Neptune, the eighth and most distant planet in the Solar System, orbits the Sun at an average distance of about 4.5 billion kilometers. That is about 30 times Earth's distance from the Sun. Neptune's orbit is almost a circle, so the distance changes only a little, from about 4.47 billion kilometers at its closest to 4.56 billion at its farthest.

Distance

Distances in the outer Solar System are often given in astronomical units. One astronomical unit (au) is about Earth's average distance from the Sun, and the International Astronomical Union defines it as exactly 149,597,870,700 meters. Neptune's average distance is about 30 au.

Every planet's orbit is an ellipse, a slightly stretched circle. Neptune's closest point to the Sun, called perihelion, is 4,471 million kilometers away, and its farthest, called aphelion, is 4,559 million kilometers away. NASA gives the average distance as midway between the two, 4,515 million kilometers. The difference between closest and farthest, about 88 million kilometers, is less than 2% of the whole distance.

The same NASA fact sheet also lists average orbital values for the year 2000, which give 30.07 au, or 4,498 million kilometers. Both figures round to about 4.5 billion kilometers, the distance NASA quotes for Neptune.

Size comparisons

• Sunlight takes about 4 hours to reach Neptune. It reaches Earth in about 8 minutes 19 seconds.
• The distance is about 12,000 times the distance from Earth to the Moon, 384,400 kilometers.
• If the red supergiant VY Canis Majoris, about 2 billion kilometers across, took the Sun's place, its surface would reach only about a fifth of the way to Neptune.
• If the Sun were shrunk to the size of a basketball, Earth would be a 2-millimeter bead 26 meters away. Neptune would be a bead less than 1 centimeter across, about 780 meters (half a mile) away, the length of seven American football fields.

A long, slow orbit

Neptune takes about 165 Earth years to go once around the Sun. It was discovered in 1846, and in 2011 it completed its first full orbit since then. Neptune's axis is tilted, so it has seasons, and each one lasts more than 40 years. Sunlight on Earth is roughly 900 times as bright as sunlight on Neptune.

Sometimes Neptune is even farther from the Sun than the dwarf planet Pluto. Pluto's stretched orbit brings it inside Neptune's for 20 years out of every 248, most recently from 1979 to 1999. The two can never collide. Pluto goes around the Sun twice for every three orbits of Neptune, and this repeating pattern keeps them apart.

Reaching Neptune

As of 2026, only one spacecraft has visited Neptune. NASA's Voyager 2 was launched on August 20, 1977, and flew past Jupiter, Saturn and Uranus on the way. On August 25, 1989, it passed about 4,800 kilometers (2,980 miles) above Neptune's cloud tops, at the end of a 7-billion-kilometer journey. The trip took 12 years.

Sources

• Neptune Fact Sheet. NASA, 2024.
• Planetary Fact Sheet Notes. NASA, 2021.
• Neptune: Facts. NASA Science, 2025.
• Voyager 2: First To Visit All Four Giants. NASA Science, 2026.
• Measuring the Universe. International Astronomical Union.
• Speed of light in vacuum. NIST CODATA, 2022.
• Moon Fact Sheet. NASA, 2024.
• Sun Fact Sheet. NASA, 2024.
• Earth Fact Sheet. NASA, 2024.
• Fundamental properties and atmospheric structure of the red supergiant VY CMa based on VLTI/AMBER spectro-interferometry. Wittkowski et al., Astronomy & Astrophysics, 2012.
• Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.
• 2026 NFL Rulebook. National Football League, 2026.