Neptune is the more massive of the two ice giant planets, the fourth-largest planet in our Solar System, and the eighth—and most distant—from the Sun.
Neptune is technically visible to the naked eye under perfect conditions. But in practice, it’s too dim. I always need a telescope or binoculars to see it.
Amazingly, the planet was first observed by Galileo in 1612 and 1613. He even noticed that it moved across the sky, but he could not resolve its disk with his weak telescope and dismissed its motion as an observational error.
Due to its distance from the Sun, only one spacecraft has visited Neptune—NASA’s Voyager 2, which flew by in 1989. No missions to Neptune are currently planned by any country or space agency, as Uranus is quicker and easier to get to and remains similarly unexplored by spacecraft.
Neptune isn’t observed often by most astronomers, though I believe it’s worth a look and fairly easy to locate.
When to Observe Neptune
Neptune is currently in the constellation of Pisces, the Fish, and will remain there until 2027 thanks to its 187-year orbital period around the Sun.
Neptune reaches opposition in late September for the next few years, and for Northern Hemisphere observers like myself, it gets very high in the sky.
Neptune doesn’t change significantly in angular size, distance, or brightness due to its distance from the Sun. It varies in distance from Earth by just two astronomical units, whereas it is 30 astronomical units from the Sun on average (1 AU average is the distance from the Earth to the Sun). Neptune hovers around magnitude 8, theoretically visible to experienced astronomers with the naked eye under ideal conditions, but in practice relegated to binoculars, finder scopes, and telescopes due to its dimness – and more often than not, also due to light pollution.
Finding Neptune
Neptune is in the constellation Pisces right now, and its bluish color is easy to confuse with that of bright stars close by. Neptune’s color is a little more of a deep blue than any star’s, but you might be hard pressed to tell the difference. In a telescope, I need at least 80x magnification to see that Neptune is “fuzzy” compared to nearby stars.
It’ll show up in a magnifying finder or binoculars easily, but consulting a very accurate paper star chart or an app with real-time location information on where Neptune is in the sky is key to success.
Observing Neptune through a Telescope
Neptune’s angular size is tiny—reaching no more than 2.5 arc seconds in diameter. That’s not much larger than Jupiter’s moons in apparent diameter. In fact, my smallest telescopes (3” or less) actually lack the resolving power to perceive Neptune’s disk at all.
Bad atmospheric conditions can also blur Neptune, making it unrecognizable as obviously “fatter” than surrounding stars. On a good night with a large telescope, however, Neptune’s dark blue disk can be resolved.
Three distinct, faint rings encircle Neptune. Unlike the prominent and highly visible rings of Saturn, Neptune’s rings are far too faint and made up of dust particles mixed with small chunks of ice. None are visible with an amateur telescope; even the gigantic James Webb Space Telescope shows them as thin slivers.
As of 2023, some observers have noted a small whitish spot in the planet’s atmosphere, which may match up with one of the whitish spots seen in the September 2022 JWST photo of the planet, which is shown below. It will require at least a 12” telescope and a magnification of 250x or greater to spot this and any other atmospheric details. I haven’t managed it myself yet.
- Neptune’s Moons
Neptune is accompanied by a system of 14 known moons. The largest and most notable is Triton, which is the only Neptunian moon massive enough to be spherical. Neptune’s moon Triton is arguably easier to see than the disk of Neptune itself.
At magnitude 13.5, Triton is brighter than Pluto or any of the moons of Uranus. I can pick it up with even a 6-8” telescopes, even under fairly light-polluted skies. Triton is about the size of Pluto but extraordinarily reflective as seen in the above JWST photo, making it quite bright despite its distance from the Sun. Thanks to Neptune’s relatively low brightness, you’ll have no issues with Triton hiding in its glare, unlike the similarly dim moons of Saturn and Uranus.
Triton is unique in the solar system because it orbits Neptune in the opposite direction to the planet’s rotation, a retrograde orbit that suggests it was likely a dwarf planet captured by Neptune’s gravity and was not originally part of the Neptune’s system. Triton’s capture is likely the reason Neptune has no other large moons; any others would have been ejected out into orbit around the Sun or flung into Neptune during the encounter.
The next largest, Proteus, is ⅙ the size of Triton and probably accumulated debris orbiting Neptune after Triton arrived.
The third largest moon of Neptune – and the most easily seen besides Triton – is Nereid, which is slightly smaller than Proteus and takes 1 year to orbit around Neptune. I need a 25” or larger telescope to see it at all on account of its apparent magnitude hovering around 19. Proteus is simply out of reach of our amateur telescopes, as are all of the other smaller and dimmer Neptunian moons.
Conjunctions and Occultations of Neptune
Neptune frequently appears in conjunction with other planets in the night sky owing to its proximity to the ecliptic plane. These events can provide thrilling opportunities for stargazers and astronomers to catch a glimpse of this distant, icy giant. Occasionally, these are close conjunctions where both objects will fit in the same telescopic field of view. For instance, on April 24th, 2027, it appears near Venus less than quarter a degree away—less than half the apparent diameter of the moon—low in the pre-dawn sky. On April 13, 2026, it will be very close to Mars.
The nimble inner planets pass by Neptune rather quickly, but throughout mid-2025 and on February 15, 2026, the ice giant will be around a degree from Saturn, and neither will appear to move much owing to their distance and slower orbital velocities.
Neptune can also be occulted, or blocked, by the Moon, though for many people only a close conjunction between the two bodies will be observed. No occula
Neptune enters a conjunction with the Sun every 367 days between oppositions, when it is unobservable and at its furthest from us. This period, known as the superior conjunction, lasts a few weeks. During this time, Neptune is located on the far side of the Sun from the Earth, making it lost in the Sun’s glare and impossible to observe.
Color Filters for Observing Neptune
Filters are not of any value on Neptune and may dim the view too much.