StarDate

StarDate

  • Interferometry II

    HL Tauri is like a newborn version of our own solar system, with a Sun-like star surrounded by a disk of gas and dust.

    ALMA view of HL TauriA remarkable image of the system reveals bright rings and dark gaps within the disk — sculpted by planets. The planets grow by sweeping up the gas and dust around them, clearing out gaps. And the planets’ gravity causes the remaining gas and dust to concentrate in the bright rings.

    This image of HL Tauri was made with a technique known as interferometry. It combines the light from two or more telescopes to create images that are as sharp as those made by a single telescope that’s as big as the distance between the individual telescopes.

    Many of the ALMA dishes shine beneath the Magellanic Clouds, two companion galaxies to the Milky Way [ESO/Christoph Malin]The picture of HL Tauri, for example, was taken by ALMA, a radio telescope in Chile. It consists of dozens of individual radio dishes that can be spread up to about 10 miles apart. That provides images that are as sharp as the view from a single radio dish 10 miles wide, but at a fraction of the cost.

    Making an interferometer work isn’t easy, though. For example, the observations from the individual telescopes have to be precisely synchronized. If the timing is off by a millionth of a second, the observations are ruined. In most radio interferometers, the observations from each dish are recorded and later combined with a powerful computer.

    A few interferometers look at visible light, which is even trickier than radio waves. We’ll have more about that tomorrow.


    Script by Damond Benningfield


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

  • Interferometry

    One of the monsters of the Milky Way climbs across the south on winter nights. Betelgeuse, the bright orange shoulder of Orion, is high in the southeast at nightfall, and due south a couple of hours later.

    The star is so huge that if it took the Sun’s place in our own solar system, it would engulf everything out to Jupiter, the fifth planet.

    Betelgeuse was the first star other than the Sun to have its size measured. But despite its great girth, it took an entirely new technique, known as interferometry, to make that measurement.

    Diagram shows how the 1920 experiment worked [Mount Wilson Observatory]Two astronomers did so back in 1920. They used a new telescope at Mount Wilson Observatory in California — the largest in the world. But they added something extra — a pair of small mirrors attached to a wide frame that was mounted atop the telescope. The mirrors were about 20 feet apart. They gathered the light from Betelgeuse, and directed it to the telescope’s main mirror.

    The extended mirrors provided two separate beams of light from the star, which were then combined. That combined view was as sharp as the view from a single mirror as wide as the separation between the two small mirrors. That allowed the astronomers to see Betelgeuse as a disk, not just a pinpoint. They measured the size of the disk at hundreds of times the diameter of the Sun — the first confirmation that stars could grow to such giant proportions.

    Despite that early success, it took a while for interferometry to catch on. More about that tomorrow.


    Script by Damond Benningfield

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

  • Faint Neighbors

    A tiny brown dwarf glows next to its stellar companion, Gliese 229, in this false-color image from Hubble Space Telescope. The brown dwarf, known as Gliese 229B, is a "failed star" -- an object that is more massive than a planet, but not massive enough to ignite nuclear fusion and shine as a true star. Gliese 229 is one of our closest stellar neighbors, at a distance of about 20 light-years. [NASA/JHU/Caltech]

    Text ©2016 The University of Texas at Austin McDonald Observatory

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

  • Faint Neighbors

    The brightest star visible in Lepus, the rabbit, is a stunner. It’s more than 30,000 times brighter than the Sun, so it’s easily visible to the unaided eye even though it’s more than 2,000 light-years away.

    The constellation’s closest star is less than 20 light-years away. Yet it’s so feeble that you need a telescope to see it. And it has a small companion that’s even fainter: a cool ember known as a brown dwarf.

    Gliese 229 is smaller and less massive than the Sun, which is the key to its faintness. A lightweight star burns through the nuclear fuel in its core much more slowly than a heavy star. That generates much less energy, so there’s not much for the star to radiate into space.

    The brown dwarf companion — Gliese 229B — probably doesn’t produce any energy in its core. It’s a few dozen times the mass of Jupiter, the largest planet in the solar system. That’s just not big enough to ignite nuclear fusion and allow it to shine as a true star.

    Gliese 229B probably formed like its bigger companion, from the collapse of a cloud of gas and dust. The cloud split apart, producing two separate objects. But there wasn’t enough material in Gliese 229B’s part of the cloud to make a star. Instead, it made a faint cosmic ember — a brown dwarf.

