Posted on by Nancy Atkinson

More Images, Details on SpaceX’s Dragon Flight

The Dragon spacecraft, in excellent condition after its 50,000 mile mission, rests in its cradle for the 500 mile ride back to Los Angeles.

[/caption]

SpaceX has released more images and more details about the successful flight of Falcon 9 and the Dragon capsule that took place on December 8, making SpaceX the first commercial company in history to re-enter a spacecraft from Earth orbit. Here’s an image of Dragon safely on board a ship after splashdown. SpaceX said Dragon orbited the Earth at speeds greater than 7,600 meters per second (17,000 miles per hour), reentered the Earth’s atmosphere, and landed less than one mile from the center of the targeted landing zone in the Pacific Ocean. Wow, that’s some pretty good precision. See more images and details of the flight below.

The above image also shows a look at Dragon’s PICA-X heat shield, which SpaceX says is highly advanced. They worked closely with NASA to develop the heat shield, a variant of NASA’s Phenolic Impregnated Carbon Ablator (PICA) heat shield, which NASA used for the Stardust sample capsule returned, which set the record for the fastest reentry speed of a spacecraft into Earth’s atmosphere — experiencing speeds of 46,510 kph (28,900 mph).

NASA made its expertise and specialized facilities available to SpaceX as the company designed, developed and qualified the 3.6 meter PICA-X shield in less than 4 years at a fraction of the cost NASA had budgeted for the effort. The result is the most advanced heat shield ever to fly. SpaceX said one heat shield can potentially be used hundreds of times for Earth orbit reentry with only minor degradation each time, and that this flight proved it. During the press conference following the successful flight of Dragon, SpaceX CEO Elon Musk said this heat shield could even withstand the much higher heat of a moon or Mars velocity reentry.

The Falcon 9 launch vehicle carrying the Dragon spacecraft, climbing from the launch pad. Credit: SpaceX/Chris Thompson

SpaceX said all nine Merlin engines performed “nominally,” which means they worked wonderfully. Together, the rocket engines generate one million pounds of thrust in vacuum, getting the entire stack off the ground and powering the first phase of flight. The rocket reached maximum dynamic pressure (the point at which aerodynamic stress on a spacecraft in atmospheric flight is maximized, also known as Max Q) approximately 1.5 minutes after launch. The first stage separation occurred a little over three minutes into flight.

After stage separation, flames are barely visible around nozzle as the second stage engine ignites and the first stage falls back to the Earth below. Credit: SpaceX

The single Merlin Vacuum engine of Falcon 9’s second stage then ignited to continue carrying the vehicle towards its targeted orbit. After stage separation, the nose cap at the front of the Dragon spacecraft safely jettisoned. The second stage fired for another four and a half minutes, until it achieved orbital velocity, and then the Dragon spacecraft separated from the second stage to begin its independent flight.

High contrast view of the Dragon spacecraft (circle at center) viewed from the top of the second stage as it departs over the curved horizon of the Earth. The rectangles indicate locations of three of the nano satellite deploying P-PODs carried on this mission. Credit: SpaceX

SpaceX said Dragon’s first-ever on-orbit performance was 100% successful in meeting test objectives including maintaining attitude, thermal control, and communication activities. While in orbit, eight free-flying payloads were successfully deployed, including a U.S. Army nanosatellite—the first Army-built satellite to fly in 50 years.

After separation of the Dragon spacecraft, the second stage Merlin engine restarted, carrying the second stage to an altitude of 11,000 km (6,800 mi). While restart of the second stage engine was not a requirement for this mission (or any future missions to the ISS), it is important for future Geosynchronous Transfer Orbit (GTO) missions, where SpaceX hopes to bring satellites for paying customers.

View from orbit from the side window of the Dragon spacecraft, received via video as it passed over Hawaii during its first orbit. Credit: SpaceX

What’s the view like from inside Dragon? Here’s a view looking out Dragon’s porthole, with a view of Hawaii. After the second stage separated, there was an expected loss of signal as the Dragon spacecraft passed over the horizon as viewed from the launch site. At that point, SpaceX activated Dragon’s video signal from a camera set up inside the capsule, delivering the first ever video sent from Dragon on orbit.

