# What am I doing wrong?

1. Nov 23, 2006

### Logarythmic

It is given that the perihelion for a certain comet is $$r_{per} = 0,2301 AU$$ and the eccentricity is $$e = 0,999846$$.
My mission is to find the aphelion.
I know that this is given by

$$r_{aph} = a(1+e)$$

And I have used that

$$a = \frac{r_{per} + r_{aph}}{2}$$

This gives me

$$r_{aph} = \frac{r_{per}(1 + e)}{1-e}$$

and then I get that $$r_{aph} = 2988 AU$$. This all seems very simple so what am I doing wrong?

The correct answer should be $$r_{aph} = 4698 AU$$

2. Nov 23, 2006

### Logarythmic

Ok, I got it. Small variations in $$e$$ and $$r_{per}$$ will give a big difference in the aphelion. ;)