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Despite perihelion in January, max speed around Sun was on Xmas day. (twitpic.com)
2 points by ColinWright on Jan 5, 2012 | hide | past | favorite | 1 comment


This graph shows the different effects on the Earth's speed around the Sun. It's complicated.

Perihelion was at 1am GMT 5 Jan.[1] However, the Earth and Moon orbit a common center of gravity[2], and when the Moon is closer to the Sun than the Earth, the center of the Earth is moving marginally faster than when the Earth is closer to the Sun than the Moon.

The Moon travels about 1 km/s in orbit (Earth relative)[3], the Earth–Moon mass ratio is about 81:1[4], and the distance to the Moon is about 60 Earth radii.[5]

References:

[1] http://1.usa.gov/AykBoB

[2] http://en.wikipedia.org/wiki/Center_of_mass#Astronomy

[3] http://www.freemars.org/jeff/speed/index.htm

[4] http://en.wikipedia.org/wiki/Orbit_of_the_Moon#Double_planet...

[5] http://en.wikipedia.org/wiki/Orbit_of_the_Moon




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