Mars at opposition, October 13, 2020
by Jeffrey L. Hunt
Mars reaches opposition on October 13, 2020, among the dim stars of southeastern Pisces. At opposition, Mars is biggest and brightest. Unlike some Internet memes, it is not as big as the moon. It shines as a bright star in the sky all night long.
Mars has captured our attention. It’s reddish appearance in the sky has cast it as a warrior in several cultures. After the inventions of larger telescopes, Mars brought the attention of many observers. Public announcements of possible civilizations there likely spurred the growth of science fiction writing and storytelling.
While Mars is close to Earth, it appears small even through a telescope. Through a telescope’s eyepiece, it appears as a red-ochre globe. A polar cap and some darker equatorial markings might be visible. At times, Mars surface cannot be seen when dust storms engulf the planet. For those with a telescope, Sky & Telescope’s Mars profiler shows what is visible on the surface on any date and time.
The Mars opposition occurs at the end of a span of 91 days, with the three Bright Outer Planets (Jupiter, Saturn, and Mars) passing their oppositions. Jupiter and Saturn are at their oppositions during a span of 6 days in July 2020.
Mars’ opposition occurs 72 days after it passes its orbital point closest to the sun (August 2, 2020), known as a planet’s perihelion, while the previous opposition occurred 49 days before perihelion (September 15, 2018). The July 27, 2018, event was called a “perihelic” opposition.
The accompanying charts show two perspectives of the planet’s motion from July 21, 2020, to January 5, 2021. The first chart shows the apparent motions of Mars as seen against the starry background in southeastern Pisces. The second chart shows the view of a section of Earth’s orbital path and Mars’ orbit as viewed from above the solar system.
In the notes in this article, the “m” numbers are measures of the planets’ and stars’ brightness. The lower the number, the brighter the celestial object. The sun has the lowest value (−26.5) on this scale. Afterall it is so bright it creates daytime on our planet and shines on the moon and other planets in its system. The planets’ brightness changes as their distances from Earth vary.
Each full digit numeric change on the magnitude scale equals a change of 2.5 times (2.512x). From the beginning of the sequence to its brightest, Mars brightness increases 25 times, a dramatic, but easily observed change of brightness. As we move away from Mars in start the new year, the planet’s brightness decreases about ten times from its brightest light. So, like an excellent golf score, the lower the number the brighter the “star.”
All Planets in Morning Sky
As the sequence opens, five naked eye planets are in the morning sky, along with Uranus, Neptune, and Pluto. At about 40 minutes before sunrise, the bright planets span nearly 168° of ecliptic longitude, stretching from horizon to horizon. Mercury (m = 0.4), a day before its greatest elongation, is quite low in the east-northeast. Use a binocular and find a clear horizon. Brilliant Venus (m = −4.6) is about 20° up in the east, to the lower left of Aldebaran. Mars (m = −0.9) is over 45° up in the south-southeast. Farther westward along the ecliptic, Saturn (m = 0.1) is about 10° up in the southwest. Bright Jupiter is 6.4° to Saturn’s lower right. Because Mercury is low in the sky, start looking for Jupiter about an hour before sunrise. Work your way eastward across the sky to find Mercury with a binocular 10-20 minutes later. I’ve seen Jupiter just a few degrees above the horizon without optical assistance. It might be possible to see all of them in the sky together.
Mars at Opposition
Here’s what to look for:
- July 21, 2020: This is the first day displayed on the charts. See the text above for a description of the menagerie of morning planets. Bright Mars (m = −0.9) is moving eastward against the starry background. As midnight approaches, the Red Planet is 5° up in the east.
- August 2: Mars (m = −1.1) is at perihelion, 1.38 AU from the sun, its closest point to the sun in its orbit. As midnight approaches, it is 10° up in the east.
- August 4: Mars (m = −1.2) passes 0.4° to the upper left of a star with the catalog name 89 Piscium (89 Psc, m = 5.1). The star is dim. Use a binocular to see Mars with the starfield.
- August 8: As midnight approaches the moon (19.5 days past the New phase, 73% illuminated) is 2.0° to the lower right of Mars (m = −1.3) that is about 13° in altitude in the east.
- August 22: Mars (m = −1.6) passes 0.5° to the upper left of Nu Piscium (ν Psc, m = 4.4). Four hours after sunset, Mars is nearly 18° in altitude in the east.
- September 5: Four hours after sunset, the moon (18.1d, 86%) – over 20° up in the east – is 0.7° below Mars (m = −1.9).
- September 9: Mars (m = −2.0) begins to retrograde; four hours after sunset, it is nearly 25° up in the east-southeast. See the first chart above Retrograde motion is an illusion. To early astronomers, this was the cosmological problem of the time. Those who thought Earth was at the center of all motion used a series of circles needed to get the planets to move westward compared to the starry background. For observers who thought all the planets revolved around the sun, Mars seems to move backwards when our faster moving planet catches, overtakes, and moves past the Red Planet. Mars and all objects in the solar system beyond it seem to back up for a period of time, then resume their eastward motion compared to the starry background as we move past. This is more obvious for the bright planets, especially Mars. The issue of Earth’s place in the solar system was not finalized until after the invention of the telescope and precision instruments were developed to measure our planet’s revolution around the sun.
