British Astronomical Association
Supporting amateur astronomers since 1890

BAA Images Andy Wilson

Observation by Andy Wilson: P Cygni H-alpha

Uploaded by

Andy Wilson


Andy Wilson


2016 Oct 02 - 19:40


2016 Nov 03 - 18:52

  • Altair Astro RC 250
  • Lhires III spectrograph 2400 l/mm
  • SXVR-H694
  • Astro-Physics AP1200

180 seconds


Yatton, Somerset

Target name

P Cygni


P Cygni H-alpha

About this image

P Cygni is a blue hypergiant. One of the brightest stars in our galaxy it is more than half a million times as luminous as our Sun.
It also lends its name to an important feature of astronomical spectroscopy, the P Cygni profile. This is a line profile that contains both an emission and absorption component. The emission comes from the bulk of the gas, while the absorption component is blue shifted. This blue shifted absorption is telling us about the motion of gas that is coming towards us along our line of sight.
This spectrum from last night is of P Cygni's H alpha profile, clearly showing both the absorption and emission features. In the case of P Cygni this is due to a powerful wind being thrown off by the star. I measured the wind speed at 150-250 km/s from the two edges of the absorption profile in my spectrum.

Files associated with this observation
Like this image