a comet is in the southern celestial hemisphere when its tail is visible.
a comet is in the southern celestial hemisphere when its tail is visible.
where is a comet when its tail is visible?
southern celestial hemisphere
a comet tail—and coma—are features visible in comets when they are illuminated by the sun and may become visible from earth when a comet passes through the inner solar system. as a comet approaches the inner solar system, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. separate tails are formed of dust and gases, becoming visible through different phenomena; the dust reflects sunlight directly and the gases glow from ionisation. most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye.
comet tail
cometary brightness is difficult to predict, especially when, as in this case, it is the first known appearance of the comet; so far c/2009 r1 is proving to be brighter than expected, so much so that sky and telescope retitled an online article from "faint comet in the june dawn" to "comet in the june dawn". c/2009 r1 is expected to eventually reach a brightness as high as magnitude 2 from june 30 to july 2, 2010, the latter date marking perihelion; however, as it brightens, its proximity to the sun will make it difficult to see, and it is likely to only be visible near the horizon at dawn and dusk. the exception to this will be the total solar eclipse on july 11 in the southern hemisphere (visible in the south pacific, touching land at mangaia, easter island, and far southern chile and argentina), which will allow the comet to be seen during the day. the comet is notable for its "impressive green coma and long ion tail", which spanned 5 degrees as of june 6, 2010, and its appearance has been likened to an "apple on a stick." by june 13, a second tail created by dust from the comet, was also visible, sharing the same green hue of the coma. the green colors in the coma are caused by the presence of cyanogen and diatomic carbon, while bluish hues in the ion tail are produced by positively charged carbon monoxide and carbon dioxide ions.
c/2009 r1