A year on Earth is approximately 365 days. Why is that considered a year? Well, 365 days is about how long it takes for Earth to orbit all the way around the Sun one time.
A year is measured by how long it takes a planet to orbit around its star. Earth orbits around the Sun in approximately 365 days. Credit: NASA/Terry Virts
It’s not exactly this simple though. An Earth year is actually about 365 days, plus approximately 6 hours. Read more about that here.
All of the other planets in our solar system also orbit the Sun. So, how long is a year on those planets? Well, it depends on where they are orbiting!
Planets that orbit closer to the Sun than Earth have shorter years than Earth. Planets that orbit farther from the Sun than Earth have longer years than Earth.
A planet orbiting close to its star has a shorter year than a planet orbiting farther from its star. Credit: NASA/JPL-Caltech
This happens for two main reasons.
- If a planet is close to the Sun, the distance it orbits around the Sun is fairly short. This distance is called an orbital path.
- The closer a planet travels to the Sun, the more the Sun’s gravity can pull on the planet. The stronger the pull of the Sun’s gravity, the faster the planet orbits.
Check out how long a year is on each planet below!
Year: 88 Earth DaysDistance from Sun: ~35 million miles
(58 million km)
Year: 225 Earth DaysDistance from Sun: ~67 million miles
(108 million km)
Year: 365 Earth DaysDistance from Sun: ~93 million miles
(150 million km)
Year: 687 Earth DaysDistance from Sun: ~142 million miles
(228 million km)
Year: 4,333 Earth DaysDistance from Sun: ~484 million miles
(778 million km)
Year: 10,759 Earth DaysDistance from Sun: ~887 million miles
(1.43 billion km)
Year: 30,687 Earth DaysDistance from Sun: ~1.78 billion miles
(2.87 billion km)
Year: 60,190 Earth DaysDistance from Sun: ~2.80 billion miles
(4.5 billion km)
Why does NASA care about years on other planets?
NASA needs to know how other planets orbit the Sun because it helps us travel to those planets! For example, if we want a spacecraft to safely travel to another planet, we have to make sure we know where that planet is in its orbit. And we also have to make sure we don’t run into any other orbiting objects — like planets or asteroids — along the way.
Scientists who study Mars also need to keep a Martian calendar to schedule what rovers and landers will be doing and when.
Mars and Earth are always moving. So, if we want to land a robotic explorer on Mars, we have to understand how Earth and Mars orbit the Sun. Watch this video to learn more about the Martian year. Credit: NASA/JPL-Caltech
*Length of year on other planets calculated from data on the NASA Solar System Dynamics website.
article last updated July 13, 2020
It is the earth’s relationship to the sun, and the amount of light it receives, that is responsible for the seasons and biodiversity. The amount of sun a region receives depends on the tilt of the earth’s axis and not its distance from the sun. The northern hemisphere experiences summer during the months of June, July, and August because it is tilted toward the sun and receives the most direct sunlight. Inversely, summer for the southern hemisphere takes place during the months of December, January, and February because that is when it receives the most direct sunlight. Did you know that the earth is approximately 3.2 million miles closer to the sun in January than in June?
Learn more about the relationship between the earth and the sun with these resources.
Subjects
Astronomy, Earth Science, Geography, Geology, Physical Geography
Kepler’s laws show the effects of gravity on orbits. They apply to any object that orbits another: planets orbiting the Sun, moons orbiting a planet, spacecraft orbiting Earth.
The orbit of a planet around the Sun (or of a satellite around a planet) is not a perfect circle. It is an ellipse—a “flattened” circle. The Sun (or the center of the planet) occupies one focus of the ellipse. A focus is one of the two internal points that help determine the shape of an ellipse. The distance from one focus to any point on the ellipse and then back to the second focus is always the same.
Kepler’s Second Law Describes the Way an Object’s Speed Varies along Its Orbit
A planet’s orbital speed changes, depending on how far it is from the Sun. The closer a planet is to the Sun, the stronger the Sun’s gravitational pull on it, and the faster the planet moves. The farther it is from the Sun, the weaker the Sun’s gravitational pull, and the slower it moves in its orbit.
Kepler’s Third Law Compares the Motion of Objects in Orbits of Different Sizes
A planet farther from the Sun not only has a longer path than a closer planet, but it also travels slower, since the Sun’s gravitational pull on it is weaker. Therefore, the larger a planet’s orbit, the longer the planet takes to complete it.