Question

When do solar and lunar eclipses occur?

Answer 1

Whatever angle the moon's orbit is at, it will cross the ecliptic twice per revolution.

Explanation:

This is why we don't get a solar and lunar eclipse every month, you need the crossing to occur in the right position on the orbit such that the sun, earth and moon are aligned, so can only occur at a new (solar) or full moon (for a lunar eclipse.)

Answer 2

There are eclipse seasons when the earth, Moon and Sun can be aligned for an eclipse to occur.

Explanation:

The Moon's orbit is inclined at about `5^@` to the plane of the ecliptic. A lunar or solar eclipse can only happen when the Moon is near one of its nodes which is when the lunar orbit crosses the ecliptic.

When Moon is close to one of its nodes and the line between nodes is pointing towards the Sun, then it is an eclipse season. Each eclipse season lasts about 34 days and there are two or three each year.

When a full moon occurs during an eclipse season there is a lunar eclipse. When a new moon occurs in an eclipse season there is a solar eclipse. There are two or three eclipses, at least one solar and one lunar, in each eclipse season.

If there are two solar eclipses in an eclipse season they are both near one of the poles and are only partial eclipses.

If a solar eclipse occurs around the middle of the eclipse season it will be a central eclipse, either annular, hybrid or total. Total eclipses only occur if the Moon is enough to the Earth to cover the Sun's disc at the time of the eclipse.

Typically each year either has 3 or 4 partial solar eclipses or an annular and an total eclipse.

The year 2057 will be rather special as there will be 2 total solar eclipses and an annular eclipse.