c/2015 V2 核心應該不是12 等應該是 8.x 等左右
http://www.cobs.si/recentC/2015 V2 (Johnson)
Total-magnitude and coma-diameter estimates:
2017 May. 21.96, 7.9, 6' (C. Harder, Jeersdorf, Germany , 0.252-m Newtonian reflector; 7.0' tail in p.a. 320)
2017 May. 21.95, 7.8, 6' (U. Pilz, 7x50 binoculars)
2017 May. 21.15, 8.4, 3.4' (S. Aguirre, Sonora, Mexico, 0.2-m Schmidt-Cassegrain)
2017 May. 21.00, 7.9, 12' (A. Scholten, Eerbeek, 8x56 binoculars)
COBS 8等的觀測紀錄全部都是整體 (total magnitude), 不是核心.
IAU資料庫最新的觀測紀錄:
C/2015 V2 (Johnson) 2017 05 21.00 12.0 N K87
核心12等.
核心亮度看第一張Sky&Telescope的照片就很明顯.
Description:
... Brightest stars in this image are around 10th magnitude, faintest around 13th
照片中的星點亮度介於10~13之間. 和核心比有亮有暗, 因此核心亮度介於10~13.