The lunar orbit is close to being a circle,
but it is actually an ellipse. If the orbit were
circular, the Moon would always be the same
distance from the Earth, but instead, the
distance varies by 13% during the orbit. On
average, the Moon is 239,000 miles (385,000 km)
from Earth and travels at an average of 2288
miles per hour (1023 m/s).
Circles and ellipses have similar
Equation for a circle:
x2 + y2 = r2
Equation for an ellipse:
(x/a)2 + (y/b)2 =
The equation for the ellipse is like a circle
with x and y stretched by different amounts, a
An example of an ellipse and a circle are
The center of the circle and ellipse are
labeled with a “C”. The ellipse also has two
additional points labeled F1 and
F2. Each of these points is a focus
of the ellipse. In the lunar orbit, the Earth is
at a focus rather than the center of the Moon’s
The second diagram shows the orbit of the
Moon (not to scale).
When the Moon is closest to the earth, it as at
the perigee and when it is farthest, it is at
the apogee. The Moon’s orbit is every elliptical
compared to the planets, which have orbits much
closer to circles (but still ellipses).
Figure 1: Example of an ellipse and circle
(left). Diagram of the lunar orbit (right).