A series of images taken by astronaut Don Pettit from the International Space Station, showing the full moon "setting" on April 16, 2003 (the "setting" being caused by the orbital motion of the Space Station). As a celestial object's light passes through our atmosphere it is bent, or refracted, making it appear thigher than it really is. As the object nears the horizon, the amount of refraction rapidly increases, so as the Moon sets, its lower limb is "lifted" more than the top, making the Moon appear vertically squashed (but leaving its horizontal width unchanged). Scattering of light by the atmosphere, greater at shorter wavelengths than longer ones, also makes the Moon look redder as it descends. The same phenomena are observable on the Earth, but because the setting Moon is "below" the Space Station, the effects are doubled, compared to the view from the ground (shown below). (Don Pettit, Les Cowley, ISS, NASA) |
