© NASA/Voyager 2

Neptune at opposition

Dominic Ford, Editor
From the Outer Planets feed

Objects: Neptune
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 reach opposition, when it lies opposite to the Sun in the sky. Lying in the constellation Aquarius, it will be visible for much of the night, reaching its highest point in the sky around midnight local time.

From Seattle, it will be visible between 22:50 and 03:41. It will become accessible around 22:50, when it rises to an altitude of 21° above your south-eastern horizon. It will reach its highest point in the sky at 01:16, 30° above your southern horizon. It will become inaccessible around 03:41 when it sinks below 22° above your south-western horizon.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

2011 apparition of Neptune

02 Jun 2011 – Neptune enters retrograde motion
22 Aug 2011 – Neptune at opposition
09 Nov 2011 – Neptune ends retrograde motion

A close approach to the Earth

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.

This happens because when Neptune lies opposite to the Sun in the sky, the Earth passes between Neptune and the Sun. The solar system is lined up with Neptune and the Earth on the same side of the Sun, as shown by the configuration labelled perigee in the diagram below:


When a planet is at opposition, the solar system is aligned such that the planet lies on the same side of the Sun as the Earth. At this time, the planet makes its perigee, or closest approach to the Earth. Not drawn to scale.

In practice, however, Neptune orbits much further out in the solar system than the Earth – at an average distance from the Sun of 30.07 times that of the Earth, and so its angular size does not vary much as it cycles between opposition and solar conjunction.

Observing Neptune

At opposition, Neptune is visible for much of the night. When it lies opposite to the Sun in the sky, this means that it rises at around the time the Sun sets, and it sets at around the time the Sun rises. It reaches its highest point in the sky at around midnight local time.

But even when it is at its closest point to the Earth, it is not possible to distinguish it as more than a star-like point of light without the aid of a telescope.

A chart of the path of Neptune across the sky in 2011 can be found here, and a chart of its rising and setting times here.

At the moment of opposition, Neptune will lie at a distance of 29.00 AU, and its disk will measure 2.4 arcsec in diameter, shining at magnitude 7.8. Its celestial coordinates at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Neptune 22h06m40s 12°12'S Aquarius 7.8 2.4"

The coordinates above are given in J2000.0.

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.

The sky on 28 September 2021
Sunrise
07:03
Sunset
18:55
Twilight ends
20:39
Twilight begins
05:19

21-day old moon
Waning Gibbous

51%

21 days old

Planets
Rise Culm. Set
Mercury 09:04 14:08 19:13
Venus 11:15 15:47 20:18
Moon 22:19 06:39 15:08
Mars 07:21 13:12 19:03
Jupiter 17:26 22:21 03:16
Saturn 16:43 21:17 01:50
All times shown in PDT.

Source

The circumstances of this event were computed using the DE430 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

22 Aug 2011  –  Neptune at opposition
24 Aug 2012  –  Neptune at opposition
26 Aug 2013  –  Neptune at opposition
29 Aug 2014  –  Neptune at opposition

Image credit

© NASA/Voyager 2

Share

Follow

Seattle

Latitude:
Longitude:
Timezone:

47.61°N
122.33°W
PDT

Color scheme