# Thread: want to calculate major axis of an ellipse but struggling with equations!

1. ## want to calculate major axis of an ellipse but struggling with equations!

Hi!

I have a circle that is tilted 23.5 degrees so that an observer sees an ellipse.

I have the minor axis (b) of the ellipse (ie the height).

How can i use the degrees of tilt of the circle, to calculate the eccentricity of the observed ellipse. Then I can use eccentricity and minor axis to calculate the major axis (width)

Thanks!

Ellipse - Wikipedia, the free encyclopedia

but i really don't even know what I'm looking for

2. When you see the circle along the axis, it appears circular. The angle is zero with respect to the vertical. If you move away from the axis, one axis shortens and it is given by R*cosθ, where R is the radius of the circle.

So b = a*cosθ.

3. Originally Posted by sa-ri-ga-ma
When you see the circle along the axis, it appears circular. The angle is zero with respect to the vertical. If you move away from the axis, one axis shortens and it is given by R*cosθ, where R is the radius of the circle.

So b = a*cosθ.
Thanks alot sa-ri-ga-ma!

b=102.74
θ=23.44
and that gave me a=111.98 yay