See other posts from November 2007

Earthrise and Earthset from Kaguya

Posted by Emily Lakdawalla

2007/11/13 10:43 CST

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Kaguya has delivered on its promise to send high-definition movies from the Moon, and it was worth the wait. This morning JAXA and the Japan Broadcasting Corporation (NHK) released several still images and a movie showing an Earthrise and an Earthset over the lunar limb captured by Kaguya on November 7. The images bring to mind the Apollo 8 and 11 Earthrise photos, but, unlike the Apollo images, the Kaguya ones feature a nearly fully lit Earth. Not to mention the fact that the Kaguya images are parts of actual movies! As someone who was too young to witness the Apollo missions and their live TV coverage, these are my first movies from the Moon.

To explain the images and movies: Kaguya is on a polar orbit. The orientation of this orbit is such that it alternately passes behind and in front of the Moon as seen from Earth, going from north to south when it passes in front of the Moon, and rising from south to north on the farside. Kaguya's high-definition movie camera has two components, one wide-angle and one narrow-angle or telephoto. On November 7, the spacecraft was oriented so that the wide-angle camera pointed forward along the orbit, and the telephoto camera pointed backward along the orbit. So the wide-angle camera was in position to watch Earth rise over the lunar north pole as Kaguya's orbital motion carried it northward, and the telephoto camera was able to watch Earth set below the lunar south pole as the spacecraft rounded the south pole. The images at right show the wide-angle Earthset shot and the narrow-angle Earthrise shot; Earth appears much larger to the narrow-angle camera than it does to the wide-angle camera. Click to enlarge these images -- they are HUGE, 1920 by 1080 pixels. I've added them to my images of Earth from planetary spacecraft page.

f course, the images are just stills from movies. They released another image consisting of five frames from the Earthset movie, which just begged to be animated. Here that is. I love the combination of Earthset and apparent motion of the lunar surface as Kaguya flies across the south pole. They did also release the actual movies of Earthrise and Earthset at a quarter of the full resolution but apparently their server is getting hammered; I can't get the movie to load. [EDIT: A day later, they have split the movie into Earthrise and Earthset chunks, and it's now loading fine for me.] Fortunately, where there is digital video, there is someone who can capture it and put it on Youtube. The resolution of the Youtube video is even lower than the already-reduced resolution of the JAXA release, so this movie doesn't do justice to the sharpness of the original, but at least you can watch it.

If these movies are like the ones previously released by the Kaguya mission, they were shot with a low frame rate so that time in the movie is sped up by a factor of eight. Even at that, the movie is nearly nine minutes long, showing first the Earthrise and then the Earthset. In the Earthrise movie, all is still, with the Moon's surface barely moving beneath the spacecraft, for almost a minute and a half, until a tiny bright arc appears just above the lunar limb and slowly, slowly rises. The Earthset video starts at about 4:20. This one is more dramatic, as Kaguya is looking across a twilit, rugged south pole with its telephoto camera. Earth almost immediately appears at the top of the frame, much larger than in the Earthrise video. As I watched it approach the horizon, my brain expected Earth to pass in front of the two lunar peaks on the horizon -- my art teacher in high school taught me that the brain sees lighter tones as being closer to the eye than darker tones -- but Earth kisses the horizon and then passes behind it. As Earth's disk disappears, the exposure suddenly adjusts on the camera. Earth, with its snow-white clouds, is more reflective than the Moon; with the exposure set for Earth, the Moon appeared dark. With Earth out of the picture, the auto-exposure adjusts to whiten the lunar mountain peaks, revealing streaks and colors on the lunar surface.

Kaguya is getting one of these Earthrises and Earthsets on every single orbit of the Moon. I don't know how much video it's shooting. I have a fantasy of a giant plasma screen somewhere showing a live HD feed from Kaguya's rear window, with the cratered surface slowly slipping backward. Every once in a while, almost by chance, a bright disk appears in the blackness of space -- our home -- and I suddenly get a feeling of vertigo, realizing that I'm watching a spacecraft watch me.

Cool.