© 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.

1999–2000 apparition of Saturn

29 Aug 1999 – Saturn enters retrograde motion
06 Nov 1999 – Saturn at opposition
11 Jan 2000 – Saturn ends retrograde motion

Observing Saturn

Saturn leaves retrograde motion as its 1999–2000 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 02h34m30s 12°37'N Aries -0.0 18.9"

The coordinates above are given in J2000.0.

From Fairfield , it will be visible in the evening sky, becoming accessible around 17:17 (EST), 53° above your south-eastern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 19:07, 61° above your southern horizon. It will continue to be observable until around 00:58, when it sinks below 9° 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 07 December 2021
Sunrise
07:04
Sunset
16:24
Twilight ends
18:04
Twilight begins
05:24

3-day old moon
Waxing Crescent

23%

3 days old

Planets
Rise Culm. Set
Mercury 07:34 12:03 16:33
Venus 09:59 14:33 19:07
Moon 10:41 15:22 20:05
Mars 05:28 10:21 15:14
Jupiter 11:29 16:43 21:56
Saturn 10:42 15:37 20:31
All times shown in EST.

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

06 Nov 1999  –  Saturn at opposition
19 Nov 2000  –  Saturn at opposition
03 Dec 2001  –  Saturn at opposition
17 Dec 2002  –  Saturn at opposition

Image credit

© NASA/Cassini

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41.14°N
73.26°W
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