Solar System Phenomena — Neptune in 2018

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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 but is soon lost in evening twilight as it approaches conjunction in March. It reappears in the morning sky and draws away from the Sun until it reaches opposition in September. It is visible in the evening sky for the rest of the year. The Moon makes a series of close passes to the planet throughout the year and the blue ice giant appears very close to Mars in early December.

01 Januarymaximum declination south
20 January1.6° north of the Moon
04 Marchconjunction
12 April1.9° north of the Moon
10 May2.0° north of the Moon
06 June2.0° north of the Moon
07 Junewest quadrature
16 Junemaximum declination north
19 Junestationary point: direct → retrograde
27 August2.0° north of the Moon
07 Septemberopposition: magnitude +7.8, apparent diameter 2.5 arc-seconds
23 September2.0° north of the Moon
25 Novemberstationary point: retrograde → direct
05 Decembereast quadrature
07 Decemberplanetary conjunction: 0.4° south of Mars


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.