Google Earth / DigitalGlobe

A satellite image of Yucca Lake in Nevada, acquired on March 13, shows what appears to be a Predator or Reaper drone being towed at a restricted airstrip.

A satellite photo that appears to show a military-style drone at a secret Nevada air base is stirring up a buzz on the Web, but don't worry: The imagery you're seeing on Google Earth is tweaked to avoid compromising national security.

The picture, which became the subject of multiple news reports over the past week, demonstrates the power of 24/7 satellite surveillance. It focuses on a dry lakebed, known as Yucca Lake, which has been used for secret projects for decades. Like the better-known Area 51, this patch of the desert (sometimes referred to as Area 6) is closely watched by amateur aficionados. It's been seen as a test site for unmanned aerial vehicles like the MQ-1 Predator, the MQ-9 Reaper and the RQ-170 Sentinel for at least the past three years.

Google / Digital Earth

A close-up taken from orbital imagery shows what appears to be an unmanned aerial vehicle sitting out at the Yucca Lake airfield.

RQ-170 Sentinels are in the news because the state-of-the-art spy drone was downed in Iranian territory, representing what appears to be a serious security setback for the U.S. military. The Nevada picture on Google Earth, which was acquired in March by one of DigitalGlobe's satellites and fed into the Google Earth system, doesn't show a Sentinel. It looks like one of the less advanced, less swoopy Predators or Reapers. Of course, there's always a chance that the craft is a decoy. (We are talking about secret air bases, after all.)

Flight Global's website, which published the image last week, speculated that the airfield is being used by the CIA to test hardware and software for its classified aerial operations. Since then, other news reports have been asking whether Google Earth is compromising national security.

U.S. satellite operators have worked out agreements with the federal government that govern the resolution of imagery made available through public databases, and you can imagine that the public images are fuzzier than the satellites' full capability. There can also be restrictions on what areas are targeted during particular times.

Potentially embarrassing images can surface, of course — such as pictures of drones in an area of Pakistan where the Pakistani government said there were no drones. And the concerns could become more acute as other countries launch imaging satellites that don't have to follow U.S. rules. But the Yucca Lake photo doesn't tell anybody who has been paying attention — including the bad guys — anything they didn't know already. The fact that the picture is still available, almost a week after it was thrown into the spotlight, suggests that national security has not been endangered.

I've made inquiries with the public relations folks for Google and DigitalGlobe, and if I hear anything back I'll update this item.

The Google Earth image serves as today's offering from the Cosmic Log Advent Calendar, which features views of Earth from space every day from now until Christmas. Check back for another image on Tuesday, and check out these previous offerings:

• The full Cosmic Log Space Advent Calendar
• Dec. 1: An ornament in outer space
• Dec. 2: The masses in Mecca
• Dec. 3: Santa's shrinking domain
• Dec. 4: The monster of Madagascar
• Dec. 5: Antarctica stripped naked
• Dec. 6: Streaking for home
• Dec. 7: Pearl Harbor from above, 1941-2011
• Dec. 8: The rise and fall of the Dead Sea
• Dec. 9: How an eclipse dims Earth
• Dec. 10: Psychedelic storm
• Dec. 11: Beauty of the Inland Sea
• Hubble calendar, from The Atlantic's In Focus
• 2011 Zooniverse Advent calendar

NASA / GSFC / METI / ERSDAC / JAROS / ASTER

A multispectral view from the ASTER imager on NASA's Terra satellite shows salt evaporation ponds in the southern Dead Sea as of 2006.

The Dead Sea is at ground zero for the biblical past — and perhaps for the Middle East's environmental future as well. For today's installment of the Cosmic Log Space Advent Calendar, we present two satellite images that show how the salty inland sea has changed over the past five years.

The orbital snapshot above was taken by the ASTER multispectral imager aboard NASA's Terra satellite in 2006. The picture below is a mosaic from Google Earth, based on orbital imagery provided this spring from DigitalGlobe, GeoEye and the French space agency CNES.   

