Seiichi Yoshida's Diary of Comet Observations (2018)

Japanese version
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Updated on December 18, 2018

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Detailed observation data in ICQ format.

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* 2018 Dec. 10-17 (1 comet)

I observed 46P/Wirtanen, passing near by Earth, in Hawaii. It looked very large with naked eyes thanks to the clear sky.

46P/Wirtanen

5.3 mag   Dia. 25'   DC 1   (10x66 monocular)

4.9 mag   Dia. 40'   DC 4   (10x66 monocular)

4.1 mag   Dia. 50'   DC 1   (naked eye)

4.8 mag   Dia. 50'   DC 4   (10x66 monocular)

3.9 mag   Dia. 70'   DC 3   (naked eye)

4.7 mag   Dia. 60'   DC 5   (10x66 monocular)

3.4 mag   Dia. 95'   DC 4   (naked eye)

4.7 mag   Dia. 55'   DC 5   (10x66 monocular)

3.6 mag   Dia. 115'   DC 3   (naked eye)

4.7 mag   Dia. 50'   DC 4   (10x66 monocular)

3.8 mag   Dia. 80'   DC 3   (naked eye)

5.0 mag   Dia. 40'   DC 3   (10x66 monocular)

On Dec. 10, I observed it in Waikiki, Honolulu, Oahu, just after I ran the Honolulu marathon. Not easy to see due to the city light.

On Dec. 12, I observed it in Kailua Kona, Hawaii.

On Dec. 13, I observed it in Mauna Kea, Hawaii, in the sunset and star watching tour.

From Dec. 14 to 17, I observed it in Kapalua, Maui.

* 2018 Nov. 30-Dec. 1 (8 comets + 1 asteroid)

I observed 8 comets and 1 asteroid visually on Nov. 30 and Dec. 1 in Kita-karuizawa, Gunma, Japan.

The sky was often covered with thin clouds.

C/2016 N6 ( PanSTARRS )

Nov. 30   12.3 mag   Dia. 1.0'   DC 3-4   (40.0-cm reflector 144x)

Dec. 1   12.6 mag   Dia. 1.1'   DC 3   (40.0-cm reflector 144x)

Not easy to see due to the moon light.

C/2018 L2 ( ATLAS )

Nov. 30   11.3 mag   Dia. 1.3'   DC 4   (40.0-cm reflector 144x)

Dec. 1   11.7 mag   Dia. 1.3'   DC 3   (40.0-cm reflector 144x)

Looks small due to the low sky condition.

21P/Giacobini-Zinner

Nov. 30   11.3 mag   Dia. 1.3'   DC 3   (40.0-cm reflector 144x)

Diffuse and hard to see.

29P/Schwassmann-Wachmann 1

Nov. 30   12.5 mag   Dia. 1.3'   DC 5   (40.0-cm reflector 144x)

Dec. 1   12.8 mag   Dia. 1.2'   DC 2   (40.0-cm reflector 144x)

Because just after a new outburst, well condensed, bright and easy to see.

On Dec. 1, I felt the condensation weak probably due to the thin clouds.

38P/Stephan-Oterma

Nov. 30   9.8 mag   Dia. 3.0'   DC 6   (40.0-cm reflector 36x)

Dec. 1   10.5 mag   Dia. 3.3'   DC 4   (40.0-cm reflector 36x)

Strongly condensed and easy to see. It looks DC=7 with 75x magnification.

46P/Wirtanen

Nov. 30   5.6 mag   Dia. 28'   DC 2   (10x70 monocular)

Dec. 1   5.6 mag   Dia. 28'   DC 3   (10x70 monocular)

Very very large! Easy to see with a small monocular.

64P/Swift-Gehrels

Nov. 30   9.1 mag   Dia. 8'   DC 4   (40.0-cm reflector 36x)

Dec. 1   9.1 mag   Dia. 6'   DC 3-4   (40.0-cm reflector 36x)

I was surprised that it became brighter and larger.

78P/Gehrels 2

Nov. 30   fainter than 13.8 mag   Dia. 0.8'   (40.0-cm reflector 257x)

Not visible.

