Happy New Year, Mars!

NASA officials wished Mars a happy new year on Twitter Friday (May 5), using the milestone as an opportunity to review exactly how the Red Planet's years work and how they differ from Earth's.

The space agency's Jet Propulsion Laboratory (JPL) in Pasadena, California, tweeted an image of a party-hat-wearing Curiosity rover watching fireworks explode in the Martian sky. An hour later, JPL tweeted a link to a new video explainer about the Red Planet year.

Mars is farther from the sun than Earth is and therefore takes considerably longer to complete one orbit: A Red Planet year lasts about 687 Earth days, compared to the 365-day year we're used to.

Scientists decided years ago, somewhat arbitrarily, that Mars years begin on the spring equinox in the planet's northern hemisphere. And now spring has sprung.

Here on Earth, we're used to seasons of equal length. But that's not the case on Mars, because the Red Planet's more eccentric path around the sun leads to varying orbital speeds. On Mars, spring and summer last 194 and 178 Earth days, respectively, whereas winter lasts 154 days and fall just 142 days, NASA officials said.  

The car-size Curiosity rover landed on Mars in August 2012, kicking off a surface mission that was initially pegged to last a single Martian year. But Curiosity continues to roll along and is now exploring the foothills of Mount Sharp, which rises 3.4 miles (5.5 kilometers) into the Red Planet's sky.  

Residents of the city of Mars, Pennsylvania, celebrate the Martian New Year with a two-day science, technology, engineering and math festival, NASA officials said in a statement. The current festival lasts until Saturday (May 6).

The next opportunity for Pennsylvania Martians to celebrate in this way won't come until March 23, 2019. After that, Mars New Year revelers will have to wait until Feb. 7, 2021.

Email Sarah Lewin at slewin@space.com or follow her @SarahExplains. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.