NASA's Goddard Space Flight Center

Artist's rendering of the Lunar Reconnaissance Orbiter spacecraft.

By Mike Wall, Space.com

A sharp-eyed NASA spacecraft celebrates four years of circling the moon this Sunday (June 23), just in time for the "supermoon."

Since arriving in orbit on June 23, 2009, NASA's Lunar Reconnaissance Orbiter (LRO) has given scientists a much deeper understanding of Earth's nearest neighbor, mission team members said.

"Not only has LRO delivered all the information that is needed for future human and robotic explorers, but it has also revealed that the moon is a more complex and dynamic world than we had ever expected," Rich Vondrak, LRO deputy project scientist at NASAs Goddard Space Flight Center in Greenbelt, Md., said in a statement. [ Celebrating LRO's Fourth Anniversary (Video) ]

Appropriately enough, LRO marks its fourth anniversary on the same day that the biggest and brightest full moon of 2013 the so-called " supermoon " lights up Earth's night sky.

The moon's path around Earth is slightly elliptical; distances between the two bodies vary from 225,622 miles (363,104 kilometers) at the closest lunar approach, known as perigee, to 252,088 miles (405,696 km) at apogee. Supermoons result when the full moon and perigee coincide.

The $504 million LRO spacecraft is about the size of a Mini Cooper car and sports seven different science instruments. It zips around the moon at an altitude of 31 miles (50 km).

LRO launched on June 18, 2009, along with a piggyback probe called the Lunar Crater Observation and Sensing Satellite. In October 2009, LRO watched from orbit as LCROSS and the duo's Centaur booster rocket slammed deliberately into a shadowed crater at the moon's south pole, blasting out surprisingly large amounts of water ice.

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NASA moon probe celebrates 4th birthday on Supermoon Sunday