ความคิดเห็นที่ 18
"แล้วทำไมดวงจันทร์ถึงมีคาบการโคจรรอบโลกเท่ากันเป๊ะกับคาบการโคจรรอบตัวเองล่ะครับ (นี่เลยเป็นสาเหตุให้เรามองเห็นดวงจันทร์แค่ด้านเดียว ด้านที่มีกระต่าย)
ไม่น่าใช่เรื่องบังเอิญ น่าจะเป็นอะไรที่ systematic"
It is called tidally locked. you are correct, it's not coincidence. Earth's gravity pull on the moon makes the moon bulge a bit (same as tide on Earth happens because of the moon pull on Earth). This bulge causes friction with the moon's surface when it rotates (when the moon rotates, the bulge must change to new position directly facing Earth.) This slows the moon's rotation down until the moon's rotation matches its revolution around the Earth. at that point, there is no more friction.
the moon's pull on earth also causes friction too (mostly between water and ocean floor). That is why the Earth's rotation rate is slowing down. The bulge on Earth is not exactly under the moon because earth is rotating and pushing the bulge ahead. It is also why the moon's distance from earth is increasing. the bulge ahead of the moon pulls on the moon too (newton's second law) and gives it extra energy making it's orbit higher. basically earth's angular momentum is transferred to the moon (conservation of energy law). If left for a loooonnnnnnnggggggg time, the earth will also be tidally locked with the moon...and only one side of the earth will face the moon.
Pluto and Sharon (their sizes are quite similar) are perfectly tidally locked to each other. So only one fact of pluto face one face of Sharon.
(let's not talk about sun's gravitational pull and eliptic and inclined orbit of the moon just :-) :) but if you wanna know, search for 'libration')
จากคุณ :
HotChoc 
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19 ก.ย. 48 14:34:53
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