# Can someone explain abberation of starlight?

Hello everyone,
I was wondering if anyone can explain how the abberation of starlight works in general terms, as well as what exactly it is. I am a first year astronomy student and this is for my astronomy/physics class, and would like a general explanation of what it is. This is all my professor would require for the upcoming midterm, so if anyone can help that would be great. Thanks!

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Simon Bridge
Homework Helper
Welcome to PF;
The best use of these forums is to give your ideas of what it is and that will help us pinpoint the source of your confusion. Have a go reading through:
http://en.wikipedia.org/wiki/Aberration_of_light
... and telling us where you get lost.

Thank you for responding Simon! I guess I should have elaborated on what I understand and what I would like to know. So I know that this is not like parallax in that it depends on velocity, so while parallax increases the further out you go in the solar system, aberration of starlight increases the closer to the Sun a planet is (because the closer to the Sun a planet is, the faster its orbital velocity). Hence, from Mercury the aberration ellipse is greater than aberration ellipses on Earth.
I guess what I'd like to know is how exactly aberration works? My professor was explaining it to be almost like walking, or running in the rain, if the rain is falling straight down (ie, perpendicular to the floor) but you are running, because of your velocity, it is like they are falling on an angle, so you would need to tilt your umbrella to shield the rain. So does the latitude of a person have an effect on the amount a telescope needs to be tilted? And what exactly does an aberration ellipse look like? Does that make sense? Thanks!

Additionally, what I read about aberration online is that what you expect to see is tan (theta) = v/c, but what you actually find is that sin (theta) = v/c. Why is this, and what does it mean? On Wikipedia it says the same thing. I'll read it in its entirety, but if you can help with that that would be great. Thanks! :)