Eclipses

Eclipses are staples when it comes to astronomical phenomena recognized by the public. Despite this, there exists a lot of misinformation about eclipses in the minds of the general public. For example, many people still subscribe to traditional explanations for the causes of eclipses, such as invoking the presence of a deity who is somehow angry at humans for certain misdemeanors. As such, there exist cultural practices that many people adhere to during an eclipse. Moreover, misrepresentation of scientific facts as well as scientific processes has resulted in pseudo-scientific explanations masquerading as “truth” among the general populace. However, there exist completely reasonable, easily understandable, scientifically accurate explanations that describe the occurrence of an eclipse, as well as eclipse characteristics.

Firstly, what causes eclipses? Fundamentally, an eclipse is caused when either the Moon comes between the Earth and the Sun, called a Solar eclipse as the Sun appears blocked by the Moon from the Earth’s surface, or when the Earth comes in between the Moon and the Sun, called a Lunar eclipse as the Moon appears darkened as a result of the Earth’s shadow. We are used to visualizing these scenarios two-dimensionally. However, the problem with that is, in two dimensions, Lunar and Solar eclipses occur every lunar cycle. This is clearly not the case. So what gives?

The answer to this question lies in the orbit of the Moon. With respect to an imaginary line between the Earth’s equator and the Sun, the Moon’s orbit is tilted or inclined at an angle of about 5 degrees. Because of this, during most full moons and new moons, the Moon passes through a point in space where it isn’t blocked by the Earth’s shadow, nor does it block the Sun as apparent from the surface of the Earth. Eclipses only occur when the Moon is at one of its nodes, the point in its orbit where it intersects the imaginary line between the Earth’s equator and the Sun. The node is not a fixed point; it moves along the orbit of the Moon. Moreover, the exact position of the Moon’s orbital points, such as its nearest point to the Earth, the perigee, change as well. Because of these factors, we have Lunar and Solar eclipses only some of the time, but at a noticeable frequency.

The factors that give rise to these eclipses can be studied by using celestial mechanics and geometry. This allows us to predict the occurrence of future eclipses. However, the ancients predicted eclipses with great accuracy as well. They did this through inductive methods – by finding patterns in the occurrence of eclipses. The equations that describe the lunar motion is complex and too difficult to grasp for the layman. This is because, while analyzing the motion of the Moon, we must remember to take into account the gravitational interactions of all major Solar System bodies with the Earth-Moon system. Nonetheless, people can get an idea about predicting eclipses by looking up on the Saros Number, which can help determine if an eclipse will occur based on a particular number, and knowledge of the exact Saros Number at a previous eclipse. This method is particularly useful at predicting eclipses, as it is very simple to use.

Speaking of predicting eclipses, the sad fact is that total solar eclipses are numbered. This is because the Moon is slowly moving away from the Earth due to orbital effects. Thus, in the future, total Solar Eclipses will cease to exist. However, all is not lost. We shall still be able to see beautiful annular eclipses. An annular eclipse occurs when the Moon is smaller in size apparent from the Earth, than the Sun, but still comes entirely in between the Earth and the Moon. This happens, because the Moon’s orbit is eccentric, i.e. its orbit is not entirely circular. Thus, there are points in its orbit from which it appears smaller than the Sun if seen from the Earth. This also means that on very rare occasions, a lunar eclipse occurs when the Moon is at perigee. If solar eclipses occur at such points, then an annular eclipse occurs. Total eclipses occur when the Earth passes through the Moon’s umbra, or when the Moon passes through the Earth’s umbra. The umbra is the darkest part of the shadow. Partial eclipses occur when either the Earth passes through the Moon’s penumbra, or when the Moon passes through the Earth’s penumbra. The penumbra is the lighter part of the shadow. One key difference between Lunar and Solar eclipses apart from the different geometrical configurations is the duration. Lunar eclipses tend to be much longer than Solar eclipses. This happens, because the Moon’s angular size is very similar to that of the Sun, and thus, takes very little time in passing across the Sun. However, the Earth’s shadow is much larger than the Moon’s angular size. Thus, the Moon takes longer in passing this shadow. Therefore, Lunar eclipses are longer than Solar eclipses.

We have so far discussed eclipses in terms of scientific ideas that can be validated. However, we also need to consider tradition and culture, since many people still believe in such ideas. In fact, I have heard people subscribing to the notion that there are “harmful rays” when eclipses occur, something that was rampant during the recent lunar eclipse. The fact remains that there are no additional rays, let alone harmful ones. This can be validated by the fact that there are many telescopes analyzing data during eclipses, and none of these telescopes detect any anomalies. Moreover, in many cultures, an eclipse signifies the coming of a tragedy. However, there is no correlation between bad events and eclipses whatsoever. This can be seen by analyzing data over long periods of time. There is no abnormal spike in disasters during or close to an eclipse. Other practices, such as refraining from eating during an eclipse, are based on interpretations of eclipses as the harbingers of disasters. Thus, there seems to be no scientific rationale to stop consumption during an eclipse.

Therefore, we see that eclipses are perfectly reasonable, scientific phenomena with clear reasons as to why they occur. The interesting thing about eclipses is that there are so many beautiful phenomena that occur during an eclipse, such as diamond spots, something which I suggest reading about on the Eclipse page of the NASA website: https://eclipse.gsfc.nasa.gov/eclipse.html. Eclipses are beautiful astronomical phenomena that will occur at least once or twice a year at any given place in the world. There is nothing to fear, however, it is very important to keep safety precautions in mind when watching an eclipse, particularly a Solar eclipse. So, the next time an eclipse occurs where you are living, remember to kick back, relax, eat, and observe with care.