StarDate

StarDate

  • Earth at Aphelion

    You’ve probably never noticed it, but the Sun appears to change size a little bit over the course of a year. The Sun itself doesn't change, though. Instead, it looks bigger and smaller because the distance to the Sun changes — by about three-and-a-half percent.

    That happens because Earth’s orbit around the Sun isn’t a circle. Instead, it’s an ellipse, which looks like a slightly flattened circle. The Sun is a bit off the center of the ellipse.

    This orbit will carry us farthest from the Sun for the entire year tomorrow afternoon, at a distance of more than 94 million miles — about three million miles farther than we were back in January.

    The change in distance affects how much energy we receive from the Sun: we get about seven percent more in January than in July. But Earth’s oceans and atmosphere are quite efficient at storing and distributing heat, so they keep our planet’s overall temperature pretty much the same year ’round.

    One other effect of the elliptical orbit is that Earth’s orbital speed changes over the year. Our planet moves fastest when we’re closest to the Sun, and slowest when we’re farthest, as we are now. That stretches out the summer season in the northern hemisphere — it lasts about five-and-a-half days longer than in the southern hemisphere.

    So enjoy the extra days of the summer season — days that are made possible by our planet’s lopsided orbit.

    -- Script by Damond Benningfield, Copyright 2015


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

  • Fireworks

    The Fourth of July is a time for beautiful lights in the evening sky. If you can’t make it to a big fireworks display, though, Mother Nature offers some lights of her own — a sprinkling of bright stars and planets across the night.

    A couple of those lights are in good view well before the color of twilight drains from the western sky. The planets Venus and Jupiter stand side by side. They’re the brightest objects in the night sky after the Moon, so you just can’t miss them. Venus is the brighter of the two. And Regulus, the heart of Leo, stands not far to their upper left.

    By the time the sky gets good and dark, the golden planet Saturn stands well up in the south. And Antares, the heart of the scorpion, is down to its lower left.

    And the dazzling Summer Triangle is high in the eastern sky. Its brightest point is also its highest — the star Vega, in Lyra, the harp. Deneb is to its lower left, at the tail of Cygnus the swan. And Altair, in Aquila, the eagle, is farther to the lower right of Vega.

    And perhaps the most spectacular nightlight of all arcs through the Summer Triangle: the glowing band of the Milky Way. It’s not nearly as bright as all those fireworks displays, so you need to be far away from city lights to see it. Yet in its own way, it’s much more impressive. It’s the combined light of millions of stars outlining the disk of our home galaxy — a special kind of fireworks display in the summer sky.


    Script by Damond Benningfield, Copyright 2015


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

  • Latest Sunsets

    Here in the northern hemisphere, the longest day of the year came a couple of weeks ago. Yet for the southernmost regions of the United States, the Sun is just now setting at its latest for the year. The difference is so tiny, though, that no one is likely to notice it.

    The longest day of the year is the summer solstice, which came on June 21st, when the Sun stood farthest north for the year.

    You might expect to see the earliest sunrise and latest sunset on the solstice as well, but that’s not the case. The earliest sunrises came a few days before the solstice, with the latest sunsets coming after the solstice. For northern parts of the country, the latest sunset was around June 27th. But for the southern tips of Texas and Florida, it’s coming about now.

    There are several reasons for the later sunsets. One is related to Earth’s tilted axis, and another is Earth’s orbit around the Sun.

    Right now, we’re farthest from the Sun for the year, so our planet moves a little slower and covers a slightly smaller distance than average each day. Because of that, Earth doesn’t have to make a full turn to catch up to the Sun in the sky. But our clocks move at a fixed rate, so they get ahead of the Sun. As a result of all that, the time of sunset keeps moving a little later for a few days.

    No matter what part of the country you’re in, though, the days are starting to get shorter — a trend that will continue until the winter solstice in December.


    Script by Damond Benningfield, Copyright 2015

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

  • Venus and Jupiter

    The Twitter-verse is likely to be filled with reports of UFOs about now — a pair of brilliant lights in the western evening sky. Those lights aren’t the first wave of an alien invasion, though. Instead, they’re Venus and Jupiter. Venus is the brighter of the two, with Jupiter quite close to its right.

