Ground Truth

Irregular (what else?) measurements of sky brightness using a Unihedron Sky Quality Meter at my observing site, as well as notes on my observing environment and equipment.


Through most of October, November, and December the cloud nebula reigned over Toronto, and few sky brightness measurements were taken.

Date and local time-weather-sky brightness (mag./sq.arcsec)

October 5 1.30 am clear but lousy transparency with 60% humidity inside the SkyShed. Mars is visible, but naked eye limit is about +1 — 17.47

October 4 12.15 am clear but poor transparency — smog alert — 17.52

November 17 11.30 pm – clear, seeing fair, transparency fair, most objects blown away by moonlight — 15.39


April 15 10.00 pm – 10°C, 64% humidity, calm, pressure 101.59 kPa. Cloud and general haze, seeing good, transparency poor, moon just risen and nothing visible except Saturn and a couple of first magnitude stars — 16.81

April 17 10.00 pm – 1.30am 5.5°C, 66% humidity, calm, pressure 101.90 kPa. Clear, seeing fair, transparency fair, Saturn. Jupiter, and stars into second magnitude — 17.79

April 28 3.38 am -o.3°C, 60% humidity, calm, pressure 102.45 kPa. Clear, seeing fair, transparency poor to fair — 18.09

April 29 2.52 am o.4°C, 61% humidity, calm, pressure 103.22 kPa. Clear, seeing fair, transparency poor to fair — 17.99

May 9 2.38 am 6.9°C, 57% humidity, calm, pressure 101.84 kPa. Clear, no estimate of seeing/transparency — 17.63

From this point I will restrict the readings to the occasional visit to darker sites – it’s depressing knowing just how bad my home location really is!

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