Hello lpaige2004

In your original post, I'm not sure what you mean by this: Originally Posted by

**lpaige2004** ...Major axis-Minor axis/2=C ...

so let me see if I can clarify things.

The equation of the ellipse, as you have said, is:$\displaystyle \frac{x^2}{a^2}+\frac{y^2}{b^2}=1$

and you have correctly calculated $\displaystyle a$ to be $\displaystyle 4.84 \times 10^8$.

These are the other things you need to know:

- The centre of the ellipse is at $\displaystyle (0,0)$.

- The foci of the ellipse are at $\displaystyle (\pm ae,0)$.

- The relation between $\displaystyle a, b$ and $\displaystyle e$ is:

$\displaystyle a^2e^2 = a^2-b^2$ (1)

- In the case of the elliptical orbit of a planet around the sun, the sun is at one of the foci of the ellipse.

- The greatest distance from a focus to a point on the ellipse is $\displaystyle a(1+e)$; the shortest distance is $\displaystyle a(1 - e)$.

**Opalg **has used this last fact, together will the values $\displaystyle a = 4.84 \times 10^8$ and $\displaystyle a(1 - e)=4.6\times10^8$, to write down an expression for $\displaystyle e$.

What you now need to do:

- Evaluate $\displaystyle e$.

- Use equation (1) above to find the value of $\displaystyle b$.

- Use your values of $\displaystyle a$ and $\displaystyle b$ to write down the equation of the ellipse.

- If you also need to know the distance of the sun from the centre of the orbit - the distance I think you have called $\displaystyle c$ - then it's $\displaystyle ae$ (as stated above).

Grandad