Eclipses have been one of the most attractive celestial and astronomical phenomena of all people. When the sun and the moon align with the earth, a lunar eclipse or a solar eclipse occurs. Of course, the topic is a little more complicated than what I said.
Why do solar eclipses occur?
As we already know, the moon rotates around the earth. In addition to this, the moon and the earth rotate around the sun. We can experience a solar eclipse if the following conditions are met.
https://www.businessinsider.com/solar-eclipse-diagram-2017-8
I said that every time the sun, the new moon, and the earth are in the same line, a solar eclipse occurs (if the sun, the earth, and the full moon are in the same line, there is a possibility of a lunar eclipse occurring). So, with this definition, we should experience a solar eclipse every month, while the maximum solar eclipse that can occur in a year is 5 times a year (at least 2 solar eclipses occur). The reason for this is that the plane on which the Earth revolves around the sun and the plane on which the moon revolves around the earth has a 5-degree angle difference. These 5 degrees have reduced the number of times these 3 objects can be precisely aligned.
The intersection of these 2 pages is a line called the node line (red line in the photo below). Solar and lunar eclipses can occur when these 3 objects are very close to this node line, in addition to being in the same direction. Therefore, it is not possible for eclipse on the right and left situations of the picture below.
https://www.virtualtelescope.eu/what-is-a-solar-eclipse/
As a result, for a solar eclipse to occur, the following conditions must be met:
1- The new moon (i.e., the crescent moon has just been seen)
2- The sun, moon, and earth are aligned.
3- This alignment happened near the node line.
Types of solar eclipses
Solar eclipses are divided into 3 categories based on the alignment of the sun, moon and earth:
https://www.virtualtelescope.eu/what-is-a-solar-eclipse/
Total solar eclipse:
This solar eclipse is the most attractive type of solar eclipse. As soon as the sky gets dark in the middle of the day, the wind starts blowing, and animals and plants think it’s night. Here, a part of the earth is in the complete shadow of the moon, and the moon completely covers the disk of the sun, and the only thing that can be seen is the Sun’s corona (the outermost point of the sun, where ion particles are ejected from the surface of the sun into outer space).
The reason for this is that the apparent size of the sun and the moon are seen to be almost the same from an earthly observer (Intercept theorem). It means that the diameter of the sun is 400 times bigger than the moon, and its distance from the earth is 400 times the distance from the earth to the moon. Of course, this type of capture has the least repetition among astronomical phenomena, so the last total eclipse that could be seen in Iran was on 11 August 1999.
Partial solar eclipse:
If a part of the earth falls within the penumbra of the moon, a partial solar eclipse occurs. This means that the moon cannot completely cover the sun, and a part of the sun can be seen behind it. In fact, a part of the earth may see the solar eclipse in a total or annular form, but the inhabitants of another part of the earth may experience it in a partial form. The important thing is that even if the solar eclipse is total, the period of time, when the moon can completely cover the sun’s disc, is about 5 minutes, and before and after that eclipse can be seen in partial form.
Annular solar eclipse:
I said that the reason why the moon can hide the entire surface of the sun for us in a total solar eclipse is that the apparent size of the moon and the sun are the same for the terrestrial observer. Now, if the moon is at its furthest distance from the earth during the eclipse (the peak), it cannot cover the entire surface of the sun, and a part of the sun’s surface can be seen in the form of a ring from behind the moon, which means that an annular eclipse has occurred.
Where on earth are total solar eclipses visible and where are they partial?
As I said, the inhabitants of the area of the earth that is in the shadow of the moon on the earth will experience a total (or annular) solar eclipse, and those who are in the area of the penumbra will experience it in a partial form. But what does this part mean? Due to the fact that the earth is rotating around itself, the area where the eclipse can be seen either in total (or annular) or in partial form forms a path.
For example, the figure below is related to the circular solar eclipse of 21 June 2020, where the residents of the orange line see the solar eclipse in a circular form, and the further we go from this path, the less eclipse people experience.
https://www.timeanddate.com/eclipse/solar/2020-june-21
Safety Note:
You should not look at the sun with the naked eye. Glasses or telescopes with special filters should be used to observe the eclipse.
How do I know about future solar eclipses?
The easiest thing to do in order not to miss any eclipse or eclipse and even to be able to get its complete information is to install eclipse-related applications on your phone. Eclipse programs for IOS and Eclipse Calculator for Android are recommended.
Sources:
Universe – by Roger Freedman, William J. Kaufmann, Translated by Shahab Saghari
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