    Despite their appearance, the two planets aren’t close to each other at all — they just happen to line up in the same direction as seen from Earth. Venus is more than 45 million miles away, while Jupiter is about a dozen times farther.

    Venus is always the brightest object in the night sky other than the Moon. That’s because it’s usually pretty close to us, and it’s covered by clouds that reflect a lot of sunlight into space.

    Jupiter is usually the next-brightest object in the night sky, but not always. It’s always bright because of the combination of its size, its distance, and the amount of sunlight it reflects. But Jupiter fades a bit when it’s near its farthest point from Earth, as it is now. That can allow Mars and Mercury to outshine it — but only when those worlds are at their best, which isn’t the case right now.

    So Venus and Jupiter reign as the brightest points of light in the night sky. They’re side by side the next couple of evenings, although the gap between them will be a little wider tomorrow night. After that, Venus will pull away from Jupiter — putting extra air between these identified objects in the evening sky.


    Script by Damond Benningfield, Copyright 2015


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

  • Short Moon

    If you love the full Moon, then we have some good news for you and some bad news. The good news is that there’s a full Moon tonight. It’s known as the Hay Moon or Thunder Moon.

    It’s also known as the Short Moon — and that’s where the bad news comes in. The name doesn’t have anything to do with the Moon’s physical size or appearance. Instead, it means that the Moon will be in view for a shorter time than any other full Moon of the year.

    That shouldn’t come as much of a surprise. The summer solstice was just a few days ago — the longest day of the year in the northern hemisphere. So if the days are especially long, then the nights must be especially short.

    The difference comes about because of Earth’s tilt on its axis. At this time of year, the north pole dips toward the Sun. As a result, the Sun soars high across the sky and remains in view for a long time — anywhere from about 13 to 15 hours for most of the United States.

    The full Moon does just the opposite of what the Sun does. So right now, the Moon scuds low across the sky as seen from the U.S., and it’s in view for a short period of time — as little as about eight-and-a-half hours from states like Maine and Washington, and even less from Alaska.

    Incidentally, this is the first of two full Moons for the month of July. The second comes on the morning of the 31st. It’ll be in view a little longer than tonight’s Moon. And it has its own special designation: the Blue Moon.


    Script by Damond Benningfield, Copyright 2015

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

  • Planetary Headlights

    The brilliant planets Venus and Jupiter stand side by side like a couple of celestial headlights in early July. Venus is the brighter of the two. It will move up and away from Jupiter over several nights. These views are about 45 minutes to an hour after sunset, looking due west.

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Leap Second

    Today is the longest day of 2015. Not the longest interval between sunrise and sunset — that came a few days ago, on the summer solstice. Instead, an extra second will be added to the world’s official timekeeping services, so today will last exactly 24 hours and one second.

    The extra second is needed because Earth’s rotation is slowing down. Today, it takes our planet between one and two milliseconds longer to make one full turn than it did a couple of hundred years ago.

    In an era of ultra-precise timekeeping, that’s a problem. Atomic clocks keep almost perfect time. But as Earth slows down, these clocks drift away from solar time — the time measured by the passage of the Sun across the sky — by between one and two milliseconds per day.

    That difference adds up. So every once in a while, the world’s timekeepers add a “leap second” to bring the atomic clocks back in line with solar time. This one will be added between 6:59:59 and 7 p.m. Central Daylight Time.

    Earth’s changing rotation rate isn’t smooth and predictable, though, so leap seconds can’t be predicted very far in the future. So they may be added in back-to-back years, or it may be several years between them.

    Adding a leap second can disrupt computers, though, so some have suggested eliminating the leap second. Scientists will vote on that proposal later this year — perhaps deciding to let atomic clocks drift away from the time kept by our home planet.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Bright Trios

    Two bright trios dazzle in the evening sky tonight. One disappears fairly quickly, but the other remains in view for most of the night.

    The group that sets first is in the west as darkness falls: the planets Venus and Jupiter and the star Regulus.

    Venus and Jupiter are the brightest objects in the night sky other than the Moon, so you can’t miss them — especially for the next few nights, because they stand almost atop each other. Right now, the difference in their brightness is greater than average. Venus is just about as bright as it gets, while Jupiter is near its faintest, so Venus shines about 13 times brighter than Jupiter.