The SpaceX crew brought Dragon back to the barge where the crane lifted it from the water. Credit: SpaceX/Mike Althofen

For this first flight under the Commercial Orbital Transportation Services (COTS) program, everything went perfectly, with a nominal flight profile that included a roughly 9.5-minute ascent, two Earth-orbits, reentry and splashdown. Falcon 9 delivered Dragon to orbit with an inclination of 34.53 degrees—a near bull’s-eye insertion, according to SpaceX.

Now, on to the next demonstration flight, which will go to the International Space Station, and maybe even dock, if SpaceX has anything to say about it.


See our previous gallery of images and videos from the launch.

Source: SpaceX

Posted on by Ken Kremer

Landfall at Santa Maria for Opportunity on Mars

Opportunity arrived at Santa Maria crater on Sol 2450 (Dec 15, 2010) and will spend the next few weeks exploring around the 80 meter wide crater. In the background is Endeavour crater, 6 km away. This mosaic was assembled from pancam images. Credit: NASA/JPL/Cornell/ Ken Kremer, Marco Di Lorenzo

[/caption]

NASA’s Opportunity Mars rover arrived today (Dec .15) at Santa Maria crater on Sol 2450. She sits just 20 meters from the crater rim. A multitude of inviting rocks and boulders are strewn about the 80 meter diameter crater, making this a Martian geologists dream.

And so it goes too for a Martian photographer with lots to shoot and with the giant 14 km wide Endeavour crater serving as backdrop and coming into ever clearer focus.

Santa Maria is just 6 km from the western rim of Endeavour (see panoramic mosaics above and below).

MRO image of Santa Maria crater from orbit with Sol markers. Credit: NASA/JPL/UA/MSSS/Eduardo Tesheiner

Opportunity has been on a swift advance since departing from Intrepid crater in mid-November and driven about 1.5 km over very smooth terrain. The rover continues to benefit from a bounty of solar power and upgraded software enabling longer and more frequent days of drives. Opportunity has now driven a total of 26.4 km.

Opportunity Sol 2450 (Dec 15, 2010) 90 degree perspective projection around Santa Maria crater. Credit: NASA/JPL/Cornell/Midnight Mars Browser

The rover team is planning for an extensive and multi week science campaign at Santa Maria using all the instruments and cameras at their disposal.

Opportunity will spend the holiday season and the upcoming Solar conjunction exploring around Santa Maria according to Matt Golembek, Mars Exploration Program Landing Site Scientist at the Jet Propulsion Laboratory (JPL), Pasadena, Calif.

There will be no uplink commanding to the spacecraft around the actual conjunction period from Jan. 28 to Feb. 12 (UTC) out of caution that the command transmission could be disrupted.

The team plans a sophisticated wide-baseline stereo-imaging survey of Santa Maria by having Opportunity drive to several positions halfway around the crater. A mineral survey will be carried out using the spectrometers, microscope and drill – known as the RAT or rock abrasion tool – located at the terminus of the rover’s robotic arm.

3 D view of the feature resembling an “Alligator’s Tail” near the rim of Santa Maria crater on Sol 2450. Credit: NASA/JPL/Cornell/Stu Atkinson

See several additional amateur mosaics below – including 3 D images – from all of us at unmannedspaceflight .com.

The rover is now at the two thirds mark of a 19 km (12 mile) journey from Victoria crater on the road to reach the rim of the scientifically rich environs of Endeavour crater sometime later in 2011. Opportunity explored the rim and interior of Victoria from mid-2006 to mid-2008.

Santa Maria is the largest feature that Opportunity will explore between Victoria and Endeavour craters. The team assigns informal names to craters visited by Opportunity based on the names of historic ships of exploration in human history. See Opportunity traverse maps below.

More than 95 percent of the data from Spirit and Opportunity are relayed by NASA’s Mars Odyssey orbiter. Today, Odyssey broke the record for being the longest-serving spacecraft at the Red Planet during it’s 3,340th day in Martian orbit.

