How long year

Other stars in the galaxy, their galactic year is different," Hawkins said. The galaxy is about , light-years across, and the Earth is about 28, light-years from its center. For stars that orbit close to the black hole — the center of the "city" — a galactic year is relatively short.

Out in the "suburbs," where our solar system lies, "the galactic years are a little longer," he said. Similar rules control variability in the length of a year between planets. For instance, Mercury, the innermost planet in our solar system, makes a complete orbit around the sun in about 88 Earth days.

Uranus, the seventh planet from the sun, orbits the sun every 84 years, by Earth standards. And the distant dwarf planet Pluto takes Earth years to finish one orbital cycle. While the physics of planetary orbits are similar to the mechanisms that shape the orbit of our solar system around the Milky Way, it's worth asking how astronomers have figured out the span of a galactic year. Hawkins says that it's actually pretty basic science that became clear in the early days of modern astronomy.

Editor's Note : This story was updated on Aug. Grant Currin is a freelance science journalist based in Nashville, Tennessee. Live Science. Grant Currin. An Earth year is actually about 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. 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.

Scientists who study Mars also need to keep a Martian calendar to schedule what rovers and landers will be doing and when. What are equinoxes and solstices? Although a common year has days in today's Gregorian calendar , we add a leap day nearly every four years to stay in sync with the tropical year. Without the correct amount of leap years , our calendar would quickly become out of sync.

This happened to the Julian calendar , which had too many leap years. Eventually, it was replaced with the Gregorian calendar.