© NASA/Voyager 2

Neptune at opposition

Tue, 05 Sep 2017 at01:13 EDT(19 days away)
05:13 UTC

Dominic Ford, Editor
From the Outer Planets feed

Please wait
Loading 0/4
Click and drag to rotate
Mouse wheel to zoom in/out
Touch with mouse to dismiss
The sky at

Neptune will be well placed for observation, in the constellation Aquarius. It will be visible for much of the night, reaching its highest point in the sky at around midnight local time.

From Ashburn (click to change), it will be visible between 21:50 and 04:24. It will become accessible at around 21:50, when it rises 24° above your south-eastern horizon, and then reach its highest point in the sky at 01:09, 43° above your southern horizon. It will become inaccessible at around 04:24 when it sinks to 25° above your south-western horizon.

Neptune opposite the Sun

This optimal positioning occurs when Neptune is almost directly opposite the Sun in the sky. Since the Sun reaches its greatest distance below the horizon at midnight, the point opposite to it is highest in the sky at the same time.

At around the same time that Neptune passes opposition, it also makes its closest approach to the Earth – termed its perigee – making it appear at its brightest and largest.

This happens because when Neptune lies opposite the Sun in the sky, the solar system is lined up so that Neptune, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as Neptune.

In practice, however, Neptune orbits much further out in the solar system than the Earth – at an average distance from the Sun of 30.27 times that of the Earth, and so its angular size does not vary much as it cycles between opposition and solar conjunction.

On this occasion, Neptune will lie at a distance of 28.94 AU, and its disk will measure 2.4 arcsec in diameter, shining at magnitude 7.8. Even at its closest approach to the Earth, however, it is not possible to distinguish it as more than a star-like point of light without the aid of a telescope.

Neptune in coming weeks

Over the weeks following its opposition, Neptune will reach its highest point in the sky four minutes earlier each night, gradually receding from the pre-dawn morning sky while remaining visible in the evening sky for a few months.

A chart of the path of Neptune across the sky in 2017 can be found here, and a chart of its rising and setting times here.

The position of Neptune at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Neptune 22h57m10s -07°41' Aquarius 7.8 2.4"

The coordinates above are given in J2000.0.

The sky on 05 September 2017
Sunrise 06:41
Sunset 19:33
Twilight ends
Twilight begins

15-day old moon
Age of Moon
15 days

All times shown in EDT.
Rise Culm. Set
Mercury 05:31 12:09 18:47
Venus 04:07 11:09 18:11
Moon 19:31 00:17 05:39
Mars 05:35 12:19 19:04
Jupiter 09:57 15:35 21:12
Saturn 14:43 19:30 00:20


The circumstances of this event were computed using the DE405 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).

This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.

Related news

05 Sep 2017, 01:13 EDTNeptune at opposition
04 Mar 2018, 08:56 ESTNeptune at solar conjunction
07 Sep 2018, 14:12 EDTNeptune at opposition
07 Mar 2019, 20:02 ESTNeptune at solar conjunction

Image credit

© NASA/Voyager 2




Color scheme