Darling Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Darling Hill Observatory clear sky chart from 2005-11-06 to 2024-11-06.

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	16% 12% 4 9% 5% 5% 4 4 5% 7% 28%	101530
	Night	16% 13% 5% 10% 6% 4 4 3 5% 6% 27%	97523
Transparency	Day	54% 6% 11% 19% 9% 1	105065
	Night	58% 6% 10% 17% 8% 1	102077
Seeing	Day	26% 18% 28% 17% 8% 2	14683
	Night	25% 18% 26% 22% 8% 1	23880

By Month

Percentage Cloud Cover NE (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	11% 24% 12% 14% 5% 4 4 2 4 3 16%	2517
	11th to 20th	Day	13% 22% 10% 16% 6% 7% 4 2 3 3 13%	2520
	21st to end	Day	16% 21% 8% 13% 11% 5% 4 3 3 4 10%	3096
February	1st to 10th	Day	14% 18% 7% 17% 9% 6% 4 3 4 3 14%	1710
	11th to 20th	Day	13% 17% 8% 19% 9% 5% 4 3 3 4 15%	1696
	21st to end	Day	18% 17% 5% 16% 9% 4 4 2 3 4 19%	1570
March	1st to 10th	Day	21% 17% 5% 11% 5% 3 4 3 4 4 23%	3195
	11th to 20th	Day	10% 22% 8% 9% 5% 4 4 3 4 5% 27%	3480
	21st to end	Day	16% 13% 6% 13% 5% 3 3 3 4 6% 28%	3992
April	1st to 10th	Day	17% 18% 5% 10% 4 3 4 4 3 5% 28%	2280
	11th to 20th	Day	17% 14% 4 7% 4 4 3 3 5% 5% 34%	2254
	21st to end	Day	20% 15% 4 7% 4 3 3 3 5% 6% 31%	2301
May	1st to 10th	Day	23% 11% 3 7% 4 4 4 3 5% 6% 31%	4357
	11th to 20th	Day	16% 9% 3 9% 6% 6% 6% 4 6% 8% 28%	4398
	21st to end	Day	13% 7% 2 6% 4 4 5% 4 6% 8% 39%	4837
June	1st to 10th	Day	20% 8% 3 7% 4 4 5% 5% 6% 7% 32%	2660
	11th to 20th	Day	17% 6% 2 6% 5% 5% 5% 5% 7% 10% 34%	2660
	21st to end	Day	15% 7% 3 7% 5% 6% 4 4 7% 10% 32%	2660
July	1st to 10th	Day	12% 6% 3 6% 5% 5% 6% 5% 8% 12% 34%	4440
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 6% 9% 11% 32%	4440
	21st to end	Day	12% 7% 2 7% 5% 6% 6% 5% 7% 8% 34%	4814
August	1st to 10th	Day	18% 6% 2 7% 5% 5% 5% 4 7% 9% 32%	4118
	11th to 20th	Day	15% 8% 4 8% 6% 5% 6% 5% 7% 8% 30%	3926
	21st to end	Day	15% 8% 3 8% 4 4 4 3 5% 7% 38%	4180
September	1st to 10th	Day	17% 6% 2 5% 5% 5% 5% 4 6% 7% 38%	2280
	11th to 20th	Day	16% 7% 2 6% 4 4 3 3 4 7% 43%	2280
	21st to end	Day	17% 8% 3 7% 5% 4 5% 4 6% 6% 34%	2023
October	1st to 10th	Day	20% 9% 3 6% 5% 5% 5% 4 5% 7% 31%	1900
	11th to 20th	Day	20% 11% 3 6% 5% 4 5% 4 5% 7% 30%	1900
	21st to end	Day	25% 17% 3 7% 4 4 4 4 4 5% 23%	2010
November	1st to 10th	Day	13% 15% 3 9% 5% 5% 5% 4 4 6% 31%	1717
	11th to 20th	Day	16% 18% 5% 10% 5% 5% 4 3 5% 4 24%	1601
