Good Hope Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Good Hope Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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% 10% 3 7% 5% 4 4 4 5% 7% 33%	100939
	Night	17% 11% 4 8% 5% 4 4 3 5% 6% 33%	98141
Transparency	Day	48% 6% 11% 21% 12% 2	104601
	Night	50% 6% 10% 20% 12% 2	102618
Seeing	Day	23% 14% 24% 22% 12% 5%	14882
	Night	23% 11% 24% 28% 13% 1	24863

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	19% 21% 9% 10% 5% 3 3 3 4 5% 19%	2836
	11th to 20th	Day	19% 20% 9% 13% 8% 4 2 2 3 3 17%	2840
	21st to end	Day	23% 22% 6% 10% 6% 3 3 2 3 5% 17%	3124
February	1st to 10th	Day	22% 15% 5% 9% 6% 4 4 2 4 5% 24%	1710
	11th to 20th	Day	21% 14% 5% 11% 5% 4 3 2 4 6% 23%	1691
	21st to end	Day	21% 16% 5% 9% 4 3 3 3 4 4 28%	1596
March	1st to 10th	Day	21% 16% 4 7% 4 3 3 3 4 6% 28%	3435
	11th to 20th	Day	15% 10% 3 7% 4 4 4 3 5% 7% 38%	3480
	21st to end	Day	21% 11% 3 7% 5% 4 4 3 5% 6% 30%	3815
April	1st to 10th	Day	17% 12% 3 8% 5% 4 5% 3 5% 6% 32%	2157
	11th to 20th	Day	17% 9% 2 7% 4 4 4 3 5% 6% 38%	2281
	21st to end	Day	20% 9% 3 6% 5% 4 4 3 6% 7% 33%	2470
May	1st to 10th	Day	21% 10% 3 8% 6% 5% 5% 4 6% 7% 26%	4082
	11th to 20th	Day	19% 9% 3 8% 4 4 5% 3 5% 6% 32%	4081
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 7% 10% 37%	4476
June	1st to 10th	Day	14% 6% 2 7% 5% 4 5% 5% 7% 9% 37%	2598
	11th to 20th	Day	13% 6% 3 7% 6% 5% 6% 4 7% 9% 36%	2660
	21st to end	Day	13% 7% 2 5% 5% 5% 5% 4 6% 10% 36%	2530
July	1st to 10th	Day	9% 5% 2 7% 4 5% 6% 4 7% 9% 41%	4120
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 4 6% 9% 39%	4120
	21st to end	Day	16% 9% 3 9% 5% 5% 5% 4 6% 7% 30%	4466
August	1st to 10th	Day	11% 8% 3 8% 5% 5% 6% 5% 8% 10% 31%	4104
	11th to 20th	Day	12% 7% 3 8% 5% 4 5% 5% 7% 9% 36%	4044
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 10% 48%	4313
September	1st to 10th	Day	14% 5% 2 6% 3 3 4 4 5% 7% 47%	2237
	11th to 20th	Day	12% 6% 2 7% 4 4 4 4 6% 8% 44%	2090
	21st to end	Day	18% 8% 3 7% 4 4 5% 4 4 6% 37%	2090
October	1st to 10th	Day	16% 7% 3 6% 4 3 3 3 4 6% 45%	1924
	11th to 20th	Day	18% 9% 2 7% 4 4 4 3 4 6% 40%	1900
	21st to end	Day	22% 9% 2 5% 4 3 4 3 4 6% 39%	2090
November	1st to 10th	Day	13% 8% 2 5% 4 3 5% 3 4 6% 47%	1888
	11th to 20th	Day	15% 13% 3 6% 5% 4 4 3 6% 8% 33%	1710
	21st to end	Day	19% 14% 4 8% 4 3 4 3 4 6% 30%	1523
December	1st to 10th	Day	25% 16% 6% 9% 4 5% 4 3 4 4 19%	1520
	11th to 20th	Day	21% 18% 6% 9% 4 3 3 2 3 5% 26%	1910
	21st to end	Day	21% 21% 6% 8% 4 4 4 3 5% 7% 17%	3028
January	1st to 10th	Night	18% 23% 7% 10% 5% 4 4 3 3 4 19%	4109
	11th to 20th	Night	20% 18% 6% 12% 7% 5% 3 3 3 4 18%	4120
	21st to end	Night	27% 18% 6% 11% 5% 3 3 2 3 3 20%	4532
February	1st to 10th	Night	19% 16% 4 10% 6% 3 4 3 4 5% 27%	2470
	11th to 20th	Night	21% 15% 4 10% 5% 5% 4 3 4 4 25%	2372