(944) Hidalgo

Nov. 30   14.3 mag   DC 9   (40.0-cm reflector 144x)

Still well visible.

* 2018 Nov. 3 (8 comets + 1 asteroid)

I observed 8 comets and 1 asteroid visually on Nov. 3 in Kita-karuizawa, Gunma, Japan.

Mountains look beautiful with autumn leaves. It was cloudy in the evening, but it was fine from midnight to morning.

C/2015 O1 ( PanSTARRS )

fainter than 13.0 mag   Dia. 0.6'   (40.0-cm reflector 257x)

Not visible.

C/2016 N6 ( PanSTARRS )

11.9 mag   Dia. 1.9'   DC 5   (40.0-cm reflector 144x)

Bright and well visible. Moderately condensed.

C/2016 R2 ( PanSTARRS )

fainter than 11.8 mag   Dia. 1.1'   (40.0-cm reflector 144x)

Not visible. The background sky of the low sky was bright.

21P/Giacobini-Zinner

11.7 mag   Dia. 1.6'   DC 1   (40.0-cm reflector 75x)

It became surprisingly faint and small only within one month.

38P/Stephan-Oterma

10.0 mag   Dia. 6'   DC 3-4   (40.0-cm reflector 36x)

Bright and well visible.

46P/Wirtanen

8.5 mag   Dia. 7'   DC 2   (40.0-cm reflector 36x)

Diffuse and large.

60P/Tsuchinshan 2

fainter than 13.7 mag   Dia. 0.7'   (40.0-cm reflector 257x)

It must be brightening rapidly, but it was not visible yet.

64P/Swift-Gehrels

9.9 mag   Dia. 5'   DC 5   (40.0-cm reflector 36x)

Getting brighter. Strongly condensed and easy to see.

(944) Hidalgo

14.0 mag   DC 9   (40.0-cm reflector 257x)

Bright and well visible.

* 2018 Oct. 6-7 (9 comets + 1 asteroid)

I observed 9 comets and 1 asteroid visually on Oct. 6 and 7 in Kita-karuizawa, Gunma, Japan.

I really enjoyed many bright comets!

On Oct. 6, a typhoon was passing through Japan, and the wind was very strong all night. On Oct. 7, it was fine with no wind.

C/2016 N6 ( PanSTARRS )

Oct. 6   12.9 mag   Dia. 0.8'   DC 6   (40.0-cm reflector 144x)

Oct. 7   13.2 mag   Dia. 0.8'   DC 5-6   (40.0-cm reflector 144x)

Well condensed.

C/2017 M4 ( ATLAS )

Oct. 7   14.0 mag   Dia. 0.4'   DC 3-4   (40.0-cm reflector 257x)

Tiny.

21P/Giacobini-Zinner

Oct. 6   9.0 mag   Dia. 5'   DC 4   (40.0-cm reflector 36x)

Oct. 7   8.9 mag   Dia. 5.5'   DC 3-4   (40.0-cm reflector 36x)

It became faint. On Oct. 7, it located very close to an open cluster M50, and I enjoyed the rendezvous.

29P/Schwassmann-Wachmann 1

Oct. 6   12.2 mag   Dia. 1.6'   DC 5   (40.0-cm reflector 75x)

Oct. 7   12.2 mag   Dia. 1.6'   DC 3   (40.0-cm reflector 75x)

It was amazing to see such bright 29P! Large and easy to see.

38P/Stephan-Oterma

Oct. 6   10.9 mag   Dia. 2.4'   DC 6   (40.0-cm reflector 75x)

Oct. 7   11.4 mag   Dia. 3.2'   DC 5-6   (40.0-cm reflector 75x)

Strongly condensed and easy to see.

46P/Wirtanen

Oct. 6   11.4 mag   Dia. 1.7'   DC 3-4   (40.0-cm reflector 75x)

Oct. 7   11.9 mag   Dia. 3.0'   DC 3-4   (40.0-cm reflector 75x)

It seems to have brightened rapidly. Now it is very bright and large.

48P/Johnson

Oct. 7   13.5 mag   Dia. 0.7'   DC 4   (40.0-cm reflector 257x)

Tiny. Unexpectedly, I could see it still now.

