Bill Ward


The Perseids have been a washout both metaphorically and literally. A ton of rain came down on Thursday night.

However ever the optimist I watched the skies closely and after 48 hours of cloud and rain there was a mysterious clearance for around 20 minutes last night. Rain stopped, wind dropped to near zero and the sky cleared. So I deployed my camera rigs as quickly as possible and I managed to capture a few meteors and one spectrum. Unfortunately the spectrum was contaminated by both scattered light and some in frame clouds. However if was well dispersed and showed some really nice detail at the red end.

The direction indicated it was a perseid fireball but the spectrum had the tell-tale emission at 557.7nm typical of high speed meteors. What was interesting about this one was the detail in the atmospheric bands. Perseids are high speed meteors and they carry a lot of energy. This energy is available for excitation as the meteors kinetic energy is transformed into heat.

Slight diversion… in 2002 astronomers at the VLT caught a spectrum by chance using the FORS1 spectrograph. After removing the redshifted lines of the supernova the remaining lines were of the atmospheric emissions of O, O2, N, N2.

As this was a highly accurate instrument the line measurements are invaluable for calibrating meteor spectrum. I thought it would be interesting to compare the results of a multi-million euro instrument against my 500 quid system…

VLT spectrum sections are in black. The modeling done by the astronomers indicates this is the profile of an emission of 4200K at a height of 95km.

As the devil is in the detail if you look closely at the model line (at around 755nm from O2) it is missing from the VLT observation but it is a distinct line in my spectrum. Another cool aspect is the “height” of the lines in the regions marked. Comparing the various scalings shows a very good ratio relation. So it would suggest that my real spectrum matches the modelling quite well. 4200K it is!

Not too terrible at all… 😉