Everything you ever need to know / by mirena



Earth rising over the Moon taken by Lunar Reconnaissance Orbiter (nasa.gov)


I wanted to be an astronaut when I grow up and thanks to the internet I guess I am. From the little comfort of my bed and my mac I watch little people take spacewalks on NASA tv, which should be the only kind of television politicians are allowed to watch. It is apparent there are no divisions out there, no fences, no one else to laugh at us for about at least million light years.

From the Earth, the daily Moonrise and Moonset are always inspiring moments. However, lunar astronauts will see something very different: viewed from the lunar surface, the Earth never rises or sets. Since the Moon is tidally locked, the Earth is always in the same spot above the horizon, varying only a small amount with the <a href="https://www.youtube.com/watch?v=PKRtZ89AMts">slight wobble</a> of the Moon. The Earth may not move across the "sky", but the view is not static. Future astronauts will see the continents rotate in and out of view and the ever changing pattern of clouds will always catch one's eye. Well at least on the nearside, but what about the farside? The Earth is never visible from the farside, imagine a sky with no Earth or Moon - what will farside explorers think with no Earth overhead?

This image was taken when LRO was 134 km above the farside crater <a href="http://bit.ly/1ReO7lT">Compton</a> (51.8°N, 124.1°E). Capturing an image of the Earth and Moon with LROC is a complicated task. First the spacecraft must be rolled to the side (in this case 67°), then the spacecraft slews with the direction of travel to maximize the width of the lunar horizon in the NAC image. All this takes place while LRO is traveling over 1600 meters per second (faster than 3580 mph) relative to the lunar surface below the spacecraft! As a result of these three motions and the fact that the Narrow Angle Camera is a <a href="http://lroc.sese.asu.edu/about/specs">line scanner</a> the raw image geometry is distorted. Also, because the Moon and Earth are so far apart, the geometric correction is different for each body. Reconstruction of the Earth-Moon image is not a simple matter – and that is just to get the black and white image!