This view of the rising Earth greeted the Apollo 8 astronauts as they came from behind the Moon after the fourth nearside orbit. The photo is displayed here in its original orientation, though it is more commonly viewed with the lunar surface at the bottom of the photo. Earth is about five degrees left of the horizon in the photo. The unnamed surface features on the left are near the eastern limb of the Moon as viewed from Earth. The lunar horizon is approximately 780 kilometers from the spacecraft. Height of the photographed area at the lunar horizon is about 175 kilometers.
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| NASA |
The land mass visible just above the terminator line is west Africa. Note that this phenomenon is only visible to an observer in motion relative to the lunar surface. Because of the Moon’s synchronous rotation relative to the Earth (i.e., the same side of the Moon is always facing Earth), the Earth appears to be stationary (measured in anything less than a geological timescale) in the lunar “sky”. In order to observe the effect of Earth rising or setting over the Moon’s horizon, an observer must travel towards or away from the point on the lunar surface where the Earth is most directly overhead (centred in the sky). Otherwise, the Earth’s apparent motion/visible change will be limited to:
- Growing larger/smaller as the orbital distance between the two bodies changes.
- Slight apparent movement of the Earth due to the eccentricity of the Moon’s orbit, the effect being called libration.
- Rotation of the Earth (the Moon’s rotation is synchronous relative to the Earth, the Earth’s rotation is not synchronous relative to the Moon).
- Atmospheric & surface changes on Earth (i.e.: weather patterns, changing seasons, etc.).