64P/Swift-Gehrels

Oct. 6   11.0 mag   Dia. 2.2'   DC 4   (40.0-cm reflector 75x)

Oct. 7   11.6 mag   Dia. 2.3'   DC 4-5   (40.0-cm reflector 75x)

Larger than expected.

78P/Gehrels 2

Oct. 7   14.1 mag   Dia. 0.6'   DC 2   (40.0-cm reflector 257x)

Unexpectedly diffuse.

(944) Hidalgo

Oct. 7   14.1 mag   DC 9   (40.0-cm reflector 144x)

Stellar.

* 2018 Sept. 16-17 (8 comets + 1 asteroid)

I observed 8 comets and 1 asteroid visually on Sept. 16 and 17 in Kita-karuizawa, Gunma, Japan.

It was cloudy or rainy in day time. But it became fine and I could see stars well at night. However, it was humid and the low sky was not clear.

C/2017 M4 ( ATLAS )

Sept. 17   fainter than 13.7 mag   Dia. 0.4'   (40.0-cm reflector 257x)

Not visible due to the strong moon light.

21P/Giacobini-Zinner

Sept. 16   8.1 mag   Dia. 6'   DC 7   Tail 8.5' (p.a. 275 deg)   (40.0-cm reflector 36x)

Sept. 16   6.9 mag   Dia. 11'   DC 6   (10x70 monocular)

Sept. 17   7.7 mag   Dia. 8'   DC 7   Tail 13' (p.a. 275 deg)   (40.0-cm reflector 36x)

Sept. 17   6.8 mag   Dia. 13'   DC 6   (10x70 monocular)

Bright! Strongly condensed, but it has a large diffuse coma. It looks very nice with a long tail.

37P/Forbes

Sept. 16   fainter than 13.5 mag   Dia. 0.6'   (40.0-cm reflector 257x)

Sept. 17   fainter than 13.1 mag   Dia. 0.7'   (40.0-cm reflector 257x)

Not visible.

38P/Stephan-Oterma

Sept. 16   11.4 mag   Dia. 2.3'   DC 4-5   (40.0-cm reflector 75x)

Sept. 17   11.5 mag   Dia. 1.3'   DC 6   (40.0-cm reflector 144x)

Very bright and easy to see.

I'm glad that finally I can see this comet!

46P/Wirtanen

Sept. 16   fainter than 13.6 mag   Dia. 0.6'   (40.0-cm reflector 144x)

Sept. 17   fainter than 13.4 mag   Dia. 0.6'   (40.0-cm reflector 257x)

Not visible.

48P/Johnson

Sept. 17   13.3 mag   Dia. 1.0'   DC 4   (40.0-cm reflector 144x)

Tiny. I felt the comet faded so much. But it was only due to the dim sky condition in the low sky.

64P/Swift-Gehrels

Sept. 16   13.2 mag   Dia. 0.8'   DC 6   (40.0-cm reflector 144x)

Sept. 17   12.2 mag   Dia. 1.6'   DC 5   (40.0-cm reflector 144x)

Well condensed. Much brighter than expected.

78P/Gehrels 2

Sept. 17   fainter than 13.8 mag   Dia. 0.6'   (40.0-cm reflector 257x)

Not visible.

(944) Hidalgo

Sept. 16   fainter than 14.4 mag   (40.0-cm reflector 257x)

Sept. 17   14.2 mag   DC 9   (40.0-cm reflector 257x)

Stellar.

* 2018 July 13 (8 comets)

I observed 8 comets visually on July 13 in Kita-karuizawa, Gunma, Japan.

The sky was fine and very clear.

I also tried to observe 66P, but I could not observe it because it overlapped on a 10-mag star.

C/2015 O1 ( PanSTARRS )

12.8 mag   Dia. 1.0'   DC 4   (40.0-cm reflector 144x)

Well visible.

C/2017 M4 ( ATLAS )

13.6 mag   Dia. 0.4'   DC 6   (40.0-cm reflector 257x)

Tiny, but clearly visible.

C/2017 S3 ( PanSTARRS )

10.2 mag   Dia. 3.5'   DC 3-4   (40.0-cm reflector 75x)

Bright. Well condensed more than expected.

