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2019-2020: Mars Until it Retrogrades


Mars (NASA Photo)

This chart shows the rising time differences for the rising times of the bright planets and stars near the ecliptic and sunrise for up to five hours before sunrise. The moon’s time differences are displayed in circles. The setting times of Jupiter and Saturn are graphed compared to sunrise. (Data from the U.S. Naval Observatory)

(This article was first published in the Northern Lights Fall Issue)

Continue reading with the opposition of Mars 2020

by Jeffrey L. Hunt

Mars begins an apparition that takes it to an opposition on October 12, 2020, 808 days following its 2018 perihelic opposition. The opposition, that will be highlighted in a future issue, brings Mars to its closest approach about a week before opposition. On October 6, the closest approach is 35.8 million miles, about 8% farther away than the preceding close passing. This corresponds to a smaller disk presented through a telescope.

The chart above, compiled with data from the U.S. Naval Observatory, shows the morning sky for 13 months beginning August 1, 2019, from Chicago, Illinois. Time intervals are noted on the chart and in the daily notes. Specific times are for Chicago, Illinois. To observe locally, refer to local sources for the times of sunrise and sunset; apply the time differentials in the notes.

The chart displays the time differences between the time of sunrise and the rising times for other planets, moon, and bright stars near the ecliptic, for up to five hours before sunrise. The moon’s rising time difference is displayed with circles. The setting time differences for Jupiter and Saturn, compared to sunrise, are displayed as well. The three phases of twilight are graphed compared to sunrise, and conjunctions are identified. The chart also notes several dates when the moon is near the bright planets.

Mars, Jupiter, and Saturn have oppositions that occur within 91 days in 2020. The interest in the Mars opposition adds a highlight to the Great Conjunction of Jupiter and Saturn that occurs late in the year. Such Jupiter – Saturn conjunctions occur about every 20 years.

The apparent sizes of Mars (in arcseconds) at its oppositions are graphed from 1930 to 2050. The larger apparent sizes occur when Mars is near perihelion and smallest when it is near aphelion. The time between oppositions for Mars, Jupiter, and Saturn are displayed for some oppositions (in days). The Great Conjunctions of Jupiter and Saturn that occur about every 20 years are displayed with yellow stars, including the time (in days) between oppositions of the two planets.

Mars’ apparent size at opposition (24.3”) is 8% smaller than the 2018 perihelic opposition and 11% smaller than the 2003 close opposition. This was described above with the close approach that is farther away in 2020 than the most recent perihelic opposition. The chart above displays the apparent size of Mars at its oppositions from 1930 through 2050. The twenty-year intervals of the Jupiter – Saturn Great Conjunction are displayed with yellow stars along with the time interval between their oppositions. For several Mars’ oppositions, the time intervals are noted for the Bright Outer Planets – Mars, Jupiter, and Saturn.

In this summary the events before opposition include monthly passages of the moon that highlight the beginning of a lunar occultation that is easier to view in the Western US, conjunctions with Jupiter, Pluto, Saturn, Ceres, and Neptune.

The apparition began with Mars’ conjunction with the sun on September 2, 2019. While dim, it began a slow crawl into the morning sky. By mid-month Mars was rising at Civil Twilight when the sun was 6° below the horizon.

At the beginning of October, the Red Planet (m = 1.8) is just above the eastern horizon, 45 minutes before sunrise, although it is a binocular object. The planet continues to rise earlier, Nautical Twilight (sun’s altitude = −12°) on October 6. Throughout October it rises earlier, rising at Astronomical Twilight on October 25. In the summary, each entry includes the planet’s magnitude, apparent size, distance from Earth in Astronomical Units, and difference between the planet’s rising time and sunrise, stated in minutes. This time changes in the summary on July 1, 2020, when the difference noted is between sunset and the rising of Mars. Here’s what to look for:

December 2019

As the year closes, Mars continues its eastward march. Early in the month, bright Mercury is to the lower left of Mars. Still over 2 Astronomical Units from Earth, Mars moves through Libra and between the pincers of the Scorpion. The planet rises about 3 hours before sunrise, but it’s low altitude and southerly location may send you on a chase to find a clear horizon.

