165 years after discovery, Planet Neptune completes first orbit

In no celestial hurry, Neptune has just completed its first orbit around the sun since being discovered 165 years ago by Earthlings.

As Space.com notes, the big blue-green gas bag is the only planet in our solar system to be discovered by mathematics. German astronomer Johann Galle located Neptune the evening of Sept. 23-24, 1846, using earlier calculations by French astronomer Urbain Le Verrier.

To commemorate the "anniversary," the Hubble Space Telescope snapped some pictures June 25-26. NASA compiled a video sequence showing the planet spinning on its tilted axis.

In 1989, the unmanned Voyager 2 spacecraft snapped a relative close-up of the giant, cold ball of hydrogen and helium.

Neptune, which travels an elliptical path, is the most distant "major planet" in our backyard, according to NASA. Its average distance from the sun is 2.8 billion miles, 30 times farther than Earth.