StarDate

StarDate

  • Hot Lake

    A giant lake of molten rock forms a dark horseshoe on the surface of Io, one of the big moons of Jupiter, in this view from the Galileo spacecraft. Io is the most volcanically active body in the solar system. Loki Patera (just below center) is the largest of its volcanic features — a lake that covers about 7,000 square miles. Fresh lava bubbles up from below to fill its basin. [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

    A giant lake spreads across the surface of Io, one of the big moons of Jupiter. You wouldn’t want to take a dip in it, though — it’s a pool of molten rock that sizzles at up to 2,000 degrees Fahrenheit.

    Io is about the same size as our own moon. But while the Moon is almost completely dead, Io is the most volcanically active body in the solar system. It’s heated by a gravitational tug-of-war between Jupiter and some of its other big moons. This conflict pulls and twists Io’s interior, melting some of its rock. Some of the molten rock pushes its way to the surface through volcanic mountains and lava lakes.

    Loki Patera is the largest of these volcanic features — a lake that covers about 7,000 square miles. Fresh lava bubbles up from below to fill its basin, which is shaped like a horseshoe.

    Over time, lava at the top of the lake cools and hardens to form a crust, so Loki Patera fades. But the crust is heavier than the molten rock below it, so it sinks, letting the hot lava rise to the surface.

    Loki Patera was especially active through much of 2013. It faded in September of that year, but brightened again in October of last year — indicating that lava was once again bubbling to the surface of this giant hot tub.

    And Jupiter is quite close to our own moon tonight. The planet looks like a brilliant star close to the upper left of the Moon at nightfall.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Moon in the Middle

    The gibbous Moon passes through the middle of a triangle of bright astronomical objects tonight: the planet Jupiter, the star Procyon, and the “twins” of Gemini.

    The brightest point of the triangle is Jupiter, which is to the left of the Moon as darkness falls. Only the Moon and the planet Venus outshine it, so it’s easy to find.

    Jupiter shines so brightly because it’s the biggest planet in the solar system — about 11 times wider than Earth. And it’s wrapped in clouds that reflect about half of the sunlight that strikes them back out into space — giving this hefty planet a hefty appearance in the night sky.

    Procyon is the second-brightest member of the triangle, standing below the Moon. It’s the leading light of Canis Minor, the little dog. It’s only about 11 light-years away, which makes it one of our closer stellar neighbors. It’s actually two stars — the bright one that’s visible to the eye alone, and a “dead” companion that’s visible only through a telescope.

    The triangle’s final point is above the Moon. We’re stretching things a bit, because it actually consists of two stars: Pollux and Castor, the twins of Gemini. Pollux is closer to the Moon, and it’s also the brighter of the two.

    Pollux is a cool, bloated star that’s nearing the end of its life. And Castor is a system of six stars or more, although their light blurs together to make a single pinpoint — one of the bright lights that surround the Moon tonight.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Narrow Escape

    An object known as G2 whips around the supermassive black hole at the center of the Milky Way galaxy in this series of images from the European Southern Observatory's Very Large Telescope. Astronomers originally predicted that the black hole would flare brightly as it ingested material from G2, which was identified as a large gas cloud. No such fireworks materialized, however, suggesting that G2 is a compact cloud of gas and dust surrounding a dense object in its core. These infrared images, which are color coded to show G2's location at different times, demonstrate that G2 was not significantly distorted by its closest approach to the black hole in May 2014, and that it survived the passage around the black hole unharmed. [ESO/A. Eckart]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • African Astronomy III

    A worldwide consortium will soon decide where to build a globe-spanning telescope array that could study some of the most energetic objects and events in the universe. If everything goes as planned, it’ll consist of a network of more than a hundred telescopes. About 20 of them will be in the northern hemisphere — in Arizona, Mexico, or the Canary Islands. But most will be in the southern hemisphere — in either Chile or Namibia.

    CTA — the Cherenkov Telescope Array — is designed to study gamma rays. They’re produced by exploding stars, hot gas around black holes, and other powerful events. They may even be created by collisions between particles of dark matter.

    Gamma rays produce flashes of blue light when they enter Earth’s atmosphere, and that’s what CTA will see. Scientists will study those flashes to learn more about the origin of the gamma rays.

