Do all orbits have a perigee and an apogee?
1 Answer
Yes. See explanation.
Explanation:
Perigee and apogee are used for nearest and farthest positions of a
( natural or artificial ) satellite, from its parent planet..
Any satellite orbit is an ellipse and and the the center of the
parent space body is at a focus of this ellipse.
The eccentricity of this ellipse is
It is 0.055, nearly, for Moon orbit.
As of now, Moon/s perigee is 36400 km and apogee is 405400 km.
ISS ( international Space Station ) orbit eccentricity is 0.00115, nearly.
ISS perigee is 400 km and apogee is 410 km, nearly.
If these orbits are scaled down to an A4 paper, in a class room, they
would look like circles, and the focus of the ellipse would be
merged with the center of the ellipse.
The distance between the focus ( the Earth's center ) and the center
of the orbit is #(405)(0.00115) = 5 km, nearly.
#Compared to mean distance 405 km, this is 1 : 81.
So, on an A4 paper, the graphs of satellite orbits would appear as
circles.
graph{(x^2/(4.05)^2+y^2/(4.05)^2-1) = 0 [-10, 10, -5, 5]}
The miniaturized ISS orbital ellipse with semi axes a = 405 km
and b = a, rounded to km.
If it appears here as an ellipse, we have to state that it is a
not-to-scale graph. For teaching purpose, we show it as, what it
really is. an ellipse.
