 10 times as massive as the Sun. At that great heft, it consumes its nuclear fuel in a hurry. It’ll soon begin to exhaust its fuel, so it’ll puff outward. The star will engulf its nearer companion, which is only a few million miles away. That’ll probably destroy the companion, perhaps sending its core spiraling into the core of the main star. That may hasten the demise of the bigger star, which is likely to explode as a supernova.

    Upsilon is a single star, but it’s also a stunner. It’s about 10 times the Sun’s mass, and it’s many thousands of times brighter.

    Although Lambda and Upsilon appear quite close together, they’re more than 150 light-years apart. Even so, the stars are related. They were born from the same giant complex of gas and dust. This region has given birth to many massive stars, including Antares, the scorpion’s bright orange heart. But the stars are only loosely bound together, so they’re moving apart — spreading their magnificence across the galaxy.


    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Moon and Companions

    The three brightest objects in the night sky congregate in the west after the Sun sets this evening — the Moon and the planets Venus and Jupiter. They don’t hang around for long, though. They all set by a couple of hours after sunset.

    Venus stands close to the upper right of the Moon. The brilliant planet has been shining as the “evening star” all year long. But that reign is about to end. Venus is dropping toward the Sun in our sky, and it’ll cross between Earth and the Sun in just four weeks. When it does so, it’ll move into the morning sky, beginning a long run as the “morning star.”

    Jupiter stands a little farther from the Moon. It’s dropping toward the Sun as well. But while Venus is closer to the Sun than Earth is, giant Jupiter orbits far outside the orbit of Earth. So instead of crossing between Earth and the Sun, it’ll pass behind the Sun.

    After that, Jupiter will move into the morning sky as well. But because Jupiter is so much farther away than Venus is, that transition will take longer, so the planet will linger near the Sun for a bit longer than Venus will. But both worlds will be in great view in the dawn sky in the middle of September, and will remain in the morning sky for the rest of the year.

    For now, though, look for these two sparkling planets low in the west as twilight drains from the evening sky, flanking the beautiful crescent Moon.

    Tomorrow: feeling the scorpion’s potent stinger.

     

    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • First Stars II

    Many of the first stars in the universe should have been stunners — monsters hundreds of times heavier than the Sun, and perhaps millions of times brighter. Yet so far, astronomers haven’t seen a single one.

    These hypothetical stars are known as Population III. They formed from the hydrogen and helium gas that were created in the Big Bang. They quickly forged carbon, oxygen, and other elements, then expelled them into space where they could be incorporated into new stars. That process continues today, with each generation of stars adding to the chemical mix from which future generations will be born.

    The Population III stars all lived billions of years ago, when the universe was quite young. Observed from Earth, that means the stars would be billions of light-years away. And at that great range, even the brightest individual star is far too faint to see with today’s telescopes.

    A recent study, though, says that clusters of these stars might be visible to future telescopes. Models by researchers at the University of Western Ontario show that gas falling into a newborn cluster could make it look especially bright. In fact, a cluster of as few as 16 of these stars could shine a hundred million times brighter than the Sun. Such a brilliant object should be visible to the James Webb Space Telescope, which is scheduled for launch in a few years. The telescope may bring the first stars in the universe into view for the first time.


    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The First Stars

    In the modern-day universe, stars face a weight limit — about 150 times the mass of the Sun. Anything heavier would be so hot and bright that it would blow away any additional gas that tried to fall on its surface, keeping it from getting any bigger.

    In the early universe, though, the weight limit might have been much higher — hundreds of times the mass of the Sun. Such stars would have blazed millions of times brighter than the Sun.

    The difference is caused by slight changes in the recipe for making stars. The early universe contained only hydrogen, helium, and a tiny smattering of lithium — elements forged in the Big Bang. As the universe expanded and cooled, these elements clumped together to make stars.

    The cores of these newborn stars were hot enough to ignite nuclear fusion, which forces lighter elements together to make heavier ones. Heavier stars plowed through their original hydrogen and helium quickly, forging carbon, oxygen, and many other elements. And when they could no longer sustain the fusion reactions, they exploded. The energy of these blasts created many more elements.

    The explosions filled the universe with many of these heavier elements, which could be incorporated into later generations of stars.

    Models of star formation say these extra ingredients inhibit the growth of stars that are born today. The stars can still grow to monstrous proportions — just not as monstrous as when the universe was young.

    More tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Ice Mountains

    Mountains tower up to two miles above the surface of Pluto in this July 14 image from New Horizons, taken from a distance of 478,000 miles (770,000 km). The mountains probably formed within the last 100 million years, according to mission scientists, making this some of the youngest terrain in the solar system. Scientists aren't sure what could power the creation of such young features on Pluto. The mountains probably are made of water ice, which is frozen as hard as granite on Pluto's frigid surface. [NASA/JHUAPL/SWRI]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Stellar Metals

    Every “normal” star is a ball of hydrogen and helium, the simplest of all chemical elements. All of the hydrogen and most of the helium were forged in the Big Bang.

    Stars also contain smatterings of heavier elements, which are known as metals. These elements were forged by the stars themselves. As the stars die, they expel some of these elements into space, where they can be incorporated into new stars. So each generation of stars contains a higher proportion of metals — everything from carbon and oxygen to iron and lead.

    Based on the amount of metals, astronomers divide stars into two broad categories — Population I and Population II.

    The Sun belongs to Population I. These stars contain fairly high percentages of metals — about two percent in the case of the Sun. These stars formed fairly recently — after earlier generations had pumped the heavy elements into space.

    The earliest generations yet seen form Population II. These stars have a much smaller percentage of metals, which means they formed when there were fewer metals around — perhaps less than a billion years after the Big Bang.

    In our home galaxy, the Milky Way, many of these stars are found in globular clusters — tightly packed balls of hundreds of thousands of stars on the galactic outskirts. The levels of metals indicate that some of these stars are up to 13 billion years old.

    The very first stars shouldn’t contain any metals at all. More about that tomorrow.


    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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