Topic of the month: 2021 Preview

Celestial Circumstances Preview

Our innermost planet MERCURY starts off 2021 rising in the western sky each evening until as it reaches greatest eastern elongation on Jan. 24, (-0.7 mag) favoring northern observers. 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. It will begin to disappear in the evening sky heading toward inferior conjunction on Feb.10, reappearing in the morning sky in a position favoring southern observers with the best views of Mercury (0.1 mag) all year. Southern observers with telescopes will be able to see the Mar. 29 conjunction with Neptune when the two planets are separated by only 1.3 deg. Mercury reaches superior conjunction on Apr. 19, returning to the evening sky. On May 13, a conjunction with the 2-day old moon should be a beautiful sight for those locations where the Sun has set, unfortunately not in N. America, but watch for the Moon and Mercury around this date. Mercury reaches greatest eastern elongation on May 17 when it will set more than 2 hours after the Sun. Bright summer twilight will make this a challenge to observe however. A second inferior conjunction on June 11 it will be too close to the Sun to be observed although it reaches greatest western elongation July 4. After superior conjunction on Aug. 1, Mercury will move toward an evening conjunction with Mars on Aug, 18 that may be visible from Hawaii but not N. America. Greatest eastern elongation at 26.8 deg. on Sep. 14 again favors southern observers. A last inferior conjunction on Oct. 9 will bring Mercury back to a position that can be best seen by northern observers. Look for greatest western elongation on the morning of Oct. 25 when -0.7 mag Mercury rises 1 hour 45 minutes before the Sun. A close conjunction with Mars occurs on Nov. 10. The planet proceeds to superior conjunction on November 29. Finally, a conjunction between Mercury (-0.7 mag) and Venus (-4.1 mag) occurs on December 28 means that the two planets will be visible together around this time closing out the year.

Earth's "sister" planet, VENUS opens the year in the morning sky in the constellation of Ophiuchus but continues its plunge into the Sun by Jan. 11. The planet Venus and Earth have a resonance where every 8 years, Venus returns to a position fairly close to the one it had previously. Venus will pass between the Earth and the Sun 5 times in these eight years. This year Venus will not be as exciting for northern observers, but some great lunar conjunctions will be coming our way. On Jan. 11, Venus and the Moon will rise about an hour before the Sun so spotting them will be a challenge. Venus reaches superior conjunction on Mar. 26. Venus and Mercury will have a couple of conjunctions this year, once on Apr. 25, very close to the Sun. On May 29, Venus and Mercury will meet up in Taurus but be very hard to view because of bright northern twilight. Use binoculars if you must but be very careful with the Sun! In May, Venus becomes visible again as it begins its climb in the evening sky. On May 12, Venus will be very close to the new crescent moon. On June 12, another similar event will occur, a bit higher in the western evening sky. Still, it will be a race against the long summer twilight. Southern latitudes should fare better. On Jul. 12, the Moon will pass 4 deg. N. of Venus. More importantly, Venus will be joined by Mars in the sky and be a mere .5 deg. N of Mars on the 13th. The Aug. 11 conjunction will be best seen from Japan. On Sep. 9, N. American observers will enjoy a nice conjunction of Venus and the 3-day old Moon ~3 deg. apart. Venus reaches greatest eastern elongation (46 deg) point on Oct. 29 when Venus is at -4.9 mag. The next favorable N. American conjunction occurs on Dec. 2 when Venus and the Moon are within 3 deg. of each other. The last conjunction of the inner planets will occur on Dec. 28, when they will be observable right after sunset in N. America.