DigitalGlobe / GeoEye / CNES / Google

A mosaic of Google Earth satellite imagery from this spring shows the salt evaporation ponds in the southern Dead Sea.

For years, environmental experts have voiced concern about shrinkage in the Dead Sea, but the situation is actually more complex: The northern part of the Dead Sea, visible toward the top edge of each image, is indeed drying up — and there's a danger that the body of water could fade away someday, just as the Aral Sea is fading away in Central Asia. The status of the highly managed southern part of the Dead Sea, which is separated from the northern part, is quite different: It's actually flooding. That's creating a salty mess on the tourist beaches that surround the southern sea.

In these pictures, you can see the southern Dead Sea sectioned off into industrial salt evaporation pools. For years, water has been pumped from the northern to the southern sea to feed those pools. If you look closely, you can tell that the water level in the north has been falling, while the level in the south is a bit more stable.

Now Middle East governments are debating what to do about the imbalance, and what to do about the prospect for future water shortages as well. One thing is certain: The rise and fall of the Dead Sea is nothing new. Scientists reported this week that the body of water nearly disappeared 120,000 years ago. The region's changing water levels may even explain the various biblical references to the Middle East as a famine-struck land or a land flowing with milk and honey.

Every day from now until Christmas, the Space Advent Calendar features pictures of Earth as seen from outer space. Check back on Friday for the next entry on the calendar, and check out these previous entries:

• The full Cosmic Log Space Advent Calendar
• Dec. 1: An ornament in outer space
• Dec. 2: The masses in Mecca
• Dec. 3: Santa's shrinking domain
• Dec. 4: The monster of Madagascar
• Dec. 5: Antarctica stripped naked
• Dec. 6: Streaking for home
• Dec. 7: Pearl Harbor from above, 1941-2011
• Hubble calendar, from The Atlantic's In Focus
• 2011 Zooniverse Advent calendar

GeoEye

A satellite picture of Pearl Harbor, acquired by the GeoEye-1 satellite on Sept. 24, shows the USS Missouri docked at Battleship Row as a museum ship, with its bow pointing toward the USS Arizona memorial at lower right. The wreck of the Arizona can be seen below the white memorial, barely visible beneath the water's surface.

Seventy years after a "date which will live in infamy," this satellite image of Pearl Harbor shows the symbols of a war's beginning and end.

The symbol of the end is more evident: The USS Missouri sits at its dock at Ford Island in the Hawaiian harbor, serving as a museum ship. In 1945, the "Mighty Mo" was the stage for the formal Japanese surrender at the end of World War II. After almost a half-century of service, the battleship was decommissioned for good in 1992 and took its place on Pearl Harbor's Battleship Row in 1998.

The Missouri wasn't even afloat on Dec. 7, 1941, when Japanese airplanes bombed the harbor and drew the United States into the war. But the battleship Arizona was. In the picture above, snapped by the GeoEye-1 satellite, the outlines of the Arizona are barely visible at upper right, beneath the surface of the water. The USS Arizona Memorial is the white structure sitting above the ship.

GeoEye-1, a polar-orbiting satellite operated by the GeoEye commercial venture, focused on Pearl Harbor on Sept. 24 from a height of 423 miles as it sped over the scene at 17,000 mph.

The scene was quite different in 1941, on what President Franklin Roosevelt dubbed a day of infamy. The aerial photograph you see below, taken from U.S. Navy archives, shows the wreckage in the harbor on Dec. 10, 1941, three days after the attack. Dark trails of oil stream from the dead and damaged ships. From this altitude, you get a sense of the attack's toll on the U.S. fleet, but not of the human cost: 2,390 Americans killed, 1,178 wounded.   

