Lunar eclipse will give NASA moon orbiters the shivers

Artist’s view of Earth eclipsing the sun next Tuesday morning April 15 as seen from the Lunar Reconnaissance’s Orbiter’s perspective. For several hours, it and NASA’s LADEE dust explorer will be cut off from sunlight. Back on Earth, we see the moon slide into our planet’s shadow. Credit: NASA

While we’re all bundled up for next Monday’s late night total eclipse of the moon, NASA will be taking special precautions to ensure its two moon probes survive the deep chill they’ll experience when the moon dives into Earth’s shadow.

NASA’s LRO has been orbiting, mapping and studying the moon since 2009. Credit: NASA

The Lunar Reconnaissance Orbiter (LRO), launched in 2009, has spent the past four-plus years photographing and mapping the moon in great detail from an orbit dipping as low as 31 miles (50 km). One of its goals is to determine future lunar landing sites. The craft also examines the moon’s radiation environment and maps the concentration of hydrogen – the main ingredient of water – across the globe. Hydrogen “hot spots” imply potential locations of water ice beneath the surfade or bound to moon rocks.

LRO will orbit the moon twice in Earth’s shadow. All instruments will be shut down since they would otherwise drain the batteries which can’t recharge without sunlight. Credit: NASA

LRO depends on sunlight to keep its batteries charged and instruments running. During the upcoming lunar eclipse, the moon will be either partially or fully within Earth’s shadow for several hours. With no sunlight reaching the probe’s solar panels, recharging the batteries isn’t possible.

To prevent damage to the either instruments or batteries, NASA plans to shut down all of LRO’s science instruments next Monday night for the duration of the eclipse. As soon as the event is over, the sun will slowly recharge the batteries and mission control will bring everything back online.

While LRO’s no stranger to eclipses,this time the spacecraft will have to pass through the complete shadow twice before the eclipse ends – longer than in any previous event.

“We’re taking precautions to make sure everything is fine,” said Noah Petro, Lunar Reconnaissance Orbiter deputy project scientist. “We’re turning off the instruments and will monitor the spacecraft every few hours when it’s visible from Earth.”


Understanding lunar eclipses

During other briefer eclipses, scientists have used the opportunity to study how the moon’s surface cools during these events, shedding light on the composition of the lunar crust. During the June 15, 2011 eclipse, temperatures on some areas of the moon dropped 180 degrees F compared to sunny, pre-eclipse conditions.

While LRO is expected to emerge from the shadow with flying colors, the forecast for NASA’s Lunar Atmosphere and Dust Explorer (LADEE) spacecraft is sketchy. The probe was never designed to withstand hours in the deep freeze of a shadowed moon.

“The eclipse will really put the spacecraft design through an extreme test, especially the propulsion system,” said Butler Hine, LADEE project manager.

Prior to impact on or before April 21, ground controllers at NASA’s Ames Research Center in Moffett Field, Calif., are maneuvering the spacecraft to fly approximately 1 to 2 miles (2-3 km) above the lunar surface to gather science measurements at the lowest altitude possible. Credit: NASA

LADEE (pronounced ‘laddie’) has been circling the moon studying dust in its extremely rarefied atmosphere since last fall. Much of the dust sputters off the surface during small meteorite impacts. If it survives the eclipse, LADEE will perform additional week of science before the mission is terminated. Rather than just shutting the probe off, mission control will direct it to crash into the moon near on or around April 21. LRO will locate study the impact site when it makes its next flyover a few months later.

Meanwhile, NASA invites you to  “Take the Plunge Challenge” and guess  what date LADEE will slam into the surface. Winners will be announced after impact and e-mailed a commemorative, personalized certificate from the LADEE program. The submissions deadline is 5 p.m. CDT tomorrow April 11.

For more information on the April 14-15 total eclipse of the moon including viewing times for your time zone, please see my earlier blog.

Brilliant Mars opening act for upcoming total lunar eclipse

Brilliant Mars shines atop dimmer Spica in the constellation Virgo in this photo taken Sunday night April 6. The planet now rises at sunset and is easy to spot around 9:30 p.m. in the southeastern sky. Yes, we still have almost 4 feet of snow here in Duluth, Minn. Credit: Bob King

Mars reaches opposition today, its closest approach to Earth since Dec. 2007 and the brightest we’ve seen it since 2012. What a sight it’s become. Last night, while walking our respective dogs, my daughter took one look at the gleaming pink-orange “star” in the southeastern sky and knew immediately it was Mars.

