© 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.

2143 apparition of Saturn

18 Jul 2143 – Saturn enters retrograde motion
26 Sep 2143 – Saturn at opposition
02 Dec 2143 – Saturn ends retrograde motion

Observing Saturn

Saturn leaves retrograde motion as its 2143 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 23h54m40s 3°13'S Pisces 0.8 18.2"

The coordinates above are given in J2000.0.

From Ashburn , it will be visible in the evening sky, becoming accessible around 17:27 (EST), 40° above your south-eastern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 19:18, 47° above your southern horizon. It will continue to be observable until around 00:07, 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 21 January 2022
Twilight ends
Twilight begins

19-day old moon
Waning Gibbous


19 days old

Rise Culm. Set
Mercury 07:23 12:33 17:42
Venus 05:47 10:55 16:03
Moon 19:57 02:57 09:48
Mars 05:16 09:55 14:35
Jupiter 09:04 14:32 20:00
Saturn 08:08 13:12 18:16
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

26 Sep 2143  –  Saturn at opposition
08 Oct 2144  –  Saturn at opposition
21 Oct 2145  –  Saturn at opposition
04 Nov 2146  –  Saturn at opposition

Image credit

© NASA/Cassini






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