On August 21 2017, people all around the world especially those here in the United States were excited to see one event after an interval of nearly a century ー a total eclipse of the Sun. This is the phenomena that the Moon covers the Sun when it is passing between the Sun and the Earth and casts darkness on the Earth. Though now it is ordinary for us to see the Sun and the Moon in the sky everyday, have we ever thought about how were those planets, including our planet Earth, were created by taking many years to be formed like we know now?


The Moon is 1/400 the size of the Sun and 1/4 the size of the Earth. It is the only satellite which goes around the Earth. I did not consider the existence of Moon deeply until Bercovici mentioned in the lecture that our Moon is weird and not a typical planet compared with a lot of moons around planets in terms of composition because the lunar mantle is very low in elements.


The origin of the Moon goes back to as same period as the Earth. There is one hypothesis to explain how the Moon was created. The giant-impact hypothesis ways that the Moon was formed by a catastrophic collision and its debris and gas consolidated. Since the Moon and the Earth have been attracting each other. Because the Moon was born in almost same period as the Earth, I feel the Moon is the Earth’s sibling. It also reminded me the Apollo program from 1969 to 1972, which was one of the biggest events in human history.  It revealed many new findings about the Moon, although  how it was created is covered in mystery. But still I believe that knowing about the Moon leads us to new discovery of the origin of the Earth and the stars.


What would happen if the Sun and the Moon vanish? If the Sun suddenly disappeared, all the planets surrounding the Sun would retain their forward motion, and they would fly off. The planets would start getting colder and colder and no life could survive under this circumstance.  If there were no moon passing around our planet, the Earth would spin faster and the length of the day would shorten to ⅓ than now. The environment, needless to say, would dramatically change and many species would be endangered. Earth’s axis, which is inclined at about 23.4 degrees by the Moon would vary over time and  we would not have seasons through a year anymore.


Considering the origin of not only the Earth but also the stars allow me to feel every single event that happened in the universe starting from the Big Bang were indispensable. The Earth has been coexisting with those stars and we are still keeping this relationship in a dynamic scale. Now every time I look up at the sky and see the Sun and the Moon, I feel that they are both important components of the Earth as it is now.