The apparent size of the Moon and the Sun in the sky is not a result of their physical dimensions but rather their distances from Earth. The Moon is about 400 times smaller than the Sun, but it is also approximately 400 times closer to Earth than the Sun. This fortuitous coincidence creates the phenomenon of total solar eclipses, where the Moon can appear to completely block out the Sun from certain vantage points on Earth.
The Moon's orbit around the Earth is elliptical, meaning its distance from Earth can vary. When the Moon is at its closest point to Earth (perigee), it can appear slightly larger in the sky, and when it is at its farthest point (apogee), it can appear slightly smaller. However, the differences in apparent size are not significant enough to disrupt the occurrence of total solar eclipses.
During a total solar eclipse, the Moon aligns precisely between the Earth and the Sun, with the three celestial bodies falling along the same line, resulting in the Moon casting a shadow on the Earth. Since the apparent size of the Moon is roughly the same as the apparent size of the Sun, when the Moon passes in front of the Sun during an eclipse, it appears to cover the entire solar disk, creating the phenomenon of totality.
It's important to note that the Moon's orbit is not perfectly stable, and over long periods, it undergoes various changes. Therefore, the occurrence of total solar eclipses can vary over time, and the Moon's distance and size may change in the future, affecting the exact alignment required for a total solar eclipse.