	21st to end	Day	17% 22% 6% 11% 5% 4 4 3 4 5% 19%	1520
December	1st to 10th	Day	16% 24% 9% 12% 5% 4 3 3 4 5% 14%	1520
	11th to 20th	Day	18% 20% 8% 13% 6% 3 3 2 4 4 19%	1906
	21st to end	Day	22% 22% 8% 11% 5% 4 4 3 5% 4 11%	2772
January	1st to 10th	Night	15% 19% 10% 21% 6% 5% 4 3 3 3 11%	4429
	11th to 20th	Night	11% 21% 10% 16% 9% 5% 4 3 4 4 14%	4440
	21st to end	Night	18% 19% 7% 16% 11% 6% 4 2 3 3 11%	4559
February	1st to 10th	Night	14% 19% 6% 16% 8% 5% 5% 3 4 4 17%	2470
	11th to 20th	Night	12% 16% 7% 17% 10% 6% 5% 4 3 5% 15%	2369
	21st to end	Night	17% 14% 6% 17% 7% 4 4 2 4 5% 19%	1884
March	1st to 10th	Night	17% 13% 6% 12% 6% 5% 3 3 4 5% 26%	3642
	11th to 20th	Night	12% 22% 8% 11% 5% 4 3 3 4 6% 22%	3479
	21st to end	Night	18% 13% 5% 12% 5% 4 4 3 3 4 28%	3640
April	1st to 10th	Night	17% 16% 5% 9% 5% 5% 4 4 4 5% 27%	1900
	11th to 20th	Night	18% 13% 4 8% 5% 5% 3 3 4 5% 33%	1875
	21st to end	Night	19% 12% 4 6% 4 4 4 3 5% 6% 33%	1895
May	1st to 10th	Night	23% 10% 3 8% 4 4 4 3 5% 6% 29%	2582
	11th to 20th	Night	15% 9% 4 7% 5% 5% 4 4 5% 7% 34%	2495
	21st to end	Night	14% 6% 3 7% 4 4 5% 4 7% 8% 39%	2738
June	1st to 10th	Night	18% 6% 4 7% 4 4 5% 3 6% 7% 36%	1520
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 4 6% 9% 38%	1520
	21st to end	Night	14% 7% 3 6% 4 4 4 5% 5% 8% 41%	1520
July	1st to 10th	Night	10% 6% 2 8% 6% 5% 5% 4 7% 8% 38%	2520
	11th to 20th	Night	11% 5% 2 6% 5% 4 5% 4 6% 8% 44%	2520
	21st to end	Night	12% 7% 3 7% 4 4 5% 4 6% 8% 41%	2739
August	1st to 10th	Night	19% 7% 2 6% 4 4 4 4 6% 7% 37%	2793
	11th to 20th	Night	13% 8% 3 9% 4 4 5% 3 5% 6% 39%	2870
	21st to end	Night	11% 8% 3 8% 4 4 5% 3 5% 7% 42%	3476
September	1st to 10th	Night	15% 7% 2 6% 4 4 5% 3 5% 7% 43%	1900
	11th to 20th	Night	14% 7% 3 5% 3 3 3 3 5% 6% 47%	1900
	21st to end	Night	17% 9% 2 6% 5% 4 5% 4 6% 6% 36%	2152
October	1st to 10th	Night	21% 8% 3 7% 5% 5% 4 4 5% 6% 32%	2280
	11th to 20th	Night	21% 10% 2 6% 5% 4 5% 3 4 6% 33%	2280
	21st to end	Night	26% 15% 3 7% 5% 3 3 3 4 5% 24%	2586
November	1st to 10th	Night	13% 16% 3 9% 5% 4 3 3 5% 6% 32%	2483
	11th to 20th	Night	18% 17% 5% 9% 4 4 4 3 4 6% 26%	2575
	21st to end	Night	15% 19% 7% 10% 6% 4 5% 3 5% 5% 21%	2660
December	1st to 10th	Night	18% 23% 8% 12% 6% 4 4 3 3 4 15%	2660
	11th to 20th	Night	18% 18% 7% 14% 6% 4 4 3 4 4 17%	3288
	21st to end	Night	24% 19% 9% 12% 5% 3 3 3 4 5% 14%	4884

