Happy Aphelion Day! On Friday the Earth was farther from the sun than it will… (NOAA )
Happy Aphelion Day!
At 9 a.m. PDT on Friday, the Earth was more than 94.5 million miles from the sun -- the farthest away it will get from our life-giving star for the entire year.
At that time we were about 1.5 million miles farther from the sun than the Earth's average distance of 93 million miles, according to EarthSky.org.
The Earth moves in a lopsided elliptical orbit as it travels around the sun. That orbit takes it closer to the sun during the Northern Hemisphere's winter, and farther from the sun during our summer. The Earth will next reach is closest point to the sun -- perihelion -- on Jan. 2, 2014.
It may sound counterintuitive that we are farthest from the sun during these warm summer days, but think back to your Earth sciences class: The seasons are not affected by the closeness of the Earth to the sun, but rather by the 23.5-degree tilt of the Earth on its axis.
In our summertime, the Northern Hemisphere is tilted toward the sun, and in our wintertime, it's the Southern Hemisphere that is tilted toward the sun.
And here's another counterintuitive bit of information: The temperature of the Earth is warmest when we are farthest from the sun, even though the sunlight falling on Earth is about 7% less intense now compared with our closest approach to the sun in January.
How does that work?
Well, sunlight heats up land more easily than water. (Think of those wild temperature fluctuations in the desert, and the relatively steady temperatures at the coasts). The Northern Hemisphere has more land, while the Southern Hemisphere has more water.
So, when the Northern Hemisphere is experiencing summer, more land is getting hit sunlight than when the Southern Hemisphere is experiencing summer. And because land heats up more than water, the entire Earth is a bit warmer.
[For the Record, 3:48 p.m., July 5: In an earlier version of this story, the word "million" was missing from the first sentence.]