    Under the current plan, the telescopes in the southern hemisphere will come in three sizes — from about 15 feet in diameter to as much as a hundred feet. Each size will be sensitive to different wavelengths, allowing scientists to study many different types of gamma-ray objects.

    Several Cherenkov telescopes are already in operation. The largest, known as HESS, is in the desert of Namibia, which has especially clear, dark skies. If Namibia gets the nod for CTA, then it would be built not far from HESS — giving that African nation the best view of the gamma-ray universe.

     

    Script by Damond Benningfield, Copyright 2015


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

  • African Astronomy II

    Some giant radio dishes in Africa are getting a second life — they’re being reborn as radio telescopes. It’s part of an effort that will make southern Africa one of the leading sites in the world for radio astronomy.

    The project is using retired communication satellite dishes that have been replaced by fiber-optic cables. The dishes are about a hundred feet across. Engineers are refurbishing their pointing systems and adding instruments that will allow them to detect radio waves from stars and other objects.

    The first telescope was completed in Ghana, with three others in the refurbishment or planning stages. Each dish can act as an individual telescope, although the goal is to link them — and perhaps others — in a continent-spanning network. Such networks provide especially sharp views of the heavens.

    The project is also providing training for scientists, technicians, and students across Africa. That’s important because southern Africa will be home to half of the world’s largest radio telescope — the Square Kilometer Array. It will consist of hundreds of radio dishes spread across several countries.

    Precursors to that project are already taking shape. One consists of seven small antennas. It’ll form part of a larger precursor that’ll have 64 dishes. And that will form part of the Square Kilometer Array — a giant telescope spread across Africa and beyond.

    We’ll talk about another type of astronomy in Africa tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • African Astronomy

    A couple of tiny constellations wheel low across the south on early spring evenings — Pyxis, the compass, and Antlia, the air pump. Both are faint, though, so you need a star chart to find them.

    They were created by Nicolas de la Caille, a Frenchman who was one of the first astronomers to study the sky from southern Africa. He spent a couple of years at Cape Town in the 1750s, where he compiled a catalog of about 10,000 stars.

    Several other European astronomers visited southern Africa during the 18th and 19th centuries, studying objects that weren’t visible from the northern hemisphere. Britain even established a royal observatory there in 1820. Its astronomers toiled in unpleasant conditions for decades, yet they made important observations of stars and other objects, and helped measure the shape of our planet Earth.

    By the 20th century, though, astronomy in southern Africa was falling behind. The European governments that controlled much of the continent weren’t interested in scientific investments there. And after countries gained independence, most of them lacked the resources or the political will to build modern observatories.

    But that’s starting to change. The Southern African Large Telescope — based on the Hobby-Eberly Telescope at McDonald Observatory — was built more than a decade ago. There’s also a gamma-ray observatory in Namibia, with radio telescopes taking shape across the region. More about that tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Spring Storm

    In the days before round-the-clock communications, Easter Sunday was one of the busiest days of the year for long-distance telephone calls. But 75 years ago today, many of those Easter calls to grandma and papa never got through. A giant storm on the Sun bombarded Earth, causing all kinds of trouble.

    The troubles were set in motion a few days earlier, when a magnetic storm on the Sun created a tremendous eruption. The blast sent billions of tons of charged particles racing through the solar system.

    The storm cloud took dead aim at Earth. Its leading edge hit on March 23rd, 1940, but the bulk of it slammed into the planet the following day — Easter Sunday.

    When it hit, Earth’s magnetic field funneled the charged particles toward the ground. They zapped an electrically charged layer of the atmosphere, knocking out long-range radio broadcasts. That deprived Americans of the latest news of the war in Europe.

    Even bigger problems came when the solar particles slammed into the ground, where they knocked out many telephone and telegraph lines in the United States and Canada. Repair crews were busy at almost every telephone switching station. Some lines were fused together, and several electric generators were knocked out.

    The storm continued to disrupt communications for several days. And a smaller storm hit four days later. So many of the phone calls to family members had to wait until April — a week or more after Easter.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Alphard

    Hydra, the water snake, is the longest of the 88 modern-day constellations. It’s so long that it takes many hours for the entire thing to climb above the horizon. Yet Hydra is also one of the fainter constellations. In fact, from most cities, only one of its stars is easy to spot.

