Based on personal experience, in order to see M44 with the naked eye from suburban location:
- Delta Cnc (mag 3.9) needs to be visible with direct vision.
- Gamma Cnc (mag 4.7) should be visible at least 50% of the time with averted vision.
- Theta (5.4) and Eta Cnc (mag 5.3) will probably be invisible.
Castor, Pollux, Mars and M44 barely visible in the pinkish hue of light pollution
How were the observations made?
- The same observing spot was used on all occasions.
- M44 at an altitude of 40 - 50°.
- The weather was very similar on all occasions.
- Dark adaptation (night vision) was limited to 5 minutes.
- The SQM-L reading was taken directly from M44 and mean value was taken based on 5 separate measurements.
- At 23.00 the city shuts down half of the streetlights on the small walking path leading to the observing spot used.
7.3.2010, 21.11 - SQM-L 17.70 (NELM ~4.85)- M44 invisible.
13.3.2010, 22.06 - SQM-L 17.98 (NELM ~4.99) - M44 fairly easily visible with averted vision.
13.3.2010, 22.36 - SQM-L 17.94 (NELM ~4.97) - M44 perhaps slightly more difficult than on the previous try.
13.3.2010, 23.06 - SQM-L 18.01 (NELM ~5.00) - M44 fairly easily visible.
13.3.2010, 23.36 - SQM-L 18.02 (NELM ~5.00) - M44 fairly easily visible.
13.3.2010, 23.56 - SQM-L 18.02 (NELM ~5.00) - M44 fairly easily visible.
14.3.2010, 21.36 - SQM-L 17.84 (NELM ~4.92) - M44 very difficult.
Naked eye limiting magnitude = (SQM reading - 8) / 2