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Q & A: Elliptical motion of the planets.

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Most recent answer: 04/06/2010
Q:
sir ....... i had a discussion with my friends about the elliptical motion of the planets ...well the idea was the space time fabric which should bend the part under sun in a circular format as per shown in the picture and assume ti to be the sun... http://ws5.com/spacetime/162571main_GPB_circling_earth3_516.jpg ..... must in turn cause the earth to revolve in a circular form if the sun is stationary with respect to the earth and the planets with this point in mind we thought of the reason of it being elliptical path.... i know circle (the perfect one ,having two focii co-incied at the center..) is a type of ellipse ... actually we extended the discussion and involved our teacher too.... so he said that the sun is also revolving around the galaxy.. so it causes the path of planets to be elliptical..... but in my knowledge sun does revolve around the galaxy ...but not with respect to the planets as they too are being dragged in the motion of the sun...like the satellite driven to move around its planet....their , i guess, the planet seems stationary...... i know these ides are very childish....... please guide me and tell me what should happen and why elliptical and not any other shape.. and does this not violate the concept of geocentric solar system and in these conditions is it that the predictions about their path do match with the observation .. thank u for ur time.. thank u so much for the reading sir......... ramesh
- ramesh (age 17)
india
A:
In the early 17th century, using the astronomical observations of Tycho Brahe, Johannes Kepler  determined that the orbits of the planets around the sun were ellipses with the sun at one focus: .  In In the late 17th century Isaac Newton developed his universal theory of gravitation positing that the force of attraction between two bodies was inversely proportional to the square of the distance between them.  Using his newly invented method of calculus plus a lot of clever geometry, he determined that indeed the orbits of the planets should be elliptical.  Circular orbits are also allowed, being special cases of ellipses. 

The sun also orbits around the center of our galaxy, the Milky Way.  The orbit is more or less circular but is affected by nearby stars.  Since the orbital period is of the order of 240 million years, astronomers will have to wait for a while in order to make an accurate measurement. 

LeeH

(published on 04/06/2010)

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