Opportunity traverse route from Victoria crater to Santa Maria crater.
Posted on by Nancy Atkinson

Become an Exoplanet Hunter With Newest Zooniverse Citizen Science Project

Artist's impression of an extrasolar planet. Image credit: CfA

[/caption]

You knew it was only a matter of time until the hunt for extrasolar planets joined the Zooniverse family of Citizen Science projects. And the time has now arrived for your chance to make one of the biggest discoveries of the 21st century by finding other planets out there in the Universe.

Planet Hunters is the latest addition to the Zooniverse, and users will help scientists analyze data taken by NASA’s Kepler mission, the biggest, badest exoplanet hunting telescope in space. The project goes live on December 16 at http://www.planethunters.org.


“The Kepler mission has given us another mountain of data to sort through,” said Kevin Schawinski, a Yale University astronomer and Planet Hunters co-founder. Schawinski was one of the original forces behind Galaxy Zoo, the citizen science project that started it all back in 2007, which enlisted hundreds of thousands of Web users round the world to help sort through and classify a million images of galaxies taken by a robotic telescope.

The Kepler telescope has been in space since 2009, continually monitoring nearly 150,000 stars in the constellations Cygnus and Lyra, recording their brightness over time. In June of this year, the Kepler team announced they had found over 750 exoplanet candidates in just the first 43 days of the spacecraft’s observations.

They also just announced they will make an early release of a complete 3 months of observations early in 2011, which will contain light curves for approximately 165,000 stars, most of which are late-type Main Sequence stars.

“The Kepler mission will likely quadruple the number of planets that have been found in the last 15 years, and it’s terrific that NASA is releasing this amazing data into the public domain,” said Debra Fischer, a Yale astronomer and leading exoplanet hunter.

Although Planet Hunters is not tied directly to the Kepler mission, the website will serve as a complement to the work being done by the Kepler team to analyze the data, the team said.

Granted, the Citizen Scientists looking for extrasolar planets will be doing a search akin to looking for a needle in a haystack. But its one of the most exciting needles to be searching for.

Because of the huge amount of data being made available by Kepler, astronomers rely on computers to help them sort through the data and search for possible planet candidates. “But computers are only good at finding what they’ve been taught to look for,” said Meg Schwamb, another Yale astronomer and Planet Hunters co-founder, “whereas the human brain has the uncanny ability to recognize patterns and immediately pick out what is strange or unique, far beyond what we can teach machines to do.”

Galaxy Zoo project has shown how successful this concept of using a network of global volunteers can be, as the Citizen Scientists has helped the Galaxy Zoo team publish over 20 papers about galaxy shapes and distributions, as well as making some unusual discoveries, like Hanny’s Voorwerp.

To participate, you don’t need to have any astronomical or exoplanet expertise. When users log on to the Planet Hunters website, they’ll be asked to answer a series of simple questions about one of the stars’ light curves — a graph displaying the amount of light emitted by the star over time — to help the Yale astronomers determine whether it displays a repetitive dimming of light, identifying it as an exoplanet candidate.

And exoplanet research is one of the hottest topics in astronomy today. Over 500 planets have been found orbiting other stars since 1995. Most of these are large, Jupiter-like planets, but astronomers are refining their searches to try and find smaller planets more the size of Earth.

“The search for planets is the search for life,” Fischer said. “And at least for life as we know it, that means finding a planet similar to Earth.” Scientists believe Earth-like planets are the best place to look for life because they are the right size and orbit their host stars at the right distance to support liquid water, an essential ingredient for every form of life found on Earth.

The point of citizen science is to actively involve people in real research,” Schawinski said. “When you join Planet Hunters, you’re contributing to actual science — and you might just make a real discovery.”

Posted on by Nancy Atkinson

Lunar Dust Transport Still a Mystery

Sketches made by the Apollo 17 crew of rays created by lofted lunar dust. Credit: NASA

[/caption]

There are times when Moon appears to have a tenuous atmosphere of moving dust particles that are leaping up from and falling back to the Moon’s surface. First seen during the Surveyor and Apollo eras, these observations were completely unexpected, and scientists today are still trying to understand this phenomenon.