    Alphard is about a third of the way up the southeastern sky as night falls. There are no other bright stars anywhere near it, so you shouldn’t have much trouble picking it out.

    Alphard is about 175 light-years away. At that great distance, the fact that we can see it so clearly tells us that the star is pretty remarkable. In fact, it’s a giant — it’s puffed up to about 40 or 50 times the diameter of the Sun.

    The star is about 400 million years old — roughly one-tenth the age of the Sun. Yet it’s also about three times as massive as the Sun. Heavier stars “burn” through their nuclear fuel more quickly than less-massive stars, so they age more quickly.

    Alphard is already entering the final stages of life. As it uses up the fuel in its core, its outer layers puff outward. They get cooler as they do so, which gives Alphard a reddish-orange color.

    In a fairly short time — astronomically speaking — those outer layers will stream away into space. That will leave only the star’s hot but dead core — a tiny remnant known as a white dwarf. It’ll be far too faint to see with the eye alone — depriving the water snake of its one bright light.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Moon and Venus

    The crescent Moon and the “evening star” stage a beautiful encounter this evening. They stand side by side as the Sun sets. They’re an especially beautiful sight before darkness falls, when they’re immersed in the glow of twilight.

    Despite its appearance, the evening star isn’t a star at all. Instead, it’s Venus, our closest planetary neighbor.

    Even before the invention of the telescope, skywatchers knew there was something different about this brilliant light. While the true stars all maintain their position relative to each other, Venus and the other “planets” change position from week to week or even night to night. In fact, that’s why they’re called planets — the name is the ancient Greek word for wanderer.

    Those wandering lights were a nuisance to those who tried to explain the workings of the heavens. Most thought that Earth was the center of the universe. And based on observations of how objects in the sky moved, that was a reasonable explanation for the Sun, Moon, and stars.

    But it was tough to explain the motions of the planets. They periodically stop and reverse course. And Venus swings between evening and morning skies without ever moving far from the Sun. The systems to explain these motions got pretty complicated, which made them hard to believe.

    In fact, it was the motions of the planets that convinced astronomers that Earth and the other planets circle around the Sun — moving Earth out of the center of the universe.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Moon and Mars

    Modern-day Mars is cold and hostile. Dried-up riverbeds meander across the ancient Martian terrain, though, so rivers must have flowed across the planet billions of years ago. But that poses a bit of a puzzle, because Mars is half-again as far from the Sun’s light as Earth is. And when Mars was young, the Sun was much fainter than it is today. So how did Mars get warm enough for rivers to flow?

    A new idea may answer the question: punctuated volcanism.

    Artist's concept of Olympus Mons, the largest volcano on present-day Mars [NASA/MOLA team]Mars has plenty of volcanoes. In fact, its largest volcanoes dwarf any on Earth. And volcanic plains cover much of the Martian surface, indicating that Mars was volcanically active for much of its history.

    According to the new idea, giant eruptions took place about 3.7 billion years ago, releasing huge amounts of sulfur dioxide gas into the atmosphere.

    Like carbon dioxide, sulfur dioxide is a greenhouse gas, so it traps heat from the Sun. The new calculations indicate that after a major volcanic eruption, regions along the equator saw daily high temperatures above the freezing mark for a good part of the year — conditions that persisted for decades or even centuries. As a result, ice melted and rivers began to flow. After a while, the planet froze again — at least until the next big eruption.

    Look for Mars close to the right of the crescent Moon shortly after sunset this evening. The little planet is a bit tough to see through the twilight, but binoculars can help you pick it out.

     

    Script by Ken Croswell, Copyright 2015


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

  • Disappearing Sun

    A Sun-watching spacecraft snapped this view of a solar eclipse on March 20. The limb of the Sun is still peeking from behind the Moon in this view, from the European Space Agency's Proba-2 mission. [ESA/ROB]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Spring Equinox

    Sunrise at the north pole will experience a brief interruption early today — a total solar eclipse. The Moon will pass in front of the Sun, causing a small glitch at the start of a “day” that’ll last more than six months.