About every two years, Mars and Earth line up on the same side of the sun at opposition. Because Mars’ orbit is eccentric (less circular than Earth’s) the two planets are closer at some oppositions than others. This year’s opposition is a relatively distant one. Illustration: Bob King

While it sounds like an act of defiance, opposition refers to Mars being on exactly opposite side of the sky as the sun. The planet rises at sunset this evening and sets when the sun pops up tomorrow morning. Not only is Mars out all night long, but being opposite the sun, it’s paired up closely with Earth on the same side of the sun as shown above.


One full rotation of Mars on April 8 created by Tom Ruen. North polar cap at top.

That’s why Mars is so doggone bright – it’s close! Of course we know that’s a relative term in astronomy. Today the Red Planet is 57.7 million miles away, which sounds rather terribly far. But keep in mind that it can be up to 249 million miles away. So yes, Earth and Mars are practically neighbors … for a little while. The same orbital motions that brought them together will also move them farther apart in the coming months.

Now here’s the kicker. Because the orbits of Earth and Mars aren’t perfect circles, the two planets are actually closest on April 14, six days past opposition. That’s the same night as the total eclipse of the moon. Even better, the moon will only be a “fist” away from the planet. What a sight they’ll make – two red orbs aglow in the southern sky.

Mars outshines its neighbors Spica and Arcturus in the east and is ever so slightly brighter than magnitude -1.46 Sirius off to the southwest. The map shows the sky around 9:30 p.m. local time tonight. Stellarium

The Red Planet far outshines the nearby stars Spica and Arcturus and at magnitude -1.5 glows a hair brighter than Sirius, the brightest star in the entire sky. While similar in brightness, their colors are dramatically different. Compare the two and tell us what you think.

One side of Mars, the side turned toward the Americas during the best observing times this week, shows relatively few features. Use the map below to help you identify other dark markings as they rotate into view in the coming days and weeks. North at bottom. Credit: Mark Justice

Mars won’t appear bigger or brighter until its next opposition in May 2016 so take a look at this miniature “eye of Sauron” beaming in the south the next clear night.

If you have a telescope, use a magnification of 150x or higher to look for the planet’s very tiny north polar cap (it’s summer there and the cap has shrunk!) and other dark markings on its surface. This week, the planet’s “blank” hemisphere is presented for observers in the Americas. Be patient. The more obvious features like Mare Erythraeum, Syrtis Major and Mare Acidalium will soon rotate into view (see map below).

Complete Mars map showing many more features. Click to learn more about Mars’ upcoming opposition. Credit: Association of Lunar and Planetary Observers (A.L.P.O).

 

Seven ways to savor the upcoming total eclipse of the moon

Next Monday night April 14-15, skywatchers across much of North and South America will get to see a total eclipse of the moon. Lunar eclipses last for hours and can be safely viewed with the naked eye. This photo was taken of the June 2011 eclipse. Credit: Muhammed Mahdi Karim

It’s been too long. The moon last slipped into Earth’s shadow for North America in Dec. 2011. Next Monday night’s eclipse will end the current dry spell and make for a thrilling night out.

Map showing where next Monday night’s (April 14-15) eclipse will be visible. The western hemisphere has prime viewing seats. Credit: Fred Espenak

This eclipse is the first of four total lunar eclipses spaced about six months apart that will be visible across most of the Americas. The others occur on Oct. 8 this year, April 4, 2015 and Sept. 27, 2015. This particular sequence of four total lunar eclipses with no partials in between is called a ‘tetrad’. While we all hope for clear skies, if the weather’s uncooperative next week, you won’t have to wait long for another eclipse.


Eclipse tetrads explained

Lunar eclipses unfold slowly, lasting up to five hours. Unlike a total solar eclipse, where the sun disappears at most a few minutes, totality during a lunar eclipse can easily last more than an hour, giving you lots of time to enjoy the spectacle.

The only downside will be the late hour. Try to get some shuteye early as most of the eclipse happens after midnight in the wee hours Tuesday morning.

