The Sky This Week, 2012 July 4 – 10 — Naval Oceanography Portal

It’s a bit hard to believe after our record heat wave of late, but the Earth is farthest from the Sun on the 4th at 11:32 EDT. At this time we will be 94,505,851 miles (152,092,424 kilometers) from Old Sol. Back on January 4 we were some 3,103,884 miles (4,995,217 kilometers) closer. As you can see, the variation in the aphelion and perihelion distances of the Earth are quite small compared to the overall mean distance to the Sun, but this quantity, known as the eccentricity of the Earth’s orbit, slowly changes over time. Eccentricity is expressed as a ratio, and currently it is about 0.017. It can vary between 0.005 (nearly circular) to 0.06 (about a 12% ellipse) with two superposed cycles of some 100,000 and 400,000 years. These variations are primarily influenced by the gravity of the giant planet Jupiter, and at times of extreme eccentricity this can have a major effect on the planet’s climate. Right now we’re trending toward a more circular pattern, though, so we can’t blame the current weather on Jupiter!

The Sky This Week, 2012 July 4 – 10 — Naval Oceanography Portal