© NASA/Cassini

Saturn enters retrograde motion

Dominic Ford, Editor
From the Outer Planets feed

Objects: Saturn
Please wait
Loading 0/4
Click and drag to rotate
Mouse wheel to zoom in/out
Touch with mouse to dismiss
The sky at

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.

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 enters retrograde motion as its 2018 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 18h38m20s 22°15'S Sagittarius 0.2 17.1"

The coordinates above are given in J2000.0.

From Ashburn , it will be visible in the dawn sky, rising at 01:23 (EST) and reaching an altitude of 28° above the southern horizon before fading from view as dawn breaks around 05:59.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

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 17 April 2018
Sunrise
06:31
Sunset
19:51
Twilight ends
21:27
Twilight begins
04:55

1-day old moon
Waxing Crescent

7%

1 day old

Planets
Rise Culm. Set
Mercury 05:40 11:46 17:52
Venus 07:35 14:41 21:46
Moon 07:49 14:43 21:45
Mars 01:59 06:41 11:23
Jupiter 21:37 02:44 07:51
Saturn 01:23 06:08 10:54
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

15 Jun 2017  –  Saturn at opposition
27 Jun 2018  –  Saturn at opposition
09 Jul 2019  –  Saturn at opposition
20 Jul 2020  –  Saturn at opposition

Image credit

© NASA/Cassini

Share

Follow

Ashburn

Latitude:
Longitude:
Timezone:

39.04°N
77.49°W
EST

Color scheme