English: Apparent sizes of the Sun and Moon depicted to scale. The Sun is about 400 times the diameter of the Moon. But it is also ~400 times farther away, so their apparent sizes when viewed from Earth are roughly the same. Both appear as roughly half a degree in diameter. With the Earth and Moon being in elliptical orbits, the apparent size varies slightly. The Sun's apparent diameter changes from 31' 36" – 32' 42" (0.5267° - 0.5450°), while the Moon has a little more variation changing from 29' 26" - 33' 30" (0.4905° - 0.5583°). The upper half of this diagram depicts the apparent size of the Sun when the Earth is at aphelion (farthest away from the Sun) and the Moon is at apogee (farthest away from the Earth). The lower half depicts perihelion and perigee, respectively.

Because there are times when the Moon appears larger than the Sun and other times when the Moon appears smaller than the Sun, this enables two distinctly different types of eclipses to occur: total and annular. During a total eclipse, the Moon will fully block the Sun. During an annular eclipse, a full ring of the Sun is still visible when the Moon is centered directly over the Sun.

This similarity with Earth's two most prominent celestial bodies has been taken to be a cosmic coincidence. Some see this fact to be evidence in support of an anthropic principle pointing to intelligent design. A common scientific attitude is to dismiss this fact as a purely random coincidence. An alternative scientific understanding is a theory that there was a causal relationship with the similarity of apparent sizes with these two bodies in being a favorable factor for the evolution of life on Earth, in that the tidal forces caused by the Moon and Sun in this specific configuration helped to stabilize the climate and environment.