January 2020

As the New Year breaks, Mars is an unimpressive “star” low in the southeast as sunrise approaches, rising about 4 a.m. CST. It continues to move through Libra and Scorpius and into southern Ophiuchus. At mid-month it passes north of its Rival, Antares.

Notice on the rising chart above that the time differential between the rising of Mars and sunrise decreases from late January through early-April. The declination of the sun is greater than Mars’ position.  The sun is moving toward the vernal equinox while Mars is approaching the ecliptic’s lowest point. The basic principle is that the farther north an object the earlier it rises. During January and February, the time interval between sunrise and Mars rising decreases nearly 20 minutes. This is reflected in the dip the Mars rising line takes on the chart. The differential increases after Mars moves farther north in declination.

February 2020

During February, Mars moves from Ophiuchus into Sagittarius, through the rich galactic background of our galaxy’s nucleus region. Use a binocular to track the planet’s motion. After mid-month, the moon occults Mars in a bright sky as sunrise approaches. Mars heads toward conjunctions with Jupiter, Pluto, and Saturn next month. Watch the gaps close during February as the Bright Outer Planets appear above the southeast horizon before sunrise.

March 20: Mars passes 0.6° to the lower right of Jupiter. Locate the planets in the southeast about an hour before sunrise.

March 2020

Mars marches eastward in Sagittarius, above the Teapot’s handle, and continues to rise earlier. By month’s end, the planet rises before 4 a.m. CDT, as the clock advances one hour on March 8. The gaps to Jupiter, Pluto, and Saturn close as Mars passes the planetary trio this month.

March 31: Mars passes 0.9° to the lower right of Saturn. The planets are in the southeast about an hour before sunrise.

April 2020

Mars is now moving away from Jupiter and Saturn and through the starfield of Capricornus. Continue to track it with low powers as it passes dimmer stars. It has a close appearance with the moon at mid-month. By month’s end the planet rises before 3 a.m. CDT.

May 2020

Mars moves from Capricornus into the dim star field of Aquarius early in the month, brightening about 45% as it nears 1.0 Astronomical Unit away. The planet is about 40 times brighter than the stars it passes during the month. Continue to use low power to track the planet on its eastward march. The moon passes at mid-month, although about a degree farther away than in April. The planet passes Ceres late in the month.  As April closes, Mars rises before 2 a.m.

June 2020

During the month, Earth moves within 1 Astronomical Unit of Mars, while the Red Planet’s brightness grows nearly 0.5 magnitude. The planet passes Neptune late in the month. As the month closes, Mars rises at about 12:30 p.m. CDT.

July 2020

The time differential in the notes changes to rising time after sunset. (On July 8, Mars rises in the east 221 minutes after sunset.) Earth begins to close in on Mars. Now brighter than all the stars, except Sirius from the Northern Hemisphere, Mars gleams from the southeast before morning twilight begins. It moves into Cetus for a short duration, still among dimmer stars. Continue to track it with a binocular, although larger scopes should start to bring in details visually. The morning sky has a planet parade of all the planets in the solar system. In addition to ruddy Mars, brilliant Venus joins, Jupiter and Saturn, although brilliant Venus shines from the eastern sky. Jupiter and Saturn pass opposition six days apart, then Mercury pops into the sky. This results in 5 naked eye planets in the sky at once. Additionally, the telescopic planets are there as well: Uranus, Neptune, and Pluto. (Historically, Pluto is a planet. Without too much description, we have many things in astronomy that are misnamed – like planetary nebula.)

August 2020

Mars, now back in the constellation Pisces, continues its eastward march, as its brightness grows. While Mars brightens, Venus dominates the morning sky. Mars passes perihelion on August 2.

September 2020

Earth closes to within 0.5 Astronomical unit of Mars. The planet is now appearing above the eastern horizon before midnight. Mars slows and stops its eastward motion against the starry background.

Until retrograde began, Mars passed four planets and a minor planet, and had an occultation with the moon. Earth is now closing in toward its closest approach and Mars’ opposition, about a month away. While not as close as the last perihelic opposition, the next opposition occurs farther north and promises great views. In a later issue, we pick up the story of Mars at opposition.

Continue reading with the opposition of Mars 2020

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