| cpsTN |
| (Pooh-Bah) |
| 07/02/09 06:57 PM |
terminator shadowing question
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When we look at photos of Earth from space, we see a definate terminator. From the ground during Sunset, however, we don't see a wall of dark barrelling for us. I assume this is due to the scattering of light by Earth's atmosphere, which causes the graduation of darkness.
Since the Moon effectively has no atmosphere, is the termintor separation like a wall of light and dark?
| Michael A. Earl |
| (vendor- Canadian Satellite Tracking and Orbit Research) |
| 07/02/09 09:10 PM |
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Re: terminator shadowing question
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Hi Charles,
Exactly. The Earth is covered by a scattering medium (the atmosphere). When the Sun sets, its light is scattered and refracted by our atmosphere which gives us our twilight glow.
A sunset on the Moon is much different. As soon as the Sun is below the horizon, you are in darkness, except for the star light (and Earthshine). It would be somewhat like a light switch: very sudden. The temperature would also drop quite suddenly too!
You can see this effect during occultations. The star does not slowly dim, but suddenly winks out. However, since the Sun has a much larger apparent angular size than a distant star, it does take more time to set.
| cpsTN |
| (Pooh-Bah) |
| 07/02/09 10:12 PM |
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Re: terminator shadowing question
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Thank you. That is what I figured, but it is always a good thing to ask. You might find out some part of the situation that had not occurred to you.
| Carol L |
| () |
| 07/03/09 12:09 AM |
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Re: terminator shadowing question
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Makes me wonder how long it would take a star to gradually fade away in our atmosphere when viewed from space. Anyone know if we've ever filmed a star being occulted by the Earth, maybe from a lunar orbiter or another craft? Not too sure if the Apollo missions left any image transmitting devices on the surface, but i imagine filming would have to be done during lunar night to escape the the skywash.. or would it, seeing as there's no atmosphere?