Way Out There and Out of Sight
Can you track down Neptune?
Thursday and Friday offer the best chance to track down the only planet never visible to the unaided eye: Neptune, the most distant planet in the solar system since Pluto’s demotion to planetoid status several years ago.
Neptune comes closest to earth on the 23rd, while the 24th marks the planet’s point of opposition, when it is opposite the sun, as seen from our skies, with earth smack-dab in the middle. That night, Neptune rises in the east at sunset, peaks near the celestial zenith around midnight and sets in the west at sunrise.
Even at its closest, the fourth-largest planet, is way out there, more than 2.8 billion miles, or 29 times as far from us as we are from the sun. That’s a long way for sunlight to travel before reflecting off its surface and back to our eyes. At magnitude +7.8, Neptune is several times dimmer than the borderline naked-eye stars of magnitude +5. Look for it amid the stars of Aquarius, one of the dimmest constellations in the sky. With binoculars, Neptune appears as a faint, star-like point of light, while a modest telescope may show the planet’s blue-green disc.
Neptune wasn’t discovered until 1846, although Galileo observed it near Jupiter in 1613, mistaking it for a star. For almost 150 years no one knew much about Neptune other than its color and its two moons. Then in 1989 Voyager II flew by, the only spacecraft to do so, measuring the planet, its rotation period and identifying eight moons. Since then, the Hubble Space Telescope has revealed 13 moons — albeit some are no more than chunks of space rock 100 miles across — and six faint rings.
Like all the outer planets, Neptune is a gas giant, its atmosphere made up of hydrogen, helium and methane swirling around a small solid core. It is covered by clouds of frozen methane with winds whipping upward of 700 miles an hour, the fastest in the solar system.