    Lepus hops below the feet of Orion, which is high in the sky at nightfall. The rabbit’s brightest star is easy to spot, but Gliese 229 remains invisible — a close neighbor hidden from sight.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Lepus

    The big, bright constellation Orionscampers across the south on February evenings. Right now it’s high in the sky at nightfall, and due south around 9 o’clock. Look for its three-star belt, flanked by bright orange Betelgeuse to the upper left, and blue-white Rigel to the lower right.

    In mythology, Orion was a hunter. And one of the creatures he hunted stands just below his feet. Lepus, the rabbit, contains a few moderately bright stars. Their proximity to Orion makes them easier to pick out.

    The brightest is Alpha Leporis. And it really is a bright star — more than 30,000 times brighter than the Sun. In fact, it’s impressive just about any way you look at it. It’s far bigger and heavier than the Sun, and it faces a more impressive fate — it will explode as a supernova.

    The star is only about 13 million years old, compared to four-and-a-half billion years for the Sun. But because it’s so much heavier, it “burns” through the fuel in its core much more quickly. As a result, it’s already nearing the end of its life. Changes in its core have caused it to puff up — big enough to extend out to the orbit of Mercury if it took the Sun’s place in the solar system.

    Soon, it’ll get even bigger and brighter. Eventually, though, it will stop producing nuclear reactions in its core. The core will collapse, while the outer layers blast out into space — briefly giving the hunter a bit of a hotfoot.

    We’ll have more about the rabbit tomorrow.


    Script by Damond Benningfield, Copyright 2015


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

  • Moon and Companions

    The major planets of the solar system boast an amazing assortment of moons — about 170 in all. Jupiter and Saturn each have more than 60, Mars has a couple of dinky ones, and Earth has a big one. Yet two planets have no moons at all. And those worlds appear quite close to our own Moon at first light tomorrow.

    Venus, the “morning star,” stands close to the right of Moon. And fainter Mercury is even closer below the Moon, although it’s so low in the sky that it’s tough to spot.

    Astronomers looked for moons around those two planets for centuries. And in the case of Venus, quite a few reported seeing a moon. The first sightings came in the 17th century, not long after the invention of the telescope. Many more sightings followed — some of them by some of the best observers around. Yet many other observers looked and looked but never saw anything.

    Eventually, astronomers decided that most of the sightings, if not all of them, were actually stars that just happened to line up close to Venus at the time. And in the modern era, spacecraft have confirmed that Venus is moonless.

    A few years back, though, a couple of researchers suggested that that hasn’t always been the case. Impacts between the young Venus and two giant space rocks may have blasted out enough debris to form moons. The first moon drifted off into space, while the second splatted back into Venus — leaving our nearest planetary neighbor without a moon to call its own.


    Script by Damond Benningfield, Copyright 2015


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

  • Moon and Venus

    At the surface of Venus, the atmosphere is so thick that walking through it would be almost like walking through water here on Earth. But in the distant past, it may have been even thicker — so dense that the bottom of the atmosphere may have turned into a sort of liquid.

    The planet’s atmosphere is made almost entirely of carbon dioxide. The atmosphere is so heavy that the surface pressure is equal to a depth of two-thirds of a mile in Earth’s oceans.

    Under that pressure, the carbon dioxide forms a supercritical fluid — a state in which it behaves like both a gas and a liquid. Today, it’s more like a gas. But according to some recent research, when Venus was younger the CO2 could have behaved more like a liquid.

    The planet’s atmosphere could have been dozens of times denser than it is today. Under that great pressure, the carbon dioxide was squeezed so tightly that it would have been more like a liquid than a gas. According to the research, the liquid could have carved valleys and other features seen on Venus today. Over time, much of the CO2 combined with other materials to make rocks, or vanished in other ways — leaving Venus with a “dry” surface.

    And Venus is the brilliant “morning star” right now, shining low in the southeast at first light. Tomorrow, it’s to the lower left of the Moon. And the fainter planet Mercury is closer to the lower left of Venus, although you might need binoculars to spot it through the early twilight.


    Script by Damond Benningfield, Copyright 2015


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

  • First Landing

    Luna 9 was the first spacecraft to land on the Moon, in Februay 1966 (artist's concept, top). The Soviet probe beamed back several panoramas of its landing site, on the edge of a small crater (bottom). It operated for several days before its batteries died. [NASA]

    Text ©2016 The University of Texas at Austin McDonald Observatory

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

  • Luna 9

    In February of 1966, the Soviet Union announced yet another “first” in the Space Race: the first spacecraft to land on the Moon. Luna 9 touched down on February 3rd, and over the next three days, it transmitted nine pictures of its surroundings in the Ocean of Storms.

    The Soviets had been trying to land on the Moon for years. But 11 previous attempts had exploded during launch, failed to leave Earth orbit, crashed into the Moon, or missed the Moon entirely.

