As heat waves continue to roast the western U.S., it may feel like the sun is dangerously close to the Earth, though according to National Geographic, the exact opposite is true for today, July 5 2013, as our planet will be the farthest from its most important star today than any other day this year.
The reason why? All of our planets in our solar system are elliptical as opposed to circular, a phenomenon first explained by 17th-century German astronomer Johannes Kepler. An elliptical orbit means that Earth will reach a point that it is closest to the sun (perihelion) and farthest from the sun (aphelion) each year.
This morning at 10:46 a.m. EST, our planet reached aphelion 94,508,959 miles (152,097,426 kilometers) from the sun. This year's perihelion was on January 1 at 11:39 p.m. EST, when Earth was 91,402,559 miles (147,098,161 kilometers) from the sun.
"The difference in dates is due more to the fact that the time it takes the Earth to complete one full orbit of the Sun [one year] is not an integer number of days, so the exact times of perihelion and aphelion vary from one year to the next," Mark Hammergren, an astronomer at the Adler Planetarium in Chicago, Illinois, said to National Geographic. Hammergren explained that the timing and distances vary slightly from year to year due to small variations in Earth's orbital elements.
The Earth is usually about three million miles (3 percent) farther from the sun at aphelion than at perihelion, causing the sun to look about 3 percent smaller in the sky, though you may not notice unless glancing through a telescope.
"This is not like the moon, where it can vary as much as 12 percent. There's no 'supersun,'" Joe Rao, a meteorologist and a guest lecturer at New York's Hayden Planetarium, told National Geographic.
The question remains: if Earth is so far from the sun, why is the Northern Hemisphere suffering from heat waves?
The answer lies in the reason behind seasons: the tilt of the Earth on its axis, not its distance from the sun. It is only by coincidence that Earth reaches aphelion when the North Pole is tilted more to the sun than the South Pole.
"Because the Earth has a tilt, it means that in the summer months [the Northern Hemisphere] receives a longer duration of sunshine-so the day is longer and the night is shorter-but also the sunlight hits the ground more vertically," Hammergren said.
The Northern Hemisphere receives twice as much sunlight during the summer than in winter because the sun takes a high angular path across the sky in the summertime.
"In the wintertime the sun takes a low path...and is in the sky for just nine hours," Rao said. "You lose six hours of daylight. The hottest time of the year doesn't coincide with the solstice, and it doesn't coincide with early July.
"The hurricane season reaches its peak on the 10th of September. That's almost three months past the summer solstice. That's because hurricanes feed on warm ocean water and the waters reach their temperature peak in the early to middle part of September."
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