DDO home David Dunlap Observatory (DDO)
Spectrum of the Toronto sky


A spectrum of the Toronto sky was obtained on May 26/27, 2002 by Michael De Robertis, Robin Fingerhut and Mel Blake of York University. Jim Thomson was the Telescope Operator.

The weather conditions were very good, but with a full Moon. The data were taken at 4:50 UT at the location: RA=12:07, dec=+39:41, HA=+3:45, AM=1.33. The spectrum was obtained with the 100 lines/mm grating giving the spectral scale of 3.65A/pixel. It was transformed to absolute units using stellar photometric standards. The accuracy of the calibration is estimated at about 30-40%. The calibration is much better in the relative sense, at the level of 10%.

The main identified emission features in the spectrum are marked by numbers. "HgI" denotes the mercury lamp lines, "NaI" the sodium lines (HPS and LPS for high and low pressure lamps), while "airglow" lines come from the natural sky emission which is related to the auroral light. The wavelengths are in Angstroms. Some of the features may be due to the metal halide bands.

  • 1, 2: HgI 4047, HgI 4358
  • 3, 4, 5: NaI 4665,4669, NaI 4748,4752, NaI 4978,4983 (HPS)
  • 7: NaI 5149,5153 (HPS)
  • 8: HgI 5461
  • 9: OI 5577 airglow
  • 10: NaI 5683,5688 (HPS,LPS)
  • 11: NaI 5890,5896 (HPS), wings extend 5500A - 6500A with self-absorption
  • 12: NaI 6154,6161 (HPS,LPS)
  • 13: [OI] 6300 airglow
Note the increase to the blue which is due to atmospheric scattering. In spite of the heavy light pollution, some parts of the spectrum are relatively dark. Note the dark region around 5300A, not far from the centre of the V-band at 5550A. The sky brightness in this region is 18.4 mag/square-arcsec. However, the strong HPS feature between 5500A - 6500A provides as much as 40% of the sky background for >5300A elevating the sky brightness to the level of 17.5 mag/square-arcsec. This was independently verified by broad-band photometry with the unfiltered ST-6 camera on the 6-inch finder. The wide, heavily contaminated ST-6 band correspons approximately to the R-filter. These measurements gave 16.8 - 17.0 mag/square-arcsec for the equatorial sky over Toronto which is distinctly brighter than the spot used for the sky spectrum described above.

Page maintained by: Slavek Rucinski, with thanks to the York team for permission to make these results available.
Last update: July 2002