U.S. Navy

This aerial photograph of Pearl Harbor's Battleship Row was captured on Dec. 10, 1941, after the Japanese attack. The sunken USS California is at upper left. The capsized Oklahoma and the Maryland are at left center, the sunken West Virginia and the lightly damaged Tennessee are at lower center, The sunken Arizona is at lower right, in the same position where it lies today. Dark streaks of oil stream from the damaged vessels.

Today, veterans, family members and dignitaries are gathering at Pearl Harbor to commemorate the 70th anniversary. Flags are flying at half-staff. And Americans are looking back at the events of 1941 from a remote perspective, as if from a great height.

These views of Pearl Harbor serve as a somber entry in the Cosmic Log Space Advent Calendar, which puts a spotlight on views of Earth from outer space every day from now until Christmas. Click on the links below for more about Pearl Harbor Day, as well as other images from the calendar:

Pearl Harbor coverage:

• Last witnesses: Memories of Pearl Harbor
• A historical look back at the Day of Infamy
• Pearl Harbor veteran recalls bewilderment of attack
• After death, Pearl Harbor survivor returns to his ship
• How Pearl Harbor Day is being commemorated
• Pearl Harbor memories live on in New Orleans exhibit
• Video: Survivors gather to recall Pearl Harbor attacks
• Search msnbc.com for articles about 'Pearl Harbor'
• Pearl Harbor pictures from the Naval History and Heritage Command

More space views from the calendar:

• Dec. 6: Streaking for home
• Dec. 5: Antarctica stripped naked
• Dec. 4: The monster of Madagascar
• Dec. 3: Santa's shrinking domain
• Dec. 2: The masses in Mecca
• Dec. 1: An ornament in outer space
• The full Cosmic Log Space Advent Calendar
• Hubble calendar, from The Atlantic's In Focus
• 2011 Zooniverse Advent calendar

BEDMAP Collaboration / BAS

This graphic shows the bedrock beneath Antarctic ice. The color scale goes from 2,250 meters below sea level (blue) to 2,250 meters above sea level (red).

A British survey suggests what the Antarctic continent would look like if it were stripped bare of all its ice.

This BEDMAP elevation image of the polar region is based on satellite imagery as well as observations made from planes, ships and even dog-drawn sleds, the British Antarctic Survey reported today. Hamish Pritchard, a researcher from the BAS, presented the digital maps at the American Geophysical Union's fall meeting in San Francisco.

Less than 1 percent of Antarctica's bedrock projects above the continent's layer of ice, the BBC reported. If all that ice were suddenly taken away, the sea would pour into the dark blue troughs shown on the BEDMAP picture. The light blue area on the graphic indicates the Antarctic continental shelf.

"In many areas, you can now see the troughs, valleys and mountains as if you were looking at a part of the earth we're much more used to seeing, exposed to the air," Pritchard told the BBC. Such imagery has helped scientists trace the roots of the Gamburtsev Mountains, a range of peaks buried two miles (3 kilometers) below the surface of the East Antarctic Ice Sheet.

In the picture above, the Gamburtsev range is the deep-red area just to the right of the continent's center. "It's fascinating to see the Gamburtsevs in the context of the other big mountains in Antarctica," Pritchard said.

BEDMAP Consortium / BAS

This graphic provides a sidelong perspective on the Antarctic bedrock, looking inward from the Antarctic Peninsula toward the center of the continent.

This survey of the naked continent, which follows up in far greater detail on an earlier BEDMAP scan, wasn't done merely to fascinate scientists (and the rest of us). Understanding Antarctica's rocky foundation could help climate researchers get a better sense of how the polar ice cap may respond to future climate change.

The key observations included radar soundings that penetrated the ice and bounced off the underlying rock, which told researchers how far down the ice went. Still more airborne surveys need to be made to flesh out BEDMAP's view in detail.

