© NASA/Cassini

Saturn ends retrograde motion

Dominic Ford, Editor
From the Outer Planets feed

Objects: Saturn
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Saturn 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.

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.

2172 apparition of Saturn

11 Jul 2172 – Saturn enters retrograde motion
28 Jul 2172 – Equinox on Saturn
19 Sep 2172 – Saturn at opposition
05 Oct 2172 – Saturn ring plane crossing
26 Nov 2172 – Saturn ends retrograde motion

Observing Saturn

Saturn leaves retrograde motion as its 2172 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
Saturn 23h34m10s 5°19'S Aquarius 0.8 18.1"

The coordinates above are given in J2000.0.

From Fairfield , it will be visible in the evening sky, becoming accessible around 17:06 (EST), 36° above your south-eastern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 19:01, 43° above your southern horizon. It will continue to be observable until around 23:39, when it sinks below 11° above your western horizon.

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

The sky on 22 January 2022
Twilight ends
Twilight begins

20-day old moon
Waning Gibbous


20 days old

Rise Culm. Set
Mercury 07:02 12:07 17:11
Venus 05:29 10:33 15:37
Moon 20:41 03:25 09:57
Mars 05:05 09:38 14:11
Jupiter 08:47 14:12 19:37
Saturn 07:52 12:51 17:51
All times shown in EST.


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

05 Oct 2172  –  Saturn ring plane crossing
09 Jan 2173  –  Saturn ring plane crossing
03 Oct 2173  –  Saturn at opposition
16 Oct 2174  –  Saturn at opposition

Image credit

© NASA/Cassini






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