July 6 - Earth at Aphelion
What the hell does that mean, you’re probably wondering.
I was wondering too, and I can’t believe I made it through the public school system and college without hearing it before. What “Earth at Aphelion” means is that today the earth will be farther from the sun than any other time of the year.
As everyone know, the earth travels around the sun, but the path is not a perfect circle. It’s an ellipse, slightly lopsided. One end is a bit closer to the sun than the other. Today, our planet will reaches the distant end — a point astronomers call “aphelion.”
In January, when we’re closest to the Sun (perihelion), the distance is 147.5 million km. This weekend we will be 152.6 million km away—a 5 million kilometer difference.
It doesn’t seem to make sense that we’re closest to the sun in the winter and farthest away in the hottest part of the summer, unless you’re a scientist who has no trouble understanding these kinds of paradoxes. But here’s the explanation, from some really smart people at NASA.
“A distant sun means less sunlight for our planet. “Averaged over the globe, sunlight falling on Earth at aphelion is about 7% less intense than it is at perihelion,” says Roy Spencer of NASA’s Global Hydrology and Climate Center (GHCC). Then why is it so warm outside?
“Seasonal weather patterns are shaped primarily by the 23.5 degree tilt of our planet’s spin axis, not by aphelion or perihelion,” he adds. “During northern summer the north pole is tilted toward the Sun. The Sun climbs high in the sky, and days are long. That’s what makes July so hot.”
But there’s more to the story: Says Spencer, “the average temperature of the whole earth at aphelion is about 4 degrees F. higher than it is at perihelion.”
All this explains why July is our planet’s warmest month: Northern continents baked by the aphelion Sun elevate the average temperature of the entire globe, the experts say. January, on the other hand, is the coolest month because that’s when our planet presents its water-dominated hemisphere to the Sun. “We’re closer to the Sun in January,” says Spencer, “but the extra sunlight gets spread throughout the oceans.”
Our planet is actually warmer when we’re farther from the Sun. Strange but true.