Because the moon’s orbit is tilted 5 degrees, the full moon normally misses the cone of shadow cast by the Earth and we see no eclipse. But several times a year, the moon’s orbit intersects Earth’s at the time of full moon and we see an eclipse. The Credit: Wikipedia

Lunar eclipses occur during full moon when the sun, Earth and moon line up in a neat row, and the moon passes into the shadow cast by our planet. You’d think eclipses would happen every full moon, but they don’t because the moon’s orbit around the Earth is tipped 5 degrees to Earth’s orbit around the sun.

The moon’s tipped orbit (red) is the reason we only get occasional eclipses at full moon. Most of the time the moon is either a little above or below the ideal alignment. Credit: Bob King

The moon spends most of the time above or below the plane of Earth’s orbit. And since Earth casts a shadow across its orbital plane, a lunar eclipse can only happen if the moon happens to be crossing that plane at the same time it’s full. That’s why eclipses are such a now and again thing.

While total solar eclipses are only visible along a narrow strip of land or ocean, a total lunar can be seen across half the globe wherever the sky is dark and the moon is up.

The moon’s past from west to east (right to left) across the dual shadow cast by Earth. The diagram shows key times (CDT) during the eclipse listed in the table below. Credit: Fred Espenak with additions by the author

Earth’s shadow is composed of two nested components – the inner umbra, where the Earth completely blocks the sun from view, and an outer penumbra, where the planet only partially blocks the sun. Because the penumbra is a mix of shadow and sunlight, it’s nowhere near as dark as the umbra.

An eclipse is divided into stages beginning with the moon’s entry into Earth’s lighter penumbral shadow. Most of us won’t notice any shading at all until about a half hour in, when the moon is deep enough inside to reveal a subtle darkening along its eastern edge. The table below lists the times for each stage of the eclipse across the four time zones:

Eclipse Events                     EDT             CDT                 MDT                PDT

Penumbra visible 1:20 a.m. 12:20 a.m. 11:20 p.m. 10:20 p.m.
Partial eclipse begins 1:58 a.m. 12:58 a.m. 11:58 p.m. 10:58 p.m.
Total eclipse begins 3:07 a.m. 2:07 a.m. 1:07 a.m. 12:07 a.m.
Mid-eclipse 3:46 a.m. 2:46 a.m. 1:46 a.m. 12:46 a.m.
Total eclipse ends 4:25 a.m. 3:25 a.m. 2:25 a.m. 1:25 a.m.
Partial eclipse ends 5:33 a.m. 4:33 a.m. 3:33 a.m. 2:33 a.m.
Penumbra visible  ——– 5:10 a.m. 4:10 a.m. 3:10 a.m.

During a total lunar eclipse (seen on Earth) an astronaut on the moon would instead see the Earth cover the sun, its atmosphere aglow with the combined light of all the sunrises and sunrises “leaking” around the rim of the planet. The light would bathe the moonscape in deep orange light. Stellarium

Partial eclipse begins when the moon treads within the dark umbra. Nibble by nibble the shadow eats away at the lunar disk. When only a sliver of the moon remains in sunlight, you’ll notice the shadowed portion glowing an eerie red or deep copper. To understand why, imagine an astronaut on the moon looking back at Earth during the eclipse.

During the next Tuesday morning’s eclipse, the moon will be just 1.5 degrees from Spica and not far from the planet Mars in the southern sky. Don’t forget to give Saturn a nod, located about two “fists” to the left of the moon. Stellarium

From her perspective, as the Earth passes in front of the sun, it’s surrounded by a glowing red-orange ring of light. Our atmosphere bends the light from all the sunrises and sunsets around the planet’s circumference into the umbra, coloring the moon red. Earth’s shadow isn’t really black after all but more a deep rusty red. Back on Earth, the moon will hang like a ghostly amber globe near the bright star Spica.

After mid-eclipse, the moon slowly exits the Earth’s shadow and performs the whole show in reverse, transitioning back to partial eclipse and finally exiting the penumbra.

Different aspects of a total lunar eclipse from start to near finish photographed in Hefei, China on Dec. 10, 2011. Credit: Reuters

You can take in the eclipse as casually as you like, but are seven cool things you might like to watch for:

#1 – When will you detect the first hint of penumbral shading? Keep an eye on the eastern (left) side of the moon for a “dented” appearance.