Mars rings in the new year at -0.2 mag. sporting a 10.4" disk. This is the largest Mars will be until it approaches its next opposition in December 2022. Still riding fairly high in Pisces, the red planet will move into Aries and pass 1.7 deg. N of Uranus on Jan. 22. This will require optical aid to see for most observers. Mars will move into Taurus in March, passing about 3 deg. below the Pleiades, On Apr. 17, the 5-day old Moon will pass 0.1 deg. below the red planet, both of them will be above the 1st-magnitude star, Aldebaran. Another close approach of the Moon occurs on May 16 after Mars moves into Gemini. On July 12-13, Mars will meet up with Venus in Leo. At this time it will be a mere 1.8 mag and may be hard to find in the bright northern twilight. Venus at -4.6 will be less challenging. On Aug. 10, Mars and Mercury (mag -0.5) meet up in Leo for their first conjunction of the year. They rise 1 hour before the Sun but may be difficult in the summer twilight. Afterward, Mars disappears in the evening twilight reaching conjunction with the Sun on Oct. 8. On Nov. 19, Mercury (mag -0.5) and Mars (1.6 mag.) meet up in Leo for their second conjunction of the year. They rise 1 hour before the Sun and will be easier to spot in the fall twilight. The last event for Mars is an occultation with the Moon on Dec. 3, but this will not be seen in N. America. Mars will begin climbing on the morning eastern horizon, heading into its next opposition on December 8, 2022.

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 December 21, 2020, Jupiter passed Saturn during the 20-year "great conjunction" so as the year opens the largest planets in the solar system appear to be a mere 1.5 degrees apart in the sky as viewed from Earth. Jupiter and Saturn are joined by Mercury on January 10, forming a triangle that covers 2.3 deg. in the sky, although it will not be visible because of the proximity of the planets to the Sun. Jupiter reaches conjunction with the Sun on Jan. 29th. Afterwards the giant planet will be visible in the morning sky beginning in mid-February. Jupiter (-2.0 mag) will meet up again with Mercury (0.1 mag.) for their Mar. 5 conjunction. Crossing through Capricornus, the giant planet slips into Aquarius at the end of April where it remain for the rest of the year. If you like to follow the Galilean moons as their shadows cross the disk, 2021 a good year to track them. Jupiter reach its first stationary point and begin retrograde motion on June 10. Jupiter is higher this year allowing better views for the northern based observers when the giant planet reaches opposition on Aug. 20. It will shine brilliantly at -2.9 when 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 may possible to see them with the naked eye for those with sharp vision especially as Jupiter is moving closer to perihelion this year. Jupiter will reach its second stationary point on Oct.18 and thereafter will resume its retrograde path through Aquarius. At the end of the year, Jupiter will be setting 3 hours after the Sun

The last planet to be discussed is the ringed-wonder, gas giant SATURN. The rings are made of ice, dust, and rock 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. This year Saturn will remain in Capricornus while Jupiter continues to widen the gap. Saturn will reach conjunction with the Sun on Jan. 13 and will not be seen until late March. Saturn reaches its first stationary point on May 23rd, going retrograde thereafter. Saturn reaches opposition on Aug. 2 shining at +0.2 mag. The rings will be tilted at 18 deg., the disk will be 18.6" and the rings will span ~40". Saturn will arrive at each second stationary point on Oct. 11, then resume its prograde motion through Capricornus. At the end of December, Saturn will set about 2 hours and 45 minutes after the Sun, prominent with Jupiter in the evening sky.

Eclipses for 2021

The eclipse season starts on May 26 with a total lunar eclipse that is the first total lunar eclipse since January 2019. This eclipse will be centered over the Pacific Ocean where the entire eclipse will be visible. The Moon will be close to perigee, but close to the edge of the Earth's umbra, so that the southern portion of the Moon will be noticeably darker than the northern. The duration of the total phase is a mere 14.5 minutes. Observers in N. and S. America will miss the final phases and those in Asia and Australia will miss the beginning. The first solar eclipse of the year occurs 2 weeks later on June 10 and is an annular eclipse lasting 3 min. 51 sec. The path of annularity is mostly within the Arctic circle partial phases of the eclipse are observable from Canada, Russia, eastern N. America, Iceland, Greenland and Europe. The second lunar eclipse for 2021 will occur on Nov. 10 and is an interesting partial with 97.4% of the Moon covered. This time a small sliver of the Moon will remain uneclipsed. Again the eclipse is centered over the Pacific Ocean, but this time the entire eclipse will be visible from N. America. Finally, there will be a total solar eclipse visible from the most remote southern region of Earth, over Antarctica. This eclipse may be observed as a partial from the southernmost tips of S. America, Australia and Tasmania. Greatest duration is 1 minute 54 seconds.

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