Earths shadow on the moon.

Smartoad

I may be wrong, and I will feel pretty stupid if i am, but i think that we can see earths shadown on the moon, thats why it has cycles right? if so, then why cant we see mountains and stuff from certain places on the earth. Is it because the moon is so far away?

russ_watters

The moon's phases are not due to earth's shadow, they are due to the fact that only half of the moon can be illuminated at a time and that half may not be facing us. See: http://www.moonphases.info/images/mo...es-diagram.gif

And I'm not sure what you mean about seeing mountains: you can see mountans on the moon from anywhere on earth. They just don't look very big because we're far away.

Smartoad

oh my gosh, I feel dumb now, see, I thought that the reason the moon had its phases was because the sun was on the other side, and the earth was blocking the light from the sun to the moon, but that only happens during lunar eclipses. It makes sense that the phases come from the moon being halfway illuminated at a time. Well then, During lunar eclipses, where the moon and son are opposite and earth in the middle, could you look at earths shadow on the moon and see earths mountains? Sorry if my questions are dumb or my grammar is bad, I'm only a sophomore in highschool

russ_watters

It's ok - everything is new the first time you think about it.

cesiumfrog

Smartoad, how large are Earth's mountains compared to Earth's radius? Also, are you interested in whether you can see, in the shadow, Earth's sunsets?

Janus

Here's an old example that might help answer your question. If you were to scale the Earth down to the size of a billiard ball, the Earth would be smoother than a billiard ball, mountains and all.

willem2

Actually Everest is higher than 1/1300 of the diameter
I don't think billiard balls with 0.04 mm irregularities on them would play well.

Of course you would be able to see the shadow of the mountains on the moon during a lunar eclipse (with a telescope) if the sun was a point light source.

Janus

The tolerance for irregularities on a billiard ball is 0.127 mm. This falls in the range of the thickness of a black hair (blond hair is finer).

jostpuur

I have a friend who had this precisely the same misunderstanding.

We took same classes in the high school, and both got good grades on courses of natural science. Later, our paths separated when we graduated from the high school. I went to one university and began my studies in physics, and my friend went to another university and began studies in biology.

We did keep in touch occasionally however, and at one night we were driving a car. I had almost gotten my masters degree, and my friend was doing pretty well with his biology studies too. We saw the moon, and talked about something. During the discussion it became clear that my friend didn't know what caused the phases of the moon, and believed that we were looking at the "shadow of the earth". It was surprising from my point of view.

You learned it faster than my friend then

davenn

As mentioned by one other thats not the earths shadow BUT not mentioned is that
when you see an eclipse of the moon then that is the moon in the earths shadow :)

just like when we get an eclipse of the sun its a narrow strip of the earths surface inside the shadow of the moon.

Dave

gttjohn

i am so happy to have found this thread i also thought the earth caused the moons diff phases now it all makes sense its the position that the moon is in relation to the sun that give it its dif phases thats brilliant

Dr Lots-o'watts

You can watch the same phases by watching a tennis ball (moon) by your living room light (Sun), and taking your own head to be "Earth".

Anyone can understand this easily, they just often don't take the time do these simple experiments.

Redbelly98

Also, the dark part of the moon has a different shape than the shadow cast by a round Earth:


http://www.astroimages.org/astrophotos/mn-3-10.jpg

(EDIT: link appears to be broken/gone)