Carlton Astronomy Campus
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Carlton Astronomy Campus clear sky chart from 2005-11-06 to 2024-07-08.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	12% 7% 3 7% 5% 5% 5% 4 6% 7% 39%	89224
	Night	13% 7% 2 5% 4 4 4 4 5% 7% 44%	90082
Transparency	Day	21% 55% 5% 9% 8% 3	89001
	Night	20% 54% 5% 9% 9% 3	89911
Seeing	Day	15% 9% 21% 24% 22% 10%	14469
	Night	15% 8% 23% 29% 21% 4	24239

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 10% 2 6% 4 3 3 3 4 7% 40%	2847
	11th to 20th	Day	14% 7% 2 5% 4 3 3 2 2 5% 53%	2850
	21st to end	Day	23% 10% 2 6% 3 4 4 3 4 4 37%	3139
February	1st to 10th	Day	17% 8% 3 7% 5% 4 4 3 5% 5% 38%	1900
	11th to 20th	Day	19% 9% 3 5% 4 3 3 3 4 5% 41%	1848
	21st to end	Day	18% 8% 3 8% 4 4 5% 3 4 6% 36%	1570
March	1st to 10th	Day	21% 10% 3 8% 6% 4 5% 4 5% 6% 27%	3426
	11th to 20th	Day	17% 8% 3 7% 5% 5% 4 4 6% 7% 33%	3480
	21st to end	Day	13% 8% 3 8% 6% 5% 4 4 4 5% 40%	3904
April	1st to 10th	Day	10% 7% 3 6% 5% 5% 5% 5% 5% 7% 42%	2280
	11th to 20th	Day	16% 8% 2 7% 5% 4 4 4 5% 7% 39%	2254
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 44%	2280
May	1st to 10th	Day	12% 8% 3 8% 6% 6% 6% 4 7% 8% 33%	3765
	11th to 20th	Day	14% 6% 2 7% 4 4 5% 4 5% 8% 41%	3764
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 7% 10% 39%	4129
June	1st to 10th	Day	9% 5% 3 8% 7% 6% 7% 6% 9% 10% 31%	2459
	11th to 20th	Day	7% 6% 2 7% 7% 7% 6% 6% 8% 10% 34%	2470
	21st to end	Day	7% 6% 3 8% 8% 7% 7% 6% 9% 10% 29%	2470
July	1st to 10th	Day	8% 8% 3 10% 7% 7% 8% 6% 9% 9% 25%	2433
	11th to 20th	Day	8% 6% 3 8% 7% 7% 7% 7% 9% 9% 28%	2340
	21st to end	Day	8% 8% 3 8% 6% 8% 7% 5% 7% 10% 31%	2488
August	1st to 10th	Day	6% 5% 3 8% 6% 7% 7% 7% 7% 9% 34%	2148
	11th to 20th	Day	11% 6% 3 8% 6% 6% 7% 5% 9% 10% 31%	2125
	21st to end	Day	11% 6% 3 8% 6% 6% 7% 4 7% 8% 33%	2376
September	1st to 10th	Day	9% 5% 3 8% 7% 6% 7% 4 8% 8% 35%	2160
	11th to 20th	Day	12% 6% 2 8% 4 6% 5% 4 6% 7% 39%	2160
	21st to end	Day	10% 6% 1 7% 4 4 4 3 5% 7% 50%	1962
October	1st to 10th	Day	7% 4 2 5% 5% 4 4 4 5% 7% 54%	1800
	11th to 20th	Day	9% 5% 1 5% 3 3 4 3 5% 5% 56%	1800
	21st to end	Day	12% 4 2 5% 4 3 3 2 4 5% 56%	1980
November	1st to 10th	Day	10% 6% 2 4 3 3 3 3 5% 6% 54%	1858
	11th to 20th	Day	10% 7% 2 5% 5% 4 3 3 5% 5% 51%	1900
	21st to end	Day	14% 7% 2 6% 4 3 4 4 5% 6% 46%	1757
December	1st to 10th	Day	15% 9% 2 6% 4 4 3 4 5% 6% 43%	1710
	11th to 20th	Day	16% 9% 3 8% 4 4 4 3 5% 6% 38%	2257
	21st to end	Day	16% 7% 2 6% 4 4 4 3 6% 7% 41%	3135
January	1st to 10th	Night	19% 8% 2 5% 3 4 3 3 4 5% 45%	4108
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 3 4 51%	4120
	21st to end	Night	26% 9% 2 4 3 3 3 2 3 5% 41%	4524
February	1st to 10th	Night	15% 9% 3 6% 4 4 4 3 4 6% 41%	2280
	11th to 20th	Night	21% 8% 2 5% 3 2 3 3 5% 6% 42%	2218
