Topic of the month: 2020 Preview

Celestial Circumstances Preview

Our innermost planet MERCURY starts off 2020 close to the Sun as it reaches superior conjunction on Jan 10, appearing in the evening twilight sky at the end of the month. Because the planet's orbital period is 87.96 days, each year this swiftly moving planet will generally cross between the Earth and Sun three times. After emerging from the Sun, Mercury reaches greatest eastern elongation on Feb. 10, 18 deg. away from the Sun, shining at -0.5 mag. The first inferior conjunction of Mercury this year occurs 16 days later. After that Mercury will emerge into the morning sky until it reaches greatest western elongation on Mar. 24 (27.7 deg. from the Sun.) The planet will then be best seen from the southern hemisphere. Mercury reaches superior conjunction on May 4, moving back into the evening sky. Mercury will pass close to Venus on May 21-22, near the star El Nath. The next greatest eastern elongation occurs on June 4 when the planet is 18.5 deg. away from the Sun. Summer twilight may make this hard to see, especially in the northern latitudes. A second inferior conjunction on July 1 will bring Mercury back to the morning sky, rising earlier each morning until greatest western elongation at July 22, shining at mag -0.8 by the end of the month. It reaches another superior conjunction on Aug. 17 becoming visible again in the evening, another opportunity for southern-based observers. A last inferior conjunction on October 25 will bring Mercury back to a position that can be best seen by northern observers. On Nov. 10, greatest western elongation brings the planet 19 deg away from the Sun, reaching mag -0.6 in the morning sky. The planet proceeds to superior conjunction December 20 and will not be seen in the last month of the year.

The next inner planet, VENUS opens the year in the evening sky in the constellation of Capricornus but moves into Aquarius by Jan. 11. The planet Venus and Earth have a resonance where every eight years, Venus returns to a position fairly close to the one it had previously. Venus will pass between the Earth and the Sun five times in these eight years. This instance of inferior conjunction favors the northern hemisphere of Earth. Keep watching the evening sky to see the bright beacon of Venus (mag -4.0) as she puts on a show in the northern sky. Yes, our lady of the sky has a date with the Sun for inferior conjunction on June 3rd and so will continue to brighten. She buzzes past Uranus on Mar. 9, shining at -4.3 mag or better. Venus will be at perihelion in its orbit on March 19, when it is .72 AU away from the Sun. On March 24, Venus reaches her greatest eastern elongation (46 deg) point that will be 19 deg. N. of the Sun. In April our sister planet will zoom through the Pleiades, yes, M-45, that bright star cluster. It has a close conjunction with Jupiter and the moon on Jan. 22 and then will be occulted by the crescent moon at the end of the month. Venus will pass Saturn on Feb. 18, approaching within 2.1 deg. Venus reaches superior conjunction on Aug. 14.

A good conjunction with Mercury occurs on May 22 when Venus at mag -4.3 passes 53' above Mercury. If you choose to view this one, make sure you take care observing any astronomical object near near the Sun. After inferior conjunction, Venus returns to the morning sky a few days later and on June 19, an occultation by the Moon will occur for observers in parts of Canada and northern Europe. (The moon will be a slender waning crescent!) Venus will continue to rise in the morning sky, growing brighter until she reaches greatest brilliancy on July 10 shining at -4.7 magnitude. Venus moves through the Hyades cluster to a conjunction with Aldebaran, passing just 1 deg. away from Alpha Tauri. Our sister planet will reach greatest western elongation on Aug. 13, 46 deg. away from the Sun. Moving into Gemini in mid-August, riding high in the morning sky, soon she will be in Leo when she meets up with the "king" of the sky, Regulus on Oct. 2. At their closest approach, Regulus and Venus will be 5' apart. Venus will be visible for the rest of the year in the morning twilight, although our sister planet fades to -3.9 mag. This northern light show will be back in eight years when Venus returns once again.

The planet MARS is another planet to watch this year as it reaches opposition on Oct. 13. The resonance between Earth and Mars roughly traces out a 15-year cycle. During that time, planet Earth will overtake Mars seven times. The moment that Mars is opposite the Sun from Earth is called "opposition." As both planets orbit the Sun, oppositions occur in roughly the same point of the planets' orbits. Our view of Mars is colored by its seasons. During this opposition Mars' southern hemisphere will be experiencing Spring, that means the southern polar cap should be prominent. Observers can find out what side of the disk is showing when they are making observations by using the Sky & Telescope Mars Profiler tool. As the red planet nears opposition this time, I hope to see Solis Lacus the so-called black eye of Mars. Syrtis Major, a dark volcanic area appearing somewhat like the India subcontinent should also be a prominent feature as long as the red planet doesn't kick up one of its planet-wide dust storms more common during perihelion. At opposition, the red planet should be shining about -2.8 with a disk that is 24.2". Observers who wish to spot the Martian moons Phoebus (mag 10.5) and Deimos (mag 11.6) can also try to see them at this time. You will need an occulting-bar to mask the bright glow of Mars, a very clear planetary night, and lots of aperture. Good Luck!