The first indication that something strange was going on with the lunar surface was in the 1960’s when cameras on the Surveyor spacecraft pointing towards the western horizon noticed a brighter hovering cloud that persisted for several hours.

“There are many other bits and pieces of observations of this kind,” said Dr. Mihaly Horanyi from the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics. “For example, the astronauts in the Apollo command modules that stayed in orbit about the Moon were hoping to take images of the dark sky, but of course there is scattered light from the dust in interplanetary space. But the brightness also appeared to follow the lunar surface, indicating that somehow dust is coming off the surface of the Moon.”

While astronauts from Apollo 8, 10, and 15 all reported such dust clouds, Apollo 17 in 1972 repeatedly saw and sketched what they called “bands,” “streamers” or “twilight rays” for about 10 seconds before lunar sunrise or lunar sunset.

Adding to the mystery, also on Apollo 17 was a dust detector placed on the surface by the astronauts, the Lunar Ejecta and Meteorite experiment, which was supposed to measure the high speed impacts of micrometeorites hitting the moon.

An Apollo 17 astronaut digs in the lunar regolith to study the mechanical behavior of moon dust. Credit: NAS

“Instead the measurements showed an increase of particle fluxes that went up a hundred fold when day turned to night and night turned into day at that location on the Moon,” Horanyi said.

“Every single one of these measurements has an alternate explanation somehow. But it seems that the whole body of these observations is best explained by recognizing that dust — even on an airless body — can move around and come to life.”

Even thought the Moon has no atmosphere, Horanyi said other processes that are likely related to the plasma and radiation environment of the Moon, “the electro-dynamic processes of the near surface lunar environment that can have strong enough electric fields and the surface can have enough electrostatic charges that can break the dust free and somehow shuffle it or move it around the surface.”

In other words, electrostatic charging of the lunar surface causes the dust to levitate, precipitated – somehow – by changes in sunlight.

Horanyi said this type of thing has been seen on other airless bodies, like on Mercury, comets and asteroids.
“For example, the near-landing on the asteroid Eros,”Horanyi said, “people noticed that the bottom of the craters are filled with fine dust, and there is not enough atmosphere, and certainly the body is too small have asteroid shakes – the asteroid version of earthquakes — so the possible transport that would trap or make dust pile up in some regions and move it from others, is most likely a plasma effect.”

Horanyi and other scientists have done lab experiments to try and replicate the lunar environment to see if a dust transport takes place.

“For the first set of experiments, imagine just a piece of surface with dust particles on it, and we shine light on this surface,” he said, “so that half is illuminated, half is not, pretending that there is a terminator region, that the sun is set on one side and is still shining light on the other. When you shine light on the surface with properties that are appropriate, you can emit photo electrons, but you only emit electrons from the lit side, and some of those electrons land on the dark side, — you have a positive charge surplus on the lit and a negative charge pile-up on the night side. Across a couple of millimeters you can easily generate a potential difference of maybe a watt, or a handful of watts, which translates actually as a small-scale, but incredibly strong electric fields. This could be like a kilowatt over a meter. But of course, it only exists over a sharp boundary, and that sharp boundary may be the key to understanding how you get dust moving to begin with.”

Horanyi said in the transient region where boundaries match up – lit and dark boundaries, or boundaries between where the surface is exposed to a plasma and where it is not – those sharp transitions could actually overcome adhesion between dust and the rest of the surface and start moving.

“And that’s where the story gets really interesting,” he said.

Hopefully, a new mission called LADEE (Lunar Atmosphere and Dust Environment Explorer) can help explain this mystery. It is slated to launch in 2013 and fly in low lunar orbit, as close to the surface as 30-50 km. Since NASA may not be sending astronaut to the Moon anytime soon, LADEE’s mission may now be a little different than previously thought, but it still has some important science to conduct.

It will carry three instruments, an infrared imager, a neutral mass spectrometer and a dust detector, which Horanyi is helping to build.

