Rho Geminids Maximize Friday, Jan. 8, and Again Thursday, Jan. 21

Summary: The Rho Geminids maximize Friday, Jan. 8, and again Thursday, Jan. 21, during their month-long shower from the end of December to the end of January.

The radiant point for the Rho Geminids is in the constellation Gemini ~ Gemini, as viewed with unaided eyes, with added connecting lines: Till Credner, CC BY SA 3.0, via Wikimedia Commons

Appearing as a minor meteor shower from Monday, Dec. 28, to Thursday, Jan. 28, the Rho Geminids maximize on Friday, Jan. 8, and then shoot stars in a secondary maximum of peak hourly rates, known in astronomy as zenithal hourly rate (ZHR), on Thursday, Jan. 21.

The Rho Geminid meteor shower’s secondary maximum on Jan. 21 has to contend with lunar brightness of the waxing gibbous phase, with over 90 percent visibility, and extensive cloud cover. The graphical sky cover forecast issued by the National Oceanic and Atmospheric Administration’s National Weather Service for the CONUS (48 contiguous states) Area for Jan. 21, the date of the Rho Geminids’ secondary maximum, indicates sky cover over the Pacific Northwest and much of the central and eastern United States. Clear skies are expected over Florida, the Southwest, and sections of the mid-Atlantic states and of New England.

Members of the Italian Meteoric Association first detected the Rho Geminids as eight meteors seeming to shoot out from the constellation Gemini’s northwestern sector. The Italian meteor shower trackers made their discovery in January 1872. Subsequent observations were made by British amateur astronomer William Frederick Denning in 1897, German astronomer Cuno Hoffmeister in 1921 and 1931, and Estonian astronomer/astrophysicist Ernst Julius Öpik in 1933.

Astronomers Gerald Stanley Hawkins and Richard B. Southworth were first to suggest the production of a regular meteor shower by the recurring January stream. In 1963, they identified four meteors from meteor orbits photographed from 1952 to 1954 by the Harvard Meteor Program as representing the suggested shower.

Meteors journey across the sky every night. Nightly meteor activity links either to a known major or minor meteor shower or to sporadic meteors with no known meteor shower associations. A variety of factors accounts for minor meteor showers such as the Rho Geminids. Small amounts of debris from the parent comet produce minor activity as Earth passes through the meteor stream. Planetary and solar forces have thinned old meteor showers by depleting or diffusing their streams. New meteor showers are in the early stages of receiving debris from their parent comets. A meteor shower’s slight grazing with Earth’s orbit also produces minor activity.

The constellation of Gemini the Twins serves as namesake of the Rho Geminids because the meteor shower appears to radiate from near Castor in Gemini’s western regions. The Rho Geminids share their constellatory radiant with one of the year’s most popular major meteor showers, December’s Geminids. The Heavenly Twins’ constellation also is linked with other minor meteor showers, such as October’s Epsilon Geminids.

Although their flashy flights appear to trace back to their namesake constellations, meteor showers are not restricted in their range. The namesake constellation serves as a convenient reference point, not as the actual point of origin for the meteor shower.

Although minor meteor showers are not as flashy as major meteor showers, their sedate show is worthwhile. The Rho Geminids offer the double excitement of two maximums. Viewers who miss the first maximum on Jan. 8 have a second chance with the second maximum on Jan. 21. Those who catch both maximums double their enjoyment of the Rho Geminids.

A bonus of watching for the Rho Geminids is easy viewing of Gemini. The meteor shower's annual appearance in January coincides with Gemini's favorable placement high overhead in the night sky.

Castor and Pollux, the Heavenly Twins: ca. 1825 depiction of Gemini by British cartographer and engraver Sidney Hall (1788-1831): Library of Congress Prints and Photographs Division, Public Domain, via Wikimedia Commons

Acknowledgment

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

Image credits:

Gemini in sky: Till Credner, CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:GeminiCC.jpg

ca. 1825 depiction of Gemini by British cartographer and engraver Sidney Hall (1788-1831): Library of Congress Prints and Photographs Division, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Sidney_Hall_-_Urania%27s_Mirror_-_Gemini.jpg

For further information:

Denning, William F. Telescopic Work for Starlight Evenings. London: Taylor and Francis, 1891.
Available via Internet Archive @ https://archive.org/stream/telescopicworkfo00dennrich#page/n5/mode/2up

Kronk, Gary. "Observing the Geminids." Meteor Showers Online.
Available @ http://meteorshowersonline.com/geminids.html

Marriner, Derdriu. "2015 Geminids Peak Monday, Dec. 14, With After-Peak High Dec. 15." Earth and Space News. Monday, Dec. 14, 2015.
Available @ https://earth-and-space-news.blogspot.com/2015/12/geminids-peak-december-14-peak-high-december-15.html

Marriner, Derdriu. “January’s Quadrantids Kick Off New Year Shooting Star Show Lineup.” Earth and Space News. Monday, Jan. 4, 2016.
Available @ https://earth-and-space-news.blogspot.com/2015/12/2015-geminids-peak-on-december-14-with.html

McClure, Bruce. “Gemini? Here’s your constellation.” EarthSky > Tonight > Constellations. Feburary 3, 2015.
Available @ http://earthsky.org/constellations/gemini-heres-your-constellation

“The night sky for January 2016.” The Jodcast. Jan. 9, 2016.
Available @ http://www.jodcast.net/sky/

Reynolds, Mike D. Falling Stars: A Guide to Meteors and Meteorites. Mechanicsburg PA: Stackpole Books, 2001.