Question

An astronomical unit is the distance from earth to the sun, right? Is the earths orbit really so prefectly circular that you can relate to that?

Answer 1

no the earth orbit is eliptical

Answer 2

So AU isnt an accurate unit

Answer 3

an au is the mean distance

Answer 4

What do you mean?

Answer 5

it is accurate, after all it is just a number...But to be more precise the AU was first defined as the length of the semi-major axis of the Earth's elliptical orbit around the Sun then they changed the definition into something more complex...

Answer 6

What is a semi-major axis?

Answer 7

Mean distance is the same as average distance

Answer 8

Which is..

Answer 9

Ellipse has 2 axis, right? So one is a bit longer then the other called major, and semi-major just means half of major.

Answer 10

Oh
so its like northeast?

Answer 11

like between the two axis

Answer 12

http://www.mathwarehouse.com/ellipse/images/picture-of-ellipse.gif
a picture says a thousand words :D

Answer 13

True! i still dont get it though...

Answer 14

I get where it is but why would you need 4 of them when you can use 2 of them

Answer 15

I don't know. I guess people find it easier to talk about the ellipse when they name every single part of :D. I just call it major and minor

Answer 16

It just seems unnecessary.. I guess it makes it easier

Answer 17

call it what you want, it's still the same thing. But when you need to be very precise and only have to use words to explain something, it's easier to know the names, so it is useful sometimes :D hehe

Answer 18

I guess xd