Here's why:

* Earth's Orbit and the Ecliptic: The Earth orbits the Sun in a plane called the ecliptic. The Moon's orbit is slightly tilted compared to this plane.

* Alignment for Eclipses: Solar eclipses happen when the Moon passes between the Earth and the Sun. Lunar eclipses happen when the Earth passes between the Sun and the Moon. For either type to occur, the Sun, Earth, and Moon need to be roughly aligned.

* The Lunar Nodes: The points where the Moon's orbit crosses the ecliptic are called the lunar nodes. Eclipses can only occur when the Sun is near these nodes.

* Six Month Cycle: As the Earth orbits the Sun, the Sun appears to move through the constellations along the ecliptic. It takes approximately six months for the Sun to move from one lunar node to the other. This is why we have eclipse seasons roughly every six months.

Important Note: Even though eclipses happen every six months, not every eclipse season will have both a solar and a lunar eclipse. The specific alignment of the Sun, Earth, and Moon needs to be just right for each type of eclipse to occur.