#2 – What color and how bright is the totally eclipsed moon? Depending upon the aerosol content of the atmosphere (greatly affected by volcanic eruptions), eclipses range from bright copper to dark brown and even black. Try rating this one on the traditional Danjon scale where “4″ is bright and “0″ is nearly invisible.

#3 – Watch for “the night within the night” phenomenon. If you thought it was dark out at the start of the eclipse, you’ll be amazed at how inky the landscape becomes during totality. As the eclipse progresses, the stars and Milky Way return to view.

#4 – With the entire moon darkened during totality, it will be relatively easy to watch it block or occult any star within its path. Many stars ranging from magnitude +8 and 12 will be occulted when viewed through small to medium telescopes. Click HERE for stars and times.

#5 – Binocular and telescope users should also look for a blue tinge to the encroaching umbral shadow as it slowly envelops the moon caused by light refracted by the upper atmosphere’s ozone layer.

#6 – Variation in the moon’s brightness. The top half will be closer to the center of the umbra and appear darker than the bottom. How obvious will this be?

#7 – Bring home a souvenir with your camera. If you have a telescope, you can hold a cellphone over the eyepiece to get great shots of the bright phases. During total eclipse, longer exposures of 1 to 10 seconds are necessary. For that you’ll need a tripod and a camera that can shoot time exposures. Telephoto lenses will pump up the moon’s size, but even a standard lens can do a great job of recording the sunset-colored moon in a landscape setting. Set your lens to its widest-open setting (f/2.8, 3.5) and expose 10-30 seconds to include the scene.

 

Don’t miss tonight’s rare triple Jupiter moon transit

All eyes will be on Jupiter tonight during the triple shadow transit. The map shows the sky facing east from the Chicago, Ill. region around midnight. Created with Stellarium

Jupiter and his four bright moons are one of the first things a beginning amateur astronomer looks at through a telescope. Watching the moons make new and surprising arrangements as they circle about the planet night after night makes for never ending observing enjoyment.

Jupiter’s moon Europa (at left) casts an inky dot on Jupiter on Sept. 24, 2013. Credit: John Chumack

Sometimes Jupiter’s shadow eclipses a moon, other times a moon passes in front of the planet and casts an inky black shadow on its cloud tops. Moons also orbit in front of Jupiter, though these events are more difficult to see unless you happen to catch the satellite right at the planet’s edge.

Tonight three of those moons – Io, Europa and Callisto – simultaneously cast their shadows on Jupiter’s cloud tops for just over an hour between 11:32 a.m. and 12:37 a.m. CDT (4:32-5:37 UT). This rare event last happened on March 28, 2004. They’re called shadow transits and single ones are fairly common. You can find online tables listing transits and satellite eclipses or use a free program like Meridian that gives you a little picture along with time information.

The March 28, 2004 triple transit. Shadows from left: Ganymede, Io and Callisto. You can also see the disks of Io (white dot) and Ganymede (blue dot) in this photo taken in infrared light by the Hubble Space Telescope. Credit: NASA/ESA

Seeing two shadows cross the planet at once is very uncommon, but three’s as rare as a blue rose. When averaged out, they happen only once or twice a decade. That’s why you should go out tonight with your telescope for a look.

If bad weather intervenes, the next transits won’t happen until June 3, 2014 (not visible in the Americas) and Jan. 24, 2015. After those we cool our heels until 2032.

Here’s the breakdown. The triple transit will be visible across the eastern half of the U.S., Europe and western Africa. East Coasters will have the best view in the U.S. with Jupiter some 20-25 degrees high in the northeastern sky around 1 a.m. local time. Things get more challenging in the Midwest where Jupiter climbs to only 5-10 degrees. By the time the planet rises in the mountain states, only Io and Europa’s shadows remain. If you live in the Pacific Time Zone and farther west, you’ll have to wait until 2015.

Jupiter polka-dotted with shadows cast by its moons Io, Europa and Callisto around midnight CDT Oct. 12. Watch for the Great Red Spot to come into view during the transit. Created with Claude Duplessis’ Meridian software

Let’s look at how each piece of the event will play out. Times below are CDT:

* Callisto’s shadow enters the disk – 10:12 p.m. Oct. 11
* Europa – 10:24 p.m.
* Io – 11:32 a.m.
** TRIPLE TRANSIT from 11:32 – 12:37 a.m.
* Callisto departs – 12:37 a.m.
* Europa departs – 1:01 a.m.
* Io departs – 1:44 a.m.