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	74% 4 8% 11% 3	2518
	11th to 20th	Day	77% 4 7% 8% 3	2520
	21st to end	Day	77% 5% 8% 6% 3	3096
February	1st to 10th	Day	76% 4 7% 10% 3	1710
	11th to 20th	Day	76% 4 6% 11% 3	1705
	21st to end	Day	71% 4 8% 12% 5%	1570
March	1st to 10th	Day	65% 6% 9% 14% 6%	3198
	11th to 20th	Day	61% 5% 13% 12% 8% 1	3480
	21st to end	Day	58% 5% 7% 18% 11% 1	3992
April	1st to 10th	Day	60% 4 8% 17% 9% 2	2280
	11th to 20th	Day	52% 5% 11% 19% 12% 1	2254
	21st to end	Day	55% 4 9% 19% 11% 2	2301
May	1st to 10th	Day	54% 5% 10% 18% 11% 2	4371
	11th to 20th	Day	52% 9% 11% 20% 7% 1	4402
	21st to end	Day	41% 8% 12% 24% 14% 1	4837
June	1st to 10th	Day	50% 7% 11% 19% 13% 1	2660
	11th to 20th	Day	45% 7% 13% 22% 11% 1	2660
	21st to end	Day	46% 8% 15% 21% 10% 1	2660
July	1st to 10th	Day	41% 7% 15% 26% 11% 1	4370
	11th to 20th	Day	41% 9% 15% 26% 9%	4365
	21st to end	Day	45% 7% 14% 24% 10%	4661
August	1st to 10th	Day	48% 7% 13% 20% 11% 1	4104
	11th to 20th	Day	49% 8% 15% 22% 6%	3965
	21st to end	Day	46% 5% 10% 31% 7% 1	4180
September	1st to 10th	Day	44% 6% 11% 26% 11% 1	2280
	11th to 20th	Day	43% 4 10% 24% 17% 1	2280
	21st to end	Day	50% 7% 10% 23% 10% 1	2023
October	1st to 10th	Day	46% 6% 10% 27% 11% 1	3160
	11th to 20th	Day	48% 4 14% 20% 14%	3140
	21st to end	Day	49% 6% 14% 24% 7% 1	3287
November	1st to 10th	Day	53% 6% 13% 17% 10% 2	1717
	11th to 20th	Day	62% 5% 10% 14% 6% 2	1601
	21st to end	Day	67% 6% 12% 12% 3	1520
December	1st to 10th	Day	74% 6% 8% 9% 3	1520
	11th to 20th	Day	71% 4 13% 9% 3	1906
	21st to end	Day	76% 6% 6% 9% 2	2772
January	1st to 10th	Night	78% 5% 8% 6% 3	4429
	11th to 20th	Night	74% 6% 6% 9% 5%	4440
	21st to end	Night	80% 4 6% 7% 2	4559
February	1st to 10th	Night	71% 5% 8% 11% 5%	2470
	11th to 20th	Night	73% 5% 7% 11% 4	2371
	21st to end	Night	67% 5% 10% 11% 6% 1	1884
March	1st to 10th	Night	61% 6% 11% 15% 7%	3652
	11th to 20th	Night	64% 5% 11% 16% 5%	3480
	21st to end	Night	60% 5% 6% 18% 10% 2	3640
April	1st to 10th	Night	59% 5% 10% 16% 8% 2	1900
	11th to 20th	Night	55% 4 9% 18% 14% 1	1875
	21st to end	Night	52% 5% 9% 19% 13% 3	1895
May	1st to 10th	Night	55% 7% 8% 17% 8% 4	2588
	11th to 20th	Night	48% 10% 14% 20% 8% 1	2496
	21st to end	Night	41% 8% 12% 21% 15% 2	2739
June	1st to 10th	Night	46% 6% 11% 22% 13% 1	1520
	11th to 20th	Night	43% 7% 13% 22% 13% 2	1520
	21st to end	Night	42% 8% 9% 28% 13% 1	1520
July	1st to 10th	Night	43% 7% 14% 22% 13% 1	2480
	11th to 20th	Night	36% 7% 15% 29% 13% 1	2472
	21st to end	Night	41% 7% 10% 26% 14% 1	2651
August	1st to 10th	Night	47% 6% 13% 24% 9% 1	2783
	11th to 20th	Night	45% 7% 13% 26% 8%	2897
	21st to end	Night	41% 7% 12% 31% 9% 1	3476
September	1st to 10th	Night	41% 6% 13% 24% 14% 2	1900
	11th to 20th	Night	37% 5% 11% 30% 16% 1	1900
	21st to end	Night	47% 7% 10% 23% 11% 1	2152
October	1st to 10th	Night	54% 6% 8% 21% 10%	3800
	11th to 20th	Night	48% 6% 12% 17% 13% 4	3779
	21st to end	Night	50% 6% 12% 25% 6% 1	4259
November	1st to 10th	Night	53% 7% 10% 17% 11% 2	2483
	11th to 20th	Night	60% 4 10% 16% 6% 3	2575
	21st to end	Night	65% 6% 12% 14% 4	2660
December	1st to 10th	Night	74% 5% 10% 9% 2	2660
	11th to 20th	Night	71% 6% 8% 11% 4	3288
	21st to end	Night	74% 6% 8% 10% 2	4884

