Mars will reach the end of its retrograde motion, ending its westward movement through the constellations and returning to more usual eastward motion instead. This reversal of direction is a phenomenon that all the solar system's outer planets periodically undergo, a few months after they pass 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.
1984 apparition of Mars
| 05 Apr 1984 | – | Mars enters retrograde motion |
| 11 May 1984 | – | Mars at opposition |
| 19 May 1984 | – | Mars at perigee |
| 19 Jun 1984 | – | Mars ends retrograde motion |
Observing Mars
Mars leaves retrograde motion as its 1984 apparition comes to an end, although it will remain visible for some weeks in the dusk sky.
Its celestial coordinates as it leaves retrograde motion will be:
| Object | Right Ascension | Declination | Constellation | Magnitude | Angular Size |
| Mars | 14h35m40s | 17°02'S | Libra | -1.3 | 15.5" |
The coordinates above are given in J2000.0.
From Columbus , it will be visible in the evening sky, becoming accessible around 21:25 (EDT), 31° above your southern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 22:13, 32° above your southern horizon. It will continue to be observable until around 02:27, when it sinks below 7° above your south-western horizon.
Over the following weeks, Mars will reach its highest point in the sky four minutes earlier each night, gradually disappearing into evening twilight.
The panels below show the month-by-month change in Mars' apparent size in coming weeks, as it recedes from the Earth:
The table below lists Mars' angular size at brightness at two-week intervals throughout its apparition:
| Date | Angular size | Mag |
| 10 Apr 1984 | 14.1” | -1.0 |
| 24 Apr 1984 | 15.9” | -1.5 |
| 08 May 1984 | 17.3” | -1.9 |
| 22 May 1984 | 17.6” | -1.8 |
| 05 Jun 1984 | 16.8” | -1.6 |
| 19 Jun 1984 | 15.5” | -1.3 |
| 03 Jul 1984 | 14.0” | -1.0 |
| 17 Jul 1984 | 12.6” | -0.7 |
| 31 Jul 1984 | 11.4” | -0.5 |
| 14 Aug 1984 | 10.4” | -0.2 |
| 28 Aug 1984 | 9.5” | -0.1 |
The sky on 16 Aug 2024
| The sky on 16 August 2024 | ||||||||||||||||||||||||||||||||||
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87% 12 days old |
All times shown in EDT.
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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
| 19 Jun 1984 | – Mars ends retrograde motion |
| 08 Jun 1986 | – Mars enters retrograde motion |
| 10 Jul 1986 | – Mars at opposition |
| 16 Jul 1986 | – Mars at perigee |
Image credit
© NASA/Hubble Space Telescope