2018 December Monocerotids Peak Sunday, Dec. 9

Summary: The 2018 December Monocerotids peak Sunday, Dec. 9, as an annual minor meteor shower radiating from Monoceros the Unicorn constellation.

December Monocerotids appear to originate in Monoceros the Unicorn constellation: Longway Planetarium @LongwayPlanetarium via Facebook April 16, 2018

The 2018 December Monocerotids peak Sunday, Dec. 9, as an annual minor meteor shower with an apparent point of origin, known as the radiant, in Monoceros the Unicorn constellation.

American amateur astronomer Robert Lunsford, who writes the weekly Meteor Activity Outlook columns for the American Meteor Society (AMS) and for the International Meteor Organization (IMO), recommends 0100 local standard time as best viewing time for the December Monocerotids. The radiant is highest above the horizon as of that hour. Dr. Jürgen Rendtel of northeastern Germany’s Leibniz Institute for Astrophysics Potsdam (AIP) notes the visibility of the December Monocerotids in both the Northern Hemisphere and the Southern Hemisphere. He points out that “the radiant area is available virtually all night for much of the globe, culminating at about 01h30m local time.”

Lunsford describes December Monocerotid meteors as entering Earth’s atmosphere with a medium velocity. December Monocerotid meteors have an entry velocity of around 41 kilometers per second (around 25 miles per second).

Dr. Rendtel has compiled the International Meteor Organization’s annual meteor shower calendar since 2016. He observes in the IMO’s 2018 Meteor Shower Calendar: “This very minor shower’s details need further improvement by observational data.”

Dr. Rendtel gives activity dates of Nov. 27 to Dec. 17 for the December Monocerotids. The 2018 calendar’s Working List of Visual Meteor Showers (Table 5) confines activity to Dec. 5 to Dec. 20. The 2018 calendar’s Table 5 agrees with the 2017 calendar’s Table 5 in activity dates. The 2017 calendar lists Friday, Dec. 8 as peak.

Dr. Rendtel bases the Sunday, Dec. 9, upon visual data. Video data from 2011 to 2016, however, reveal Dec. 14 as the date of maximum activity.

Lunsford offers activity dates of Nov. 28 through Dec. 27 for the 2017 Monocerotids. Peak is predicted on Wednesday, Dec. 13. Activity for the 2016 December Monocerotids runs from Nov. 27 through Dec. 17. Maximum activity in 2016 occurs Friday, Dec. 9.

American amateur astronomer Gary W. Kronke identifies activity dates of Nov. 9 to Dec. 18. He also notes that Czech and American astronomer Zdenek Sekanina’s revived Radio Meteor Project (1968-1969) indicated a duration of Nov. 16 to Dec. 14. Kronke places annual peak around Dec. 11.

The December Monocerotid meteor shower’s name connects the annual display with an apparent point of origin in Monoceros the Unicorn constellation. December Monocerotid meteors appear to radiate outward from the Unicorn.

Monoceros straddles the celestial equator, the imaginary circle projected by astronomy and navigation from Earth’s equator outward into space. The Unicorn stretches northward into the Northern Celestial Hemisphere and southward into the Southern Celestial Hemisphere. Astronomy and navigation project Earth’s surface outward into space as an imaginary sphere that mirrors Earth’s hemispheres.

Monoceros claims well-known constellations as neighbors. Orion the Hunter lies to the west. Gemini the Twins constellation touches the Unicorn’s northern border. Canis Major the Greater Dog, with the night sky’s brightest star, Sirius (Alpha Canis Majoris, α Canis Majoris; Alpha CMa, α CMa), borders Monoceros to the south. Hydra the Sea Serpent, largest of the 88 modern constellations, slithers along the Unicorn’s eastern boundary.

Monoceros separates Canis Major from Canis Minor the Lesser Dog constellation. Canis Minor harbors the night sky’s eighth brightest star, Procyon (Alpha Canis Minoris, α Canis Minoris; Alpha CMi, α CMi).

In the week prior to peak activity, Saturday, Nov. 25, to Friday, Dec. 1, 2017, Lunsford finds the radiant in northern Orion, at 3 degrees northwest of Betelgeuse (Alpha Orionis, α Orionis; Alpha Ori, α Ori). Reddish Betelgeuse is the night sky’s ninth brightest star.

In the week of peak activity, Saturday, Dec. 9, to Friday, Dec. 15, 2017, Lunsford identifies the radiant position as lying in northwestern Monoceros, at 4 degrees southwest of Xi Geminorum (ξ Geminorum; Ksi Gem, ξ Gem) in Gemini the Twins constellation. Lunsford cautions that the radiant’s location lies only 7 degrees south of the November Orionid meteor shower’s radiant.

In the week of peak activity Saturday, Dec. 3, to Friday, Dec. 9, 2016, Lunsford finds the December Monocerotid radiant in northwestern Monoceros, at 7 degrees east of Betelgeuse. He notes the radiant’s position lies only 6 degrees south of the November Orionid meteor shower’s radiant. He cautions care in distinguishing the two showers’ radiants as observers trace back meteor paths.

In the week succeeding peak activity, Saturday, Dec. 10, to Friday, Dec. 16, 2016, Lunsford places the radiant in northern Monoceros. Its position is 5 degrees south of Xi Geminorum.

The takeaway for the 2018 December Monocerotids’ peak Sunday, Dec. 9, is that the minor shower’s meteors compete with November Orionid meteors of similar velocity radiating from the same area of the sky.

December Monocerotids’ radiant constellation, Monoceros the Unicorn, claims distinctive neighbors: Learn to Skywatch ‏@Learntoskywatch via Twitter Jan. 25, 2016

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

December Monocerotids appear to originate in Monoceros the Unicorn constellation: Longway Planetarium @LongwayPlanetarium via Facebook April 16, 2018, @ https://www.facebook.com/LongwayPlanetarium/posts/1880684941976037

December Monocerotids’ radiant constellation, Monoceros the Unicorn, claims distinctive neighbors: Learn to Skywatch ‏@Learntoskywatch via Twitter Jan. 25, 2016, @ https://twitter.com/Learntoskywatch/status/691697483261415424

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