“That hopefully will be capable of measuring tiny, tiny, small particles that people argue are lofted from the surface,” Horanyis said. “And we hope that in combination these instruments might put an end to this argument that we’ve had since the early 1970’s whether dust is really actively transported and shuffled around on the lunar surface or not.”

Listen to a 365 Days of Astronomy podcast where Dr. Horanyi discusses the “Mysterious Moving Moon Dust.”

Posted on by Nancy Atkinson

Spectacular Night Launch for Soyuz Crew

Expedition 26 Flight Engineer Paolo Nespoli is seated in the Soyuz TMA-20 during its ascent to orbit. Nespoli and Flight Engineers Dmitry Kondratyev (at bottom) and Catherine Coleman (out of frame) launched on time to the International Space Station. Credit: NASA TV

With a spectacular night launch, the remainder of the Expedition 26 crew are now headed to the International Space Station on board a Soyuz TMA-20 spacecraft. NASA astronaut Cady Coleman, Russian cosmonaut Dmitry Kondratyev, and European Space Agency astronaut Paolo Nespoli lifted off from the Baikonur Cosmodrome in Kazakhstan at 2:09 p.m. EST Wednesday (1909 UTC and 1:09 a.m. local in Kazakhstan) on Wednesday, Dec. 16. Video from inside the capsule showed the crew riding comfortably during their ascent.


The trio are scheduled to dock to the station’s Rassvet docking port at 3:12 p.m EST onFriday, Dec. 17. Just in time for the holidays, they will join Expedition 26 Commander Scott Kelly and Flight Engineers Alexander Kaleri and Oleg Skripochka, already on board the ISS.

[/caption]

You can watch the docking on NASA TV, beginning at 2:30 p.m. EST Coverage of the hatches opening and a welcoming ceremony aboard the station will begin at 5:30 p.m.

With a full compliment of six, Expedition 26 will be busy with scientific research and regular maintenance, but there will also be two Russian-segment spacewalks, and a variety of visiting resupply ships: a Japanese HTV cargo ship will arrive at the end of January, a Russian Progress re-supply ship will also come just before, hopefully, space shuttle Discovery arrives in early February — given the repairs of the external tank go well, and then a European Automated Transfer Vehicle, or ATV, arrives at the end of February.

After that, The shuttle Endeavour is scheduled launch in early April along with another Progress later that month.

Soyuz launch on Dec. 15, 2010. Photo credit: NASA/Carla Cioffi
Posted on by Nancy Atkinson

No Asteroid Particles Found in Second Hayabusa Compartment, But More in First

Artist concept of the Hayabusa spacecraft, which visited asteroid Itokawa in 2005 and returned samples to Earth in 2010. Credit: JAXA
Artist concept of the Hayabusa spacecraft, which visited asteroid Itokawa in 2005 and returned samples to Earth in 2010. Credit: JAXA

[/caption]

No visible material from asteroid Itokawa was found inside the second compartment of a canister returned to Earth by the Hayabusa spacecraft. However, JAXA also announced that more micron-sized grains have been found in the first compartment, opened earlier this year. Reportedly, the first compartment has about 1,500 tiny particles, however some might be aluminum particles from the container itself. But about 20 grains were rocky or mineral-based. However, according to the Daily Yomiuri Online, no visible material was inside the second chamber, although further investigations of the second compartment will be done with a special microscope.

Hayabusa attempted to land on Itokawa twice. The cylindrical canister was divided into two chambers, and the second chamber was to contain material collected during the spacecraft’s first landing.
JAXA officials expect the second compartment to contain more microscopic particles from Itokawa since the first landing was longer than the second.

As far as the particles from the first chamber, several have been observed with an electron microscope, and according to UmannedSpaceflight.com, the “rocky” ones are 30 microns in size, with several larger ones are about 100 microns.

JAXA hopes to provide more insight on the nature of the grains by the end of the year.