For those with further interest, the variable star Mira (ο Cet) is predicted to reach its brightness. This paragraph describes more Mira’s brightness prediction and its location to Mars Predicted dates for the brightest phase range from mid-September to late in the month. The brightest magnitude is uncertain, ranging from 2.0 to 4.0. On September 15, Mira is about 12° to the lower left of Mars. For the latest observations of Mira’s brightness, check with the American Association of Variable Star Observers (https://www.aavso.org/).
- October 2: Three hours after sunset, Mars (m = −2.5) is 24° up in the east-southeast. The bright gibbous moon (15.7d, 98%) is 1.3° to the lower right of the planet.
- October 6: Earth and Mars (m = −2.6) are at their closest. The planet passes 0.4° to the lower right of Mu Piscium (μ Psc, m = 4.8). Use a binocular to see the dimmer star with Mars. Three hours after sunset, the Red Planet is over 25° in altitude in the east-southeast.
- October 13: Earth is between Mars and the sun. When the sun sets, Mars is rising in the eastern sky. Around midnight (about 1 a.m. during Daylight Saving Time), Mars is in the south. Mars sets in the western sky at sunrise. Mars and sun are opposite in the sky. Mars is at opposition, 1.43 AU from the sun and 0.419 AU from Earth. Three hours after sunset, the planet is over 30° up in the east-southeast.
- October 23: Mars (m = −2.4) passes 0.6° to the lower right of 80 Piscium (80 Psc, m = 5.5). Use a binocular to see the star with Mars. Two hours after sunset, Mars is over 25° in altitude in the east-southeast.
- October 29: Two hours after sunset, the bright moon (13.2d, 98%) is nearly 26° up in the east-southeast. Mars (m = −2.2) is 4.8° to the upper right of the gibbous moon.
- November 13: Mars’ (m = −1.7) retrograde ends. Mars begins to move eastward compared to the starry background. Two hours after sunset, the planet is nearly 40° up in the southeast.
- November 25: At the end of evening twilight, Mars (m = −1.3) is over 40° in altitude in the southeast. The moon (10.8d, 84%) is 5.1° to the lower left of Mars. (The end of twilight occurs about 100 minutes after sunset.)
- December 4: Mars (m = −1.0) passes 1.0° below Epsilon Piscium (ε Psc, m = 4.2). Use a binocular to track Mars compared to the dimmer starry background. At the end of evening twilight, Mars is over 45° in altitude in the southeast.
- December 12: Mars (m = −0.7) passes 0.6° above Zeta Piscium (ζ Psc, m = 5.2). Another dim star. You’ll likely need a binocular to see the star. At the end of evening twilight, find the Red Planet 50° up in the southeast.
- December 21: Forty-five minutes after sunset, Mars (m = −0.5) is nearly 48° up in the southeast. The half-full moon (7.3d, 50%), over 40° up in the south-southeast, is about 24° to the lower right of Mars. This is the evening of the once-every-generation Great Conjunction of Jupiter (m = −2.0) and Saturn (m = 0.6). The conjunction is about 14° in altitude above the southwest horizon. Mar and Jupiter are nearly 83° apart.
- December 23: At the end of evening twilight, Mars is 55° up in the south-southeast. The moon (9.3d, 69%) is 5.6° to the lower left of Mars.
- December 31: Mars (m = −0.2) passes 1.0° to the lower left of Pi Piscium (π Psc, m = 5.5). A binocular is needed to see the dim star and the planet together. At the end of evening twilight, Mars is nearly 60° in altitude in the south-southeast.
- January 5, 2021: This is the last day displayed on the charts. At the end of evening twilight, Mars (m = −0.1) is 60° in altitude in the south-southeast.
The sequence ends with Jupiter and Saturn approaching their solar conjunctions. The giant planetary pair is 15 days past the December 21, 2020, Great conjunction. Jupiter is 1.7° east of Saturn. During mid-twilight, Jupiter is about 6° up in the southwest. Along with Mercury, Jupiter and Saturn are less than 20° east of the sun. Mars is over 85° of ecliptic longitude from Jupiter. In the morning sky, Venus is about 5° up in the southeast during morning twilight. While the sun is between them, Venus is over 37° in ecliptic longitude from Jupiter.
What’s Next for Mars
Mars heads toward brighter starfields during 2021. During March, it passes the Pleiades and the Hyades, and moves between the Bull’s horns in mid-April. Mars strolls through the Beehive Cluster in late June, although the pair is low in the west-northwest during evening twilight. During mid-July, Venus passes Mars in the western evening sky. Later in the month, Mars passes Regulus with Venus higher in the sky, although the Mars – Regulus pair is very low in the sky during mid-twilight. Then, Mars makes a slow slide into evening twilight. It reaches its solar conjunction on October 7, 2021. The next opposition is December 7, 2022. Mars is farther away, 0.549 AU. This is followed by the January 15, 2025, opposition, when the Martian distance increases to 0.734 AU.