	21st to end	Night	20% 9% 3 5% 4 3 4 4 5% 6% 38%	1884
March	1st to 10th	Night	23% 12% 3 7% 4 4 4 3 5% 6% 30%	3454
	11th to 20th	Night	15% 9% 3 7% 5% 4 5% 4 6% 7% 35%	3480
	21st to end	Night	15% 8% 2 6% 4 4 4 3 5% 6% 42%	3725
April	1st to 10th	Night	13% 7% 2 4 4 4 3 4 6% 8% 44%	1900
	11th to 20th	Night	12% 6% 2 7% 4 4 4 4 5% 7% 44%	1875
	21st to end	Night	9% 5% 2 5% 4 3 3 4 6% 7% 53%	1900
May	1st to 10th	Night	13% 6% 3 6% 4 4 4 4 6% 8% 42%	3130
	11th to 20th	Night	14% 7% 3 6% 4 3 4 4 5% 7% 43%	3129
	21st to end	Night	8% 6% 2 6% 5% 5% 6% 4 7% 11% 41%	3426
June	1st to 10th	Night	7% 5% 2 7% 5% 5% 4 5% 7% 11% 42%	1715
	11th to 20th	Night	3 5% 1 5% 4 5% 5% 5% 9% 11% 48%	1710
	21st to end	Night	6% 5% 1 6% 6% 6% 5% 6% 9% 12% 38%	1710
July	1st to 10th	Night	5% 5% 3 6% 5% 5% 5% 6% 10% 12% 39%	1692
	11th to 20th	Night	5% 4 1 5% 5% 5% 5% 6% 9% 12% 43%	1620
	21st to end	Night	5% 6% 2 5% 5% 5% 6% 5% 7% 13% 40%	1826
August	1st to 10th	Night	3 4 1 5% 4 5% 5% 5% 8% 14% 47%	1790
	11th to 20th	Night	5% 4 1 7% 5% 6% 6% 5% 8% 15% 39%	1776
	21st to end	Night	9% 4 2 6% 5% 6% 5% 6% 7% 11% 40%	1980
September	1st to 10th	Night	7% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	1800
	11th to 20th	Night	8% 7% 2 6% 5% 4 4 4 7% 10% 44%	1800
	21st to end	Night	9% 5% 2 5% 4 4 4 3 6% 8% 51%	1973
October	1st to 10th	Night	7% 4 1 4 3 2 3 4 5% 7% 60%	2160
	11th to 20th	Night	8% 5% 2 4 3 3 3 4 4 5% 58%	2160
	21st to end	Night	11% 6% 2 4 4 3 2 3 4 5% 55%	2376
November	1st to 10th	Night	11% 4 1 4 4 3 3 2 4 7% 57%	2220
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 4 5% 55%	2280
	21st to end	Night	14% 7% 2 5% 4 4 4 3 5% 6% 47%	2414
December	1st to 10th	Night	16% 8% 3 5% 4 3 2 3 4 6% 46%	2470
	11th to 20th	Night	14% 10% 3 7% 5% 4 4 3 4 6% 42%	2925
	21st to end	Night	19% 11% 3 6% 4 3 3 3 4 5% 41%	4532

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	30% 37% 4 9% 17% 3	2848
	11th to 20th	Day	20% 37% 4 13% 19% 7%	2850
	21st to end	Day	32% 39% 3 7% 13% 6%	3139
February	1st to 10th	Day	19% 65% 3 5% 5% 4	1900
	11th to 20th	Day	18% 64% 2 6% 8% 2	1858
	21st to end	Day	19% 65% 3 2 6% 4	1570
March	1st to 10th	Day	40% 42% 5% 8% 5% 1	3426
	11th to 20th	Day	32% 42% 4 13% 8% 2	3480
	21st to end	Day	29% 41% 5% 7% 13% 5%	3904
April	1st to 10th	Day	16% 65% 2 6% 8% 4	2280
	11th to 20th	Day	19% 66% 3 5% 4 3	2254
	21st to end	Day	13% 66% 4 7% 7% 3	2280
May	1st to 10th	Day	29% 45% 6% 12% 6% 2	3800
	11th to 20th	Day	26% 41% 6% 9% 16% 2	3768
	21st to end	Day	21% 43% 10% 20% 6% 1	4141
June	1st to 10th	Day	16% 66% 4 6% 6% 1	2459
	11th to 20th	Day	19% 67% 4 5% 4 1	2470
	21st to end	Day	17% 67% 7% 6% 3	2470
July	1st to 10th	Day	17% 64% 8% 8% 3	2369
	11th to 20th	Day	17% 66% 7% 8% 2	2271
	21st to end	Day	13% 63% 6% 11% 5% 1	2350
August	1st to 10th	Day	15% 66% 8% 8% 3	2136