	21st to end	Night	22% 15% 5% 8% 4 3 4 4 4 6% 26%	1856
March	1st to 10th	Night	23% 12% 3 6% 4 4 4 3 4 6% 31%	3418
	11th to 20th	Night	17% 13% 5% 7% 4 4 3 3 4 5% 34%	3480
	21st to end	Night	17% 10% 3 7% 4 3 3 3 5% 5% 39%	3817
April	1st to 10th	Night	19% 11% 3 6% 5% 4 3 4 4 6% 33%	2022
	11th to 20th	Night	17% 7% 2 5% 4 4 4 4 6% 9% 38%	1865
	21st to end	Night	15% 7% 3 8% 5% 4 4 3 6% 6% 39%	1710
May	1st to 10th	Night	27% 11% 4 8% 5% 4 4 3 4 6% 25%	2813
	11th to 20th	Night	19% 9% 3 8% 4 4 4 3 5% 7% 35%	2812
	21st to end	Night	14% 8% 2 7% 6% 5% 5% 4 6% 7% 36%	3079
June	1st to 10th	Night	11% 8% 3 6% 4 4 4 4 7% 9% 41%	1572
	11th to 20th	Night	10% 7% 3 6% 5% 5% 6% 5% 7% 9% 39%	1520
	21st to end	Night	13% 6% 2 5% 4 4 5% 4 6% 9% 42%	1640
July	1st to 10th	Night	10% 7% 3 7% 5% 5% 5% 6% 7% 9% 37%	2840
	11th to 20th	Night	11% 7% 4 6% 5% 5% 5% 4 6% 9% 38%	2840
	21st to end	Night	13% 8% 3 7% 5% 5% 5% 4 7% 7% 35%	3087
August	1st to 10th	Night	13% 8% 3 8% 5% 6% 6% 4 7% 9% 32%	2825
	11th to 20th	Night	13% 9% 2 7% 5% 5% 5% 4 5% 7% 38%	2785
	21st to end	Night	7% 4 2 6% 4 4 5% 4 6% 9% 47%	3311
September	1st to 10th	Night	12% 6% 3 6% 4 5% 5% 3 5% 7% 45%	1940
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 7% 50%	2090
	21st to end	Night	16% 7% 2 6% 4 5% 4 4 5% 6% 41%	2090
October	1st to 10th	Night	14% 5% 3 7% 4 3 4 3 5% 7% 45%	2256
	11th to 20th	Night	15% 6% 2 6% 5% 4 4 3 5% 6% 44%	2280
	21st to end	Night	23% 7% 2 6% 3 3 3 3 4 5% 41%	2508
November	1st to 10th	Night	13% 8% 3 6% 4 4 3 4 4 5% 46%	2391
	11th to 20th	Night	19% 13% 3 7% 3 3 5% 3 5% 6% 33%	2470
	21st to end	Night	18% 12% 3 9% 6% 5% 4 3 4 5% 32%	2653
December	1st to 10th	Night	23% 17% 5% 10% 5% 4 3 3 4 5% 22%	2660
	11th to 20th	Night	21% 17% 6% 10% 4 4 3 2 4 4 25%	3285
	21st to end	Night	21% 18% 6% 9% 5% 5% 4 3 4 5% 21%	4623

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	68% 6% 10% 12% 4	2837
	11th to 20th	Day	74% 4 7% 11% 5%	2840
	21st to end	Day	71% 5% 6% 14% 4 1	3124
February	1st to 10th	Day	63% 5% 8% 17% 6%	1710
	11th to 20th	Day	63% 4 10% 14% 8% 1	1700
	21st to end	Day	62% 4 8% 15% 10% 1	1596
March	1st to 10th	Day	56% 5% 9% 20% 8% 1	3435
	11th to 20th	Day	44% 6% 10% 28% 11% 1	3480
	21st to end	Day	53% 5% 8% 20% 12% 1	3815
April	1st to 10th	Day	52% 7% 10% 16% 12% 3	2157
	11th to 20th	Day	45% 6% 11% 17% 18% 3	2281
	21st to end	Day	49% 7% 11% 20% 11% 2	2470
May	1st to 10th	Day	56% 8% 10% 18% 7% 1	4120
	11th to 20th	Day	50% 8% 11% 20% 11% 1	4085
	21st to end	Day	38% 10% 16% 21% 12% 3	4489
June	1st to 10th	Day	41% 9% 14% 21% 14% 1	2598
	11th to 20th	Day	44% 9% 14% 21% 12% 1	2660
	21st to end	Day	42% 8% 14% 23% 12% 1	2530
July	1st to 10th	Day	38% 7% 14% 24% 14% 3	4055
	11th to 20th	Day	41% 5% 10% 30% 13% 1	4051
	21st to end	Day	51% 5% 10% 18% 14% 1	4324
August	1st to 10th	Day	46% 7% 14% 26% 7%	4091