C/2018 N1 ( NEOWISE )

12.0 mag   Dia. 1.8'   DC 2-3   (40.0-cm reflector 144x)

Diffuse.

21P/Giacobini-Zinner

10.0 mag   Dia. 4'   DC 5   (40.0-cm reflector 36x)

Very bright. Very strongly condensed with higher magnification.

29P/Schwassmann-Wachmann 1

fainter than 13.5 mag   Dia. 0.8'   (40.0-cm reflector 144x)

Not visible.

37P/Forbes

13.5 mag   Dia. 1.0'   DC 3   (40.0-cm reflector 144x)

Fainter than expected.

48P/Johnson

13.3 mag   Dia. 0.5'   DC 7   (40.0-cm reflector 144x)

Central condensation is very sharp.

* 2018 May 3-4 (4 comets)

I observed 4 comets and 1 nova visually on May 3-4 in Kita-karuizawa, Gunma, Japan.

In addition to 4 PanSTARRS's comets, I also observed a naked-eye nova discovered by Yuji Nakamura. The contrast of orange nova and a nearby blue star was beautiful.

V392 Per:
  May 3.50: 8.4 mag (S. Yoshida, Gunma, Japan, 0.40-m f/4.5 reflector);
  May 4.49: 8.7 mag (S. Yoshida, Gunma, Japan, 0.40-m f/4.5 reflector);

C/2015 O1 ( PanSTARRS )

May 3   13.5 mag   Dia. 0.8'   DC 4-5   (40.0-cm reflector 144x)

May 4   13.1 mag   Dia. 1.2'   DC 5   (40.0-cm reflector 144x)

Well condensed and easy to see.

C/2016 M1 ( PanSTARRS )

May 3   10.5 mag   Dia. 1.7'   DC 4   (40.0-cm reflector 144x)

Hard to see due to the bright moon.

C/2016 N6 ( PanSTARRS )

May 3   12.3 mag   Dia. 1.4'   DC 5   (40.0-cm reflector 144x)

May 4   12.7 mag   Dia. 1.1'   DC 5   (40.0-cm reflector 144x)

Well condensed and easy to see.

C/2016 R2 ( PanSTARRS )

May 3   13.1 mag   Dia. 0.9'   DC 3-4   (40.0-cm reflector 257x)

May 4   13.2 mag   Dia. 0.6'   DC 2   (40.0-cm reflector 257x)

It became faint, although it is at the perihelion now.

* 2018 Mar. 12 (4 comets)

I observed 4 comets visually on Mar. 12 in Mt. Hanadate, Ibaraki, Japan.

The weather was fine with no clouds in the evening, but the sky was dim.

The sky was covered with clouds in the morning. But I could observe only C/2015 O1 through a gap of clouds in short time.

C/2015 O1 ( PanSTARRS )

12.8 mag   Dia. 1.4'   DC 3   (40.0-cm reflector 144x)

Bright, but the condensation is weaker than expected.

C/2016 N6 ( PanSTARRS )

12.7 mag   Dia. 1.1'   DC 6   (40.0-cm reflector 144x)

Small, strongly condensed, and easy to see.

C/2016 R2 ( PanSTARRS )

about 11.6 mag   Dia. 1.5'   DC 3   (40.0-cm reflector 75x)

Overlapping on a 12.8 mag star, so somewhat difficult to observe. But still bright and well visible.

185P/Petriew

about 12.5 mag   Dia. 1.3'   DC 1   (40.0-cm reflector 144x)

Hard to see because the background sky was very bright.

* 2018 Jan. 6 (2 comets)

I observed 2 comets visually on Jan. 6 in Mt. Hanadate, Ibaraki, Japan.

I also tried to observe C/2017 O1 passing near by an open cluster NGC 188. But I could not see the comet due to a nearby double star of 14.5 mag stars.

C/2016 R2 ( PanSTARRS )

11.1 mag   Dia. 2.6'   DC 5   (40.0-cm reflector 75x)

Bright. Near by Hyades.

C/2017 T1 ( Heinze )

10.3 mag   Dia. 4'   DC 1   (40.0-cm reflector 36x)

Bright, but very diffuse.

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