These pictures serve as today's offerings from the Cosmic Log Space Advent Calendar, which features views of Earth from space every day from now until Christmas. Check back on Tuesday for the next "treat," and check out these links for previous entries as well as other space-themed Advent calendars:

• Dec. 4: The monster of Madagascar
• Dec. 3: Santa's shrinking domain
• Dec. 2: The masses in Mecca
• Dec. 1: An ornament in outer space
• The full Cosmic Log Space Advent Calendar, going back to 2010
• Hubble Advent calendar, presented by The Atlantic's In Focus
• 2011 Zooniverse Advent calendar

DigitalGlobe

Worshipers crowd around the Kaaba shrine in the Saudi city of Mecca, venerated as the most sacred site in Islam, in a satellite picture from DigitalGlobe. The image was captured from orbit on Nov. 2, just before the beginning of the annual Hajj pilgrimage. During the Hajj, millions of Muslims walk counterclockwise seven times around the Kaaba.

'Tis the season for religious holidays, including Hanukkah for Jews and Christmas for Christians. But the Muslim world has already marked its biggest religious observance of the year, with an orbiting satellite as a witness.

Today's offering for the Cosmic Log Space Advent Calendar adds an Islamic twist to the holiday countdown: Here's a picture from DigitalGlobe showing thousands of people gathering around the Kaaba shrine in Mecca on Nov. 2, just before the annual Hajj pilgrimage. Participating in the Hajj is a duty able-bodied Muslims are required to perform at least once in their lives. The capstone of the experience is the Eid al-Adha, a festival that commemorates the willingness of Abraham to sacrifice his son Ishmael to God.

The scriptural story serves to illustrate the linkages between different religious traditions. Whether you observe Eid al-Adha or Hanukkah, Advent or none of the above, here's wishing you wider perspectives on the world and its inhabitants during this holiday season.

Some of those wider perspectives are on view in our Month in Space Pictures slideshow, which we've just published for November. Here's a lineup of links for the pictures included in the slideshow, plus pointers to some other space-themed Advent calendars:

• On the beam: Laser at ESO observatory in Chile
• Moon over air: Our planet and the moon, seen from orbit.
• On to Mars! Launch of the Mars Science Laboratory.
• After the landing: Recovery team converges on Soyuz craft. 
• Chilly homecoming: Japanese astronaut back on Earth.
• Does Pacman have teeth? WISE view of a colorful nebula.
• Southern exposure: Partial solar eclipse seen from New Zealand.
• Trail of trouble: Stranded Russian probe streaks across sky.
• Back from a mock Mars: Volunteers end 520-day simulation.
• Quartet of moons: Cassini spots four satellites amid Saturn's rings.
• A little lunar base: Exhibit takes shape at New York museum.
• Flooding in Bangkok: DigitalGlobe's view of high waters in Thailand.
• The Tarantula roars: Space telescopes focus on a spidery nebula. 
• Blastoff in a blizzard: Soyuz rocket takes off for space station. 
• Freakishly flat: ESO looks at a remarkably flat galaxy.
• The first and the last: Shuttle crews from STS-1 and STS-135.
• Crazy storm on Saturn: Cassini documents long-lasting cloud system.
• Welcome to the aliens: Greetings from New Zealand seen by satellite.
• Go with the flow: NASA satellite tracks lava from Hawaii volcano.
• After the launch: NPP satellite liftoff leaves behind a trail in the sky.
• More space slideshows from msnbc.com.
• Hubble Advent calendar from The Atlantic's In Focus.
• Space Advent calendar from Zooniverse.

Check back on Saturday for the next installment of our Advent calendar, which will be featuring new views of Earth from space every day until Christmas.

• The Cosmic Log Space Advent Calendar so far
• Dec. 1: Ornament in space

Correction for 2:10 a.m. ET Dec. 3: Space consultant Charles Lurio pointed out that in Islamic tradition, it's Ishmael who is offered to God by Abraham. I originally went with Isaac, in accordance with Genesis 22, but in this context I guess I should go with the Koran's version of the story. Many thanks to Charles for setting me straight.

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.