On Fri, Mar 8, 2013 at 2:08 AM, Igor Roshchin <[email protected]> wrote: > A good comet will have the dust tail extend at > least 45deg or so. > <<<<<
I believe this sentence must be a typo. Coincidentally, comet expert John Bortle posted to the comets mailing list this morning this interesting post regarding PanSTARRS' tail presentation: - - - As I had pointed out quite some time back, PanSTARRS' dust tail is unlikely ever to be impressive visually, in spite of probably being very long in reality. While dust tails are often very broad (particularly the one associated with C/2011 L4 it would seem) they are very thin in cross section. Normally only when viewed from a relatively low angle do they gain great prominence and length. While the C/2011 L4 has grown ever brighter in recent weeks it has been viewed against an ever brighter twilight sky as its elongation from the Sun has dwindled. This basically offset any brightness gains the dust tail has experienced. Compound this with the fact that currently our view of PanSTARRS' dust tail is almost perfectly face-on, rendering the lowest possible surface brightness as seen from Earth, and you get a relatively weak tail presentation. Although the visual (and photographic) length of the comet's dust tail will certainly grow as it moves away from the twilight regions I wouldn't really anticipate any spectacular presentation since the comet remains in or near the fringes of twilight and at very low elevation in the western sky for such a protracted interval. By the time PanSTARRS does get well clear of these it will have faded considerably, along with physically having drawn well away from the Sun and the nucleus' out-gassing become greatly reduced. J.Bortle -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
