Why did Edwin Holmes
not see the outburst before November 7th?
- Full Moon was on November
4th 1892. The Moon would have been close to Andromeda in the sky and made
both deep sky observing and even the naked eye detection of a 4th magnitude
comet difficult or impossible.
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- This is the situation in the sky
the day when the 1892 outburst of 17P/Holmes presumably started. On 1892
November 2 the 95% illuminated Moon was in Pisces, only about 30% from the comet,
which was then close to M31. Although a 4th magnitude star would be detectable,
if its position was known in advance, the 4th magnitude Comet Holmes would have
been totally hidden from view and no one would have chosen to observe the nearby
M31 in these conditions. Note that even with the Moon no longer visible at the
start of the night the discovery was telescopic, not visual.
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On November 6th, 4 days after
outburst, the still almost full Moon was above the horizon soon after
twilight ended. The image shows the position of the Moon at 19:00UT on
November 6th, well above the eastern horizon.-
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However, on November 7th, there
was a short dark period at the start of the night. This image shows the Moon
at 18:45UT, just after it had risen. This was the first night for a week and a
half that observation of M31 would have been practical during the evening.
