C/2009 F6 (Yi-SWAN)
C/2009 F6 is moving east in Cassiopeia in the morning northern
sky. It is at a very low altitude and shortly will become easier to observe
in the evening. The comet is very diffused and does not come out well in
photographs taken by Geisei's 70cm telescope. How well diffused comets
like this can be photographed is determined by the telescope's f-ratio,
regardless of the aperture. Even with an aperture of 70cm, the image of
the comet is extended and diffused, if the optics are slow. I may so far
as to say that a 10cm f/7 and a 70cm f/7 will produce the same results.
When Comet Ikeya-Seki of 1965 was receding and becoming extremely
diffused, something odd occurred. My 35mm f/2 standard lens captured the
comet, while a large aperture of the 91cm f/5 telescope at Dodaira Observatory
could not. Large-aperture telescopes with slow optics are not always effective
for diffused objects. The 70cm telescope barely captured this comet, though
it was bright enough to visually observe.
Geisei Observatory was set up for observing comets and the
70cm telescope was designed to achieve f/5, but it actually turned out
to be much slower than f/7. It hasn't been rectified by the manufacturer
yet.
CK09F060 2009 04 12.79826 00 49 08.32 +56 19 38.5 12.5 N 372
CK09F060 2009 04 12.80139 00 49 09.84 +56 19 40.1 372
CK09F060 2009 04 12.80521 00 49 11.90 +56 19 42.8 372
CK09F060 2009 04 12.80868 00 49 13.63 +56 19 44.6 372
CK09F060 2009 04 18.79549 01 40 20.03 +56 34 07.2 12.7 N 372
CK09F060 2009 04 18.79826 01 40 21.45 +56 34 06.3 372
