# Calcuate Orbital Speed (without using distance)

1. Sep 8, 2011

### ldv1452

How would I go about calculating the orbital speed of a planet without using the distance of its path. In other words, only using the motion around the plane of ecliptic?

My first thought was using the angle of the path somehow, but I'm a bit stumped here.

Thanks for any input!

2. Sep 9, 2011

### Filip Larsen

Assuming "distance of its path" is referring to the semi-major axis of the orbit, a, you can replace a with knowledge of other orbital parameters such as orbital period T and eccentricity e. Assuming further that e is close to zero (orbit is near circular) you can find average orbital speed as a function T alone. To do this you probably need to look for some equations in your text books that relate these parameters to each other and combine them, or you could read some of the references that come up when you search for "orbital speed" ... *cough* wikipedia *cough*

3. Sep 19, 2011

### ldv1452

Thanks for taking the time to reply. I think I need a better understanding of some of these fundamental concepts before I can solve this.