posted by Thomas .
I have to find the eccentricity of an elliptical orbit with one focus, earth's center, E. I know the formula to find eccentricity is sqrt(1-)(b^2/a^2), but I don't know where to use the radius or if I need it. Do I just need to use the eccentricity formula to find it?
all elliptical orbits have two focus loci. The Center of Earth is NOT a foci of Earths orbit, as the Earth is always moving. Foci do not travel in orbit. Neither is the Sun at a foci, but very near to it. Other planets pull on the Sun, so it moves slightly in time.
Use the eccentricity to find it.