For observers in the umbra, the entire Sun is obscured, and the solar eclipse is total. In the penumbra, a partial solar eclipse is seen. If the Moon happens to be too far from Earth for its disk to completely hide the Sun, an annular eclipse occurs. Because the Moon's orbit around Earth is slightly inclined with respect to the ecliptic, solar and lunar eclipses do not occur every month, but only a few times per year. Surveyors on Earth use triangulation to determine the distances to distant objects.
Astronomers use the same technique to measure the distances to planets and stars.
The cosmic distance scale is the family of distance-measurement techniques by which astronomers chart the universe. Parallax is the apparent motion of a foreground object relative to a distant background as the observer's position changes. The larger the baseline, the distance between the two observation points, the greater the parallax. Astronomers use parallax when measuring the distances to the planets by triangulation. The same geometric reasoning is used to determine the sizes of objects whose distances are known.