© NASA/Hubble Space Telescope

Mars enters retrograde motion

Dominic Ford, Editor
From the Outer Planets feed

Objects: Mars
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Mars 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.

2014 apparition of Mars

01 Mar 2014 – Mars enters retrograde motion
08 Apr 2014 – Mars at opposition
14 Apr 2014 – Mars at perigee
19 May 2014 – Mars ends retrograde motion

Observing Mars

Mars enters retrograde motion as its 2014 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
Mars 13h45m30s 7°53'S Virgo -0.5 11.7"

The coordinates above are given in J2000.0.

From Ashburn , it will be visible in the morning sky, becoming accessible around 22:36, when it reaches an altitude of 9° above your eastern horizon. It will then reach its highest point in the sky at 03:23, 43° above your southern horizon. It will be lost to dawn twilight around 06:22, 27° above your south-western horizon.

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Over the following weeks, Mars 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 panels below show the month-by-month change in Mars' apparent size in coming weeks:

Mars
04 Jan 2014
Mars
01 Feb 2014
Mars
01 Mar 2014
Mars
29 Mar 2014
Mars
26 Apr 2014

The table below lists Mars' angular size at brightness at two-week intervals throughout its apparition:

Date Angular size Mag
21 Dec 20136.4”1.0
04 Jan 20147.1”0.8
18 Jan 20147.9”0.5
01 Feb 20148.9”0.2
15 Feb 201410.2”-0.1
01 Mar 201411.7”-0.5
15 Mar 201413.2”-0.9
29 Mar 201414.5”-1.3
12 Apr 201415.2”-1.5
26 Apr 201414.8”-1.3
10 May 201413.8”-1.0
The sky on 01 March 2014
Sunrise
06:42
Sunset
18:02
Twilight ends
19:34
Twilight begins
05:14

30-day old moon
Waxing Crescent

1%

30 days old

Planets
Rise Culm. Set
Mercury 05:38 10:55 16:12
Venus 04:17 09:24 14:31
Moon 06:35 12:36 18:47
Mars 21:45 03:23 09:00
Jupiter 12:52 20:17 03:42
Saturn 23:54 05:02 10:10
All times shown in EST.

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

05 Mar 2012  –  Mars at perigee
08 Apr 2014  –  Mars at opposition
14 Apr 2014  –  Mars at perigee
22 May 2016  –  Mars at opposition

Image credit

© NASA/Hubble Space Telescope

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