	11th to 20th	Day	43% 4 11% 28% 13%	4083
	21st to end	Day	31% 6% 15% 30% 17% 2	4313
September	1st to 10th	Day	36% 7% 11% 20% 22% 4	2237
	11th to 20th	Day	38% 6% 11% 26% 16% 3	2090
	21st to end	Day	46% 7% 11% 19% 16% 1	2090
October	1st to 10th	Day	33% 3 7% 26% 27% 3	3197
	11th to 20th	Day	40% 3 10% 24% 16% 7%	3140
	21st to end	Day	32% 3 9% 32% 20% 4	3428
November	1st to 10th	Day	40% 4 10% 25% 17% 4	1888
	11th to 20th	Day	49% 6% 9% 18% 15% 3	1710
	21st to end	Day	55% 5% 9% 17% 13%	1523
December	1st to 10th	Day	68% 5% 8% 14% 4 1	1520
	11th to 20th	Day	63% 3 9% 17% 7% 1	1906
	21st to end	Day	66% 6% 11% 13% 4	3028
January	1st to 10th	Night	70% 5% 8% 12% 5% 1	4109
	11th to 20th	Night	71% 4 10% 12% 2	4120
	21st to end	Night	71% 4 6% 14% 4 1	4532
February	1st to 10th	Night	61% 4 11% 15% 9%	2470
	11th to 20th	Night	63% 4 9% 15% 9%	2374
	21st to end	Night	59% 7% 9% 14% 9% 2	1856
March	1st to 10th	Night	54% 5% 8% 22% 10% 1	3418
	11th to 20th	Night	51% 6% 9% 24% 9% 1	3480
	21st to end	Night	46% 5% 10% 23% 14% 2	3817
April	1st to 10th	Night	52% 5% 9% 19% 13% 2	2022
	11th to 20th	Night	41% 8% 12% 18% 15% 5%	1865
	21st to end	Night	44% 7% 12% 21% 14% 2	1710
May	1st to 10th	Night	60% 7% 8% 15% 9% 2	2840
	11th to 20th	Night	47% 10% 12% 21% 10% 1	2813
	21st to end	Night	42% 10% 15% 20% 10% 3	3087
June	1st to 10th	Night	38% 9% 12% 24% 15% 2	1572
	11th to 20th	Night	39% 11% 14% 21% 13% 2	1520
	21st to end	Night	36% 10% 15% 22% 15% 2	1640
July	1st to 10th	Night	43% 7% 12% 21% 15% 3	2795
	11th to 20th	Night	42% 6% 10% 28% 12% 1	2786
	21st to end	Night	46% 7% 10% 19% 16% 2	2988
August	1st to 10th	Night	47% 6% 17% 23% 7% 1	2814
	11th to 20th	Night	45% 6% 9% 22% 18% 1	2812
	21st to end	Night	34% 5% 11% 32% 15% 2	3311
September	1st to 10th	Night	39% 6% 12% 19% 20% 5%	1940
	11th to 20th	Night	32% 7% 13% 23% 22% 3	2090
	21st to end	Night	42% 6% 12% 20% 18% 1	2090
October	1st to 10th	Night	34% 4 9% 27% 22% 5%	3763
	11th to 20th	Night	37% 4 8% 22% 20% 8%	3779
	21st to end	Night	34% 2 6% 28% 25% 4	4120
November	1st to 10th	Night	39% 6% 11% 20% 19% 6%	2391
	11th to 20th	Night	52% 5% 8% 18% 15% 3	2470
	21st to end	Night	56% 4 9% 18% 11% 1	2653
December	1st to 10th	Night	66% 5% 8% 15% 4 1	2660
	11th to 20th	Night	63% 4 10% 15% 7%	3288
	21st to end	Night	66% 6% 9% 14% 6%	4623

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	32% 29% 22% 12% 4 1	270
	11th to 20th	Day	40% 25% 28% 7% 1	270
	21st to end	Day	37% 28% 25% 7% 3	297
February	1st to 10th	Day	35% 23% 31% 8% 2	270
	11th to 20th	Day	46% 25% 21% 7% 1	270
	21st to end	Day	40% 24% 28% 8%	251
March	1st to 10th	Day	35% 17% 29% 15% 4	460
	11th to 20th	Day	31% 25% 25% 13% 5% 1	460
	21st to end	Day	32% 16% 31% 16% 5%	506
April	1st to 10th	Day	30% 22% 23% 19% 6%	460
	11th to 20th	Day	27% 18% 25% 17% 8% 4	452
	21st to end	Day	28% 19% 27% 17% 7% 2	460
