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.
2120–2121 apparition of Mars
| 31 Dec 2120 | – | Mars enters retrograde motion |
| 08 Feb 2121 | – | Mars at perigee |
| 09 Feb 2121 | – | Mars at opposition |
| 21 Mar 2121 | – | Mars ends retrograde motion |
Observing Mars
Mars leaves retrograde motion as its 2120–2121 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 | 08h50m50s | 21°16'N | Cancer | -0.3 | 11.1" |
The coordinates above are given in J2000.0.
From Cambridge , it will be visible in the evening sky, becoming accessible around 19:14 (EST), 53° above your south-eastern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 21:37, 68° above your southern horizon. It will continue to be observable until around 04:04, when it sinks below 9° above your 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 Jan 2121 | 12.3” | -0.7 |
| 24 Jan 2121 | 13.4” | -1.0 |
| 07 Feb 2121 | 13.9” | -1.2 |
| 21 Feb 2121 | 13.5” | -1.0 |
| 07 Mar 2121 | 12.4” | -0.7 |
| 21 Mar 2121 | 11.1” | -0.3 |
| 04 Apr 2121 | 9.8” | -0.0 |
| 18 Apr 2121 | 8.7” | 0.3 |
| 02 May 2121 | 7.8” | 0.6 |
| 16 May 2121 | 7.1” | 0.8 |
| 30 May 2121 | 6.5” | 1.0 |
The sky on 24 Nov 2024
| The sky on 24 November 2024 | ||||||||||||||||||||||||||||||||||
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29% 23 days old |
All times shown in EST.
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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
| 21 Mar 2121 | – Mars ends retrograde motion |
| 03 Feb 2123 | – Mars enters retrograde motion |
| 15 Mar 2123 | – Mars at opposition |
| 18 Mar 2123 | – Mars at perigee |
Image credit
© NASA/Hubble Space Telescope