European amateurs have the best view with Jupiter high in the southern sky before dawn. In the eastern U.S., Jupiter’s up some 20-25 degrees in the eastern sky around mid-transit time. That should be high enough to escape the worst of the low-lying atmospheric turbulence that tends to blur planet images when using higher magnifications. The Midwest will see a Jupiter only 5-10 degrees high. Let’s hope the air is calm and clear!

Curiosity snaps sharpest-ever photos of “ring of fire” eclipse on Mars

Phobos, the larger of the two Martian moons at 17 miles across (27 km), creates an annular or ring eclipse as seen through the telephoto eye of the Mars Curiosity rover on Aug. 17. Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.

Now that’s what I call crisp! NASA just released a series of high resolution pictures of Phobos transiting the sun on August 17. Taken with the 100mm telephoto lens mounted on Curiosity’s mast, they’re the sharpest ever of an eclipse from another world.

Curiosity paused during its drive toward Mt. Sharp and aimed its mast camera straight at the sun to make the sequence of views three seconds apart. Because the sun was nearly directly overhead at the time, Phobos was at its closest and biggest, covering the maximum amount of the sun’s disk as possible.

Sequence showing the sun before, during and immediately after an annular or “ring of fire” eclipse. This eclipse occurred on May 10, 1994 over central Illinois. Credit: Bob King

When one object passes in front of another but only blocks a small portion of it, astronomers call it a transit, but Phobos is big enough and its passage so central, this event is better described as an annular or ring eclipse. We have ring eclipses on Earth too, but because the moon is nearly spherical and much larger than Phobos, it leaves a much narrower “ring of fire”.

Two additional photos from the Phobos eclipse sequence showing the moon entering (left) and exiting the sun. Credit: NASA

Astronomers will measure the moon’s position as it moved across the sun to more precisely calculate Phobos’ orbit. As described in a recent blog, Phobos is gradually moving closer to Mars and will one day be broken to pieces. If you care to browse additional and original pix of the eclipse, check out this Curiosity raw image page and scroll down to the Mast Cam section.

Curiosity sees unearthly moondance in Martian skies


Mars’ moon Deimos is occulted by Phobos on Aug. 1 as seen by Curiosity

What fun to live on a planet with TWO moons. Imagine stepping out into the Martian night to watch the moons Phobos and Deimos chase each other across the sky. NASA’s Curiosity rover did just that on Aug. 1 when mission control pointed its mast camera at the pair of tiny moons and snapped 41 photos as the larger and closer Phobos passed directly in front of little Deimos. In real time the “eclipse” took 55 seconds; the movie compresses that to 11. Even on Mars it was a marvelous night for a moondance.

With only one moon here on Earth, we miss out on the pleasures of dual moon gazing. The only thing that might come close is watching a cargo ship like the recent HTV-4 catch up and dock with the International Space Station.

Phobos orbits closer to Mars than Deimos and therefore completes a revolution around the planet more quickly, regularly overtaking its brother. The photos are the very first ever taken from Mars of an eclipse of one moon by the other.

Comparison showing how big the moons of Mars appear to be, as seen from its surface, in relation to the size that our moon appears to be seen from the Earth’s surface. Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.

A 100mm telephoto lens was used to make the images which clearly show some of the larger craters on Phobos.

Both moons are tiny compared to our own. Deimos’ diameter is 7.5 miles (12 km) and Phobos 14 miles (22 km). It takes me longer to drive to work than cross the length of Deimos.

Even though Phobos is only about twice the size of Deimos, it appears much larger from the surface because it orbits much closer to the Red Planet – 3,700 miles (6,000 km) vs.12,400 miles (20,000 km).

Orbiting above the Martian equator and so close to the surface, Phobos can’t be seen from Mars’ polar regions. Its great speed also means it overtakes the planet’s rotation rate, rising in the west and setting in the east during the Martian night. Here on Earth, the moon moves in the same west to east direction but much more slowly, so that the faster-rotating Earth shuttles it from east to west during the night.

