British Astronomical Association
Supporting amateur astronomers since 1890

BAA Images Hugh Allen

Observation by Hugh Allen: Comet 46P/Wirtanen spectrum

Uploaded by

Hugh Allen


Hugh Allen


2018 Dec 13 - 21:00


2018 Dec 16 - 10:26


46P Wirtanen

Planetarium overlay



Field centre

RA: 22h47m
Dec: -46°48'
Position angle: +93°38'

Field size

0°12' × 0°06'

  • 8" Meade LX90 at f6.3
  • Alpy 600 spectroscope
  • Atik 314L camera
  • BASS software

Oakhill Somerset

Target name

Comet 46P/Wirtanen


Comet 46P/Wirtanen spectrum

About this image

Spectrum of Comet 46P/Wirtanen in a clear(ish) sky on Thursday night. I would not describe the comet as particularly bright even in a telescope, its 5th magnitude being spread over a large surface. My unguided set-up struggled to pull much signal from above the noise even by keeping the bright nucleus on or near the slit. So for presentation I ran the final 1D spectrum through a weak Gaussian filter to smooth some of the noise and make the stronger features more visible. I also manually 'snipped' the sky background out of the spectrum rather than subtract the sky background which would have introduced even more noise (I snipped light pollution lines at 5461Å [mercury], 5577Å [oxygen airglow], and 5893Å [sodium]). Nevertheless, the 'classic' cometary emission lines are clearly visible: Swan emission bands from C₂ radicals, C₃ radicals, and an intense near-UV emission from CN radicals. Even NH₂ radicals can be identified. The spectrum is response corrected using the (then) nearby B9V star Xi Tau. All in all I found this a more difficult target than I expected.

Files associated with this observation
Like this image
Nick James
Nick James, 2018 Dec 16 - 14:30 UTC

Great to see spectroscopists having a go at this comet. It is a challenge but the results are really good.

Copyright of all images and other observations submitted to the BAA remains with the owner of the work. Reproduction of work by third parties is expressly forbidden without the consent of the copyright holder. By submitting images to this online gallery, you grant the BAA permission to reproduce them in any of our publications.