Solar System Phenomena — Mars in 2021

The path of Mars against the background stars in 2021

The upper chart shows the path of Mars across the background stars over the course of the year. Stars to magnitude +4.5 are shown with some fainter objects included to complete constellation patterns. The white circles represent the planet on the first day of the month and are scaled according to apparent magnitude. The faint paths before the first circle and after the last circle represent the planet's positions in December of last year and January of next. In general, the planet moves from right to left except when it's in retrograde and proceding in the opposite direction.

The lower chart shows how the appearance of Mars changes over the year. Below each image is listed the date, the apparent magnitude, the apparent diameter of the disk (in arc-seconds), the geocentric distance (in au) and the percentage of the disk which is illuminated. Note that Mars appears distinctly gibbous near the times of quadrature.

With neither opposition nor retrograde motion happening this year, Mars proceeds in an orderly fashion across the sky, beginning as a bright zero magnitude object in Pisces before dimming to second magnitude by the middle of the year. It recovers its brightness slightly and ends up at magnitude +1.5 in Ophiuchus. Mars is an evening sky object at the outset of 2021, visible before sunset for the first half of the year. Conjunction is in October, after which the red planet reappears in the east at dawn. Mars is occulted by the Moon three times this year (April and December) and passes just south of the open star cluster Praesepe in late June. Its closest appulse with another planet occurs in August when Mercury appears just 0.1° south of Mars.

05 JanuaryPiscesAries
20 Januaryplanetary conjunction: 1.6° north of Uranus
01 Februaryeast quadrature
07 Februaryequinox: spring in the northern hemisphere and autumn in the southern hemisphere
23 FebruaryAriesTaurus
19 March1.9° north of the Moon
17 Aprillunar occultation: 0.1° north of the Moon
23 Aprilmaximum declination north
24 AprilTaurusGemini
07 Maystellar occultation: HD 47020
16 May1.5° south of the Moon
08 JuneGeminiCancer
13 June2.8° south of the Moon
23 June0.3° south of the open star cluster M44 (known as Praesepe or the Beehive Cluster)
10 JulyCancerLeo
13 Julyaphelion
planetary conjunction: 0.5° south of Venus
29 July0.6° north of Regulus
19 Augustplanetary conjunction: 0.1° north of Mercury
25 Augustsolstice: summer in the northern hemisphere and winter in the southern hemisphere
05 SeptemberLeoVirgo
08 Octoberconjunction
09 Octoberplanetary conjunction: 2.4° north of Mercury
04 November2.3° south of the Moon
10 Novemberplanetary conjunction: 1.0° south of Mercury
11 NovemberVirgoLibra
02 Decemberlunar occultation: 0.7° south of the Moon
15 DecemberLibraScorpius
19 Decemberdescending node
24 DecemberScorpiusOphiuchus
31 Decemberlunar occultation: 0.9° north of the Moon
maximum declination south


The dates, times and circumstances of all planetary and lunar phenomena were calculated from the JPL DE406 solar system ephemeris using the same rigorous methods that are employed in the compilation of publications such as The Astronomical Almanac. Seasonal information was obtained from A post-Pathfinder evaluation of areocentric solar coordinates with improved timing recipes for Mars seasonal/diurnal climate studies, Michael Allison and Megan McEwen, Planetary and Space Science, 48, 215–235 (February 2000).