Why don’t eclipses of the Sun and Moon happen every month?


On December 4 of this month, a total solar eclipse occurred over Antarctica. This phenomenon could only be observed over this continent. The next solar eclipse will take place on April 30, 2022. But many people wonder why solar and lunar eclipses do not occur every month, and why each time eclipses can be seen from a different place? We will try to answer these and other questions about dimming in this article.

In general, there are two types of blackouts: solar and lunar. A solar eclipse occurs when our satellite passes between the Earth and the Sun, while casting a shadow on the surface of our planet. If you are in the path of this shadow, you will see a total solar eclipse. The width of this strip, where a solar eclipse can be seen, is at a maximum of about 270 kilometers. Partial phases of blackout can already be seen in a wider band. This is why not everyone will see the full eclipse phase right away. The shadow on the surface of the Earth looks like an oval spot that travels across the Earth from west to east at a speed of about 1 kilometer per second. The average duration of such a phenomenon in any particular place is about 2-3 minutes.

Interestingly, this phenomenon, although periodic, does not occur monthly. The orbit of our Moon is tilted to the plane of the ecliptic at a slight angle — 5.14 degrees. Although this angle is small, at a distance of 380,000 kilometers, where the Moon is located, the difference is quite noticeable. Therefore, the Moon can pass 37,000 km above or below the central part of the Earth’s shadow. Thus, the shadow from our satellite bypasses the Earth and no blackout occurs. In this case, there are points where the orbit of the Moon intersects with the plane of the ecliptic. These points are called lunar nodes. During the time when the new moon passes through one of these nodes, a solar eclipse occurs. In addition, these nodes also move, which is why eclipses do not occur every revolution of the Moon around the Earth.

In a certain place during the year, there are from two to five eclipses of the Sun, of which no more than three are complete. On average, in the same place, a complete blackout occurs once every 370 years. But there are also exceptions.

Another interesting fact. Unfortunately, we will not be able to observe a total solar eclipse in 600 million years, since the Moon moves away from the Earth by 4 centimeters every year. Therefore, after this time, the angular dimensions of the Moon will be smaller and the complete darkening of the Sun will become impossible, but it will be possible to observe annular and partial phases.

An annular eclipse is also quite a beautiful phenomenon. Now it occurs when the Moon, passing through the lunar node, at this time is close to the aphelion of its orbit. Then its apparent angular dimensions decrease and it will not be able to cover the disk of the Sun with itself.

An eclipse of the moon occurs when the moon is located behind the earth in relation to the sun and, as during a solar eclipse, passes through the lunar node. Then the Earth casts a shadow and penumbra on the surface of our satellite. The duration of this blackout is longer than the sun and can sometimes last 1 hour and 40 minutes. In one year, 2-5 such phenomena can occur across the planet. A lunar eclipse in a certain place occurs more often, since this phenomenon is visible from almost the entire night hemisphere of the Earth, where the Moon is above the horizon.

During an eclipse of the moon, our satellite turns red. The reason for this phenomenon is the same as that of the red moon or sun during their sunrise or sunset. In simple terms, the atmosphere filters out the greenish to purple range, allowing only the red portion of the range to pass through. Also, the Earth’s atmosphere refracts sunlight so that it bends and thus illuminates the Moon during an eclipse.

Author: Alexey Nimchuk.

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