© 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.

2016 apparition of Saturn

25 Mar 2016 – Saturn enters retrograde motion
03 Jun 2016 – Saturn at opposition
13 Aug 2016 – Saturn ends retrograde motion

Observing Saturn

Saturn leaves retrograde motion as its 2016 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 16h32m30s 20°17'S Ophiuchus 0.2 17.2"

The coordinates above are given in J2000.0.

From Ashburn , it will become visible around 20:39 (EST), 30° above your southern horizon, as dusk fades to darkness. It will then sink towards the horizon, setting at 01:06.

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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 13 August 2016
Sunrise
06:19
Sunset
20:07
Twilight ends
21:51
Twilight begins
04:39

11-day old moon
Waxing Gibbous

78%

11 days old

Planets
Rise Culm. Set
Mercury 08:43 14:57 21:11
Venus 07:56 14:29 21:03
Moon 16:26 21:31 02:42
Mars 15:06 19:46 00:25
Jupiter 09:07 15:21 21:34
Saturn 15:19 20:12 01:06
All times shown in EDT.

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

03 Jun 2016  –  Saturn at opposition
15 Jun 2017  –  Saturn at opposition
27 Jun 2018  –  Saturn at opposition
09 Jul 2019  –  Saturn at opposition

Image credit

© NASA/Cassini

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Ashburn

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Longitude:
Timezone:

39.04°N
77.49°W
EST

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