On August 25, 1989, in its last planetary encounter, Voyager 2 swooped within 4,950 km (3,080 mi) of Neptune's north pole.

Some of the earliest recorded observations ever made through a telescope, Galileo's drawings on 28 December 1612 and 27 January 1613, contain plotted points that match up with what is now known to be the position of Neptune. On both occasions, however, Galileo seems to have mistaken Neptune for a fixed star.

A day on Neptune is 16 hours, 6 minutes and 36 seconds.

The innermost ring of Neptune is called the Galle ring after Johann Gottfried Galle, the first person to see Neptune through a telescope (1846).

Neptune's upper atmosphere is composed of 80% hydrogen, 19% helium, and 1% methane.

Neptune's rings had been observed from Earth many years prior to Voyager 2's visit, but the close inspection revealed that the ring systems were full circle and intact. A total of four rings were counted.

The Lassell ring, also known as the plateau, is the broadest ring in the Neptunian system. It is the namesake of William Lassell, the English astronomer who discovered Neptune's largest moon, Triton.

A 100-pound person who stood, or floated, on the surface of Neptune would weigh about 113 pounds. Although Neptune is much more massive than Earth, it's far less dense, so the acceleration of gravity at its surface is weaker than expected for a planet that is 17 times Earth's mass.

Only about one thousandth of the sunlight received by our planet reaches Neptune, resulting in an average temperature on Neptune of minus 392 degrees Fahrenheit (minus 200 degrees Celsius).

Neptune has 14 known moons, six of which were discovered by Voyager 2 when it whizzed past in 1989.