Visions of Earth through the Yutu Rover’s Eyes

Earth eclipses the sun from Chang'e 3's location in the Sea of Rains on April 15, 2014. At the same time, we'll see a total lunar eclipse from the ground. Stellarium

Last night I used my telescope to eye-hike the volcanic plains of the Sea of Rains (Mare Imbrium) where the Yutu rover and lander sit beneath a blistering sun. With no atmosphere to speak of and days that last two weeks, noontime temperatures can hit 250 degrees Fahrenheit (122 C) . That’s hot enough that mission control at the Beijing Aerospace Command and Control Center has decided to draw the shades and give the rover a nap from science duties until December 23 when things cool down a bit.

While studying the subtle gray hues of the Imbrium lava flows I got to wondering what the sky might look like if I could don a spacesuit and visit the landing site “where the skies are not cloudy all day” (to quote a famous song). With no atmosphere to speak of, stargazing can be done both day and night on the moon though I suspect it’s better at night when there’s less glare from your surroundings. Night, defined as the time from sunset to sunrise (no twilights here), lasts about 14.5 Earth days. Days are equally long.

Lunar landscape photographed by the Chang'e 3 lander on Dec. 15, 2013. Credit: CCTV
Lunar landscape photographed by the Chang’e 3 lander on Dec. 15, 2013. Credit: CCTV


From Yutu’s point of view, it’s very nearly lunar noon today (Dec. 19) with the sun halfway up in the southern sky.  Looking at the map of the sky from the lander’s location, you’ll see a few familiar constellations and one very familiar planet – Earth!

Phases of the moon and Earth are complementary. When the moon is full, Earth's a crescent. This map shows the Earth in Capricornus on Dec. 20 as thin blue crescent. Stellarium
Phases of the moon and Earth are complementary. When the moon is full, Earth’s a crescent. This map shows the Earth in Capricornus on Dec. 20 as thin blue crescent. Stellarium

Today Earth appears as a very thin crescent a short distance to the left or east of the sun. Because the moon takes just as long to rotate on its axis as it does to revolve around the Earth, the same face of the moon always faces our planet. Because the two are in synchrony, astronomers call it synchronous rotation.

From the perspective of someone standing on the moon, Earth stands still in one spot of sky throughout the 29.5 day lunar day-night cycle. Well, not perfectly still. Because the moon’s orbit is inclined about 5 degrees to Earth’s orbit and its speed varies along its non-circular orbit, Earth describes a little circle in the lunar sky about 10 degrees in diameter every four weeks.

As the sun slowly moves off to the west, our blue planet remains nearly stationary from Yutu’s perspective and undergoes all the familiar phases we see the moon experience back here on Earth: an evening crescent to start followed by a first quarter Earth, Full Earth last quarter and finally, New Earth. I like the ring of that last one.

The lunar landscape at the rover's location is bathed in pale blue light on Dec. 31, 2013 during "Full Earth". Stellarium
The lunar landscape at the rover’s location is bathed in pale blue light on Dec. 31, 2013 during a Full Earth. Stellarium

Yutu and the lander will see the sun drift to the west while Earth moves east, rises higher in the lunar sky and putting on the pounds phase-wise. Today Earth’s glides across the border of Sagittarius into Capricornus. The next Full Earth happens on New Year’s Eve when the sun is directly opposite the Earth in the lunar sky.

Full Earth always happens around local midnight or about one week before sunrise during the long lunar day. On the moon the sun is up for about  two weeks and then disappears below the horizon for another two weeks before rising again.  At Full Earth time, the sun remains hidden around the lunar backside. When the nights are blackest, the bright ball of Earth spreads a welcome blue glow over the desolate landscape.

Earth covering the sun with a flash of the "diamond ring effect" just before total solar eclipse on April 15 and Oct. 8 next year. Stellarium
Simulated eclipse of the sun by the Earth just before totality on April 15 and Oct. 8 next year. On both dates, we’ll see a  total lunar eclipse from the ground.  Stellarium

Things really get interesting during lunar eclipses when the moon moves behind the Earth into the planet’s shadow. The next one’s on April 15, 2014. Here on the ground we’ll see the moon gradually munched into by Earth’s  shadow until totality, when sunlight from all the sunrises and sunsets around the rim of the planet are refracted by the atmosphere into the shadow, coloring the moon a coppery red.

