Distance of each planet from the Sun

A map with no scale

By the time Kepler published his third law in 1619, astronomers already knew the layout of the solar system in proportion. That law ties each planet's year to its distance, so a planet that takes 11.9 years to go around must sit about 5.2 times as far out as Earth. Every planet's distance could be written as a multiple of Earth's. What nobody knew was the size of that one unit.

It was like owning a perfect map with no scale bar. Mars could be shown to be 1.52 times farther from the Sun than we are, but not whether that meant tens of millions of kilometers or hundreds of millions. Finding the scale meant measuring a single distance in space in kilometers, and then every other number would follow. That one distance is the astronomical unit, the AU.

Distance from the Sun

One AU is Earth's average distance from the Sun. Orbits are ovals, so every planet has a nearest and a farthest point. Values from the NASA Planetary Fact Sheet.

How the ruler was finally set

The first serious attempt came in 1672. Giovanni Domenico Cassini watched Mars from Paris while Jean Richer watched it from Cayenne, in French Guiana, and the tiny shift in Mars's position against the stars, seen from two places so far apart, gave a distance to Mars. From that the Sun's distance followed, at roughly 140 million kilometers, within about 10 percent of the truth. It was the first sensible estimate of the size of the solar system.

In 1716 Edmond Halley suggested a better method: time a transit of Venus across the Sun from places far apart. The transits of 1761 and 1769 set off an international scramble, and James Cook sailed to Tahiti to watch the second. An optical smear called the black drop effect blurred the timings, but the combined results landed near 94 million miles, close to the real 93 million.

The decisive step came with radar. In 1961 a team at NASA's Jet Propulsion Laboratory aimed the big Goldstone dish at Venus and caught the faint echo, and the timing of that echo gave the distance directly. Radar measurements in the early 1960s fixed the AU far more tightly than any earlier method, at about 499 light-seconds. In 2012 the International Astronomical Union stopped measuring it altogether and defined the AU as exactly 149,597,870,700 meters.

An average that hides a swing

Every figure in the table is an average, and no planet sits at its average. Earth's distance from the Sun runs from 147.1 to 152.1 million km, a swing of about 5 million km. Earth is closest in early January and farthest in early July, which is one reason people are surprised to learn that distance doesn't cause the seasons. Tilt does.

Mercury swings far more: from 46.0 to 69.8 million km, so it's 1.5 times farther from the Sun at the far end of its orbit than at the near end. Pluto ranges from 4,436.8 to 7,375.9 million km, so for part of every orbit it's closer to the Sun than Neptune is.

How far is each planet from Earth?

Distance from the Sun is fixed by the orbit, but distance from Earth is a moving target, because both planets are circling. The closest and farthest figures below are from the fact sheet's pages for each planet.

Mars shows the effect best. It can come as close as 54.6 million km and as far as 401.4 million km, a spread of about 7 to one. The two planets line up at their closest roughly every 2.1 years, which is why missions to Mars leave in windows about every 26 months. The Mars opposition page has the dates, and the travel time page shows what the trip takes.

Light is the yardstick

Light travels 299,792 km every second, so distances in the solar system turn into waiting times. A radio message to Mars takes 3.0 minutes at best and 22.3 minutes at worst, and a rover team can never steer in real time. The light travel time calculator does the sum for any distance you type in.

At 30 AU, sunlight takes 4.2 hours to reach Neptune, and the Sun looks about 911 times fainter there than it does from Earth, because light thins out with the square of the distance.

What distance does to sunlight

Sunlight thins out with the square of the distance. Double the distance and a patch of space gets a quarter of the light. Mercury sits 2.6 times closer to the Sun than Earth does, so each square meter there gets about 6.7 times Earth's 1,361 watts, by the fact sheet's own detail pages. Neptune is 30 times farther out, and its sunlight is about 911 times weaker than ours. That's why the distance list on this page also reads as a list of how warm each world could be.

A very long road

The numbers in the table are easy to read and hard to feel. A jet cruising at 900 kilometers an hour would need about 19 years of nonstop flying to cover the distance from Earth to the Sun, and about 572 years to reach Neptune's orbit. Spacecraft are much faster, and they still take years. Voyager 2 left Earth in 1977 and passed Neptune in 1989, a trip of 12 years. The Voyager 2 page tells that trip in full.

A check that the map is right

Kepler's third law says that the cube of a planet's average distance in AU, divided by the square of its orbit time in years, is the same number for every planet. The fact sheet figures give 1.00 for Earth, 1.00 for Mars and 1.03 for Neptune. The match across such different distances is what made the AU measurable in the first place: once the shape of the solar system was known from the orbit times, a single distance in kilometers set the scale of everything else. You can see the effect on the year-length page.

Questions people ask

How far is the Sun from Earth?

An average of 149.6 million km, which is one AU. Sunlight takes 8.3 minutes to arrive.

How far is Mars from the Sun?

Mars is 228.0 million km from the Sun on average, 1.52 AU.

How far is Neptune from the Sun?

4,515.0 million km on average, 30.2 AU. Sunlight takes 4.2 hours.

How close can a planet get to Earth?

Venus comes closest, within 38.2 million km at its nearest.

Keep exploring

Distance becomes time on the travel time pages.