	11th to 20th	Day	15% 67% 5% 8% 3 1	2125
	21st to end	Day	16% 65% 6% 7% 4 1	2376
September	1st to 10th	Day	15% 65% 6% 7% 6% 2	2160
	11th to 20th	Day	13% 64% 5% 9% 7% 2	2160
	21st to end	Day	13% 64% 5% 11% 5% 1	1962
October	1st to 10th	Day	11% 64% 5% 10% 8% 3	1800
	11th to 20th	Day	10% 63% 3 7% 13% 5%	1800
	21st to end	Day	14% 62% 2 5% 11% 6%	1980
November	1st to 10th	Day	17% 59% 4 8% 8% 5%	1858
	11th to 20th	Day	18% 60% 3 6% 9% 5%	1900
	21st to end	Day	16% 60% 3 8% 9% 4	1757
December	1st to 10th	Day	19% 59% 3 7% 7% 4	1710
	11th to 20th	Day	21% 48% 2 7% 16% 6%	2255
	21st to end	Day	28% 38% 5% 11% 16% 2	3135
January	1st to 10th	Night	29% 37% 4 8% 16% 7%	4108
	11th to 20th	Night	22% 37% 4 11% 17% 8%	4120
	21st to end	Night	30% 39% 3 12% 13% 4	4524
February	1st to 10th	Night	16% 65% 2 6% 7% 3	2280
	11th to 20th	Night	16% 64% 2 7% 8% 3	2219
	21st to end	Night	18% 65% 3 5% 5% 5%	1884
March	1st to 10th	Night	40% 42% 6% 6% 4 1	3454
	11th to 20th	Night	30% 43% 5% 11% 9% 3	3480
	21st to end	Night	28% 42% 4 11% 13% 3	3725
April	1st to 10th	Night	15% 66% 3 5% 8% 4	1900
	11th to 20th	Night	16% 66% 4 7% 5% 3	1875
	21st to end	Night	12% 65% 4 7% 8% 3	1900
May	1st to 10th	Night	25% 44% 8% 11% 9% 3	3160
	11th to 20th	Night	27% 42% 6% 14% 11% 1	3130
	21st to end	Night	22% 44% 9% 17% 7% 1	3435
June	1st to 10th	Night	12% 67% 5% 9% 7% 1	1715
	11th to 20th	Night	11% 68% 8% 8% 4 1	1710
	21st to end	Night	15% 66% 7% 9% 3	1710
July	1st to 10th	Night	10% 63% 11% 12% 4	1647
	11th to 20th	Night	11% 66% 11% 10% 2	1566
	21st to end	Night	8% 64% 7% 13% 7% 1	1724
August	1st to 10th	Night	11% 65% 12% 9% 3	1778
	11th to 20th	Night	12% 68% 8% 8% 3 1	1776
	21st to end	Night	12% 67% 8% 8% 3 2	1980
September	1st to 10th	Night	11% 66% 7% 8% 6% 3	1800
	11th to 20th	Night	10% 65% 7% 10% 6% 3	1800
	21st to end	Night	14% 64% 5% 11% 4 2	1973
October	1st to 10th	Night	10% 64% 6% 10% 8% 2	2160
	11th to 20th	Night	9% 63% 3 9% 12% 4	2160
	21st to end	Night	15% 61% 2 4 10% 6%	2376
November	1st to 10th	Night	17% 59% 5% 7% 9% 4	2220
	11th to 20th	Night	17% 60% 2 6% 10% 5%	2280
	21st to end	Night	15% 60% 3 8% 10% 4	2414
December	1st to 10th	Night	19% 60% 3 9% 7% 3	2470
	11th to 20th	Night	22% 48% 2 4 13% 10%	2926
	21st to end	Night	31% 38% 4 11% 12% 4	4532

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	24% 23% 31% 17% 4 1	270
	11th to 20th	Day	26% 15% 38% 17% 4	270
	21st to end	Day	27% 25% 36% 11% 2	297
February	1st to 10th	Day	28% 22% 33% 13% 3	270
	11th to 20th	Day	37% 15% 31% 12% 4	270
	21st to end	Day	26% 29% 38% 6% 1	225
March	1st to 10th	Day	26% 19% 37% 14% 3	270
	11th to 20th	Day	27% 21% 37% 13% 1	270
	21st to end	Day	19% 22% 33% 21% 5% 1	349
April	1st to 10th	Day	18% 17% 35% 21% 7% 1	460
	11th to 20th	Day	25% 15% 30% 19% 10% 2	452
	21st to end	Day	12% 12% 33% 28% 12% 2	460
