Story from the discoverer. Translation by
Shigeki Murakami, discoverer of 2 comets.
On the discovery of
C/2021 O1 Nishimura
Hideo Nishimura
Translated
by
Shigeki Murakami
1. Discoverer
Hideo
Nishimura,
age 72
Kakegawa
City,
Shizuoka Prefecture, Japan
2. Site and date
Date and time of shooting: 2021 07 21.78306 (UT), 2021 07 22 3:47
(JST) (1), Exposure time 15 seconds
Observing
site:
Tea plantation: Gomyo, Kakegawa City, Shizuoka Prefecture, Japan
3. Materials
Camera:
CANON
EOS 6D, 200mm f/3.2 Telephoto lens
Equatorial mount: Takahashi EM200
4. Summary of the
discovery
I
have completed a nova hunting session, which is my major target of
searching, and I still had an extra time. Then, I conducted a comet
hunting session in the northeastern sky, and I was lucky enough to
shoot a green glowing comet. I checked the position and I wondered if
it was an outburst of 8P Tuttle. However, I found the position was
different from that of 8P by some 2°, and reported as it a possible
new comet.
5. Discovery course
I
concentrated on the visual searching of comet until around 2000, and
was able to meet a new comet (2). After that I have come to interest
in a nova hunting, and I kept searching spending 90% of my activity
for nova hunting and 10% for comet.
It was cloudy at dusk on the day before the discovery, and could not
take photos for nova hunting in the Milky Way Galaxy. So, on the day I
got up at 1:30a.m. local time and headed for the tea plantation where
a quarter-hour of drive from my residence. Most part of the summer
Milky Way was in the western sky, and I started shooting the Milky Way
at 2:08a.m. up to around the constellation of Cassiopeia.
As there was enough time until the start of the twilight, I began to
take photos to search for a comet from the southeastern sky, and put
the northeast on the backburner where I photographed the day before at
predawn.
At the low altitude the sky grew brighter when the shooting area got
close to the northeastern sky, and I hurried to take photos with
shorter exposure time. Eventually, I finished the hunting session at
4a.m. leaving some planned area to be searched.
I got home and tried to detect objects that are not in the past images
using my PC, among which I checked if there was any new object. I
noticed a non-stellar object seemingly having some apparent diameter
just before the end of the checking work. I thought that I identified
a known comet again, and I confirmed using MP checker but no comet was
detected.
To make sure what it was I adjusted the brightness of the image using
Photoshop Elements and the green star appeared that is typical for a
comet.
I emailed Syuichi Nakano, an Associate of the Central Bureau for
Astronomical Telegrams and the Minor Planet Center, in Sumoto, Japan,
that reported the object is a new comet without doubt. I calmed down
and I confirmed if there were any known comets around the position. I
found that 8P Tuttle being brightening was near the possible new
comet. Immediately, I told Nakano the fact and he said the predicted
position of 8P was different from that of the object of interest by
some 2°. I remeasured the position of the possible new comet.
Nakano reported the position to IAU and the new comet had been
confirmed.
I think back to the situation with a cool head, and I found I was
pretty lucky. If I had taken the photo a little bit earlier, the comet
would not have been photographed due to the low altitude from the
horizon, i.e., the unadjusted image looked like an overexposure photo
taken in the daytime. Conversely, if I had shotten a little later, it
would have been disappeared in the twilight.
Note of translator
(1) The beginning of the twilight on the day was 3:09a.m. JST (local
time). That meant Nishimura took the photo 38 minutes after the start
of the twilight.
(2) Nishimura
discovered his first comet in 1994: C/1994 N1
Nakamura-Nishimura-Machholz.
Discovery images. One color, one
black/white. The black lines are the power lines in the background of
the discoverer. See the image below.
