This image appears on Page 79 of the May 2015 issue of Sky & Telescope

Object Information

Messier 81, or Bode's Galaxy (left) is a grand design spiral galaxy in the constellation Ursa Major. It was discovered in 1774 by Johann Elert Bode, along with Messier 82 (right). A handful of observers have claimed to see this object with the naked eye under exceptional seeing conditions. If this is true, it would make this galaxy the furthest object seen by an unaided human eye, at approximately 12 million light-years away!

Messier 82, or the Cigar Galaxy, is an irregular galaxy, which is gravitationally interacting with M81. This interaction has had observable effects; the pronounced spiral arms in M81, for example, result from close passes with M82 in the past. Additionially, it is possible that gravitational disturbance of M82 may be a possible cause of the high rate of star formation in this galaxy. It has been suggested that the most recent encounter between these two galaxies was hundreds of millions of years ago. Nonetheless, the two galaxies are only about 150,000 light-years apart, and will one day merge to form a single galaxy.

Both M81 and M82 have had observed supernovae, with the most recent and notable being SN 2014J, which was discovered on 21 January 2014 in M82.

Image Information

NOTES

This image was taken on the coldest night of the year in 2014, at a chilling -37°C. The number of equipment issues I had was staggering, but it was equally surprising that everything worked out in the end. The subframes have exceptionally low noise as a result of the cold.

EQUIPMENT

  • Canon T3i (unmodified)
  • Celestron AVX Mount (Guided: Orion StarShoot, PHD1)
  • Skywatcher 80ED (600mm f/7.5)

DATA

  • 36x 5min exposures @ ISO-1600 (3 hours) ~ -10°C
  • 5x Darks
  • 40x Biases

PROCESSING

Processing was done in PixInsight v1.8. The images were calibrated using ImageCalibration and ImageIntegration. The integrated image was then processed for colour and deconvolution. The luminance was extracted, and MultiscaleMedianTransform was used to reduce noise in low SNR areas. HDRMultiscaleTransform was used to equalize dynamic range between the two galaxies, and the luminance and original were stretched. The new luminance and the original's current luminance were fitted, and recombined.

SCNR was used to remove a green tint, and ACDNR was used to remove leftover noise in low SNR areas of the combined image. LocalHistogramEqualization was used on each galaxy separately to maximize the dynamic range of the individual galaxy. TGVDenoise was used on chrominance only to smooth out sharp colours. Then CurvesTransformation was then used to improve contrast and colour. The galaxies were then sharpened slightly using UnsharpMask. The stars were reduced slightly using MorphologicalTransformation, and ColourSaturation was used to remove purple clipping in the brightest stars.

LOCATION

Data was collected on the night of January 2, 2014, at the Torrance Barrens Dark Sky Preserve in Ontario, Canada. This is a Bortle 4 site.