Posted on by Nancy Atkinson

Near-Synchronous Explosions Connect Across the Vast Distances on the Sun

The solar corona, as observed by SDO’s AIA, for temperatures from 1 million degrees (blue), through 1.5 million (green), and 2 million (red), on 2010/08/01. This image serves as a background for magnetic field lines emerged onto the Sun. The locations of the major changes coincide with major solar activity on August 1, 2010. Credit: NASA, Lockheed Martin’s Solar and Astrophysics Laboratory.

For several decades, scientists studying the sun have observed solar flares that appear to occur almost simultaneously but originated in completely different areas on the Sun. Solar physicists called them “sympathetic” flares, but it was thought these near-synchronous explosions in the solar atmosphere were too far apart – sometimes millions of kilometers distant – to be related. But now, with the continuous high-resolution and multi-wavelength observations with the Solar Dynamics Observatory, combined with views from the twin STEREO spacecraft, the scientists are seeing how these sympathetic eruptions — sometimes on opposite sides of the sun — can connect through looping lines of the Sun’s magnetic field.

“The high-quality simultaneous data we received from SDO and the STEREO spacecraft, and our subsequent analysis, enable us to present unambiguous evidence that solar regions up to 160 degrees away are involved in defining the large-scale coronal field topology for flares and CMEs,” said Dr. Carolus Schrijver, who co-presented his team’s findings at the American Geophysical Union meeting in San Francisco.

“From the very first observations with SDO we saw small events seemed to impact large regions of the sun,” said Alan Title of the Solar and Astrophysics Lab at Lockheed Martin, and co-author of the paper, speaking at a press briefing, “but because we are scientists and are sometimes not very clever, we have to sometimes be beaten over the head, and went searching for some kind of causality. It has been in last couple of months where we worked out this picture together.”

The hammer on the head was a series of solar events that took place on August 1, 2010, where nearly the entire Earth-facing side of the Sun erupted in a tumult of activity, with a large solar flare, a solar tsunami, multiple filaments of magnetism lifting off the solar surface, radio bursts, and half a dozen coronal mass ejections (CMEs).

SDO, which launched in February of this year, along with the two Solar Terrestrial Relations
Observatory (STEREO) spacecraft — were ideally positioned to capture both the action on the Earth-facing side of the Sun, and most activity around the backside, leaving a wedge of only 30 degrees of the solar surface unobserved.

SDO’s Atmospheric Imaging Assembly (AIA) continuously observes the full solar corona and can trace perturbations over long distances, even if short-lived. The STEREO spacecraft were able to provide perspectives on activity on most of the “back side” of the Sun, and perhaps most importantly, SDO’s Helioseismic and Magnetic Imager (HMI) provided global magnetic field connections.

[/caption]

As seen in the image above, the looping magnetic field lines connected the various events on August 1. Subsequent observations have revealed similar events.

“The magnetic field lines connect to other flares and other major events, with the eruptions and flares frequently coupled across large distances,” said Schrijver. “Previously, we had been looking for the cause of explosions just in the regions from where the explosions were coming from. That might be a good way to do it, but these observations show another aspect. If we wish to know why the flare goes off, we need to know not just properties of region but also a large fraction of the solar surface, in fact sometimes not even part we can see. So maybe reason we had difficulty figuring this out was that we were not seeing everything. We have to expand our view and look at everything.”

Title compared finally figuring out that these near synchronous events are related to how scientists finally figured out continental drift. “Everyone could see how Africa and South America could have once fit together, but no one could imagine the physical processes that could make that happen,” he said, “but all of a sudden someone measured it and figured out sea floor spreading and it made perfect sense.”

In response to a question of whether the magnetic field on the Sun has areas similar to fault lines on the Earth where magnetic lines emerge repeatedly, Schrijver told Universe Today that the magnetic field lines come from the deep within the solar interior, but why it chooses to emerge in certain areas repeatedly is a mystery. “There are successive nests, where they come up one after another, or preferred regions,” he said, but our details on this are fairly weak. Most of time we don’t know where magnetic field lines will emerge from the sun.”

Title said heliophysics research is still in its infancy, but the new resources SDO provides might bring a new era in this area of study.

