Happy Aphelion Day! Earth is farther from the sun today (July 4) than at any other time of the year.
The exact moment of aphelion happens at 6 p.m. EDT (2200 GMT), when Earth will be 94,511,180 miles (152.1 million kilometers) away from the sun. That's more than 1.5 million miles (2.5 million km) farther than the planet's average distance of about 93 million miles (150 million km) — and 3 million miles (5 million km) farther away than it is at perihelion, or the shortest distance from the sun, which happened on Jan. 3.
When Earth orbits the sun, it doesn't travel in a perfect circle. Rather, its orbit is elliptical, or oval-shaped, with the sun situated about 1.5 million miles (2.5 million km) off-center. [25 Weirdest Facts About the Solar System]
Our planet reaches aphelion only once a year, and the event typically falls approximately 14 days after the June solstice, which marks the first day of summer for the Northern Hemisphere and the first day of winter for the Southern Hemisphere. Similarly, perihelion happens two weeks after the December solstice.
In the cosmic scheme of things, these annual changes in Earth's distance from the sun are tiny. Earth's distance at aphelion and perihelion differ from the average distance between Earth and the sun by less than 2 percent. Aphelion and perhelion are not related to the seasons, and people on Earth won't notice any difference in the weather or climate because the Earth is farther away from the sun, NASA officials have said.
"Seasonal weather patterns are shaped primarily by the 23.5-degree tilt of our planet's spin axis, not by the mild eccentricity of Earth's orbit," George Lebo, an astronomer with NASA's Marshall Space Flight Center in Huntsville, Alabama, said in a statement.
"During northern summer, the North Pole is tilted toward the sun. Days are long, and the sun is shining more nearly straight down — that's what makes July so warm," Lebo said.
But this doesn't necessarily mean that Earth's longer distance from the sun has no noticeable effects, Roy Spencer, of the Global Hydrology and Climate Center in Huntsville, Alabama, said in the same statement. "Averaged over the globe, sunlight falling on Earth in July (aphelion) is indeed about 7 percent less intense than it is in January (perihelion)," Spencer said.
Strangely, this doesn't mean that Earth is any cooler when it's farther from the sun. "The average temperature of Earth at aphelion is about 4 degrees Fahrenheit (2.3 degrees Celsius) higher than it is at perihelion," Spencer said.
This may seem counterintuitive, but the reason has to do with the distribution of land and water on our planet. "Earth's temperature averaged over the entire globe is slightly higher in July, because the sun is shining down on all that land" in the Northern Hemisphere, "which heats up rather easily," Spencer said.