All of the planets, comets, and asteroids in the solar system orbit the Sun. The average distance between the Earth and the Sun is 92,955,807 miles (149,597,870 km). Most people just round it up to 93 million miles. This distance is called an astronomical unit or AU and is used to measure and compare other distances in space.
Key Takeaways: How Far Is the Sun From Earth?
- The average distance from Earth to the Sun is ~93 million miles (150 million km), called an astronomical unit (AU).
- Earth’s distance from the Sun varies throughout the year due to its elliptical orbit.
- The Sun is closest to Earth (perihelion) in January and farthest (aphelion) in July.
- Modern measurements use spacecraft signals and radar; early methods relied on geometry and parallax.
- The AU is now defined as exactly 149,597,870,700 meters.
Closest and Farthest Distance to the Sun
Because the Earth’s orbit is elliptical or oval, sometimes the Earth is closer than 1 AU to the Sun and sometimes it is further away. The closest approach to the Sun is called perihelion. This occurs in early January, when the Earth is only about 91 million miles (146 million kilometers) away from the Sun. The Earth is farthest from the Sun at aphelion. Aphelion happens in early July when the Earth is approximately 94.5 million miles (152 million kilometers) from the Sun. The change in distance is fairly dramatic. On NASA’s Earth overview site, the distance updates in real-time. The Earth moves a mile closer or further from the Sun about every four seconds!
Impact of Distance to the Sun on Seasons
It’s a common misconception that Earth’s changing distance from the Sun causes the seasons. In reality, seasons result from Earth’s axial tilt, not its distance from the Sun.
Earth is tilted at about 23.5 degrees relative to its orbital plane. This tilt means that as Earth orbits the Sun, different hemispheres receive varying amounts of sunlight during the year:
- Summer occurs in a hemisphere when it’s tilted toward the Sun, receiving more direct sunlight.
- Winter occurs when the same hemisphere is tilted away from the Sun, receiving less direct sunlight.
However, Earth’s elliptical orbit does play a small role. During perihelion (early January), Earth is closest to the Sun, and during aphelion (early July), it’s farthest away. This means the Southern Hemisphere’s summer (which coincides with perihelion) is slightly warmer than the Northern Hemisphere’s summer — but the effect is minor compared to the influence of axial tilt.
Another interesting effect: because Earth moves faster in its orbit when it’s closer to the Sun (Kepler’s second law), the Northern Hemisphere’s summer lasts a few days longer than the Southern Hemisphere’s summer.
Measuring the Distance
Obviously, you can’t just whip out a tape measure to find the distance between the Earth and Sun. It must be calculated.
Aristarchus
The first person to find the distance to the Sun was the Greek astronomer Aristarchus around 250 B.C. Aristarchus used geometry to find the distance. He figured that the Earth, Sun, and Moon form a right angle when the Moon is half full. He measured the sizes of the Sun and the Moon and the angles between them and found that the Sun is 19 times further from Earth than the Moon. Since the Sun and the Moon are about the same size in the sky (which is why we get total solar eclipses), Aristarchus thought the Sun was also 19 times larger than the Moon. His measurements contained a lot of error, mainly because he couldn’t precisely determine the centers of the Sun or Moon or find the exact instant the Moon was half full. While his math was off, Aristarchus did conclude the Earth orbits around the Sun a whole 1700 years before Copernicus proposed the heliocentric theory.
Christiaan Huygens
Christiaan Huygens calculated the distance between the Earth and Sun in 1653. His method was similar to that used by Aristarchus, but he used the angles formed between Venus, Earth, and the Sun. When Venus was half full, the planet, Earth, and the Sun form a right angle. Huygens estimated the size of Venus to measure the distance. His guess wasn’t too far off, so his number was close to the true distance to the Sun.
Giovanni Cassini
Giovanni Cassini used parallax to find the distance to the Sun and to Mars in 1672. He measured the position of Mars against background stars in Paris, while a colleague did the same in French Guiana. Cassini triangulated these measurements with the known distance between Paris and French Guiana. From the distance to Mars, Cassini calculated the distance to the Sun.
Modern Measurements
Cassini’s measurement was close to the true distance, but scientists use a more direct approach today. A signal sent from a spacecraft travels at the speed of light, so knowing the time between sending and receiving the signal, the distance can be calculated. Another option is bouncing a radar signal off a remote object. We know how long it takes between sending the signal and receiving the echo, so distance can be determined.
Defining the Distance
Although the actual distance between Earth and the Sun changes throughout the year due to Earth’s elliptical orbit, astronomers needed a consistent unit of measurement for calculations and comparisons. For centuries, the astronomical unit (AU) was defined based on observations and estimates, but it remained tied to the laws of celestial mechanics and gravitational constants that introduced small variations.
To solve this problem, in 2012, the International Astronomical Union (IAU) officially redefined the astronomical unit as a fixed number based on the speed of light. The new definition sets 1 AU as exactly:
149,597,870,700 meters (or about 92.956 million miles)
This definition simplifies astronomical calculations and ensures consistent values across scientific disciplines. It’s based on the distance that light travels in a vacuum in about 499.004 seconds (or 8 minutes and 20 seconds), the average light travel time from the Sun to Earth. By basing the AU on a universal constant — the speed of light — astronomers use it with greater precision in models of planetary motion, spacecraft navigation, and communication.
FAQ: How Far Is the Sun?
Q: Is the Earth always 93 million miles from the Sun?
A: No. That’s just the average distance. Earth’s distance from the Sun ranges from about 91 million miles (146 million km) at perihelion to about 94.5 million miles (152 million km) at aphelion.
Q: How long does it take light to travel from the Sun to Earth?
A: Light takes approximately 8 minutes and 20 seconds to travel the 1 AU distance from the Sun to Earth.
Q: Does Earth’s distance from the Sun cause the seasons?
A: No. Earth’s axial tilt causes seasons, not how far Earth is from the Sun. The hemisphere tilted toward the Sun experiences summer.
Q: Has the distance from Earth to the Sun changed over time?
A: On short timescales, the distance varies due to the shape of Earth’s orbit. Over millions of years, the shape of Earth’s orbit and the distance slowly changes due to gravitational interactions with other planets.
Q: Is the distance between the Earth and the Sun measured from their surfaces or centers?
A: The standard distance is measured from the center of the Earth to the center of the Sun. This is how astronomers define distances between celestial bodies, since their shapes and surface features vary. Measuring center-to-center ensures consistency and accuracy in calculations like orbital dynamics and gravitational interactions.
Q: Why is the astronomical unit important?
A: The AU provides a standardized unit for measuring and comparing distances across the solar system. It simplifies calculations and helps scientists communicate astronomical distances consistently.
References
- Brumfiel, Geoff (2012). “The astronomical unit gets fixed: Earth–Sun distance changes from slippery equation to single number”. Nature. doi:10.1038/nature.2012.11416
- Halley, E. (1716). “A new method of determining the parallax of the Sun, or his distance from the Earth”. Philosophical Transactions of the Royal Society. 29 (338–350): 454–64. doi:10.1098/rstl.1714.0056
- International Bureau of Weights and Measures (2024). The International System of Units (9th ed.). ISBN 978-92-822-2272-0.
- Luque, B.; Ballesteros, F.J. (2019). “To the Sun and beyond”. Nature Physics. 15 (12): 1302. doi:10.1038/s41567-019-0685-3