“We’ve reached a turning point in our ability to forecast space weather,” said Title. “We now have evidence that multiple events can be triggered by other events that occur in regions that cannot be observed from Earth orbit. This gives us a new appreciation of why solar flare and CME predictions have been less than perfect. As we seek to understand the causes of eruptive and explosive events that will improve our ability to forecast space weather, it is clear that we must be able to analyze most of the evolving global solar field, if not all of it.”

Posted on by Tammy Plotner

Total Lunar Eclipse – December 21, 2010

Both lunar and solar eclipses can only occur when the Earth, Sun and Moon are directly aligned… and that alignment is about to happen just four days before Christmas! While the winter treat of totality will lend itself to North America, many other parts of the world will be able to enjoy a partial eclipse as well. Just remember your time zones and I’ll post specific times and locations just a little closer to the date. Right now, let’s learn more!

What is a partial eclipse or totality? When the Earth’s shadow engulfs the Moon, it is a lunar eclipse which occurs in two phases. The outer shadow cone is called the penumbra and the dark, inner shadow is called the umbra. A round body, such as a planet, casts a shadow “cone” through space. When it’s at Earth, the cone is widest at 13,000 kilometers in diameter, yet by the time it reaches the Moon it has narrowed to only 9,200 kilometers. Considering the distance to the Moon is 384,401 kilometers, that’s hitting a very narrow corridor in astronomical terms!

As a rule of thumb, remember that the Moon moves about its own diameter each hour, so the very beginning of a penumbral eclipse will be difficult to notice. Slowly and steadily, the coloration will begin to change and even inexperienced eclipse watchers will notice that something is different. The Moon will never completely disappear as it passes through the Earth’s umbral shadow cone, either. Thanks to our atmosphere bending the sunlight around us, it scatters the light and refracts the signature red and copper coloration we associate with lunar eclipse. Why? Just the small particles in our air – dust and clouds – the shorter wavelengths of light from the Sun are more likely to be scattered (in this case, red) and that’s what we see. Exactly the same reason sunset and sunrise appears to be red! If you’d like to dedicate a portion of your mind to science, then try judging the eclipse coloration on the Danjon scale. It was was devised by Andre Danjon for rating the overall darkness of lunar eclipses:

L=0: Very dark eclipse. Moon almost invisible, especially at mid-totality.
L=1: Dark Eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.
L=2: Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright
L=3: Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.
L=4: Very bright copper-red or orange eclipse. Umbral shadow is bluish and has a very bright rim.

Now we know what to plan for! Time to get your winter gear ready. Photographing or video taping an eclipse is easy – but remember if you live where it is very cold that your batteries will expire fast – so keep an extra set in a warm place next to your body.

Be sure to check back for specific times and locations here at UT on December 20th… and tell your family and friends about the very special Christmas present that’s coming your way!

Eclipse Images Courtesy of Doug Murray (top), Tom Ruen (bottom) and NASA (center illustration). We thank you!

Posted on by Nancy Atkinson

Hot Plasma Explosions Inflate Saturn’s Magnetic Field

This is an artist's concept of the Saturnian plasma sheet based on data from Cassini magnetospheric imaging instrument. It shows Saturn's embedded "ring current," an invisible ring of energetic ions trapped in the planet's magnetic field. Credit: NASA/JPL

[/caption]

From a JPL press release:

A new analysis based on data from NASA’s Cassini spacecraft finds a causal link between mysterious, periodic signals from Saturn’s magnetic field and explosions of hot ionized gas, known as plasma, around the planet.

Scientists have found that enormous clouds of plasma periodically bloom around Saturn and move around the planet like an unbalanced load of laundry on spin cycle. The movement of this hot plasma produces a repeating signature “thump” in measurements of Saturn’s rotating magnetic environment and helps to illustrate why scientists have had such a difficult time measuring the length of a day on Saturn.

“This is a breakthrough that may point us to the origin of the mysteriously changing periodicities that cloud the true rotation period of Saturn,” said Pontus Brandt, the lead author on the paper and a Cassini team scientist based at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “The big question now is why these explosions occur periodically.”

