April 3, 2020

AstroEvent of the Week: 13.04.09: New Comet Yi-SWAN!

We interrupt our usual astro-event of the week to bring you a last minute shout-out a tad early; a fairly bright comet has recently been announced by the Central Bureau of Astronomical Telegrams (CBAT) in Cambridge, Massachusetts (really; does anyone actually send telegrams any more? Time to change the name, guys!) Dubbed Yi-SWAN after its co-discovers, Korean amateur Dae-am Yi who sighted the comet on March 26th and the European Space (ESA)’s SWAN, the Solar Wind Anisotropies satellite, Comet Yi Swan is expected to maintain around 8th magnitude for the next month or  so.

As last week’s Full Moon moves out of the sky, Yi-SWAN should become a pretty decent binocular target. It will be ranging through the star fields of Cassiopeia and Perseus April through May. Early morning will provide the highest elevation views for northern hemisphere viewers, when Cassiopeia will be high in the north eastern sky. Comet Yi-SWAN will it reach perihelion on May 8th, at 1.27 Astronomical Units (A.U.s) from the Sun, when it will be almost 2 A.U. from the Earth. Some highlights and guide targets it will pass by are Schedar, or Alpha Cassiopeiae on April 11th (about 0.4 degrees south) and April 23-24th, when it will slide 1.2 degrees south of the Double Cluster in Perseus, an excellent photo op! Incidentally, Comet Yi-SWAN will be technically circumpolar for mid- to high-northern latitude observers throughout its apparition… your first moonless viewing opportunity may well come this week in the early evening!


The Astro Word of the Week is Coma. In astronomy, the term coma means something entirely different than in medical terminology. When talking about comets, this is the fuzzy “Q-tip head” which envelopes the nucleus of the comet. This could be considered an atmosphere of sorts, and is composed mostly of dust and ice sublimating as the comet nears the Sun. Trace gases, such as cyanogen, which caused “Comet hysteria” when the Earth passed through Halley’s tail in 1910, have been detected in comas via spectroscopic analysis. Don’t worry, the tail of a comet is so wispy, it is still effectively a vacuum. If the comet is large enough and makes a close pass by the Sun, a long, beautiful tail might be seen. The coma is the most visually obvious part of cometary anatomy through binoculars or a small telescope.  How bright will Yi-SWAN get? Will it display a tail or remain a fuzz ball? Comets are notoriously unpredictable. This one deserves keeping a close eye on!



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