StarDate

StarDate

  • Neptune at Opposition

    Big chunks of ice float atop Earth’s oceans: icebergs. Bergs may float inside the giant planet Neptune as well, made of a different kind of “ice”: diamond.

    Neptune is the fourth-largest planet in the solar system — it’s about four times the diameter of Earth. Its outer layers consist mainly of hydrogen and helium. Thousands of miles down, though, the composition changes to a mixture of ices — water, ammonia, and methane.

    Laboratory experiments suggest that under the extreme temperatures and pressures at those depths, the methane may break apart into its component molecules, including carbon.

    The pressure may then squeeze the carbon enough to form diamonds, which “rain” toward the planet’s core. Researchers speculate that a layer of liquid diamond may surround the core, with chunks of solid diamond floating inside that bizarre ocean.

    That scenario could also apply to Uranus, the third-largest planet — giving the solar system two worlds with chunks of “ice” floating deep below their surfaces.

    And Neptune itself is floating through Aquarius, the water bearer. The planet is putting on its best show of the year. It lines up opposite the Sun, so it rises around sunset and remains in view all night. It shines brightest for the year as well. Unfortunately, it’s still too faint to see with the eye alone. But it’s easy to find with a telescope — floating to the upper right of the Moon this evening.

    More about Neptune tomorrow.


    Script by Damond Benningfield, Copyright 2015


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

  • Hunting Planets IV

    Hunting for exoplanets can take some patience. Astronomers at McDonald Observatory, for example, have been hunting for planets around a set of 200 target stars for more than 15 years. Yet the search isn’t over. Michael Endl is the project’s lead scientist:

    ENDL: It seems like it should be obvious that, after so many years of observing, we should know which star has a planet or doesn’t. We’re searching now for planets that have orbital periods of a decade or more.

    Such a planet is big and heavy, but it’s far away from its star. The planet’s gravitational pull causes a change in the star’s motion toward or away from Earth. But the change is so tiny that it can take years to see it and confirm the planet’s presence.

    The scientists are looking for such planets because they can tell us a great deal about how our own solar system compares to others. In many systems, the giant planets have moved closer in, perhaps destroying small planets like Earth and Mars in the process. But astronomers aren’t sure how many systems look like that, and how many resemble our own.

    ENDL: From a human, philosophical viewpoint, that’s really what we’re interested in — seeing if our solar system is still something relatively rare and special, to have this collection of small, rocky planets in the interior, and in the habitable zone, and then have the giant planets farther out....We still don’t know whether we are living in a typical planetary system or not.

    So the search continues — many years after it began.


    Script by Damond Benningfield, Copyright 2015

    Today's program was made possible in part by a grant from the National Science Foundation.

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

  • Hunting Planets III

    It’s been only a couple of decades since astronomers discovered the first planets in other star systems. Yet they’re starting to figure out not just what some of those systems look like today, but what they might have looked like in the distant past.

    Astronomers are using the Harlan J. Smith Telescope at McDonald Observatory to hunt for exoplanetsOne of the keys is a class of planets known as “cold Jupiters.” They’re roughly the same size and mass as Jupiter, the giant of our solar system, and about the same distance from their parent star.

    Many of the planets discovered so far are hot or warm Jupiters. Such a planet is a giant, like Jupiter, but it’s quite close to its star.

    The problem, though, is that there doesn’t seem to be any way for such a planet to form so close in — the star would destroy the ingredients that make up such a bulky world.

    Instead, such a world probably formed much farther out, as Jupiter itself did. But interactions with the disk of material around the star, as well as other effects, pushed the planet closer in. That may have had disastrous consequences for smaller planets that were born closer to the star — they may have been pushed into the star.

    To better understand that process, astronomers at McDonald Observatory are looking for cold Jupiters — giants that stayed close to where they were born. How frequently such planets occur will tell us how likely it is that worlds like Earth survive the process — worlds that are the most likely homes for life.

    More about the search tomorrow.


    Script by Damond Benningfield, Copyright 2015

     

    Today's program was made possible in part by a grant from the National Science Foundation.

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

  • Young Giant

    A young Jupiter-like planet orbits far from its star in this artist's concept. McDonald Observatory astronomers are looking for similar planets in about 200 star systems. Such a giant planet may move closer to its star when it is young, perhaps forcing Earth-like worlds to fall into the star. How frequently such giant planets occur will help scientists understand how likely it is that Earth-like worlds survive the process of planet formation. [NASA/JPL]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Hunting Planets II

    MICHAEL ENDL: We are in the control room of the Harlan J. Smith 2.7-meter telescope at McDonald Observatory. And we are here because I have an observing run — four nights to use the telescope to search for extrasolar planets.

