© NASA/Cassini

Saturn enters retrograde motion

Dominic Ford, Editor
From the Outer Planets feed

Objects: Saturn
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Saturn will enter retrograde motion, halting its usual eastward movement through the constellations, and turning to move westwards instead. This reversal of direction is a phenomenon that all the solar system's outer planets periodically undergo, a few months before they reach 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.

2021 apparition of Saturn

23 May 2021 – Saturn enters retrograde motion
01 Aug 2021 – Saturn at opposition
10 Oct 2021 – Saturn ends retrograde motion

Observing Saturn

Saturn enters retrograde motion as its 2021 apparition gets underway, although it has already been visible for some weeks in the pre-dawn sky.

Its celestial coordinates as it enters retrograde motion will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Saturn 21h03m30s 17°27'S Capricornus 0.4 17.3"

The coordinates above are given in J2000.0.

From Seattle , it will be visible in the dawn sky, rising at 01:26 (PDT) – 3 hours and 56 minutes before the Sun – and reaching an altitude of 21° above the south-eastern horizon before fading from view as dawn breaks around 04:38.

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Over the following weeks, Saturn will reach its highest point in the sky four minutes earlier each night, gradually becoming visible in the evening sky, as well as the pre-dawn sky, as it approaches opposition.

The sky on 23 May 2021
Sunrise
05:22
Sunset
20:50
Twilight ends
23:26
Twilight begins
02:46

12-day old moon
Waxing Gibbous

90%

12 days old

Planets
Rise Culm. Set
Mercury 06:26 14:32 22:38
Venus 06:14 14:11 22:09
Moon 17:26 23:04 04:31
Mars 08:23 16:21 00:20
Jupiter 02:09 07:18 12:28
Saturn 01:26 06:09 10:52
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

20 Jul 2020  –  Saturn at opposition
01 Aug 2021  –  Saturn at opposition
14 Aug 2022  –  Saturn at opposition
27 Aug 2023  –  Saturn at opposition

Image credit

© NASA/Cassini

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