    Regulus pales compared to these two, but it does a nice job of rounding out the trio. It’s to the upper left of Venus and Jupiter, at the heart of Leo.

    The other trio is in the south-southeast: the Moon, the planet Saturn, and the star Antares. Saturn looks like a bright golden star to the upper right of the Moon, with orange Antares a little closer to the lower right.

    Saturn is near its brightest for the year as well. Like Venus and Jupiter, its brightness varies because it’s orbiting the Sun. As a result, its distance from Earth changes over the months as Earth and Saturn follow their separate paths. Earth and Saturn were at their closest last month, so Saturn was brightest then. It’s starting to fade a bit, but it’s still an impressive sight — shining brightly until it sets in the wee hours of the morning.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Stormy Skies

    A giant storm swirls all the way around Saturn in this 2010 view from the Cassini spacecraft. Such storms have popped up in Saturn's atmosphere every few decades, and they can last for months. [NASA/JPL/SSI]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Moon and Saturn

    The Moon and the planet Saturn snuggle quite close tonight. Saturn is just to the lower right of the Moon at nightfall, and looks like a bright star.

    Seen through a telescope, Saturn itself usually looks pretty bland. Its atmosphere is divided into bands that are tinted in subtle shades of yellow and tan. Storms twirl through those bands, but they’re difficult to see from Earth.

    Most of the time, that is. Every few decades, a giant storm bursts into view. Its white core is as big as Earth. And in months, it can stretch half way around the planet.

    The storms are like thunderstorms here on Earth. Their clouds are made of water vapor, and they produce lightning and major downpours. The first of these storms was seen in 1876, and the most recent popped up in 2010.

    Researchers at Caltech say they know why the storms are so infrequent.

    The water in the clouds is much denser than the hydrogen and helium that make up much of Saturn’s atmosphere. So most of the time, the water stays in a layer far below Saturn’s cloudtops.

    Eventually, though, the atmosphere above the water gets much colder, which makes it denser. That makes it easier for the warm water vapor to rise high into the atmosphere, creating a massive new storm. But that warms the atmosphere again, so the denser storm quickly rains itself away.

    The researchers say it takes several decades for this cycle to play out — leaving a long dry spell between Saturn’s giant storms.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Deceptive Giant

    Appearances can be deceiving — especially among the stars.

    For an example, look at the stars that mark the points of the Summer Triangle, which is in the east and northeast at nightfall. The brightest point is Vega, one of the brightest stars in the entire night sky. Yet Vega looks so bright in large part because it’s close by — only about 25 light-years away.

    The true luminary of the Summer Triangle is Deneb, which stands to the lower left of Vega during the evening hours. It’s probably a thousand times brighter than Vega, and tens of thousands of times brighter than the Sun. Astronomers are a bit uncertain of its true brightness because estimates of its distance vary by hundreds of light-years.

    Deneb is a supergiant. Its diameter is probably a couple of hundred times that of the Sun. If it took the Sun’s place in our solar system, the star would swallow all three of the innermost planets — including Earth.

    Deneb is also a couple of dozen times as massive as the Sun. That means it burns through the nuclear fuel in its core much faster than the Sun does, which is one reason why it’s so bright. And it’ll live a much shorter life than the Sun; it could blow itself to bits as a supernova in the next couple of million years.

    Look for Deneb low in the northeast in early evening, and high overhead later on, trailing Vega across the early summer sky.

    Tomorrow: pondering giant storms on a giant planet.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Brilliant Encounter

    Venus and Jupiter, the brightest objects in the night sky other than the Moon, are staging a spectacular encounter in the western evening sky. These illustrations depict their changing positions in two-day intervals. Regulus, the brightest star of Leo, is close by as well. These views are looking due west about 45 minutes to an hour after sunset.

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Venus and Jupiter

    Venus and Jupiter are heading toward an especially close rendezvous in the evening sky. They’re in the west at nightfall and shine like a pair of celestial headlights — they’re far brighter than any other planets or stars. Venus is the brilliant “evening star,” with fainter Jupiter not far to its upper left.

    Right now, the difference in their brightness is greater than average. Venus is just about as bright as it gets, while Jupiter is near its faintest, so Venus shines about 13 times brighter than Jupiter.