    Michael Endl is continuing a search that’s been going on for a decade and a half. A score of McDonald Observatory astronomers and students have used the same telescope and spectrograph that Endl is using to keep a sharp eye on about 200 stars. They’re looking for planets in orbit around those stars — especially worlds that are similar to Jupiter in our own solar system: giant planets in distant orbits.

    ENDL: The measurements that we are trying to perform are extremely exquisite. They’re very, very precise....We are measuring the velocities of stars. And we are looking for changes in the velocities of the stars due to an orbiting companion.

    An orbiting planet exerts a gravitational pull on its parent star. As seen from Earth, that causes the star to “wiggle” back and forth a bit. But that wiggle is tiny — it might change the star’s apparent speed by just a few miles per hour.

    Detecting such a change takes many observations, spaced over several years. In fact, the Texas astronomers have spent more than a thousand nights at the Harlan Smith Telescope, and have made up to a hundred or more observations of each target star.

    We’ll talk about how their work is helping us understand how our solar system compares to others tomorrow.

    Script by Damond Benningfield, Copyright 2015

    Today's program was made possible in part by a grant from the National Science Foundation.

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

  • Hunting Planets

    MICHAEL ENDL: The goal is that, inside the dome, the temperature is at the same level as the expected nighttime temperature — that’s why it’s already cooled down a little bit. But, of course, when we open up everything will take some time to settle down.

    Michael Endl is getting ready to hunt for planets. The McDonald Observatory astronomer is standing below the Harlan J. Smith Telescope. Air conditioners whirr around him, keeping the telescope and its 107-inch primary mirror cool, which keeps its view of the night sky sharp and clear.

    Over the next few hours, Endl will use the telescope to examine 30 or 40 stars — targets that he and colleagues have been watching for years. They’re looking for giant planets in distant orbits around the stars — planets similar to Jupiter in our own solar system.

    But getting ready to look at those stars takes some time. The instrument that Endl is using — a spectrograph, which breaks starlight into its individual wavelengths or colors — has to be properly calibrated, for example. Endl has to make sure the telescope’s tracking software is working. And from the control room, he has to keep an eye on some thunderstorms moving in from the southwest.

    ENDL: And now we have just opened up the dome. The weather is actually fine now. Now we are basically waiting for it to get dark enough so that we can point the telescope to one of the planet-search targets and take data — take a spectrum, as we call it.

    We’ll have more about the planet search tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

    Today's program was made possible in part by a grant from the National Science Foundation.

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

  • Shergotty

    Odd things sometimes fall from the sky — from mud to fish and toads. And 150 years ago today, a piece of Mars fell on the Indian village of Shergotty. Around 9 a.m., witnesses heard a loud boom. A few minutes later, they saw an 11-pound rock fall to the ground. It was soon identified as a meteorite. But it took more than a century to identify its Martian origin.

    Scientists have confirmed more than a hundred Mars meteorites. They’ve done so by examining tiny bubbles of gas inside the rocks. The ratios of different forms of oxygen and other elements in those bubbles match those measured in the Martian atmosphere by several Mars landers.

    The Shergotty meteorite formed as recently as 165 million years ago, when molten rock from a Martian volcano cooled and hardened. The rock probably formed near Mars’s equator, which is the site of the planet’s most recent volcanic activity.

    The meteorite is made mainly of silicon dioxide and iron oxide — the “rusty” mineral that gives Mars its orange color. It also contains tiny amounts of water, suggesting that it spent part of its lifetime in a wet environment.

    A few million years ago, an asteroid slammed into the Martian surface. The impact was powerful enough to blast the Shergotty meteorite and other bits of the Martian crust out into space. Most of these rocks are still orbiting the Sun. But at least one made it to Earth — where it fell from the sky 150 years ago today.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Stellar Sparkler

    The globular star cluster M22 sparkles brilliantly in these two views. The image at left shows the entire cluster, revealing its spherical shape. The one at right, from Hubble Space Telescope, is a zoomed-in view revealing thousands of individual stars. The cluster is in the constellation Sagittarius, near the lid of the "teapot" formed by eight of its stars. [N.A.Sharp/REU program/NOAO/AURA/NSF; NASA/ESA/STSCI]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Messier 22

    There’s more than one way to “discover” an astronomical object. The most obvious is to just see it. And by that standard, the object known as Messier 22 was discovered as soon as people started paying attention to the night sky. It looks like a hazy smudge of light close to the lid of the teapot — a pattern of eight bright stars in Sagittarius. You need dark skies to see it, though.