    Daytime is just getting started at the north pole because today is the March equinox — the beginning of spring in the northern hemisphere.

    We have seasons because Earth is tilted on its axis. As Earth orbits the Sun, the poles take turns nodding toward the Sun. The south pole nods sunward in December, and the north pole in June. But neither pole tilts sunward on the equinoxes.

    Because of this change in perspective, each pole sees six months of night followed by six months of daylight — or close to it. Because Earth’s orbit is slightly stretched out, there’s a slightly longer “day” for the north pole than for the south.

    And that day is extended even more by the way we mark sunrise and sunset. Officially, sunrise occurs at the moment the first bit of the solar disk peeks above the horizon, with sunset coming only when the entire Sun drops below the horizon.

    What’s more, Earth’s atmosphere acts as a lens, “bending” the Sun’s light. That means the Sun is in view for a while even when it’s physically below the horizon. These effects add extra hours to the long Arctic day.

    According to the U.S. Naval Observatory, the Sun rose at the north pole on Wednesday afternoon, and won’t set until September 25th — more than six months later.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Solar Eclipse

    The Sun will disappear across a narrow strip of Arctic waters early tomorrow during a total solar eclipse. The only land in the path of the eclipse is a few small islands. But viewers across Europe and parts of Asia and Africa will see a partial eclipse.

    Solar eclipses occur when the new Moon passes directly between Earth and the Sun. The Sun is about 400 times wider than the Moon, but it’s also about 400 times farther away. As a result of that coincidence, the Moon and Sun are almost exactly the same size in our sky, so the Moon can completely cover the solar disk.

    Geometry of a total solar eclipseThe dark inner part of the lunar shadow — the path of the total eclipse — is only about 300 miles wide. But there’s a partial eclipse across hundreds of miles on either side of that path, with the Moon covering part of the Sun.

    This eclipse begins in the wee hours of the morning here in the U.S., when the shadow first touches Earth, northeast of Newfoundland. The shadow then sweeps between Iceland and the British Isles and past Norway.

    Although no big cities are in the path of totality, a few will see pretty good partial eclipses. From Reykjavik, Iceland, the Moon will cover about 98 percent of the Sun, while Glasgow and Edinburgh in Scotland will see the Moon cover more than 90 percent of the Sun’s disk.

    The eclipse ends at the North Pole — a spot that’s just starting to see the Sun at all after six months of darkness. More about that tomorrow.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Small Steps

    50 years ago today, Cosmonaut Alexei Leonov went for a little stroll — 300 miles above Earth’s surface. He became the first person to walk in space — a walk he barely survived.

    Alexei Leonov takes the first spacewalk, March 1965It was an important early step in the Space Race. It proved that a person could live and move around outside his capsule — a capability that was crucial to walking on the Moon or building a space station.

    Leonov spent more than 10 minutes floating outside his Voskhod 2 capsule. But his spacesuit puffed up so much that he couldn’t get back in through the small hatch, so he had to let out air to deflate it. He also had to come in head first instead of feet first as planned, then turn around inside the tight airlock.

    Leonov’s troubles didn’t end there. The landing system malfunctioned, so Voskhod 2 landed hundreds of miles off course, in deep snow inside a dense forest. Leonov and his fellow cosmonaut spent a bitterly cold night inside their capsule, surrounded by wolves.

    Even so, Leonov’s accomplishments put the Soviets clearly ahead of the Americans. But the U.S. got back in the game just a few days later with the first manned flight of the two-seat Gemini spacecraft. Astronauts Gus Grissom and John Young circled Earth three times in a nearly flawless mission. They didn’t walk in space — that would come with the next mission. But they did take a small but important step in the race to the Moon.

     

    Script by Damond Benningfield, Copyright 2015



    Known as Gemini 3, the first Gemini mission launched on March 23, 1965. Grissom and Young orbited Earth three times in less than five hours. Their capsule was nicknamed "Molly Brown" for the title character from "The Unsinkable Molly Brown," after Grissom's Liberty Bell 7 Mercury capsule sank shortly after splashdown. Mission highlights included the first orbital change by a manned spacecraft.