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	31% 28% 28% 10% 3	180
	11th to 20th	Day	37% 29% 24% 8% 1 1	180
	21st to end	Day	27% 30% 33% 9% 1	290
February	1st to 10th	Day	39% 29% 27% 5% 1	270
	11th to 20th	Day	38% 31% 28% 3	303
	21st to end	Day	40% 22% 27% 9% 2	382
March	1st to 10th	Day	33% 23% 30% 11% 3	460
	11th to 20th	Day	34% 24% 27% 12% 3	460
	21st to end	Day	36% 23% 26% 11% 3 1	506
April	1st to 10th	Day	35% 23% 27% 11% 4	460
	11th to 20th	Day	30% 28% 21% 10% 7% 3	452
	21st to end	Day	34% 17% 28% 15% 5% 1	460
May	1st to 10th	Day	29% 21% 29% 14% 6% 2	463
	11th to 20th	Day	23% 14% 32% 19% 9% 2	487
	21st to end	Day	18% 14% 32% 23% 10% 2	529
June	1st to 10th	Day	26% 14% 29% 21% 8% 1	490
	11th to 20th	Day	17% 15% 32% 24% 10% 2	490
	21st to end	Day	20% 19% 31% 21% 6% 2	490
July	1st to 10th	Day	15% 10% 31% 28% 13% 4	485
	11th to 20th	Day	14% 10% 32% 27% 14% 3	484
	21st to end	Day	14% 10% 38% 24% 11% 3	532
August	1st to 10th	Day	15% 10% 29% 26% 13% 6%	486
	11th to 20th	Day	18% 12% 27% 24% 12% 7%	479
	21st to end	Day	17% 13% 28% 23% 12% 7%	539
September	1st to 10th	Day	20% 11% 25% 23% 14% 7%	490
	11th to 20th	Day	16% 10% 26% 21% 18% 9%	490
	21st to end	Day	21% 16% 28% 20% 11% 4	490
October	1st to 10th	Day	25% 16% 25% 17% 13% 4	490
	11th to 20th	Day	28% 21% 28% 15% 8% 1	490
	21st to end	Day	38% 18% 26% 15% 3	496
November	1st to 10th	Day	27% 25% 22% 19% 7% 1	381
	11th to 20th	Day	36% 25% 24% 13% 2 1	261
	21st to end	Day	38% 24% 31% 7%	180
December	1st to 10th	Day	39% 22% 29% 7% 2 1	180
	11th to 20th	Day	36% 29% 27% 8% 1	180
	21st to end	Day	34% 28% 32% 5% 1	198
January	1st to 10th	Night	29% 30% 28% 11% 2 1	760
	11th to 20th	Night	29% 24% 28% 15% 3	760
	21st to end	Night	23% 26% 32% 17% 2	836
February	1st to 10th	Night	30% 25% 29% 15% 1	760
	11th to 20th	Night	29% 27% 30% 12% 2	743
	21st to end	Night	32% 24% 27% 13% 3	628
March	1st to 10th	Night	27% 24% 30% 17% 2	760
	11th to 20th	Night	28% 24% 26% 19% 3	760
	21st to end	Night	31% 21% 26% 16% 6% 1	836
April	1st to 10th	Night	28% 20% 29% 19% 3	760
	11th to 20th	Night	29% 20% 25% 20% 6% 1	751
	21st to end	Night	29% 14% 27% 24% 6%	755
May	1st to 10th	Night	24% 14% 24% 28% 9% 1	422
	11th to 20th	Night	18% 12% 31% 30% 9% 1	374
	21st to end	Night	14% 9% 30% 33% 13%	411
June	1st to 10th	Night	19% 8% 26% 33% 12% 1	380
	11th to 20th	Night	17% 11% 24% 34% 14%	380
	21st to end	Night	16% 7% 28% 39% 10% 1	380
July	1st to 10th	Night	10% 3 25% 44% 16% 2	370
	11th to 20th	Night	12% 4 22% 42% 19% 2	368
	21st to end	Night	14% 6% 25% 40% 14% 1	416
August	1st to 10th	Night	16% 5% 25% 33% 20% 1	548
	11th to 20th	Night	16% 6% 19% 32% 23% 3	610
	21st to end	Night	15% 7% 23% 34% 19% 1	836
September	1st to 10th	Night	17% 9% 25% 31% 15% 3	760
	11th to 20th	Night	18% 8% 17% 32% 22% 4	760
	21st to end	Night	20% 14% 23% 25% 16% 2	760
October	1st to 10th	Night	25% 14% 23% 20% 16% 1	760
	11th to 20th	Night	29% 16% 27% 21% 7% 1	760
	21st to end	Night	37% 16% 27% 17% 3	836
November	1st to 10th	Night	26% 19% 29% 19% 7%	764
	11th to 20th	Night	32% 22% 26% 14% 5% 1	760
	21st to end	Night	27% 26% 26% 16% 4	760
December	1st to 10th	Night	35% 26% 23% 13% 3	760
	11th to 20th	Night	32% 24% 26% 14% 3	760
	21st to end	Night	32% 29% 26% 11% 2	836

Page generated at 2024-11-03 13:19:05. Version ac07

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