Phobos and Deimos up close as photographed by spacecraft. NASA scientists are studying the recent Curiosity images to determine precise orbits for the two moons as well as to gain a better understanding of the interior of Mars. Credit: NASA

Phobos’ tight orbit will ultimately lead to its demise. Its gravity induces tidal bulges in the crust of Mars which lag behind the fast-orbiting moon, causing it to gradually slow down and drop closer to the planet’s surface. In 50-100 million years Phobos will spiral in close enough for Mars’ gravity to break it to pieces. Deimos alone will remain to dimly light the Martian night.

In darkness the moon is reborn

If we could see the moon today, it would be a very thin crescent only a few degrees from the sun. Tomorrow it’s in new moon phase. Maps created with Stellarium

What’s old today but instantly becomes young again tomorrow? If you guessed the moon, you’re right! Today the moon winds up its current cycle of phases as an exceedingly thin crescent so close to the sun it’s invisible in the solar glare.

The moon’s cycle has always been a metaphor for life. Every month it’s born again as a thin crescent in the western evening sky, grows to a half-pie seven days later and reaches its full power and radiance when full at 14 days. After full, the moon’s radiance declines as its phase wanes to last quarter (21 days) and then to a whiskery crescent at dawn. Before it finally disappears in the sun’s glare, the moon, now 28 days old, reaches the end of its “life” cycle. But only briefly. The very next day, moments after new moon phase, it’s reborn again as an evening crescent.

When we run into troubles in our lives, we might look to the ever-renewing moon for inspiration.

The sky looking west-southwest a half hour after sunset Monday evening Feb. 11, 2013. You might be able to spot dimmer Mars in binoculars.

Tomorrow morning at 2:20 a.m. (CST) the moon will be exactly lined up with the sun and pass through new moon phase. Skywatchers in the western hemisphere won’t see the moon either day because it’s in the same direction as the sun and swamped by glare.

By Monday Feb. 11 however, the moon’s orbital motion will remove it far enough from the sun to be visible during evening twilight.  And there’s a bonus. The crescent will float a few degrees above the planet Mercury.

I’ve removed the atmosphere in this illustration so you can see where the moon is today at noon (CST), tomorrow morning when it reaches new moon phase and tomorrow Feb. 10 at noon. It passes north of the sun, which is in the constellation Capricornus. Notice all the planets in the neighborhood.

If we were to follow the moon today through new moon and into tomorrow, we’d notice it passes well north of the sun. Most of the time, the new moon is either north or south of the sun because its orbit is tipped about 5 degrees relative to Earth’s orbit.

The moon’s tilted orbit causes it to swing north or south (pictured here) of the sun from Earth’s perspective. A couple times a year however it crosses directly in front and a total solar eclipse is visible from somewhere on Earth. Illustration: Bob King

Over the course of its monthly cycle, it bobs up and then down along its tilted orbit. But 2 or 3 times a year, when the moon intersects the plane of Earth’s orbit at the same time as new moon phase, it crosses directly in front of the sun and we see a total solar eclipse. In fact, this is the only time we can see a new moon with the naked eye. It looks exactly like what you’d expect – a blank, black disk scrubbed free of its past life, waiting to begin the next as a tender crescent.

The new moon – black disk – is plainly visible silhouetting the sun during a total solar eclipse. Credit: Luc Viatour

Asteroid 2012 XE54 may be eclipsed during close flyby tonight

The path of 2012 XE54 (in blue) during tonight’s close flyby.  At minimum distance, it will be about 139,500 miles away. Credit: NASA/JPL

Newly-discovered asteroid 2012 XE54 will fly by Earth tonight only 139,500 miles away or slightly more than half the distance to the moon. The rocky body, estimated at between 50-165 feet across (15-50 meters), was discovered only yesterday and will reach minimum distance tomorrow morning around 4:10 a.m. (CST) as it zips through northern Puppis southwest of Sirius. For a few hours before and after that, the asteroid should be visible in 8-inch and larger telescopes at around 13th magnitude. As with all these small bodies, 2012 XE54 will look like a starlight point of light on the move.

When brightest this evening at around 12.9-13.0 magnitude, the asteroid will be cruising through Orion and Monoceros. Positions are shown each hour starting at 9 p.m. CST. Created with Chris Marriott’s SkyMap software

According to Pasquale Tricarico, research scientist at the Planetary Science Institute, there’s a good chance the asteroid will be partially eclipsed by Earth’s shadow between 7:22 – 8 p.m. (CST), an unusual if obscure event. Amateurs and professionals watching at that time might see a drop in the 2012 XE54′s brightness.