    But there’s another way to discover something, and that is to understand its true nature. By that standard, M22 was discovered 350 years ago this week by Abraham Ihle, an amateur astronomer in Germany.

    Ihle was using a small telescope to study the planet Saturn, which was passing through Sagittarius at the time. When he looked at that nearby hazy patch of light, he found that it was a swarm of thousands of individual stars.

    Today, that swarm is known as a globular cluster — a collection of many stars packed into a tight ball. In fact, M22 was the first globular to be seen as anything other than a fuzzy ball of light.

    Like all globulars, M22 contains some of the oldest stars in the galaxy. That indicates that these clusters were some of the first clumps of stars to form in the entire galaxy.

    M22 also contains black holes and several free-floating planets — objects bigger than Earth that don’t orbit any star. They help make M22 one of the most diverse and interesting globulars in the galaxy.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Gemini 5

    A few carmakers are starting to build automobiles that are powered by fuel cells. The cells use a chemical reaction to combine hydrogen and oxygen, producing electricity and water.

    Some of the first fuel cells were built to power the two-seat Gemini spacecraft. In fact, the first test model was orbiting Earth 50 years ago today, aboard Gemini 5.

    Gemini was designed to develop and test the equipment and techniques needed to get astronauts to the Moon. Gemini 5 was scheduled to last eight days — the minimum time expected for a trip to the Moon and back. Gemini couldn’t carry enough batteries for such a long flight, though, so engineers developed fuel cells to keep its lights burning.

    Gemini 5 launched on August 21st, 1965.

    AUDIO: 3, 2, 1, 0, ignition. Liftoff! We’re off on the hour...

    When they reached orbit, astronauts Gordon Cooper and Pete Conrad were trying to rendezvous with a small pod they’d ejected into space. After the flight, Cooper explained what happened next:

    COOPER: About this period of time, we had a small problem that started occurring.... The fuel cell oxygen was decreasing rather rapidly in pressure. I made the decision that we should go through a power down.

    The problem threatened to scuttle the mission. But the system eventually settled down, allowing Gemini 5 to spend the full eight days in orbit.

    Fuel cells later powered the Apollo flights to the Moon and the space shuttle. And someday, they may even power many of the cars cruising on American highways.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Moon, Saturn, and Antares

    Almost from the day it’s born, a star is on a constant weight-loss plan. It blows some of the hot gas on its surface out into space in a steady “wind.” The Sun, for example, expels enough material to make a body as massive as Earth every 150 million years.

    For some stars, though, the wind is much more furious. An example is Antares, the bright orange star at the heart of Scorpius, the scorpion. It expels enough material to make an Earth-mass body in just a couple of years.

    The main reason for the difference is the star’s size. Antares is hundreds of times wider than the Sun. Since the star’s surface is a long way from its core, the surface gravity is much weaker than the Sun’s. That makes it easier for material to escape. And the surface area of Antares is roughly a half-million times greater than the Sun’s, so gas is streaming into space from a much larger region.

    The combination creates a thick nebula around Antares. It’s lumpy, indicating that Antares blows more material into space at some times than at others. And a hot, bright companion star stirs up the nebula and creates a big structure that looks like an open umbrella. So the space around Antares is busy and turbulent — the result of the star’s own weight-loss plan.

    And Antares is in good view this evening. It stands to the lower left of the Moon. The golden planet Saturn is closer to the Moon’s lower right — completing a beautiful triangle in the evening sky.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Moon and Saturn

    Despite years of observations by spacecraft, and centuries by ground-based telescopes, there’s still a lot to learn about the giant planets of the solar system. One of the mysteries is whether Jupiter and Saturn have solid cores. Planetary scientists think they do, but they’re still not certain.

    In the case of Saturn, models say it probably has a rocky core that’s about as big as Earth, but perhaps 10 to 20 times heavier. According to a leading idea about how the planets formed, the gravity of that heavy core pulled in vast amounts of hydrogen and helium that was left over from the birth of the Sun. So Saturn grew to giant proportions — it’s the second-largest planet in the solar system.

