© NASA/Cassini

Jupiter enters retrograde motion

Dominic Ford, Editor
From the Outer Planets feed

Objects: Jupiter
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Jupiter 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 Jupiter

08 Mar 2018 – Jupiter enters retrograde motion
08 May 2018 – Jupiter at opposition
10 Jul 2018 – Jupiter ends retrograde motion

Observing Jupiter

Jupiter 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
Jupiter 15h23m30s 17°20'S Libra -2.2 39.2"

The coordinates above are given in J2000.0.

From Seattle , it will be visible in the morning sky, becoming accessible around 00:45, when it reaches an altitude of 7° above your south-eastern horizon. It will then reach its highest point in the sky at 04:29, 25° above your southern horizon. It will be lost to dawn twilight around 06:17, 20° above your south-western horizon.

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Over the following weeks, Jupiter 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 08 March 2018
Sunrise
06:37
Sunset
18:05
Twilight ends
19:49
Twilight begins
04:53

21-day old moon
Waning Crescent

47%

21 days old

Planets
Rise Culm. Set
Mercury 07:05 13:17 19:30
Venus 07:11 13:13 19:15
Moon 00:39 05:32 10:23
Mars 02:31 06:43 10:56
Jupiter 23:46 04:29 09:13
Saturn 03:23 07:40 11:57
All times shown in PST.

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

07 Apr 2017  –  Jupiter at opposition
08 May 2018  –  Jupiter at opposition
10 Jun 2019  –  Jupiter at opposition
14 Jul 2020  –  Jupiter at opposition

Image credit

© NASA/Cassini

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