    Luna 9 finally succeeded. During three days of operations, it beamed back panoramas of its landing site, on the slope of a small crater. The images revealed small rocks and a powdery “soil” known as regolith. To the relief of those working on sending astronauts to the Moon, the regolith was firm enough to support the lander’s weight — it didn’t sink from sight, as some had feared.

    At first, the Soviets didn’t release any of Luna’s pictures. But that didn’t stop the world from seeing them. The Jodrell Bank Observatory in England was monitoring Luna 9 with a big radio telescope. Engineers realized that the pictures were being transmitted in the same format used to send pictures to newspapers. So they brought in a receiver from a London paper, captured the images, and released them to the world. Soviet officials got a bit huffy, but they eventually released the pictures on their own — the first views from the surface of the Moon.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Moon and Saturn

    The Moon has a couple of bright companions before dawn tomorrow. The planet Saturnlooks like a golden star just below the Moon. And the true star Antares is to their lower right, shining bright orange.

    Saturn is famous for its brilliant rings. And two space telescopes discovered a new ring that’s the biggest in the solar system.

    Both telescopes are sensitive to the infrared — wavelengths of light that are longer than those visible to the human eye. In 2009, Spitzer Space Telescope detected the feeble infrared glow of dust grains far outside Saturn’s visible rings. These tiny particles are hundreds of degrees below zero, but sunlight warms them enough to make them glow in the infrared.

    And more recently, another infrared-seeking spacecraft, known as WISE, found that the ring is even larger than first thought. According to the new measurements, the ring’s inner edge is about four million miles from Saturn, while the outer edge is 10 million miles from the planet. If Saturn were a basketball at the center of an NBA court, the outer edge of the new ring would span the entire court.

    The ring probably gets its dust from collisions between comets and some of Saturn’s distant moons. The impacts kick up dust and debris that go into orbit around Saturn. This debris produces a faint but enormous ring, far beyond the much brighter rings that make Saturn one of the most beautiful sights in the solar system.

    Tomorrow: lunar landing.


    Script by Ken Croswell, Copyright 2015


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

  • The Whole Gang

    A rare line-up highlights the morning sky the next few weeks. All five of the planets that are easily visible to the unaided eye are in view at the same time. The window is a bit tight, but you shouldn’t need any help to find them.

    At first light tomorrow, look in the southeast for Venus, the brilliant “morning star.” It’s brighter than anything else in the night sky except the Moon, so it’s hard to miss. It’s quite low in the sky, though, so you probably need a clear horizon to spot it.

    The trickiest of the five planets is Mercury, which is close to the lower left of Venus. It’s just about at its farthest point from the Sun, so it stands highest in the sky. It’s also quite bright. And like Venus, it’s quite low in the sky. But with Venus to point the way, you should be able to pick it out.

    The other three planets rise long before the Sun, so they’re higher in the sky at first light. Saturn stands far to the lower left of the Moon tomorrow. Mars is closer to the upper right of the Moon, and shines with a distinctly orange hue. It will brighten over the next couple of months, making that color even more vivid.

    Finally, the largest of the planets, Jupiter, is over in the western sky. It outshines everything except the Moon and Venus, making it an easy target as well.

    All of these planets will remain in view for most of the month — a beautiful line-up of the worlds of the solar system.

    We’ll have more about one of those worlds tomorrow.


    Script by Damond Benningfield, Copyright 2015

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

  • The Whole Gang

    All five of the planets that are easily visible to the unaided eye remain in view in the dawn sky, spreading out from southeast to west-southwest. This diagram shows the configuration on the morning of February 2, about 45 minutes before sunrise. All but Venus and Mercury will stay close to these positions for several days. You may need binoculars to spot Mercury through the waxing twilight, although nearby Venus, the brilliant "morning star," can help you pick it out. The Moon moves through the lineup as well, as indicated by the dates.

    Text ©2016 The University of Texas at Austin McDonald Observatory

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

  • Moon and Mars

    One of the moons of Mars may be disintegrating right in front of our eyes. But it’s a slow process — the little moon is expected to survive for tens of millions of years.

    Phobos is a potato-shaped rock that’s about 17 miles long. It orbits closer to its parent planet than any other known moon — only about 3700 miles away. At that height, it moves so fast that it rises in the west and sets in the east — twice a day.

    Martian gravity pulls a little more strongly on the side closest to Mars than on the far side. That creates a powerful stress across the entire moon. Eventually, that will pulverize Phobos, perhaps creating a short-lived ring around the Red Planet.

