The star attraction in the month of October ‘10 seems to be 103P Comet
Hartley.
The comet promises to be visible with the naked eye in the entire month.

Normally comets are at their brightest intrinsically when their distance to the
sun decreases to a minimum, in the course of their orbit. This happens when the
comet reaches its perihelion, by definition. The brightness of a comet as seen
from the Earth is a combination of factors such as its intrinsic brightness,
distance from the Earth and elongation from the Sun, i.e. if the comet is
visible during twilight or true night.

Comet Hartley is closest to Earth on 21st October 2010. The perihelion of Comet
Hartley occurs on 28th October 2010. The elongation of the comet in this period
ranges from 121 to 116 degrees, i.e. it is far from the Sun and remains visible
most of the night in the entire month of October 2010.

This set of circumstances are quite favourable for amateur observations, when
the comet is closest to the Sun, it lies right opposite to the Sun as seen from
Earth. The distance of P103 Hartley from the Sun is just a little greater than 1
au, making the observation circumstances perfect.

The magnitude of the comet on 1st October is estimated to 5.8, and at the end of
October at magnitude 4.7. Full moon occurs on 23rd October, so about 3 days on
either side of Full Moon the Comet’s glory will be diminished a little. The
magnitude of the comet tries to compete with the full moon, it reaches a maximum
estimated magnitude of 4.4 on 22nd October.

The comet starts the month of October in the constellation of Cassiopeia, on 7th
October it moves in Perseus, 13th October into Camelopardalis for a brief period
and moves back into Perseus on 14th, 18th into Auriga, 26th into Gemini and
remains in the same constellation till the end of the month.

All of these constellations lie in the high density star fields of Milky Way
with plenty of nebulae and deep sky objects strewn across the path of the comet.
The comet rendezvous many clusters and nebulae in the month of October as listed
below:
October 1st & 2nd near Pacman Nebula, NGC 281, in Cassiopeia,
October 4th near Owl Cluster in Cassiopeia,
October 8th very near to Double Cluster in Perseus,
October 14th very near to NGC 1491 in Perseus,
October 21st, 22nd & 23rd near M36, M37, M38 the three open clusters in Auriga,
October 25th near M35, Open cluster in Gemini,
October 27th & 28th near a gibbous Moon.

I hope the monsoon weather does clear up for a grand view of Comet P103 Hartley
in October.

Ajay Talwar




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