Why eclipses don't happen every month
The Moon's orbit is inclined to the ecliptic by approximately 5° 9′, so during most new moons the Moon passes above or below the Sun. An eclipse is only possible when a new or full moon occurs near the orbital node.
These periods are called eclipse seasons, occurring roughly twice a year and lasting about 34 days. There are between four and seven eclipses in a year.
- •The Moon's orbital inclination is 5° 9′.
- •Solar eclipse at New Moon near a node, lunar eclipse at Full Moon
- •4 to 7 eclipses per year in two corridors