Wednesday, March 11, 2009

Foreshortening effects on C/2007 N3 (LULIN)

Comet C/2007 N3 (LULIN) was a nice show in late February this year, when it passed relatively close (nearly 0.42 AU, on Feb. 24th). At about its perigee, another phenomena occurred: its phase angle reached a minimum value, then it quickly started to grow-up again. Nearly simultaneosly we witnessed an abrupt change in the appearance of the comet, due to the consequent foreshortening effect: the ion tail, in a matter of hours, switched from North-West to South-East.

Possibly another, less cospicuous, change in comet's LULIN aspect may be under course: according to our follow-up, some effects of the foreshortening change seems to be readily visible also in a series of images we secured from various sites & through with different scopes, in the past few weeks.

As you may notice from the following panels, the prominent feature (kind of "fan" structure) originating from the central condensation toward South-West (i.e. at about PA 220 deg), plus a secondary one, toward North-East (i.e. at about PA40 deg) that was reported by several observers, visible till March 2nd, now seems to be over:

March 11th:

March 2nd:

Februaty 27th:

February 19th:

More data need to be secured to definitely clarify the situation, however at a first glance we have the impression that this might be a foreshortening effects as well. Apparently, the changing geometry really plays a strong role, when interpreting the inner coma details sometimes reported on comets (alleged fans, jets, etc.).

by Giovanni Sostero, Ernesto Guido, Paul Camilleri & Virgilio Gonano

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