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Why do the Sun and the Moon Appear to be of the Same Size?

by Nabjot Kaur

Why do the Sun and the Moon Appear to be of the Same Size?

July 2, 2021

Did you ever wonder about how Sun and Moon completely overshadow each other during the eclipses? Despite being completely different in size, they appear to be the same.

In our solar system, Sun is that one big source of mass and all other planets orbit around it. Moons are the natural satellites present in our solar system and they exist in stable orbits around different planets. While, Planets like Jupiter, Saturn, Uranus, and Neptune are surrounded by multiple moons, planet Earth witnesses just one moon, likely formed due to a giant impact. Our Moon happens to be identical in angular size to the Sun.

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From Earth, it may seem like sun and moon are both the same size, but in reality, the sun and Earth are equidistant from the moon.

Coincidence?

Whether you believe it or not, but it is a coincidence. The diameter of the Sun is 400 times larger than the diameter of the Moon and the Sun is also 400 times away from our Moon, making both Moon and Sun appear similar in size as seen from Earth. Due to this, we can witness total lunar and solar eclipse from Earth. However, this was not always the case. Due to Tidal interactions, the Moon moves four inches away from Earth every year. In the past, the Moon was so close to Earth that, it used to block the entire disk of the sun causing a total eclipse. It would be safe to say that our distant ancestors did not witness the beauty of coronal displays, which we enjoy now. Talking about the future, 50 million years from now the moon will spiral farther away from Earth, and humans will only be able to see annular eclipses.

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How did it Form Naturally?

Upon examining the Moon, researchers found strong evidence to support their claims. There are four types of moons. The ones which formed from the initial Solar System material, ones that formed from accreted ring systems, and the ones which got captured gravitationally. These three types of moons are found only around the giant gas worlds existing in our solar system. The fourth type, are the moons which are found around small terrestrial worlds like Mars, Earth, Pluto, Haumea, and Eris.

The Apollo missions further provided evidence to support this. The Apollo missions returned to the Earth with the samples of the lunar surface. On further analysis, they confirmed that the material composing the Earth’s and Moon’s crust have a common origin, while the surface of Moon was once molted. On measuring the orbital parameters and composition of Mars’s moons, it is revealed that they were created by a giant impact. The most recent measurements by New Horizons states that Charon and Pluto’s giant moon originated from a similar giant impact as well. The Moon has an iron core similar to Earth, but it’s very small in comparison to Earth’s core. The stable-isotope ratios for the Moon and Earth are identical, while both Moon and Earth differ from all the other planets in the Solar System.

Further Analysis

There are three types of eclipses experienced by the Earth. Total solar eclipse, an annular solar eclipse, and Hybrid solar eclipse. Earth experiences all these three kinds of eclipses because the Moon can appear smaller or larger than the Sun in its elliptical orbit around the Earth. This is exclusive to Earth because no other planet experiences all three eclipses with their moons. However, this was not always the case, considering the ever-changing relationship between Moon, Sun, and Earth. 

For billions of years until a few hundred years ago, Earth only witnessed total eclipses as Moon was close enough to block out the Sun from our perspective. In another 570 million years Earth will witness its last total solar eclipse and in another 80 million years Earth will be experiencing its last hybrid solar eclipse. After that, Earth will only be able to experience Annular eclipses. 

All this concludes that today, when we look at the Moon from Earth, comparing its angular size to that of the Sun, it looks like both Sun and Moon are almost similar in size. Although, this situation is temporary.

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