© NASA/Voyager 2

Neptune ends retrograde motion

Dominic Ford, Editor
From the Outer Planets feed

Objects: Neptune
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Neptune will reach the end of its retrograde motion, ending its westward movement through the constellations and returning to more usual eastward motion instead. This reversal of direction is a phenomenon that all the solar system's outer planets periodically undergo, a few months after they pass opposition.

This motion was known to ancient observers, and it troubled them as they could not reconcile it with models in which the planets moved in uniform circular orbits around the Earth, as they believed.

The retrograde motion is caused by the Earth's own motion around the Sun. As the Earth circles the Sun, our perspective changes, and this causes the apparent positions of objects to move from side-to-side in the sky with a one-year period. This nodding motion is super-imposed on the planet's long-term eastward motion through the constellations.

The diagram below illustrates this. The grey dashed arrow shows the Earth's sight-line to the planet, and the diagram on the right shows the planet's apparently movement across the sky as seen from the Earth:


The retrograde motion of a planet in the outer solar system. Not drawn to scale.

2033 apparition of Neptune

23 Jul 2033 – Neptune enters retrograde motion
11 Oct 2033 – Neptune at opposition
27 Dec 2033 – Neptune ends retrograde motion

Observing Neptune

Neptune leaves retrograde motion as its 2033 apparition comes to an end, although it will remain visible for some weeks in the dusk sky.

Its celestial coordinates as it leaves retrograde motion will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Neptune 01h04m30s 5°06'N Pisces 7.9 2.3"

The coordinates above are given in J2000.0.

From San Diego , it will be visible in the evening sky, becoming accessible around 17:52 (PDT), 61° above your southern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 18:25, 62° above your southern horizon. It will continue to be observable until around 22:53, when it sinks below 21° above your 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.

Over the following weeks, Neptune will reach its highest point in the sky four minutes earlier each night, gradually disappearing into evening twilight.

The sky on 27 Dec 2033

The sky on 27 December 2033
Sunrise
06:46
Sunset
16:49
Twilight ends
18:17
Twilight begins
05:18

6-day old moon
Waxing Crescent

47%

6 days old

Planets
Rise Culm. Set
Mercury 07:05 11:58 16:52
Venus 06:42 11:40 16:37
Moon 10:49 16:55 23:07
Mars 10:49 16:39 22:28
Jupiter 10:11 15:44 21:18
Saturn 17:40 00:43 07:45
All times shown in PST.

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

27 Dec 2033  –  Neptune ends retrograde motion
25 Jul 2034  –  Neptune enters retrograde motion
13 Oct 2034  –  Neptune at opposition
30 Dec 2034  –  Neptune ends retrograde motion

Image credit

© NASA/Voyager 2

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32.72°N
117.16°W
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