Sept. 23 notes Neptune at opposition and the anniversary of the planet’s discovery. Since its initial detection, the ice giant has completed little more than one Neptunian year, taking about 164 Earth-years to orbit the sun. Mathematics drove the discovery of this faraway planet, a planet that is sometimes farther from the sun than the popular dwarf planet, Pluto. Pluto’s orbit is extremely oval-shaped. For twenty years, its path dips inside the orbit of Neptune. The most recent occurrence was from 1979 to 1999. But it was the study of Uranus and its gravitational fluctuations that intrigued astronomers to seek another planet. Based on calculations by French mathematician Urbain Le Verrier and English mathematician John Couch Adams, astronomer Johann Gottfried Galle located the mysterious planet X, only one-degree off from the proposed estimates.

So distant from the sun, at high noon Neptune would appear to be illuminated only in dim twilight. Its icy gas composition, mostly hydrogen, ammonia, and methane, extends deeply into the planet, eventually merging into a heavy, small, rocky core. It is the densest of the planets and the windiest. Powerful winds whip up speeds three times stronger than Jupiter’s storms and nine times more powerful than those on Earth.

Visited once by the spacecraft Voyager 2, more recent exciting images and information have been revealed by the James Webb Space Telescope.