It’s not often we get to see an asteroid eclipse. The first known case happened in 2008 when 2008 TC3 passed into Earth’s shadow for an hour before entering the atmosphere, where it shattered and dropped about 10 lbs. of meteorites over Sudanese desert.

Just so we’re clear, we’ve nothing to fear from tonight’s flyby. The asteroid will pass safely by Earth like so many others have in recent years. The map above gives you a general idea of 2012 XE54′s path across the sky. To create your own detailed map to find it in a telescope, click over to the JPL HORIZONS site. There you can set your location and time interval and then plot the asteroid’s positions on a detailed star map. Or you can input its orbital elements into your star-charting program. To see a very cool animation of the possible eclipse, check out Pasquale Tricarico’s website.

Is NASA hiding something? No, but the Earth is

Pictures of the sun snapped every 15 minutes by the orbiting Solar Dynamics Observatory. Data appears to be missing from the middle five frames. Credit: NASA

So what’s up with those blank squares? You’re looking at a screen capture of a page of pictures of the sun in photographed in ultraviolet light by NASA’s Solar Dynamics Observatory (SDO). The photos were shot 15 minutes apart starting Wednesday evening into Thursday morning this week.

Since SDO circles Earth in a geosynchronous orbit about 22,000 miles high, it “sees” the sun continuously both day and night from a vantage point high above Mexico and the Pacific Ocean. About 1.5 terabytes of solar data or the equivalent of half a million songs from iTunes are downloaded to antennas in White Sands, New Mexico every day. The space station, which orbits much closer to Earth, would make a poor solar observatory since Earth blocks the sun for half of every 90 minute orbit.

SDO’s eclipse season started around 1 a.m. September 6 when the observatory shot a photo of the Earth (top middle) cutting across the sun. Credit: NASA

Did I say SDO watches the sun continuously? Well, not quite. Twice a year for a period of about three weeks around the equinoxes, the Earth gets in the way of the sun from the space craft’s point of view, causing a total solar eclipse. The latest round of eclipses began on September 6 and will conclude on the 26th.

Now you know the reason for the blank frames – it’s a conspiracy by the Earth to block out the sun. The blackness is none other than the planet itself.

Normally the Earth is out of the way of the sun from SDO’s perspective but twice a year its orbit and Earth’s orientation to the sun cause Earth eclipses. Credit: NASA

Total eclipse happens every day between 1 and 2 a.m. local time (Mountain Daylight Time) when the Earth blocks the sun from SDO’s view. In similar fashion, we experience a solar eclipse on the ground when the moon covers up the sun. You can watch for pictures of the partial eclipse as Earth gets out of the way sometime next Tuesday the 25th by going to the SDO website. Follow these simple steps to find and view the images:

* Click on the Data tab and select AIA/HMI Browse Data
* Click on the Enter Start Date window, select a start date and click Done
* Click on Enter End Date and click Done
* Under Telescopes, pick the color (wavelength) sun you want
* Select Images in the display box
* Click Submit at the bottom and then browse the pictures

Not only does the Earth cross the sun from the observatory’s perspective, so does the moon (left) on occasion. The moon’s”bite” smaller and sharper. Earth’s atmosphere gives our planet a soft, diffuse edge compared to the airless moon’s. Photo at right was taken on September 6, 2012 at eclipse season start. Credit: NASA

While watching an eclipse of the sun by the Earth is one of the joys of living in the space age, there are other cool things to see from SDO’s perspective. Look at the drastic difference between the moon’s sharp outline and Earth’s fuzzy edge. Our planet “bites softly” into the sun because its substantial atmosphere grades from thick to thin, filtering the sunlight that passes through it. The moon’s a big baldy. With no air to grade and soften the light, the sun shines crisply right up to its edge.


Video of a partial eclipse of the sun by Earth. Refraction of light by Earth’s atmosphere causes the sun to bend at its edges. Credit: NASA SDO / Stanford University for HMI

We’ve seen how air can also bend or refract sunlight in strange ways, going so far as to “lift” the sun  into view when it’s still below the horizon.  You can see the same effect in a brand new way in this short video of an SDO partial eclipse. Watch the sun’s edge bend as the Earth rolls by. Compare it to a similar eclipse by the moon below.


