## 02ps-07 Size Of The Moon Solution

• 0:00 - 0:04
To solve this the first thing I want to know is how many moons can fit into the earth's shadow?
• 0:04 - 0:09
How many moons widths are there associated with this time spent in eclipse.
• 0:09 - 0:15
Well, 205 minutes is 3.42 hours.
• 0:15 - 0:17
Now, I have this conversion factor here,
• 0:17 - 0:21
which relates hours to moon widths, so why don't I use that?
• 0:21 - 0:28
3.42 hours times--well, now I want to invert this, because I want the hours to cancel out.
• 0:28 - 0:30
This guys has got to go downstairs.
• 0:30 - 0:39
Times 1 moon width per 0.93 hours. Hours cancels. Sorry. This should have been a 2.
• 0:39 - 0:44
This equals 3.68 moon widths.
• 0:44 - 0:47
Since we said the shadow was the same size as the earth,
• 0:47 - 0:50
this is equal to one earth width.
• 0:50 - 0:54
Let's divide this by 3.68, because I want to know what 1 moon width is.
• 0:54 - 0:57
I find it's one earth width divided by 3.68.
• 0:57 - 1:01
The moon is 3.68 times smaller than the earth.
• 1:01 - 1:03
I don't actually want width. I want circumference.
• 1:03 - 1:09
Let's go over here and say the moon's circumference, MC,
• 1:09 - 1:13
is equal to, well, 1 earth's circumference divided by 3.68.
• 1:13 - 1:19
That's going to be 40,000 km--that's the earth's circumference--
• 1:19 - 1:26
divided by 3.68, and the circumference of the moon is about 10,900 km.
• 1:26 - 1:29
Great work. This is really amazing.
• 1:29 -
You've calculated the circumference of the earth and the circumference of the moon.
Title:
02ps-07 Size Of The Moon Solution
Video Language:
English
Team:
Udacity
Project:
PH100 - Intro to Physics
Duration:
01:33