    Venus is near its peak because it’s getting ready to cross between Earth and the Sun in mid-August, so it’s especially close to us. If you look at the planet through a telescope, it looks like a crescent Moon. But because Venus is so close, that crescent covers a large area of the sky. And when the planet is closer to us, more of the sunlight that reflects from its surface makes its way to Earth, adding to its luster.

    Jupiter, on the other hand, will pass behind the Sun just a few days after Venus’s passage, so it’s farther from us than average. At that range, it makes a smaller target in our sky, and it reflects less sunlight in our direction, so it appears fainter.

    Still, it combines with Venus to put on a great show in the west beginning not long after sunset. The planets will move even closer together over the next few nights, and stand side by side next week — two bright but unequal headlights in the evening sky.

     

    Script by Damond Benningfield, Copyright 2015

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

  • More Fred Hoyle

    As a youngster, one of Fred Hoyle’s favorite activities was finding ways to skip school. Another was reading — especially about astronomy and other sciences. It’s not surprising, then, that Hoyle made a career as a scientist, writer — and contrarian.

    Hoyle was born 100 years ago in Yorkshire, England. After grammar school, he won a scholarship to Cambridge, where he studied under some of the leading scientists of the day. He worked on British radar development during World War II, then returned to Cambridge as a teacher and researcher.

    While there, he published the concept of nucleosynthesis — the idea that stars create almost all of the chemical elements through nuclear reactions. The idea earned one of his collaborators a Nobel Prize — but not Hoyle.

    In part, that may be because of his role as a contrarian. He left Cambridge after he became disgusted with academic politics. And he eschewed the idea that the universe began with a Big Bang — a term he coined during a BBC radio broadcast. Instead, Hoyle thought that new matter was created as the universe expanded. He also championed the idea that life on Earth originated in space.

    Hoyle remained popular with the public, though. While at Cambridge, he presented a series of BBC radio programs about the universe, and he began writing science fiction. He wrote novels, a play, and two television serials. He continued his writing and research until the late 1990s. He died in 2001.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Fred Hoyle

    Antares, the bright orange heart of the scorpion, stands low in the south at nightfall. It’s one of the biggest and heaviest stars in the galaxy. As such, it’s busily creating new elements in its core and in layers around the core. And before long, it’ll explode as a supernova, which will create even more elements.

    Understanding that process of creation was one of the major accomplishments of British scientist Fred Hoyle, who was born 100 years ago today.

    By the 1940s, astrophysicists had already discovered that stars like the Sun shine by “fusing” hydrogen atoms to make helium, which releases a lot of energy. But they were unclear about how all the other elements were created. It didn’t seem possible to make them in stars.

    Hoyle published several papers explaining that it was possible. He found a process by which three helium atoms could combine to make carbon. And he calculated that massive stars could create most of the other elements — either in their cores, or during their violent deaths.

    The most influential of those papers was published in 1957, in collaboration with three colleagues. It outlined the entire process of nucleosynthesis — how stars create heavier and heavier elements. It’s one of the most important papers of 20th-century astronomy.

    One of the team members later won a Nobel Prize for the work — but not Hoyle. Some feel he was left out because he was a bit of a contrarian. We’ll talk about that tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Martian Methane

    Every few months, the region around the Curiosity Mars rover seems to get a bit “gassy” — it emits puffs of methane, the main ingredient in natural gas.

    Here on Earth, methane is produced mainly by the decomposition of dead plants, and in the digestive tracts of cattle and other animals. Because of that biological origin, finding it on other worlds could indicate the presence of life. On the other hand, methane can also be produced by volcanoes and other geological processes, so it’s not a guarantee of extraterrestrial life.

    In recent years, ground-based telescopes have detected small amounts of methane in the atmosphere of Mars. So has the Mars Express orbiter. These observations created a debate about the source of the methane: geology versus biology. Some argue that it’s created by microbes living below the surface, while others say it most likely comes from chemical reactions in the rocks and dirt.

    Curiosity landed on Mars almost three years ago. Its instruments can analyze the Martian atmosphere for methane and other key compounds.

    At first, it found almost no methane at its landing site inside a large crater. Since then, though, it’s detected two jumps in the amount of methane — each to about 10 times the normal level.

