© 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.

2012–2013 apparition of Jupiter

04 Oct 2012 – Jupiter enters retrograde motion
02 Dec 2012 – Jupiter at opposition
30 Jan 2013 – Jupiter ends retrograde motion

Observing Jupiter

Jupiter enters retrograde motion as its 2012–2013 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 05h00m20s 21°54'N Taurus -2.6 42.6"

The coordinates above are given in J2000.0.

From Fairfield , it will be visible in the morning sky, becoming accessible around 22:27, when it reaches an altitude of 8° above your eastern horizon. It will then reach its highest point in the sky at 05:02, 70° above your southern horizon. It will be lost to dawn twilight around 06:35, 62° 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 04 October 2012
Sunrise
06:51
Sunset
18:31
Twilight ends
20:03
Twilight begins
05:23

18-day old moon
Waning Gibbous

79%

18 days old

Planets
Rise Culm. Set
Mercury 08:23 13:44 19:05
Venus 03:31 10:14 16:58
Moon 20:18 03:43 11:11
Mars 10:56 15:42 20:29
Jupiter 21:37 05:02 12:28
Saturn 08:22 13:53 19:23
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

28 Oct 2011  –  Jupiter at opposition
02 Dec 2012  –  Jupiter at opposition
05 Jan 2014  –  Jupiter at opposition
06 Feb 2015  –  Jupiter at opposition

Image credit

© NASA/Cassini

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