    And a recent study says we may already be seeing the moon start to shatter. Long rays and grooves stretch across Phobos. At first, scientists thought they were created by a powerful impact that blasted out a big crater. But the grooves don’t line up with the crater, so they probably weren’t caused by the collision.

    Instead, the study says they may be the first signs that the little moon is being pulled apart. They suggest that Phobos is built like a pile of rubble wrapped in a thick coating. As Mars’s gravity pulls on Phobos, the interior shifts around, causing the surface coating to crack — early signs that the little moon is beginning to disintegrate.

    Look for Mars quite close to the lower right of our moon at first light tomorrow. The planet looks like a bright orange star.


    Script by Damond Benningfield, Copyright 2015


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

  • Moon and Companions

    Two bright lights flank the Moon at dawn tomorrow. The star Spica stands to the right of the Moon. And the planet Mars looks like a bright orange star to the lower left of the Moon.

    Mars has two moons of its own. But Phobos and Deimos aren’t very impressive. Each looks like an asteroid: dark, potato-shaped, and scarred by countless craters. And since Mars resides next to the asteroid belt, scientists have long thought that the moons really were asteroids that Mars grabbed for itself. But some recent computer simulations have bolstered another idea: that the moons formed much as Earth’s moon did.

    Our moon probably formed when another planet slammed into the young Earth. The impact blasted debris into orbit. Much of this material coalesced to form the Moon.

    Likewise, some scientists have suggested that Phobos and Deimos formed after a large asteroid hit Mars. But the proposal is so controversial that it took two decades for a paper advocating the idea to get published.

    Inspired by that work, other scientists have conducted simulations that indicate that such an impact could indeed create moons like Phobos and Deimos.

    But the simulations don’t provethat an impact created the moons. Instead, solving the issue probably requires a visit by a spacecraft. If the moons formed after an impact, they would have been too hot to have any ice. So if a spacecraft finds ice inside the Martian moons, they probably really are captured asteroids.

    More about Phobos tomorrow.

     

    Script by Ken Croswell, Copyright 2015


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

  • Moon and Spica

    The gibbous Moon passes over a bright star at dawn tomorrow. Spica, the leading light of Virgo, shines just a few degrees below the Moon, so you can’t miss it.

    Something else you can’t miss is the dark markings on the lunar surface. The biggest is near the left edge of the lunar disk — the Ocean of Storms. In fact, it’s the biggest of all the Moon’s dark markings, so it’s the only one known as an “ocean” — the others are called seas or other smaller bodies of water.

    Of course, there’s not a drop of liquid water anywhere in the Ocean of Storms. Instead, it’s a volcanic plain — a bed of ancient rock.

    There’s been some disagreement lately over how it formed. One group of scientists said it was the result of processes within the Moon itself. Another said it was the result of a giant impact.

    The first group found traces of cracks in the crust around the Ocean of Storms. Those cracks could have formed as the young Moon cooled and its crust contracted. The cracks then allowed molten rock from below to bubble to the surface.

    The other group used a Japanese satellite to measure the composition of the rock. Its observations suggested an impact origin. A giant space rock slammed into the young Moon, gouging out a wide basin, which then filled with molten rock from below. That scenario matches the generally accepted idea for the creation of most of the Moon’s volcanic plains — dark scars left over from the Moon’s violent past.


    Script by Damond Benningfield, Copyright 2015


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

  • IC 1396

    One of the most active stellar nurseries in the galaxy has already given birth to thousands of stars, and is forming many more stars even now. Yet its days as a nursery are numbered, because its brightest stars are blowing away the supplies of gas and dust that make stars.

    IC 1396 stands about a third of the way up the northwestern sky at nightfall. It’s visible through binoculars high above Deneb, the bright star at the tail of the swan.

    IC 1396 is a complex of diffuse gas, dense blobs of gas, and newborn stars that spans dozens of light-years. A hot, vigorous star at its center, and a few others that are only slightly less impressive, produce enormous amounts of radiation. The energy heats the edges of dense blobs of gas and dust embedded in the cloud.

    The energy also creates shockwaves that travel through the blobs, causing pockets of gas and dust to collapse and form new stars. Most are found in two clusters, each of which contains many hundreds of stars of varying size, mass, and temperature. But quite a few are found in much smaller blobs that contain just a handful of stars.

    All of this activity has happened over just a few million years. And it’s continuing today. But it won’t continue for that much longer. The radiation that helps trigger the birth of new stars is also blowing away the raw materials to make stars. So in a few million years, all the gas and dust will have disappeared — leaving an impressive cluster of young stars.