    But there’s a lot of uncertainty about the size of the core, and whether it even exists. In large part that’s because there’s uncertainty about many of the planet’s details — from how fast it spins on its axis to the amount of helium in its outer layers.

    And even if Saturn did have a solid core to begin with, a layer of metallic helium around it could have eroded some or all of the core. So it’s going to take a lot more work to fully understand the insides of this giant world.

    And giant Saturn is in great view tonight. It stands to the left of the Moon as night falls, and looks like a bright golden star. The true star Antares — the heart of the scorpion — is to Saturn’s lower left. We’ll have more about this lineup tomorrow.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Polaris Flare

    Stars are born in vast clouds of gas and dust. Astronomers can study the very first stage of starbirth by observing clouds that haven’t yet given birth to any stars. One such cloud is in the far northern sky, near the North Star, Polaris. It’s called the Polaris Flare.

    Its exact size and distance aren’t known, although it’s probably about 400 to 800 light-years from Earth, and probably spans about a hundred light-years. It consists mostly of molecular gas — the cold, dense type of gas that’s most likely to create new stars.

    So far, though, the Polaris Flare has yet to spawn a single star. With no stars inside to warm it up, the cloud is frigid — around 430 degrees below zero.

    Still, it contains hundreds of dense clumps of gas. Many of these clumps may disperse, with their gas simply filtering away into space. But some of them may be the kernels of future stars.

    These dense knots of material may collapse under their own weight. As that happens, the gravitational energy of the collapse is converted into heat, so the object begins to glow — and a new star is born.

    In any event, the Polaris Flare gives us the chance to observe an interstellar cloud before its star-making career begins.

    Although the gas cloud is invisible to the eye, Polaris is not. To find it, line up the two stars at the outer edge of the Big Dipper’s bowl. Extend that line above the bowl until you come to the first moderately bright star: Polaris.

     

    Script by Ken Croswell, Copyright 2015

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

  • Heating Saturn

    The beautiful planet Saturn is lining up between the balance scales and the head of the scorpion right now. It looks like a bright golden star, about a third of the way up the southwestern sky at nightfall. The scales of Libra line up to the right of Saturn, with the scorpion to its lower left.

    Saturn is the solar system’s second-largest planet. It’s best known for its beautiful rings. But a team of researchers recently peered deep into the giant planet’s interior. They didn’t get anywhere near Saturn, though. Instead, they used the Z machine at Sandia National Laboratories, which simulated conditions thousands of miles below Saturn’s cloudtops.

    Astronomers have theorized that Saturn’s interior contains a layer of hydrogen that’s squeezed so tightly that it forms a metal. The metallic hydrogen may mix with helium, forming droplets that “rain” toward the core. The droplets are squeezed by Saturn’s gravity, which heats the planet’s interior.

    The Z machine uses powerful pulses of electricity to generate a strong magnetic field. Researchers used the magnetic field to squeeze a sample of deuterium, which is a heavy version of hydrogen. They then measured the pressure at which the deuterium changed to a metallic form.

    The researchers say their results will help astronomers model Saturn’s interior more accurately. That’ll provide a better understanding of how the helium rain forms and how it heats the insides of this beautiful planet.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Last Visit

    Saturn's moon Dione stands in front of Saturn and its rings in this August 17 view from the Cassini spacecraft. The rings form a horizontal line behind Dione, and cast shadow bands across Saturn at the top of the image. This is Cassini's final visit to Dione. Its mission will end in late 2017 when the craft plunges into Saturn's atmosphere. [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.

  • Iron Rain

    The young planet Earth may have received some occasional showers. Not cooling rain showers like you might hope for on a summer afternoon, but showers of liquid iron — the aftermath of collisions between Earth and big asteroids.

    Researchers came to that conclusion after vaporizing bits of iron in the Z machine, a test chamber at Sandia National Laboratories. The machine uses powerful pulses of electricity to create X-rays and strong magnetic fields.

    The researchers were trying to understand why there are blobs of iron in Earth’s mantle — the layer of hot rock beneath our planet’s crust.

    The iron probably came from iron-rich asteroids that slammed into the young Earth. But that’s a puzzler, because big blobs of iron should have settled into Earth’s iron core.

    So the researchers wondered if perhaps the iron vaporized in the collisions, then condensed and fell to Earth as rain. The smaller iron “raindrops” would have then collected in the mantle.

    Theoretical models say the conditions in the impacts shouldn’t have been extreme enough to vaporize the iron. But the researchers used the Z machine to instantly squeeze and heat small samples of iron. Their tests showed that the iron vaporized at pressures similar to the conditions found in asteroid collisions — suggesting that the young Earth could have been pelted with showers of iron.

