Thursday, March 18
A comparison of visibility between a glass eyepiece and Night Vision: for C/2020 T2 Palomar and C/2020 R4 ATLAS
This is the fifth comet hunting session in March. I have observed C/2020 T2 Palomar and C/2020 R4 ATLAS before the searching session. In recent days I used NV instead of glass eyepiece because transparency has been poor due to disperse of Japanese cedar pollen with that of other plants. Though I have already observed the two comets, one of the objectives to see them was to compare the visibility of the glass eyepiece with that of NV.
First, I observed C/2020 T2 with the glass eyepiece, Ethos 21 mm, 97x. I trained my telescope at the comet using SkySafarai 6 Pro, a digital map, which was connected with Nexus DSC. At a glance I could not notice any comet-like objects in the FOV. I tried to compare the arrangement of stars in the FOV with that on the map to identify C/2020 T2. It took several minutes to confirm the position of the comet that was at an altitude of around 70º: at higher altitude the accuracy of locating object gets worse for Dobsonian. Though what I observe was not a comet-like object but a star-like one with the magnitude of 13 to 14, I was sure it was C/2020 T2. Then, I saw C/2020 R4 ATLAS employing the same eyepiece. It was easy to observe in spite of the low altitude of some 12º above the horizon. I estimated the comet as 10th magnitude, apparent diameter of 3' and DC=2 by intuition.
I changed the eyepiece to NV with 37x and aimed my telescope at C/2020 T2. I noticed an object that could be recognized as a comet at a glance, and observed as a magnitude of 12, apparent diameter of 1' and DC=7. I was sure to be able to spot the object of this image during my hunting session. I trained my comet seeker at C/2020 R4 with the same eyepiece, and I surely notice the existence of the comet, but somewhat hard to see it due to lower magnification in comparison with the image seen by using Ethos 21 mm. It looked darker than using the glass eyepiece and estimated as the magnitude of 11, apparent diameter of 2' and DC=2.
Which eyepiece is better for comet hunting, the glass eyepiece or NV?
The answer: it is dependent of nature comets and as I have ever written it also depends on the sky condition things like moonlight and the degree of light pollution. As Tsutomu Seki's famous quote, there is no secret plan to discover a new comet.
I have spent some 15 minutes for the above-mentioned observation, and finally, I was ready to start the comet hunting session at 4:18am. I began with Altair, alpha Aquilae, using NV. All the DSOs I identified were globular clusters. They were only three: NGC6934, M2 and M15. All were resolved into stars with NV. It was impressive that some stars of M2 at the periphery were resolved even though it came into the FOV at the altitude of only 6º.
View of Mt. Sobosan from the observing site after burning the dead grass in the field.
Movies: burning the dead grass in the field
https://www.youtube.com/watch?v=nSuDaaJipyI
Four days ago, the dead grass was burned in the field around the site, and we are seeing drastic change in landscape. On the photo taken last month there was Japanese pampas grass in front of Mt. Sobosan, but it completely disappeared on the one shown above taken today; it looks like a shot from another site. Thanks for the burning. It keeps a good view of the site.
Friday, February 19
I arrived at the observing site at 3:45am. The condition was wonderful with air temperature of -8 ºC, no wind and the snow depth of 3 cm. Though the snow depth was merely 3 cm, I had to shovel the snow to some extent, and it took more time to set up my telescope than usual. I spent as long as 50 minutes after arrival to prepare the session, though it takes half an hour to do under the normal conditions. When I lived in Niigata it also took some 50 minutes to set up the telescope after the arrival during the winter season with snow.
Prior to the comet hunting session, I observed Omega Centauri, a globular cluster. The cluster was about 9º above the horizon, and it was easy to spot with the naked eye. The view was awesome with 46 cm 78x using Planokular 30 mm and Paracorr.
To turn my eyes to the southeastern horizon, the central part of our galaxy shined like clouds and the Milky Way extended to the northern sky. In the middle of it, just under Altair, Mt. Sobosan displayed a sacred silhouette. How beautiful the scenery was!
I employed a glass eyepiece because it was moonless night with good transparency. I reached a conclusion that the glass eyepiece is better than Night Vison (NV) under the condition that the night is moonless and transparency is fair, because the glass eyepiece is more sensitive to blue-colored comets and unlikely to overlook them. Nonetheless, I used a combination of Planokular 30 mm with Paracorr 78x instead of Ethos 21 mm 98x due to poor seeing. At 4:40am I began with the azimuth of Rasalhague, α Ophiuchi. That was to say, the altitude of the star was 41º above the horizon at that time, and I searched the area from the same azimuth as the star with the altitude of 30º or less only.