Two pictures of the ring of sunset-sunrise fire around the Earth as it totally eclipsed the sun from the moon. Credit: NASA
Two pictures of the ring of sunset-sunrise fire around the Earth as it totally eclipsed the sun from the moon. Credit: NASA

Yutu will see just the opposite. Looking back toward the Earth from inside its shadow, the rover will witness a total eclipse of the sun by the Earth. If by some wonder the Chinese are able to photograph the event, we’ll see photos of the black ball of Earth rimmed in red fire from sunset and sunrise light refracted by our atmosphere. My interpretation using sky mapping software only hints at the wonder of the scene. Beijing Aerospace, if you’re reading this, please make it happen.

Earth eclipses the sun filmed by Japan’s Kaguya lunar orbiter. There are really two eclipses here – the Earth eclipsed by the limb of the moon at the video’s start followed by the solar eclipse.

On two other occasions, our robotic emissaries have photographed solar eclipses from Luna. NASA’s Surveyor 3 snapped a couple crude pictures of the April 24, 1967 eclipse from inside a crater in Mare Cognitium, the Sea that has Become Known. Japan’s orbiting Kaguya probe did the job much more eloquently on video during the February 9, 2009 penumbral lunar eclipse. In a penumbral eclipse (seen from Earth) the moon misses Earth’s dark inner shadow called the umbra, passing only through the outer penumbra, but because the Earth is three times larger than the sun (seen from the moon), it easily covered the sun completely in the complementary total solar eclipse.

And the best thing about watching eclipses from the moon? Guaranteed clear skies!

Best Views Yet of Historic Apollo Landing Sites

LROC image of the Apollo 11 landing site, acquired Nov. 5, 2011 (NASA/GSFC/Arizona State University)


Just over 42 years after Neil and Buzz became the first humans to experience the “stark beauty” of the lunar surface, the Lunar Reconnaissance Orbiter captured the remnants of their visit in the image above, acquired Nov. 5, 2011 from an altitude of only 15 miles (24 km). This is the highest-resolution view yet of the Apollo 11 landing site!

The Lunar Module’s descent stage, a seismic experiment monitor, a laser ranging reflector (LRRR, still used today to measure distances between Earth and the Moon) and its cover, and a camera can be discerned in the overhead image… as well as the darker trails of the astronauts’ bootprints, including Armstrong’s jaunt eastward to the rim of Little West crater.

The crater was the furthest the Apollo astronauts ventured; in fact, if you take the total area Neil and Buzz explored it would easily fit within the infield of a baseball diamond!

Neil Armstrong’s visit to the crater’s edge was an unplanned excursion. He used the vantage point to capture a panoramic image of the historic site:

Panorama of the Apollo 11 site from Little West crater. (NASA)

“Isn’t that something! Magnificent sight out here.” Armstrong had stated before he was joined by Aldrin on the lunar surface. “It has a stark beauty all its own. It’s like much of the high desert of the United States. It’s different, but it’s very pretty out here.”

Previously the LROC captured the Apollo 15 landing site, which included the tracks of the lunar rover — as well as the rover itself! And, just yesterday, the LROC site operated by Arizona State University featured the latest similarly high-resolution view of the Apollo 12 site. This location has the honor of being two landing sites in one: Apollo 12 and the Surveyor 3 spacecraft, which had landed on April 20, 1967 – two and a half years earlier!

The Apollo 12 landing site in Oceanus Procellarum. (NASA/GSFC/Arizona State University)

Even though the US flag planted by Apollo 12 astronauts Pete Conrad and Alan Bean isn’t itself visible, the shadow cast by it is.

Apollo 12 was the only mission to successfully visit the site of a previous spacecraft’s landing, and it also saw the placement of the first Apollo Lunar Surface Experiments Package (ALSEP), which included a seismometer and various instruments to measure the lunar environment.

Read more about this image on the LROC page here, and check out the video tour below of the Apollo 12 site.

Images and video courtesy of NASA/GSFC/Arizona State University