Why don lunar and solar eclipses happen every month?
An eclipse requires the lining up of the earth and the moon relative to the sun. If the moon orbited the earth in the exact plane of the earth’s solar orbit, then there would indeed be lunar and solar eclipses every month. However this does not happen because the moon orbits the earth at a slight angle to the orbit of the earth around the sun. As a result the moon “crosses” the orbital plane of the earth for a brief period twice every month. In order for an eclipse to occur, the earth and sun must line up exactly with the moon at the precise moment that the moon crosses the earth’s orbital plane. This happens about four to seven times a year, although lunar eclipse are far more common than solar eclipses.
