How Far Is Earth From The Sun?
QUICK ANSWER
Earth orbits an average of 93 million miles (149.6 million km) from the Sun, a distance defined as 1 astronomical unit (AU). Because Earth's orbit is slightly elliptical, the actual distance varies from about 91.4 million miles in January to 94.5 million miles in July.
Earth sits 93 million miles from the Sun on average. The number is fixed enough to be used as a basic unit of distance in astronomy, but it's not perfectly constant. Earth gets slightly closer and slightly farther over the course of a year, and the timing might surprise you.
What is Earth's average distance from the Sun?
According to NASA, Earth's average distance from the Sun is about 93 million miles (149.6 million kilometers), or roughly 8 light-minutes. This distance is so important to astronomy that it's been given its own name: 1 astronomical unit (AU). All other distances in the solar system are measured against it. Mercury sits at 0.39 AU, Mars at 1.52 AU, and Pluto at about 39.5 AU.
Does Earth's distance from the Sun change?
Yes, but not by much. Earth's orbit is slightly elliptical, with an eccentricity of 0.0167. The closest point (perihelion) happens around January 3 each year, when Earth is about 91.4 million miles from the Sun. The farthest point (aphelion) happens around July 4, at about 94.5 million miles. That's a variation of roughly 3 million miles over the year, or about 3 percent of the average distance.
Why aren't winters when Earth is farthest from the Sun?
This is the counterintuitive part. Northern Hemisphere winter happens in January, which is when Earth is closest to the Sun, not farthest. Seasons aren't caused by distance from the Sun, they're caused by Earth's 23.5 degree axial tilt. When the Northern Hemisphere is tilted away from the Sun, it gets less direct sunlight and experiences winter, regardless of how close Earth is to the Sun at the time. The small distance variation is far less significant than the tilt.
How long does sunlight take to reach Earth?
About 8 minutes and 20 seconds. When you look at the Sun, you're actually seeing it as it was about 8 minutes ago. Light travels at roughly 186,000 miles per second, and at 93 million miles away, the Sun's light takes that long to cross the distance. This means if the Sun suddenly disappeared (which it won't), Earth would continue receiving light and orbiting normally for another 8 minutes before anything noticeable happened.
Earth orbits the Sun at an average distance of 93 million miles, varying by only a few million miles over the course of a year. The small distance variation isn't enough to cause seasons; Earth's axial tilt does that work. The 8-minute light delay is a reminder that what we see of the Sun is always slightly old news.
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