How Often Do Eclipses Occur?

This post is also available in: Indonesian

Solar eclipse occurs when Sun – Earth – Moon are in alignment or when the Moon passes between the Sun and the Earth. Solar eclipse occurs during the new moon phase the same as Lunar eclipse always occurs during full moon. But not every new moon or full moon, eclipses will occur. Why is that?

why05The moon moves around the Earth every 27,3 days and if the Moon orbiting the Earth in the same ecliptic plane of the Earth,  then we will have 2 eclipses in a month. A lunar eclipse during full moon and solar eclipse in a new moon 2 weeks later. Which means people on Earth are lucky enough to have 24 eclipses in a year and full moon become rare.

Unfortunately not!

The Moon’s orbit is inclined 5.2 degrees to the ecliptic plane, which is the plane of the Earth’s orbit around the Sun.  As a result of this inclination, eclipses won’t occur every new moon or full moon because the Moon will not align with the Earth and Sun every time it passes between them. The inclination of the Moon orbit made it sometimes passing through the plane of the Earth’s orbit, other times passing high above or below under. Twice a month the moon intersects the ecliptic at points called nodes (ascending and descending nodes).  If the full moon or new moon is close to one of these nodes, then an eclipse is inevitable.

Nonetheless, we won’t have 2 eclipses in a month, but in a year the possibility of each eclipse either Solar eclipse or Lunar eclipses stretched from two to five times. In general, the combination of Lunar and Solar eclipses every year will be 4 – 7 times and the composition are 2 lunar eclipses and 2 solar eclipses or 2 lunar eclipses and 5 solar eclipses and vise versa.

Out of the possibility of Solar eclipses, 28% are total, 35% partial, 32% annular and 5% hybrid eclipses.

Loosely translated from langitselatan: Mengenal Gerhana Matahari

Ditulis oleh

Avivah Yamani

astronomer. astronomy communicator by day. co-founder of langitselatan. new media practitioners. story teller and podcaster in the making. social media observer. web developer and web administrator by accident.

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