© 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 Mars. Not drawn to scale.

1956 apparition of Mars

10 Aug 1956 – Mars enters retrograde motion
07 Sep 1956 – Mars at perigee
10 Sep 1956 – Mars at opposition
10 Oct 1956 – Mars ends retrograde motion

Observing Mars

Mars enters retrograde motion as its 1956 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 23h48m20s 7°42'S Aquarius -2.3 21.9"

The coordinates above are given in J2000.0.

From Jacksonville , it will be visible in the morning sky, becoming accessible around 22:55, when it reaches an altitude of 7° above your eastern horizon. It will then reach its highest point in the sky at 03:59, 51° above your southern horizon. It will be lost to dawn twilight around 06:36, 36° 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
15 Jun 1956
Mars
13 Jul 1956
Mars
10 Aug 1956
Mars
07 Sep 1956
Mars
05 Oct 1956

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

Date Angular size Mag
01 Jun 195611.5”-0.5
15 Jun 195613.0”-0.8
29 Jun 195614.9”-1.1
13 Jul 195617.0”-1.5
27 Jul 195619.4”-1.9
10 Aug 195621.9”-2.3
24 Aug 195623.9”-2.6
07 Sep 195624.8”-2.8
21 Sep 195623.8”-2.7
05 Oct 195621.5”-2.3
19 Oct 195618.7”-1.8

The sky on 28 Sep 2024

The sky on 28 September 2024
Sunrise
07:16
Sunset
19:14
Twilight ends
20:34
Twilight begins
05:56

25-day old moon
Waning Crescent

10%

25 days old

Planets
Rise Culm. Set
Mercury 07:09 13:11 19:13
Venus 09:40 15:10 20:40
Moon 03:27 10:29 17:24
Mars 00:52 07:53 14:54
Jupiter 23:17 06:16 13:14
Saturn 18:18 00:02 05:45
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

10 Aug 1956  –  Mars enters retrograde motion
07 Sep 1956  –  Mars at perigee
10 Sep 1956  –  Mars at opposition
10 Oct 1956  –  Mars ends retrograde motion

Image credit

© NASA/Hubble Space Telescope

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