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.
2018 apparition of Saturn
| 17 Apr 2018 | – | Saturn enters retrograde motion |
| 27 Jun 2018 | – | Saturn at opposition |
| 06 Sep 2018 | – | Saturn ends retrograde motion |
Observing Saturn
Saturn leaves retrograde motion as its 2018 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 | 18h09m50s | 22°42'S | Sagittarius | 0.2 | 17.1" |
The coordinates above are given in J2000.0.
From Columbus , it will be visible in the evening sky, becoming accessible around 20:25 (EDT), 27° above your southern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 20:37, 27° above your southern horizon. It will continue to be observable until around 00:08, when it sinks below 10° above your south-western horizon.
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 6 Sep 2018
| The sky on 6 September 2018 | ||||||||||||||||||||||||||||||||||
|
10% 26 days old |
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
| 06 Sep 2018 | – Saturn ends retrograde motion |
| 29 Apr 2019 | – Saturn enters retrograde motion |
| 09 Jul 2019 | – Saturn at opposition |
| 18 Sep 2019 | – Saturn ends retrograde motion |
Image credit
© NASA/Cassini