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2020, October 13: Mars at Opposition

Mars from Hubble during 2018

NASA’s Hubble Space Telescope photographed Mars on July 18, 2018, during a dust storm and near its closest approach to Earth since 2003. (NASA photo)

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The Red Planet from the Mars Global Surveyor shows the effects of a global dust storm (NASA)

Mars is at opposition, October 13, 2020.

by Jeffrey L. Hunt

Link to pdf of this article.

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.

This chart shows the apparent motion of Mars compared to the starry background, during a 168-day interval that includes the planet’s opposition.

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.

Slideshow of images for Mars Opposition 2020

This chart views the motions of Earth and Mars from north of the ecliptic during the same time interval as the retrograde chart above.

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.

Celestial Brightness

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:

As midnight approaches the moon is 2.0° to the lower right of Mars that is about 13° in altitude in the east.

2020, September 5: The moon and Mars, (Composite of two images)

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/).

Three hours after sunset, Mars is 24° up in the east-southeast. The bright gibbous moon is 1.3° to the lower right of the planet.

Two hours after sunset, the bright moon is nearly 26° up in the east-southeast. Mars is 4.8° to the upper right of the gibbous moon.

At the end of evening twilight, Mars is over 40° in altitude in the southeast. The moon is 5.1° to the lower left of Mars.

At the end of evening twilight, Mars is 55° up in the south-southeast. The moon is 5.6° to the lower left of Mars.

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.

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