Moon eclipsing sun via SDO 

SDO orbits about 22,000 miles above Earth, tracing out a figure-8 (called an analemma) above the Pacific and Mexico every 24 hours. Credit: NASA

SDO amazes with its spectacular pictures of the sun taken in 10 different wavelengths of light every 10 seconds; additional instruments study vibrations on the sun’s surface, magnetic fields and how much UV radiation the sun pours into space.

It’s the latest, greatest “Swiss Army knife” used by scientists to pry open the inner workings of the sun. The eclipses, while a gap in the data stream,  are a sweet bonus all their own.

My favorite Martian

The first Martian (top) sighted on Mars smiles back from the rover’s calibration panel. The panel also features a 1909 Lincoln penny. Look closely at the penny and you’ll see a grain of Mars sand under Lincoln’s ear. It’s only 0.2 mm (.008 inches) across. Geologists classify sand grains this size as “fine sand”. Credit: NASA/JPL-Caltech/MSSS

Curiosity has traveled all of 466 feet along the dust, gravelly floor of Gale Crater since landing on August 6. It’s on its way to Glenelg to scoop up and analyze a soil sample. Earlier this week, mission controllers opened the recloseable dust cover on the Mars Hand Lens Imager (MAHLI) mounted on the rover’s robotic arm and snapped closeups of Curiosity’s underbelly, wheels and calibration target. The camera can focus on objects less than an inch away and acts as a magnifying glass similar to what a geologist would use in the field.

Wide view of Curiosity’s calibration target taken by the MAHLI imager. You can already see the orange coating of  Mars dust. Credit: NASA/JPL-Caltech/MSSS

My favorite photo of the bunch is the calibration target showing color reference swatches, a metric bar graphic, a penny and below it, a stair-step pattern for depth calibration. The 1909 VDB penny harks back to the geologists’ tradition of placing a coin,  rock pick or another object of known size in pictures of individual rocks or rock formations. It gives the viewer an idea of a feature’s size at a glance. Ken Edgett, MAHLI principal investigator, purchased the penny for the mission.

Moving in closer, we see there’s something else in the MAHLI image – a drawing of a Martian waving from a rock!

“Joe the Martian” is a character created by Edgett for the children’s science periodical “The Red Planet Connection” when Edgett directed the Mars outreach program at Arizona State University in the 1990s.

MAHLI photo of the underside of Curiosity with a view out to the horizon. Since the camera can focus anywhere from 0.8 inches all the way to infinity  it can capture both extreme closeups and landscapes. Credit: NASA/JPL-Caltech/MSSS

Joe goes back even further to when Edgett was 9 years old. He drew the character as part of a school project at the time of the 1975 Viking missions to Mars, the first to safely land probes on the planet. It was Viking that inspired him to become a Mars researcher. Joe’s appearance on Mars is most fitting.

Back in the 1960s I enjoyed watching episodes of My Favorite Martian, a TV sitcom about a Martian spaceship that crash lands near Los Angeles. Tim O’Hara, an LA Times reporter, discovers the wreck and the pilot, a Martian anthropologist dressed in a shiny aluminum jump suit. O’Hara nicknames him “Uncle Martin”. Antics ensue. Joe now joins Uncle Martin as my two favorite Martians.

12-mile-diameter Phobos nudges into the sun on September 13. Curiosity aimed its mastcam camera skyward and used a solar filter to take the photo. Credit: NASA

Digging through Curiosity’s stockpile of raw images today, I found this one taken by the mastcam of the moon Phobos partially eclipsing the sun on September 13. Nice bite!

Eclipse is slightly inaccurate. Because Phobos is so small, it’s technically called a transit. The little moon is only 3600 miles from Mars – much closer than the moon is from the Earth – so eclipses (transits) are fairly common.

According to Phil Plait of Bad Astronomy, Phobos crosses the sun about once a year from Curiosity’s site. Scientists  study transits of Phobos and Mars’ other moon Deimos to gauge the thickness of clouds and dust in the atmosphere. More images of the event should show up in the next few days. When they do, I’ll post a higher res version.


Transits of Phobos have been photographed before by the Mars Opportunity Rover. Click the video to see one recorded on November 9, 2010.