     

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

  • Reborn Stars

    The star cluster M3 contains many "reborn" stars among its half-million members. These stars have merged with other stars or had their outer layers stripped away, making them look especially blue, which is a sign of stellar youth. In reality, the stars are probably all more than 11 billion years old. [Robert J. Vanderbei/Wikipedia]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • M3

    A star cluster with a lot of deceptively young-looking stars ascends the eastern sky tonight. It’s to the upper left of the bright yellow-orange star Arcturus, which climbs into good view by about 10 o’clock. The cluster is visible through binoculars as a small, round, faint smudge of light.

    M3 is a tight ball of half-a-million stars known as a globular cluster. It spans a couple of hundred light-years, although most of its stars are jammed together in the middle. They’re so tightly packed that each star probably has thousands of neighbors within just five light-years; by comparison, only one star system is that close to the Sun.

    Among M3’s myriad stars are many that appear to be much younger than they really are.

    M3 probably was born more than 11 billion years ago. All of its most vigorous stars, which were bright and blue, have long since died. So the cluster’s remaining stars should be fairly red. Yet M3 contains quite a few blue stars, known as blue stragglers.

    The leading ideas suggest that these stars drank from a sort of stellar fountain of youth, making them look young again.

    The stars probably have binary companions. In one possible scenario, the stars merge to form a single star, which would be hot and blue. And in another scenario, one star dumps its cool, red outer layers onto its companion, exposing its hotter interior.

    A recent study found that both processes are probably at work in M3 — reinvigorating some old stars.

     

    Script by Damond Benningfield, Copyright 2015


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

  • The Hunting Dogs

    Several hunting dogs bound across the evening sky right now. Canis Major, the big dog, is low in the south as darkness falls. It’s marked by Sirius, the brightest star in the night sky. And Canis Minor, the little dog, is to its upper left, punctuated by another bright star, Procyon. They represent the dogs of nearby Orion, the hunter.

    At the same time, two dogs who attended another mythological character are about a third of the way up the eastern sky. They form the constellation Canes Venatici, the hunting dogs. Unfortunately, though, they’re not nearly as impressive as Orion’s dogs — you need dark skies to see much of anything in this relatively barren patch of sky.

    In fact, that area is so bereft of bright stars that Canes Venatici wasn’t created until the late 1600s. German astronomer Johannes Hevelius drew the constellation as a pair of dogs attending Bootes, the herdsman, which rises below the dogs.

    While the constellation is quite bland to the eye alone, a telescope reveals several astronomical treasures. Perhaps the most impressive is M51, the Whirlpool galaxy. It consists of a bright spiral galaxy that we see face-on, revealing its beautiful arms in great detail. A smaller galaxy sits at the end of one of those arms. It skimmed quite close to the larger galaxy, causing giant clouds of gas there to collapse and give birth to new stars.

    We’ll talk about another of the constellation’s deep-sky wonders tomorrow.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Close Twins

    The two stars that form the system MY Camelopardalis are so close together that they share their outer layers of gas, as shown in this artist's concept. The stars may eventually spiral together and explode as a supernova. [Javier Lorenzo (Universidad de Alicante)]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • MY Camelopardalis

    If you look to the northern sky tonight, you’ll see an array of familiar star patterns, including the Big Dipper and the W-shaped constellation Cassiopeia. But the northern sky also features a constellation that’s so dim that you can’t see it from cities and many suburbs. Yet Camelopardalis, the giraffe, boasts one of the most extraordinary double stars in the galaxy.

    MY Camelopardalis is about 13,000 light-years away. It consists of two hot blue stars that are tied together by their mutual gravitational pull. Both stars are far bigger and heavier than the Sun.

    Their most remarkable property, though, is their proximity to each other. Their cores are so close together that they whirl around each other once every 28 hours. Even more remarkable, the outer layers of these two giants are actually touching each other.

    The two stars eventually will merge to form an even greater star — one of the hottest, brightest, and most massive stars in the galaxy. It won’t last long, though — it’ll blast itself to bits as a supernova.

    Right now, MY Camelopardalis is so far away that you need binoculars or a telescope to see it. But when it explodes, it’ll become one of the brightest stars in the heavens — and transform faint Camelopardalis into a dazzling cosmic spectacle.

     

    Script by Ken Croswell, Copyright 2014


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

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