May	1st to 10th	Day	15% 10% 31% 30% 12% 3	463
	11th to 20th	Day	15% 4 25% 30% 18% 8%	487
	21st to end	Day	9% 5% 21% 32% 22% 10%	529
June	1st to 10th	Day	9% 4 15% 34% 29% 10%	669
	11th to 20th	Day	8% 3 16% 34% 30% 9%	680
	21st to end	Day	9% 3 12% 30% 29% 17%	680
July	1st to 10th	Day	7% 4 5% 27% 39% 19%	658
	11th to 20th	Day	6% 2 4 24% 41% 23%	618
	21st to end	Day	8% 3 6% 23% 42% 18%	626
August	1st to 10th	Day	6% 3 6% 18% 41% 26%	446
	11th to 20th	Day	10% 1 3 15% 44% 27%	439
	21st to end	Day	13% 4 7% 21% 29% 25%	495
September	1st to 10th	Day	11% 3 6% 24% 36% 20%	450
	11th to 20th	Day	12% 3 11% 22% 36% 16%	450
	21st to end	Day	14% 3 9% 28% 34% 12%	432
October	1st to 10th	Day	8% 6% 21% 39% 21% 6%	270
	11th to 20th	Day	10% 7% 21% 36% 20% 5%	270
	21st to end	Day	21% 10% 26% 28% 12% 3	297
November	1st to 10th	Day	16% 6% 29% 33% 13% 3	270
	11th to 20th	Day	16% 14% 34% 23% 11%	270
	21st to end	Day	18% 15% 36% 20% 9% 2	270
December	1st to 10th	Day	21% 13% 36% 22% 7% 1	270
	11th to 20th	Day	23% 14% 36% 21% 6%	270
	21st to end	Day	29% 17% 31% 17% 4 1	297
January	1st to 10th	Night	24% 15% 32% 23% 6%	950
	11th to 20th	Night	22% 15% 30% 25% 8% 1	950
	21st to end	Night	25% 14% 33% 24% 5%	1037
February	1st to 10th	Night	20% 17% 36% 24% 4	760
	11th to 20th	Night	27% 16% 29% 24% 5%	743
	21st to end	Night	25% 21% 33% 18% 3	628
March	1st to 10th	Night	20% 14% 33% 27% 6%	594
	11th to 20th	Night	18% 14% 34% 29% 6%	570
	21st to end	Night	16% 11% 39% 26% 8%	627
April	1st to 10th	Night	17% 10% 37% 26% 9% 1	570
	11th to 20th	Night	17% 10% 34% 28% 11% 1	563
	21st to end	Night	11% 9% 36% 30% 14% 1	570
May	1st to 10th	Night	11% 5% 30% 38% 15% 1	570
	11th to 20th	Night	11% 4 24% 37% 21% 3	561
	21st to end	Night	7% 4 19% 39% 25% 5%	617
June	1st to 10th	Night	8% 3 10% 39% 35% 5%	570
	11th to 20th	Night	4 1 11% 41% 34% 8%	570
	21st to end	Night	6% 2 8% 32% 36% 15%	570
July	1st to 10th	Night	5% 2 4 26% 48% 15%	549
	11th to 20th	Night	5% 2 5% 25% 45% 18%	522
	21st to end	Night	7% 1 5% 25% 49% 12%	591
August	1st to 10th	Night	5% 1 4 24% 48% 18%	537
	11th to 20th	Night	6% 1 3 24% 49% 17%	534
	21st to end	Night	10% 1 6% 25% 41% 17%	594
September	1st to 10th	Night	8% 3 4 26% 46% 13%	540
	11th to 20th	Night	10% 3 7% 30% 43% 8%	540
	21st to end	Night	10% 2 12% 31% 39% 6%	700
October	1st to 10th	Night	8% 3 18% 35% 33% 4	720
	11th to 20th	Night	9% 6% 23% 35% 23% 3	720
	21st to end	Night	16% 8% 21% 31% 22% 2	792
November	1st to 10th	Night	13% 6% 22% 34% 23% 2	740
	11th to 20th	Night	16% 9% 28% 32% 14% 1	760
	21st to end	Night	19% 9% 30% 28% 14% 1	760
December	1st to 10th	Night	19% 12% 29% 30% 10%	760
	11th to 20th	Night	22% 10% 32% 28% 8%	815
	21st to end	Night	27% 13% 27% 26% 6%	1045

Page generated at 2024-07-05 10:05:39. Version ac07

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