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Based on the long-term weather records (1971-2000) from Kingston,
100 km south of the site, it is estimated that one should expect
about 1125 clear, dark observable hours per year.
At Kingston they measure the total hours of 'Bright Sunshine'
per month. From this we extrapolated the total clear dark observable
hours, based on end of evening twilight to beginning of morning
twilight, effectively the length of the night.
Actually is possible that we get more than 900 hours because
the skies often clear at night, especially in spring, summer and
the fall. Thereby this could be as much as 25% more than the daytime
forecast (1,125 hours)
| Month |
Bright Sunshine Hours |
Night Hours per Day |
Night Hours per Month |
Observing Hours per Month |
Percent Clear % |
| |
|
|
|
|
|
| January |
95 |
12 |
372 |
95 |
26 |
| February |
119 |
11 |
308 |
100 |
32 |
| March |
141 |
8.5 |
263 |
77 |
29 |
| April |
177 |
6.5 |
195 |
66 |
34 |
| May |
222 |
4.5 |
139 |
52 |
37 |
| June |
244 |
3.5 |
105 |
42 |
40 |
| July |
280 |
4 |
124 |
47 |
38 |
| August |
242 |
6 |
186 |
81 |
44 |
| September |
163 |
8 |
240 |
82 |
34 |
| October |
146 |
9 |
279 |
88 |
32 |
| November |
88 |
11 |
330 |
75 |
23 |
| December |
75 |
12 |
372 |
75 |
20 |
| |
|
|
|
|
|
| Totals |
1,846 |
|
2,913 |
880 |
|
| Average |
153 |
8 |
243 |
73 |
32 |
The sitel average observing hours per month based on 30-year
Kingston data. In reality we expect about 10% more clear nights
due to the lake effect from Lake Ontario that Kingston encounters.
Next: Sky Brightness
Map
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