Keep your eye on the morning sky in March as Mars overtakes Jupiter when the two planets reach conjunction on the 20th. Mars will be at .9 mag while Jupiter glows at -2.1. The difference in brightness between the two outer planets demonstrates how much brighter Mars will get during this year's conjunction. Mars will be brighter at opposition than Jupiter is on the night of conjunction. Mars will catch up and pass Saturn on March 31st when this pair is in conjunction.

The solar system's behemoth planet is the gas giant JUPITER. Jupiter may be the amateurs' favorite planet, as it is observable for 12 months every 13-month period. Its super fast rotation speed, that makes a revolution every 9h 51m, allows observers to study its many features: belts, festoons, giant storms and many other effects that one can't really predict. The planet's largest moons, called the Galilean Moons after their discoverer: Io, Europa, Ganymede, and Callisto transit the disk of Jupiter leaving super round black shadows that crawl across the disc. The planet is a favorite target for astrophotographers. On July 14, Jupiter reaches opposition, now shining brilliantly at -2.8. The disk will be 100-percent illuminated. Those fabled Moons will be larger than ever, appearing as small disks in a telescope and binoculars. Larger telescopes will reveal slight color differences between them. Ganymede is the brightest at 4.7 mag and Callisto is the faintest at 5.8 mag. It is possible to see them with the naked eye for those with sharp vision.

This year we are in for a special treat as the giant planet Jupiter will overtake Saturn in its orbit. Because Jupiter orbits the Sun in 11.86 years and Saturn takes 29.46, Jupiter will only catch up with Saturn twice in those 29 years. (Actually 2.48 times) This year Jupiter and Saturn will spend several months close each other in the sky on the eastern side of the constellation Sagittarius. Jupiter reaches its first stationary point on May 14th and begins retrograde motion, following Saturn that reached stationary 3 days earlier. The two planets move in retrograde motion until they pass opposition and continue their eastward (prograde) motion in September. This rendezvous of the two outer planets reminds us how the expression "dance of the planets" was invented. This arrangement between Jupiter and Saturn repeats every 20 years when they trace out a similar pattern in Earth's sky.

The last planet to be discussed is the ringed-wonder, gas giant SATURN. The rings are made of ice crystals orbiting the planet at various distances. This is somewhat like the ridges on a vinyl record album. There is one large gap near the center of them, dividing them into two pieces called "The Cassini Division." This gap can be seen with small telescopes, there are others that can be seen with larger amateur instruments on a clear night. Saturn starts the year reaching conjunction with the Sun on Jan. 13 and will not be seen well until late March, in time to be seen with Jupiter and Mars for their Mar. 20 conjunction. At that time, Saturn will be ~7 degrees away in the constellation of Capricornus. The ringed planet will be low in the sky for northern observers so telescopic observing will not be as good as it is when it is higher in the sky. In the midst of its dance with Jupiter, Saturn reaches opposition on July 20th shining at +0.1 mag. The rings will be tilted at 21.7 deg., the disk will be 18.4" and the rings will span ~42". On Sep. 20, the ringed wonder will stop and return to prograde motion heading back toward Capricornus. Now Jupiter will be seen to move toward Saturn until the two planets come together for a fine conjunction on Dec. 21 when they are separated by a mere .1 degree at the edge of Sagittarius. Sadly, this dance of Jupiter and Saturn is about to come to an end as Jupiter speeds away from the slower planet Saturn. In 2040, Saturn and Jupiter will meet up again and perform a similar dance, this time at the western side of the constellation Virgo.

Eclipses for 2020

The eclipse season starts on Jan. 10 with a penumbral lunar eclipse that is followed up by another on July 5 and later on Nov. 30. Unfortunately, 2020 features no partial or total lunar eclipses that are easier to see and generally more interesting. The first solar eclipse of the year occurs on the solstice date of June 21 and is an annular eclipse where nearly 99% of the solar disk will be covered. The path of annularity crosses Asia, northern India, the Arabian peninsula, and eastern Africa. A partial eclipse will be visible for areas north and south of the path. The best eclipse for 2020 will occur on Dec. 14 with the path of totality beginning in the pacific ocean, crossing over the southern end of S. America with Chile (passing over Villarrica and Pucon, two well-known tourist towns on Lake Villarrica) and crossing into Argentina where it passes near the small town of Piedra del Aguila, plunging into the Argentina Sea and then crosses the Atlantic until it disappears just before landfall in Africa. Maximum duration of this eclipse is 2m 9.7sec at greatest eclipse.

Remember more details on these and other celestial observations are available at What's Up in the Night Sky? every month at Astra's Stargate!

--See You Under the Stars!
Astra for Astra's Almanac