    We’ll talk about another Z machine experiment tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Cassini at Dione

    The Cassini spacecraft is continuing a farewell tour today. It’s scheduled to take its final close look at Dione, one of the larger moons of Saturn. It’s one of several “final encounters” with the giant planet’s moons before Cassini’s mission ends in 2017.

    The encounter with Dione is almost like a double farewell. That’s because there’s a big difference between Dione’s leading and trailing hemispheres — almost like two different worlds. The leading hemisphere, which faces in the direction of Dione’s orbital motion around Saturn, is quite bright, and it’s less rugged than the trailing hemisphere.

    One reason for the brightness is that Dione receives a constant spray of ice from geysers at the south pole of Enceladus, another big moon.

    But the fact that the leading hemisphere is less rugged is tougher to explain. That hemisphere should sweep up more space debris as Dione orbits Saturn, just as a car’s windshield gets splattered by more bugs and gravel than its back window.

    More splats should mean more and bigger craters on the leading hemisphere. Instead, it’s just the opposite. That could mean that Dione was spun all the way around by one or more powerful impacts billions of years ago — after most of the craters had formed on what was then the leading hemisphere. So today, those craters are on the moon’s backside, not on its front — contributing to the two-faced appearance of this intriguing moon.

     

    Script by Damond Benningfield, Copyright 2015


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

  • Stellar Tourism

    When Lick Observatory opened near San Jose in 1887, a few local businessmen saw an opportunity. They figured the new facility would attract visitors from across California and beyond. So they decided to build a grand hotel to house them all.

    The 150-room, $250,000 Hotel Vendome opened in 1888, and it featured Lick in its ads, postcards, and other materials.

    An 1890s postcard promotes the new Lick ObservatoryGetting to the observatory wasn’t easy, though. It was only about 20 miles from the hotel, but the road to the top of Mount Hamilton climbed several thousand feet, and it featured 365 turns.

    So another business was formed to get all those overnight guests up the mountain: the Mount Hamilton Stage Company. For a few dollars, passengers got a three-hour ride to the observatory in an open coach, lunch at a small hotel along the way, and a three-hour ride back to San Jose. They were encouraged to wear a handkerchief around their necks in case travel conditions were dusty, which they often were. The coaches left at 7:30 in the morning and got back by about 6 in the afternoon. Coaches also made the trip on Saturday evening, when Lick offered public viewing through its big new 36-inch telescope.

    Other businesses got involved as well. The Southern Pacific Railroad offered special package deals from San Francisco, for example. They helped turn Lick Observatory into a major tourist spot — setting an example for other observatories to follow in the decades ahead.

    Script by Damond Benningfield, Copyright 2015


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

  • Busy Comet

    The Rosetta spacecraft snapped this sequence of images of Comet Churyumov-Gerasimenko on August 12, just hours before the comet reached its closest point to the Sun. The images show gas and dust streaming into space from the comet's surface, with a big outburst of material near the middle of the sequence. Rosetta was less than 200 miles from the comet. [ESA/Rosetta/MPS for Rosetta Team]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Changing Addresses

    The light of the “evening star” has been switched off. But the “morning star” will switch on in just a few days. That’s because the planet Venusis changing addresses today. It’ll cross the line between Earth and the Sun, moving from the evening sky to the morning sky. It’ll be lost in the Sun’s glare for a few days, but will climb into easy view by month’s end.

    It seems obvious that the morning star and evening star are the same object. They’re the same brightness, they’re in view for the same amount of time — and like Bruce Wayne and Batman, you never see both of them at the same time.

    Yet it took some cultures a while to figure that out. The Greeks, for example, thought of the morning and evening stars as two separate objects. The morning star was known as Phosphoros, while the evening star was Hesperos. The Greeks didn’t unite the two until about 2500 years ago.

    One culture that wasn’t fooled by Venus’s dual identity was the Maya of Central America. Venus was the most important object in the night sky — it played key roles in everything from festivals to warfare. So the Maya carefully plotted Venus’s motions across the sky. They developed tables that allowed them to predict just where Venus would be far in the future — morning or evening.

    And you can start looking for Venus in just a few days, quite low in the east just before sunrise. It’ll quickly take its place as the brilliant morning star — a spot it’ll keep until spring.


    Script by Damond Benningfield, Copyright 2015


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

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