About every 26 months, 780 days, the planet Mars appears to pause in its eastward orbital motion and for a period of time, about 72 days, move toward the west before again pausing and returning to its eastward orbital motion. This is known as retrograde motion, and is an apparent, not actual, motion that all planets undergo relative to the Earth’s orbital motion. All outer planets, dwarf planets, and asteroids will have a retrograde motion period each time the Earth moves past them. Picture two race cars circling a track. The inner most car, moving faster, passes the outer car and from the perspective of the inner car it could look like the slower moving car was moving backward.
This particular retrograde motion has Mars approach the planet Saturn and the reddish star Antares, the “Equal of Mars“.
You could plot the retrograde motion of Mars on this equatorial star chart. It is part of a set of free star charts made available from the Department of Physics and Astronomy at Stephen F. Austin State University.
R.A. is the Right Ascension or hour circle position of Mars and is in units of hours minutes. This is similar to meridians of longitude on Earth except they are numbered from 0 to 23 and there is only east. Dec is the Declination of Mars and is degrees and minutes. Declination is like latitude with degrees north and south from the celestial equator.
Coordinate Positions for Mars
Date Right Declination Approx Constellation Ascension Mag. Mar. 31 16h21m49s -20°37'48" -0.9 Scorpius Apr. 08 16h26m02s -20°57'38" -1.1 Ophiuchus 15 16h27m58s -21°14'11" -1.3 Ophiuchus 22 16h27m27s -21°27'32" -1.4 Ophiuchus May 01 16h22m53s -21°39'27" -1.7 Scorpius 08 16h16m22s -21°43'44" -1.8 Scorpius 15 16h07m38s -21°42'55" -1.9 Scorpius 22 15h57m29s -21°36'59" -2.0 Scorpius Jun 01 15h42m27s -21°21'46" -2.1 Libra 08 15h33m03s -21°09'38" -2.0 Libra 15 15h25m41s -21°00'01" -2.0 Libra 22 15h20m54s -20°55'46" -1.9 Libra Jul 01 15h18m54s -21°00'51" -1.8 Libra 08 15h20m33s -21°13'42" -1.6 Libra 15 15h24m53s -21°33'57" -1.5 Libra 22 15h31m37s -22°00'23" -1.4 Libra Aug 01 15h44m56s -22°45'34" -1.2 Libra 08 15h56m33s -23°20'01" -1.1 Scorpius