At present I employ 18"
F4.5 Dobsonian with an eyepiece of 30 mm, 88 degrees apparent field (Planocular),
made in Germany. Thus, the actual field D is 1.3 degrees with a magnification of 68. However, recently, I often use Paracorr (TeleVue, USA) and
this combination yeilds D = 1.1 degrees with x78.
I search for 40 (vertical dimension) x 30 (horizontal dimension) degrees range in a typical comet search
session in one hour and half. I spend two hours at most in one session,
because it is the maximum time I can concentrate on a searching. I sweep
vertically, from an altitude of about 40 degrees to the horizon: this
distance h is shown in the figure.
How to seep the sky.
I sweep the sky downward only.
D = 1.3 or 1.1 degrees, h = 40 degrees, d = 0.4 - 0.9 degrees
When the field reaches to the horizon, I move the telescope counter
clock wise horizontally. i.e. the northward for eastern sky search
session, and to the southward in western sky. Its angular distance d, which is measured in reference to the horizon,
depends on the direction of the telescope. Minimumdis 0.4 degrees in the northern sky, as horizontal diurnal motion
is small and maximum is 0.9 degrees in the southern sky.
After this small horizontal motion, I swing the telescope upward to an
altitude of some 40 degrees at once without looking into the eyepiece.
From this altitude I start sweeping the sky again, that is, I search downward
only pushing down the wood bar connected to the top ring of the telescope
through string.
Pushing down the telescope by the right hand for vertical search.
Note that I grasp the ladder by the left hand and lean to it to
keep a comfortable position.
There are two advantages for vertical search as Tsutomu Seki pointed
out. First, vertical sweeping is more sensitive to diffuse objects like
comets than horizontal sweeping, because human eyes tend to move horizontally.
Second, you do not overlook objects especially in the eastern and western
sky in comparison with horizontal sweeping. A disadvantage is that large
area near horizon set down before you seek in the western sky at dusk and
large risen area before twilight leave unsearched in the eastern sky at
dawn.
I completely rely on the digital setting circles, "NGC Sky
Vector", to identify deep sky objects. It has "Identify" mode
that you can identify more than 11,000 deep sky objects.
Syogo Utsunomiya, the most successful comet hunter in recent years,
contributed an article entitled "Comet hunting and My devices" to the
Journal of Oriental Astronomical Association, "The Heavens", No. 875, pp.161-164,
Apr 1998, and outlined it.
Against trouble for the digital setting circles and positioning
of a new comet, 50 mm right angle erect and Telrad finders are installed
though I have never had any trouble with digital setting circles except
the death of batteries.
I always bring Uranometria
2000, Yagai-seizu 2000 (8 pages, Seibundo-Shinkosya,
Tokyo), Deep Sky Browser (iPod App.) and Starmap Pro (iPod App.) with me in my car when I go for a comet hunting. In addition to
these atlases I have installed a digital atlases,Guide 9.
In my opinion you cannot measure comet hunter's effort by the
hours only. I spent almost the same time to drive to the observation
site and assembling a telescope in comparison with the actual comet hunting hours.
I had lived in Tsukuba City, Ibaraki Prefecture until March 2001, 60
km NE of Tokyo where light pollution was getting worse every year. In
Tsukuba it took 40 minutes to the site where I could observe 6th magnitude
star near zenith under excellent condition, but at low altitude light pollution
was very strong except from east to north. We had a lot of fine days in
winter on the Pacific side, however, generally speaking it is hazy even
if there is no cloud in summer.
In April 2001 I transferred to Tohkamachi City, Niigata Prefecture
200 km NNW of Tokyo. The sky condition is much better here in Tohkamachi
than in Tsukuba but it is not as good as what I expected before I came
here. Now it takes 15-20 minutes from my house to my usual observation
sites (about 450 m or 1480 feet above sea level) by car, and takes 30
minutes to start sweeping the sky after arrival including assemble the
telescope and wearing winter clothes. I selected several observation sites
and there are two reasons for this. First, the favorable sites for eastern
sky at dawn and for western sky at dusk are different. Second, many roads
that lead to farmland and mountainous areas are closed in winter due to
snow.
I can see 6.5th magnitude star with averted vision and even at low
altitude it is rather dark. Under usual sky condition M13 is discernible
easily with the naked eye, however, I can seldom see M33.
My observation sites are not fixed and I sometimes drive to a darker
site spending an hour where an altitude is 1000 m (3300 feet) above sea
level.
In contrast to Pacific side like Tokyo and Tsukuba, on the Sea of
Japan side bad weather with a lot of snow fall lasts in winter. We have
2.3 meters (8 feet) snow on average and more than 3 memters some years in Tohkamachi.
Several days after my discovery of C/2002 E2 Snyder-Murakami, a
certain Japanese comet observer contacted me and said that my positioning
in the discovery report was so precise that he wanted to know the method.
I did nothing special, however, as a result, it was very precise as he
mentioned: my measurement reproduced ephemerides based on the provisional
orbit within 0.4'.
Reproduced from MegaStar
The grid interval of the Declination is 5 arc minutes.
What I did was very simple. I marked the position of the comet in
Uranometria 2000 and selected three stars A, B, and C near the comet in
the field as shown in the figure. All these three guide stars are
printed in Uranometria 2000. Luckily, All those stars were shown in
Uranometria, but if only you have identified at least one reference
star shown in the map, you can select
darker stars to make triangle(s). You can identify those darker
stars at home using ditigal map. Then, I memorized the shapes of two
triangles. Fortunately,
A, B, and the comet formed a right triangle, and B, C, and the comet
did an isosceles
triangle. Try to find special shape‚“ like this if you can.
I got home and turned on PC to start MegaStar. MegaStar displayed
the three stars and I remembered the shapes of two triangles and clicked
the the position of the comet to know the coordinates.
I believe you can position within 1' precision using this method.
