Solar System Phenomena — Neptune in 2023

The path of Neptune against the background stars in 2023

The chart shows the path of Neptune across the background stars over the course of the year. Stars to magnitude +10.5 are shown. The white circles represent the planet on the first day of the month and are scaled according to apparent magnitude. The faint paths before the first circle and after the last circle represent the planet's positions in December of last year and January of next. In general, the planet moves from right to left except when it's in retrograde and proceding in the opposite direction.

The lower chart shows how the appearance of Neptune changes over the year. Below each image is listed the date, the apparent magnitude, the apparent diameter of the disk (in arc-seconds) and the geocentric distance (in au). Because the relative distance of Neptune does not greatly vary throughout the year, neither does its appearance through a telescope.

Neptune is the most distant planet in the solar system from the Sun and the smallest of the four gas giants. Because of its great distance, it is not visible to the naked eye so a small telescope is always necessary to observe it. Neptune begins the year as an evening sky object in the constellation of Aquarius. It moves into Pisces in March, only to briefly re-enter Aquarius in November whilst in retrograde; it ends the year back in Pisces. At conjunction in mid-March, the blue ice giant reappears in the morning sky afterwards and gradually distances itself from the Sun The dim planet passes close by the fifth-magnitude star 20 Piscium just a week before opposition in September when it is visible all night. Neptune is also occulted by the Moon three times, twice in September and once in December.

1maximum declination south: −4.05°
252.7° north of the Moon
15planetary conjunction: 0.01° south of Venus
212.5° north of the Moon
16planetary conjunction: 0.4° south of Mercury
212.4° north of the Moon
172.3° north of the Moon
152.2° north of the Moon
112.0° north of the Moon
19west quadrature
27maximum declination north: −2.18°
30stationary in ecliptic longitude: direct → retrograde
1stationary in right ascension: direct → retrograde
81.7° north of the Moon
41.5° north of the Moon
1lunar occultation: 1.4° north of the Moon (visible from Antarctica)
120.1° north of the fifth-magnitude star 20 Piscium
19opposition: magnitude +7.8, apparent diameter 2.53 arc-seconds
28lunar occultation: 1.4° north of the Moon (visible from Antarctica)
261.5° north of the Moon
221.5° north of the Moon
6stationary in ecliptic longitude: retrograde → direct
7stationary in right ascension: retrograde → direct
17east quadrature
19lunar occultation: 1.3° north of the Moon (visible from Antarctica)


The dates, times and circumstances of all planetary and lunar phenomena were calculated from the JPL DE406 solar system ephemeris using the same rigorous methods that are employed in the compilation of publications such as The Astronomical Almanac.