May	1st to 10th	Day	27% 19% 27% 15% 7% 5%	463
	11th to 20th	Day	23% 14% 27% 22% 10% 4	487
	21st to end	Day	15% 12% 24% 26% 16% 8%	529
June	1st to 10th	Day	15% 9% 25% 29% 16% 6%	490
	11th to 20th	Day	17% 8% 25% 26% 17% 7%	490
	21st to end	Day	14% 10% 31% 27% 13% 5%	490
July	1st to 10th	Day	15% 5% 21% 26% 20% 14%	485
	11th to 20th	Day	11% 6% 23% 33% 19% 8%	484
	21st to end	Day	17% 6% 22% 28% 20% 8%	532
August	1st to 10th	Day	14% 5% 19% 31% 20% 12%	486
	11th to 20th	Day	18% 7% 17% 30% 19% 10%	479
	21st to end	Day	12% 4 20% 30% 22% 12%	539
September	1st to 10th	Day	16% 6% 18% 29% 21% 11%	490
	11th to 20th	Day	13% 3 17% 31% 25% 12%	490
	21st to end	Day	22% 10% 23% 27% 13% 4	490
October	1st to 10th	Day	17% 9% 24% 24% 21% 5%	490
	11th to 20th	Day	21% 13% 25% 24% 13% 3	490
	21st to end	Day	27% 16% 25% 20% 11% 1	539
November	1st to 10th	Day	19% 13% 28% 24% 13% 3	432
	11th to 20th	Day	30% 20% 23% 19% 6% 1	270
	21st to end	Day	28% 19% 36% 12% 3 1	181
December	1st to 10th	Day	31% 26% 27% 11% 3 2	180
	11th to 20th	Day	33% 24% 22% 17% 3 1	180
	21st to end	Day	38% 21% 22% 14% 5%	270
January	1st to 10th	Night	32% 21% 27% 17% 3	760
	11th to 20th	Night	35% 17% 27% 19% 2	760
	21st to end	Night	31% 19% 30% 18% 2	836
February	1st to 10th	Night	29% 16% 29% 24% 2	760
	11th to 20th	Night	32% 21% 31% 15% 1	743
	21st to end	Night	33% 17% 32% 17% 2	628
March	1st to 10th	Night	29% 16% 28% 24% 3	760
	11th to 20th	Night	32% 16% 28% 18% 6% 1	760
	21st to end	Night	27% 15% 31% 22% 4	836
April	1st to 10th	Night	26% 17% 28% 23% 5%	760
	11th to 20th	Night	20% 15% 30% 24% 11% 1	741
	21st to end	Night	17% 12% 32% 32% 7%	570
May	1st to 10th	Night	23% 10% 27% 29% 10% 1	570
	11th to 20th	Night	19% 8% 29% 31% 11% 1	561
	21st to end	Night	12% 5% 22% 32% 25% 4	617
June	1st to 10th	Night	11% 5% 24% 39% 20% 1	432
	11th to 20th	Night	14% 3 22% 38% 22% 2	380
	21st to end	Night	14% 3 21% 40% 20% 1	500
July	1st to 10th	Night	13% 3 15% 37% 28% 4	555
	11th to 20th	Night	12% 2 15% 35% 32% 4	552
	21st to end	Night	13% 3 15% 38% 29% 3	624
August	1st to 10th	Night	10% 2 14% 39% 32% 3	567
	11th to 20th	Night	15% 3 12% 38% 29% 4	564
	21st to end	Night	12% 4 12% 34% 33% 6%	736
September	1st to 10th	Night	15% 3 15% 35% 28% 5%	760
	11th to 20th	Night	15% 3 16% 31% 32% 4	760
	21st to end	Night	18% 7% 22% 31% 21% 2	760
October	1st to 10th	Night	17% 7% 18% 31% 24% 4	760
	11th to 20th	Night	19% 10% 27% 31% 13% 1	760
	21st to end	Night	27% 10% 19% 31% 11% 1	836
November	1st to 10th	Night	17% 9% 26% 32% 15% 1	779
	11th to 20th	Night	29% 12% 25% 25% 8% 1	760
	21st to end	Night	26% 14% 27% 25% 7% 1	760
December	1st to 10th	Night	33% 18% 25% 19% 4	760
	11th to 20th	Night	27% 19% 26% 24% 4	760
	21st to end	Night	30% 15% 27% 26% 2	836

Page generated at 2024-11-07 06:55:49. Version ac07

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