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GreyWanderer
2004-Mar-23, 07:22 PM
Right now the dark part of the moon seems really lit up. I can actually see the mountains etc. While at other times it's impossible to see that the moon is actually round when it's not full. I assume it's because of light from the earth. But why the difference?

Hamlet
2004-Mar-23, 08:23 PM
Right now the dark part of the moon seems really lit up. I can actually see the mountains etc. While at other times it's impossible to see that the moon is actually round when it's not full. I assume it's because of light from the earth. But why the difference?

Your refering to Earthshine and it is caused by reflected light from the Earth. The reason you can see it now is that it's just past New Moon and there's only a thin crescent lit by the Sun. Once the moon ages and the Sun lights a greater and greater portion of the Moon, the Earthshine effect gets washed out in the brilliance of the waxing Moon.

I hope this helps.

Ut
2004-Mar-23, 09:20 PM
It's more than just that. This was discussed in another thread, too, but part of it has to do with the fact that the Moon is still facing a large part of the illuminaged Earth. As the Moon waxes, it sees less and less of the light side of the Earth, and thus has less and less Earthshine falling on it.

Drakheim
2004-Mar-23, 09:24 PM
It's more than just that. This was discussed in another thread, too, but part of it has to do with the fact that the Moon is still facing a large part of the illuminaged Earth. As the Moon waxes, it sees less and less of the light side of the Earth, and thus has less and less Earthshine falling on it.

Earthshine? Dose that taste anything like Moonshine?

** ducks ** :lol:

Maksutov
2004-Mar-23, 10:31 PM
It's more than just that. This was discussed in another thread, too, but part of it has to do with the fact that the Moon is still facing a large part of the illuminaged Earth. As the Moon waxes, it sees less and less of the light side of the Earth, and thus has less and less Earthshine falling on it.

Earthshine? Dose that taste anything like Moonshine?

** ducks ** :lol:

Man, I could see that coming 230,000 miles away! Time for LOI! 8)

AGN Fuel
2004-Mar-23, 11:32 PM
It's more than just that. This was discussed in another thread, too, but part of it has to do with the fact that the Moon is still facing a large part of the illuminaged Earth. As the Moon waxes, it sees less and less of the light side of the Earth, and thus has less and less Earthshine falling on it.

Yes, the phases of the Earth & Moon are complementary as seen from the other. So, if we see a slim crescent moon, an observer on the moon would see a gibbous, near full Earth.

Because of this, when the moon is just pre- or post-new, the 'Earthshine' is at a maximum and allows the un-(sun)lit part of the moon to be seen more easily. The bright crescent cradling the darker rest of the disk has prompted the very poetic description of 'the old moon in the new moon's arms'.

Hamlet
2004-Mar-24, 12:49 AM
It's more than just that. This was discussed in another thread, too, but part of it has to do with the fact that the Moon is still facing a large part of the illuminaged Earth. As the Moon waxes, it sees less and less of the light side of the Earth, and thus has less and less Earthshine falling on it.

Quite right. I didn't think through my explanation far enough. #-o

Brady Yoon
2004-Mar-24, 08:01 AM
How bright would the Earth appear from the moon? Does this mean that if someone lived on the near side of the moon, he/she would never be able to see the stars because the Earth is so bright?

JohnOwens
2004-Mar-24, 08:26 AM
How bright would the Earth appear from the moon? Does this mean that if someone lived on the near side of the moon, he/she would never be able to see the stars because the Earth is so bright?
No, you just have to make sure the Earth isn't in your field of view when you try to look at the stars. For a great deal of debate on the matter, you can check the Lunar hoax info either on the board here in "Lunar Conspiracies" (http://www.badastronomy.com/phpBB/viewforum.php?f=3), or the Apollo hoax write-up (http://www.badastronomy.com/bad/tv/foxapollo.html) on the site this board is attached to. To sum up, anything exposed to sunlight will trash your night vision, and make it almost-to-completely impossible to see the stars, but if you angle your view so that nothing in your field of view is sunlit (including the Earth and the Sun itself), with no atmosphere to scatter light into your eyes, you should then be able to see the stars.

jfribrg
2004-Mar-24, 03:27 PM
How bright would the Earth appear from the moon?


Here is my back of the envelope calculation: Comparing albedos(.12 for the moon, .367 for the Earth), the Earth reflects 3.05 time as much light per unit area as the moon. Also, The moon subtends a .51 degree angle in the sky, while the Earth subtends a 1.9 degree angle in the lunar sky (assuming a mean distance of 384000km). Therefore the Earth has almost 14 times more area visible. This combined with the Earth's reflectivity being triple the moon's, the Earth is 42 times brighter. One last consideration is that at a full Earth, the Earth is 384000 km closer to the sun, than a full moon. This results in 1/2 of 1% more light from the sun per unit area. The final unrounded result is 42.65 times as much light. The log base 2.5 of 42.65, gives a 4.07 magnitude difference. IIRC, the moon is magnitude -12.7, so the Earth's magnitude from the moon is about -16.8 .