Why are there eclipses?

Eclipses, those natural phenomena in which either the sun or the moon darken for some minutes, have intrigued people since the dawn of time. In the past, they were thought to be foreboding of bad news. These days, however, we know what they are, why they happen, and —further— when they happen too.

The first thing you should learn about eclipses is that they are a game of shadows. In our Solar System, the moon revolves around the Earth, and the Earth, around the sun; so now and then the three celestial bodies will unavoidably line up. When this happens, the shadow of one body blocks the light that would usually pass if it was not there, causing a temporary darkening on the other body. This temporary darkening is the eclipse. They are lovely natural phenomena we can enjoy if we are patient and careful enough.

Eclipses do not happen every day, but why?

Eclipses do not happen every day. This is because there are two requirements for an eclipse to happen: the first one is that the Earth and the moon must be perfectly aligned. This only happens during a full moon or a new moon. During the rest of the lunar phases the moon is not aligned with the Earth and there cannot be eclipses. The second requirement is that these two heavenly bodies must be aligned, in turn, with the sun; something which does not happen often because the Earth and the moon do not revolve in a same line compared to the sun. There is a slight inclination of about five degrees between the angle in which the moon revolves around the Earth and the angle in which the Earth revolves around the sun. This difference prevents eclipses from happening more often.

Yet they align anyway, and eclipses happen. When the moon aligns between the sun and the Earth we see a solar eclipse; when it aligns so that the moon gets just behind the Earth compared to the sun, we will see a lunar eclipse. It is a game of shadows.

Six types of eclipses

From the above-mentioned, we can understand that there are two kinds of eclipse: solar and lunar. The classification does not end there, though. Taking into account that the alignment of the three celestial bodies is not perfect, there can be three types of eclipse of each kind: total, partial, and annular (sun) or penumbral (moon).

If the solar eclipse is total, the sun gets fully covered by the moon, and there will be darkness on our planet for some minutes. If it is annular, the sun gets partially covered by the moon, creating a ring around it. If the solar eclipse is partial, the moon will cover only a section of the sun, and it will look like a bitten cookie. In turn, if there is a total lunar eclipse, the moon gets fully covered by the shadow of the Earth. If it is partial, the shadow of the Earth covers only a section of the moon. If it is penumbral, the shadow of the earth covers the moon but just indirectly. People notice just a slight darkening of the satellite.

How long does an eclipse last?

Eclipses do not last long. As the moon revolves around the Earth slowly compared to the speed in which the Earth revolves around the sun, the alignment does not last much time. On the bright side, it is a fact that both the earth and the moon revolve in a stable manner which makes eclipses absolutely predictable. There is more than one calendar available. Actually, I'm including one below.

Can I see an eclipse?

Yes, you can, but you must be careful. All in all, lunar eclipses can be seen, admired and enjoyed without any caution. Solar eclipses, however, need ocular protection.

Upcoming eclipses in 2016

During 2016 there will be four eclipses:

+ The first eclipse will be on March 9^th. It will be a total solar eclipse, and it will be mainly seen from Oceania and the islands in the centre of the Pacific ocean.

+ The second eclipse will be on March 23^rd. It will be a penumbral lunar eclipse, and it will be mainly see in the Pacific ocean again, between Australia and California.

+ The third eclipse will be on September 1^st. It will be an annular solar eclipse, and it will be seen in Central Africa and the Indian Ocean region.

+ The fourth and last eclipse of the year will be on September 16^th. It will be a penumbral lunar eclipse, and it will be seen in all areas near the Indian Ocean, from Eastern Europe and Central Africa to the central areas of Australia.

Knowledge + Why?