Thursday, July 24, 2008

morning moon

morning moon, originally uploaded by skippy haha.

why only sometimes


Omnibus said...

When the earth is generally between the sun and the moon we cannot see it because it is in our shadow (full moon). When the moon is generally between the sun and the earth we cannot see it because the source of light is behind it(new moon). Sometimes it isn't in our sky at all because it is chilling out on the other side of the planet. Sometimes it is cloudy.

skippy haha said...

can you make a diorama?

jason said...

skippy... the short answer is geometry.

Omnibus's answer is partially right. And I'm sorry for being the nit-pickety internet nerd, but physics and astronomy are my background.

When the earth is generally between the sun and moon, yes it is a full moon. There are only a few times when that geometry causes the moon to pass through the earth's shadow... those are lunar eclipses. Even then we can still *see* the moon, but it does dim depending on if it passes through the penumbra or umbra of the earth.

I'm not so sure about this next part *scratches head* but... as far as I know, the moon is visible in every night sky so long as it isn't a new moon (or obscured by weather). It isn't the case that sometimes we can't see the moon at nightbecause it's on the other side of the planet. It is true that sometimes we cannot see the moon during the day, because it is below our horizon. For what it's worth, only full moons and moons very close to new cannot be seen during the daylight, all other phases can. When the moon is opposite the sun in the sky (full moon), it rises as the sun sets, and sets as the sun rises. Thus, a full moon can only be seen at night. As days go by, and the moon gets further away from full, the more the moon is visible during the day.

Also, if it is a full moon where you live, it is a full moon for everyone else in the world.

yikes... nerd overload. I don't think about these things that often but when someone or something (skippy's question) gets me going, I realize how fascinating the moon is.

Sorry folks! Skippy's place is usually pretty laid back, and I fear I've upset that balance!

Omnibus said...

Cool! I was only guessing, and I am not an astronomer, so don't feel bad or beleive a word I say ;)I cannot make a diorama but I can make a sweet taco. Balance restored.

skippy haha said...

thank you so much jason! that makes lots of sense!

jason said...

ok... see... I was wrong about that part I said I was unsure about. A quick check of moon rise and set times confirmed that sometimes the moon is not visible because it has set before nighttime. Which means, it is in fact, "chilling out on the other side of the planet." So my apologies.