    Script by Damond Benningfield, Copyright 2015


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

  • Winter Milky Way

    The frosty outline of our own home galaxy arcs high overhead on these winter evenings. It stretches across or near some of the brightest stars in the night sky — from Sirius, the brightest of them all, low in the southeast; up past bright orange Betelgeuse above it; by yellow-orange Capella high overhead; and down to Deneb, the tail of the swan, low in the west.

    That feeble band of light — the Milky Way — represents the combined glow of millions of stars in the disk of the Milky Way galaxy. Yet it’s especially faint at this time of year because we’re looking away from the galaxy’s busy heart and toward its thinly populated hinterlands.

    Even so, with even a modest pair of binoculars, you can see some impressive sights within that faint glow.

    Many of those sights are star clusters. Each of these groups of scores or hundreds of stars formed from a single giant cloud of gas and dust. The stars remain gravitationally bound to each other, so they travel through the galaxy as a group.

    The brightest of them all is within the Orion Nebula, a giant cloud of gas and dust that looks like a fuzzy star below Orion’s three-star Belt. It’s given birth to perhaps a couple of thousand stars in the last few million years. Most of them remain bound together, forming a cluster — one of the youngest and largest in the entire galaxy.

    A similar combination of nebula and star cluster sits over in the northwest, and we’ll have more about that tomorrow.


    Script by Damond Benningfield, Copyright 2015


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

  • Moon and Jupiter

    Jupiter, the largest planet in the solar system, is attended by the largest family of known moons — almost 70. The four biggest are worlds in their own right. Io is the most volcanically active body in the solar system. Europa is considered a possible home for life, with a deep ocean of liquid water beneath a thin crust of ice. And Ganymede is the biggest moon in the solar system.

    The fourth big moon, Callisto, has its own distinction. It’s probably the most in-active moon around. During its four-and-a-half-billion-year history, it’s been pounded by countless space rocks, so its surface is the most heavily cratered of any known moon or planet. But nothing much else has happened. There’s no evidence of volcanoes, earthquakes, or any other process to reshape the surface.

    Callisto is almost as big as the planet Mercury. It orbits Jupiter at a distance of more than a million miles. There’s evidence of an ocean far below its surface, but it’s not considered a good home for life.

    Photographs reveal thousands of impact craters of all ages and sizes. That means that nothing has happened to erase the craters except more impacts. So this big moon sits quietly on the edge of the Jovian system — waiting for the next collision with a space rock.

    And Jupiter stands close to our own moon tonight. It looks like a bright star to the lower left of the Moon as they climb into good view by about 10 p.m. Callisto and Jupiter’s other big moons are visible through binoculars.


    Script by Damond Benningfield, Copyright 2015


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

  • Moon and Regulus

    The Moon keeps company with a “royal” star tonight. Regulus, the brightest star of Leo, the lion, is quite close to the left of the Moon as they climb into good view around 8 or 9 o’clock.

    The name “Regulus” means “the little king.” It comes from an ancient idea that the star was one of the rulers of heaven.

    The star that we see as Regulus is quite impressive. It’s bigger and heavier than the Sun, and several hundred times brighter. And like any monarch, it has an entourage — at least three companion stars.

    One of them is a white dwarf — a stellar corpse that orbits quite close to Regulus. The star was once the more impressive of the two. As it neared the end of its life, though, it expelled its outer layers of gas. Some of the gas fell onto Regulus, making it bigger and brighter, and causing it to spin much faster.

    The other companions are much farther away from Regulus — about a hundred times the distance from Earth to Pluto. Through a small telescope, their light blurs together to form a single pinpoint.

    The two stars are known as Regulus B and C, and they form their own binary — they orbit each other, and the pair orbits Regulus and its close companion. One of the stars is a little smaller and fainter than the Sun, and glows yellow-orange. The other is smaller still — a faint ember known as a red dwarf. It’s only about a third as massive as the Sun, and less than one percent as bright — a feeble attendant for a “regal” star.


    Script by Damond Benningfield, Copyright 2015


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

  • Five in a Row

    All five of the planets that are easily visible to the unaided eye climb across the dawn sky for a few days. This diagram shows the configuration on the morning of January 26, about 45 minutes before sunrise. All but Venus and Mercury will stay close to these positions for several days. Venus will move closer to Mercury, making it easier to spot the solar system's innermost planet in the last few days of January and the first few days of February. You may need binoculars to spot Mercury through the waxing twilight. The Moon will stand well to the lower right of Jupiter on the 26th, then will move past all the planets over the following mornings.

    Text ©2016 The University of Texas at Austin McDonald Observatory

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

Real time web analytics, Heat map tracking
Valid XHTML & CSS | Template Design LernVid.com and ah-68