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396B Posssibility of Asteroid Hitting Earth (2)
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84. How far does Earth's Gravity Extend?I live in Guatemala, Central America, and I was wondering something.
Do you know at which distance (miles) and object in space gets attracted or caught by the Earth gravity, and brought down to Earth.
ReplySupposedly, a very similar question occurred to Isaac Newton in 1666, possibly when he saw an apple fall from a tree. The apple was attracted to the Earth, which made it fall. How far from Earth did this pull extend? In particular, the Moon must also be attracted to the Earth--otherwise it would wander off into space. Did this same force extend all the way to the moon, and keep it in its orbit?
Newton's answer was "yes." Assuming that the force decreased with distance r like r-squared, he calculated the orbital period the Moon should have, and came out with the correct number. You will find all this, including the calculation, on
or in Spanish
Whether an object is brought down to Earth or enters an orbit around it depends on its velocity relative to the Earth. Objects at rest relative to the Earth are brought down, objects with appreciable velocity transverse to the line between them and the center of the Earth are not.
85. How far is the Moon?Hello
How far away from the Earth is the moon?
ReplyAbout 60 Earth radii, fluctuating a bit because the orbit is an ellipse. An earth radius is 6371 km, and you can do the multiplication yourself.
A much more interesting question is "How do we know that"? A clever Greek astronomer, Aristarchus, figured that out more than 2000 years ago--without telescopes, using just a few simple observations and logic. See
86. Twinkle, twinkle little star
Help me please ! I am trying to help my young sister in-law with some research for a project and I cannot find the information I need on stars. I need to know their locations in the sky, their sizes, what they are made up of and what impact they have on the Earth. I need this information as soon as possible as she has an assignment to hand in Friday the 6th of September. If you can help me I know we would both be so grateful...