The data show how plasma injections, electrical currents and Saturn’s magnetic field — phenomena that are invisible to the human eye — are partners in an intricate choreography. Periodic plasma explosions form islands of pressure that rotate around Saturn. The islands of pressure “inflate” the magnetic field.

A new animation showing the linked behavior is can be seen at the Cassini website.

The visualization shows how invisible hot plasma in Saturn’s magnetosphere – the magnetic bubble around the planet — explodes and distorts magnetic field lines in response to the pressure. Saturn’s magnetosphere is not a perfect bubble because it is blown back by the force of the solar wind, which contains charged particles streaming off the sun.

The force of the solar wind stretches the magnetic field of the side of Saturn facing away from the sun into a so-called magnetotail. The collapse of the magnetotail appears to kick off a process that causes the hot plasma bursts, which in turn inflate the magnetic field in the inner magnetosphere.

Scientists are still investigating what causes Saturn’s magnetotail to collapse, but there are strong indications that cold, dense plasma originally from Saturn’s moon Enceladus rotates with Saturn. Centrifugal forces stretch the magnetic field until part of the tail snaps back.

The snapping back heats plasma around Saturn and the heated plasma becomes trapped in the magnetic field. It rotates around the planet in islands at the speed of about 100 kilometers per second (200,000 mph). In the same way that high and low pressure systems on Earth cause winds, the high pressures of space cause electrical currents. Currents cause magnetic field distortions.

A radio signal known as Saturn Kilometric Radiation, which scientists have used to estimate the length of a day on Saturn, is intimately linked to the behavior of Saturn’s magnetic field. Because Saturn has no surface or fixed point to clock its rotation rate, scientists inferred the rotation rate from timing the peaks in this type of radio emission, which is assumed to surge with each rotation of a planet. This method has worked for Jupiter, but the Saturn signals have varied. Measurements from the early 1980s taken by NASA’s Voyager spacecraft, data obtained in 2000 by the ESA/NASA Ulysses mission, and Cassini data from about 2003 to the present differ by a small, but significant degree. As a result, scientists are not sure how long a Saturn day is.

“What’s important about this new work is that scientists are beginning to describe the global, causal relationships between some of the complex, invisible forces that shape the Saturn environment,” said Marcia Burton, the Cassini fields and particles investigation scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “The new results still don’t give us the length of a Saturn day, but they do give us important clues to begin figuring it out. The Saturn day length, or Saturn’s rotation rate, is important for determining fundamental properties of Saturn, like the structure of its interior and the speed of its winds.”

Plasma is invisible to the human eye. But the ion and neutral camera on Cassini’s magnetospheric imaging instrument provides a three-dimensional view by detecting energetic neutral atoms emitted from the plasma clouds around Saturn. Energetic neutral atoms form when cold, neutral gas collides with electrically-charged particles in a cloud of plasma. The resulting particles are neutrally charged, so they are able to escape magnetic fields and zoom off into space. The emission of these particles often occurs in the magnetic fields surrounding planets.

By stringing together images obtained every half hour, scientists produced movies of plasma as it drifted around the planet. Scientists used these images to reconstruct the 3-D pressure produced by the plasma clouds, and supplemented those results with plasma pressures derived from the Cassini plasma spectrometer. Once scientists understood the pressure and its evolution, they could calculate the associated magnetic field perturbations along the Cassini flight path. The calculated field perturbation matched the observed magnetic field “thumps” perfectly, confirming the source of the field oscillations.

“We all know that changing rotation periods have been observed at pulsars, millions of light years from our solar system, and now we find that a similar phenomenon is observed right here at Saturn,” said Tom Krimigis, principal investigator of the magnetospheric imaging instrument, also based at the Applied Physics Laboratory and the Academy of Athens, Greece. “With instruments right at the spot where it’s happening, we can tell that plasma flows and complex current systems can mask the real rotation period of the central body. That’s how observations in our solar system help us understand what is seen in distant astrophysical objects.”

Source: JPL