    But the rover’s instruments can’t determine the source of the methane. So it’ll take more work to determine whether those outbursts come from living Martians.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Methane

    Methane colors the skies of Neptune blue, fills lakes on Saturn’s moon Titan, and powers homes and businesses here on Earth. And it could someday provide evidence of life on planets in other star systems.

    Methane is a fairly simple organic molecule. Here on Earth, it’s produced by the decomposition of dead plants, and in the digestive tracts of cattle and other animals. It can also be extracted from coal.

    Methane is the main ingredient in natural gas, which provides more than a quarter of American electricity. It’s also a powerful greenhouse gas, so any that escapes into the air enhances global warming.

    Methane is common in the atmospheres of the planets Uranus and Neptune. It absorbs red wavelengths of light, so it makes Neptune look blue, and Uranus blue-green.

    It’s also common on Titan, the largest moon of Saturn. Temperatures are so cold there that the methane is in liquid form, so it fills the role that water fills here on Earth. Along with ethane, it forms clouds and rain, and fills lakes and seas.

    Since much of the methane on Earth is a byproduct of life, it’s considered a good marker for life on other worlds as well. So scientists are looking for the chemical signature of methane in the atmospheres of planets in other star systems — possible markers of extraterrestrial life.

    In fact, there’s a debate over whether the methane in the atmosphere of Mars comes from life or from simple chemical reactions. More about that tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • June Solstice

    Summer arrives in the northern hemisphere today. The Sun stands farthest north for the entire year, bringing long, hot days.

    Today, the solstice is just another date on the calendar — something people might not even notice unless they see a tweet about it. In ages past, though, solstices played a key role in the lives of villages and entire regions. They were times for religious ceremonies, festivals, or other events.

    A site in Peru, for example, seems to have been built to mark the June solstice, which is the start of winter in the southern hemisphere.

    The site is in the Chincha Valley, a desert region that was between thriving communities along the coast and in the mountains. It consists of several large mounds, piles of rocks, and long, straight lines on the desert floor. The lines are similar to those found at Nazca, which also depict animals and other figures. But recent research says the lines at Chincha were created about 2300 years ago — several hundred years before those at Nazca.

    Researchers have found several alignments with the point at which the Sun set on the June solstice. These alignments include the lines on the desert floor, as well as U-shaped mounds and other structures.

    The researchers speculate that the site was a gathering place for villages from the coast to the mountains. Perhaps they came together at the solstice to trade, celebrate, or give thanks to the gods — a gathering timed to the motions of the Sun.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Hiding an Ocean

    A deep ocean may lie far below the icy crust of Ganymede, the largest moon of Jupiter. In this image, compiled from several satellite views, dark regions are the oldest on Ganymede's surface, while lighter regions are much younger. The bright feature at bottom was formed by a recent impact, which created a crater and splashed out bright, fresh ice across hundreds of miles. [NASA/JPL]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Moon and Jupiter

    The worlds of the solar system hold many secrets. The largest moon, for example, conceals an ocean far below its icy crust. It may contain more water than all of Earth’s oceans combined.

    Ganymede is the largest moon of Jupiter, the solar system’s largest planet. It’s half again the diameter of our own moon. Unlike the Moon, though, its surface consists mainly of ice.

    Ganymede is the only moon that’s known to generate its own magnetic field. More than a decade ago, the Galileo spacecraft detected variations in that field. The most likely cause was the sloshing of an underground fluid — probably a salty ocean.

    More evidence of an ocean was reported this year. Scientists used Hubble Space Telescope to study interactions between Ganymede’s magnetic field and the field of nearby Jupiter. Those interactions produce a slight offset in Ganymede’s aurorae, which are like the northern and southern lights here on Earth. The offset is best explained by a salty ocean.

    The ocean is probably about 60 miles deep — more than 20 times the average depth of Earth’s oceans. But it’s buried beneath Ganymede’s crust, about a hundred miles below the surface — a watery secret on a giant moon.

    Jupiter is in good view tonight. The bright planet is close to the upper right of the Moon at nightfall, with the even brighter planet Venus to the lower right of Jupiter. Through binoculars, Ganymede and Jupiter’s other big moons look like tiny stars near the brilliant planet.

     

    Script by Damond Benningfield, Copyright 2015

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

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