At perihelion, when Earth is closest to the Sun, around January 3.
http://aa.usno.navy.mil/data/docs/EarthSeasons.php
http://aa.usno.navy.mil/faq/docs/seasons_orbit.php
http://aa.usno.navy.mil/data/docs/EarthSeasons.php
http://aa.usno.navy.mil/faq/docs/seasons_orbit.php
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The Earth is closest to the sun in its elliptical orbit on January 4.
Kepler's 3rd law basically says a planet moves faster when its closer to the sun.
Kepler's 3rd law basically says a planet moves faster when its closer to the sun.
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The Earth moves most rapidly in its orbit around January 2, when it is closest to the sun.