Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Michael Zuk on 15/12/2010 01:30:03

Title: How can we see only a half moon?
Post by: Michael Zuk on 15/12/2010 01:30:03

Michael Zuk  asked the Naked Scientists:
   
Hello all!

I just started listening (http://www.thenakedscientists.com/HTML/podcasts/) about a month ago, and [the podcasts] are just splendid! Keep up the fantastic work!

With all of the planets and moons being round, how is it we can see a half moon? You can't get a flat edge from something round.

Thank you so much! Looking forward to your response. Have a great day!

Thank you.

Sincerely,
Michael Zuk

What do you think?

Title: How can we see only a half moon?
Post by: SteveFish on 15/12/2010 02:47:37

Michael, perhaps your problem has to do with suggesting that a moon is round. It isn't. Moons and planets are oblate spheroids. Take one of these shapes from your kitchen, such as an apple, and shine a focused light on it from the side and you will be able to see the the flat edge of the shadow. On the other hand, I think you might just just be a funnin us. Steve

Title: How can we see only a half moon?
Post by: graham.d on 16/12/2010 11:17:55

I don't think the lack of perfect roundness is an issue; it's close enough. As Steve says though, if you illuminate an object from the side (at right angles to the direction from which you are viewing it) then, providing the source of light is some distance away and that the room is large enough that secondary reflections are minimal, the illuminated part will appear as a semicircle.

Sometimes you can see the dark part of the moon because of illumination from reflections from the earth (earthlight).