Eridanus Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eridanus Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	12% 6% 2 6% 4 4 4 4 5% 7% 46%	101181
	Night	12% 6% 2 5% 4 3 4 3 5% 7% 49%	98602
Transparency	Day	36% 5% 11% 25% 19% 4	104826
	Night	33% 5% 11% 25% 21% 5%	103097
Seeing	Day	17% 9% 24% 26% 18% 6%	15551
	Night	16% 9% 25% 31% 17% 2	25375

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	15% 10% 2 6% 3 3 3 3 4 3 47%	2847
	11th to 20th	Day	11% 8% 2 6% 3 3 3 3 5% 5% 50%	2850
	21st to end	Day	23% 8% 3 5% 2 2 2 2 3 4 45%	3135
February	1st to 10th	Day	16% 9% 4 7% 3 4 3 3 3 5% 43%	1710
	11th to 20th	Day	16% 8% 2 7% 5% 4 4 3 4 6% 42%	1780
	21st to end	Day	16% 10% 4 6% 4 4 4 3 5% 6% 38%	1570
March	1st to 10th	Day	20% 10% 2 5% 3 3 3 3 4 4 43%	3436
	11th to 20th	Day	14% 6% 2 5% 4 3 3 3 4 6% 50%	3480
	21st to end	Day	15% 7% 3 7% 5% 4 4 3 5% 5% 43%	3863
April	1st to 10th	Day	11% 7% 3 7% 5% 3 4 3 5% 6% 46%	2280
	11th to 20th	Day	16% 6% 2 6% 4 5% 4 4 6% 6% 41%	2254
	21st to end	Day	17% 8% 3 8% 3 4 4 4 4 6% 39%	2280
May	1st to 10th	Day	14% 7% 3 6% 5% 5% 5% 4 6% 8% 37%	3779
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 4 6% 8% 40%	4082
	21st to end	Day	13% 7% 2 8% 5% 5% 5% 4 6% 7% 37%	4748
June	1st to 10th	Day	8% 5% 2 6% 6% 5% 5% 5% 7% 9% 43%	2660
	11th to 20th	Day	5% 4 1 5% 5% 4 6% 6% 7% 10% 47%	2660
	21st to end	Day	4 4 2 4 5% 4 5% 5% 7% 10% 50%	2660
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 8% 43%	4227
	11th to 20th	Day	5% 3 1 5% 4 4 5% 4 7% 11% 51%	4120
	21st to end	Day	8% 7% 3 8% 6% 6% 6% 5% 7% 10% 34%	4465
August	1st to 10th	Day	4 3 1 4 3 3 4 4 5% 9% 60%	4104
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 7% 10% 43%	3768
	21st to end	Day	5% 3 2 5% 4 5% 4 4 6% 9% 54%	4180
September	1st to 10th	Day	10% 6% 2 6% 4 5% 4 4 5% 8% 47%	2280
	11th to 20th	Day	13% 6% 2 5% 3 4 4 4 5% 8% 45%	2280
	21st to end	Day	9% 5% 2 4 4 3 4 3 5% 8% 53%	1999
October	1st to 10th	Day	8% 4 2 5% 3 4 4 3 5% 6% 57%	1900
	11th to 20th	Day	14% 5% 2 5% 2 3 3 2 4 4 56%	1900
	21st to end	Day	18% 5% 2 5% 3 3 2 3 4 6% 49%	2090
November	1st to 10th	Day	12% 6% 2 5% 2 3 2 2 3 5% 57%	1958
	11th to 20th	Day	10% 6% 3 5% 4 3 4 3 5% 5% 52%	1816
	21st to end	Day	18% 8% 3 5% 3 3 3 3 3 5% 48%	1718
December	1st to 10th	Day	15% 7% 2 5% 3 4 4 3 4 6% 46%	1560
	11th to 20th	Day	14% 9% 2 8% 5% 3 4 3 4 4 44%	1918
	21st to end	Day	13% 13% 3 8% 5% 4 5% 4 6% 6% 35%	2824
January	1st to 10th	Night	15% 7% 3 6% 4 4 5% 4 5% 6% 42%	4108
	11th to 20th	Night	14% 6% 2 6% 4 4 3 2 3 5% 49%	4120
	21st to end	Night	22% 11% 2 5% 2 3 2 2 3 5% 43%	4532
February	1st to 10th	Night	16% 10% 3 6% 4 4 4 3 4 6% 41%	2470
	11th to 20th	Night	15% 8% 3 6% 4 4 3 3 4 6% 45%	2285
	21st to end	Night	17% 7% 2 4 4 4 3 3 5% 5% 46%	1884
March	1st to 10th	Night	21% 8% 3 5% 3 3 3 3 4 5% 43%	3433
	11th to 20th	Night	15% 6% 2 5% 3 2 3 3 4 5% 52%	3480
	21st to end	Night	13% 7% 2 6% 4 5% 5% 3 5% 6% 44%	3768
April	1st to 10th	Night	11% 7% 2 5% 4 4 4 3 5% 6% 51%	1900
	11th to 20th	Night	14% 5% 2 6% 4 3 3 3 5% 5% 49%	1875
	21st to end	Night	15% 7% 3 5% 3 3 4 4 6% 8% 43%	1900
May	1st to 10th	Night	17% 5% 2 5% 4 3 4 3 5% 7% 44%	3113
	11th to 20th	Night	14% 7% 2 5% 3 4 4 4 6% 8% 44%	2823
	21st to end	Night	12% 7% 2 5% 4 4 5% 3 6% 9% 43%	2817
June	1st to 10th	Night	8% 4 2 4 3 3 4 4 7% 9% 52%	1520
	11th to 20th	Night	3 3 1 4 2 3 3 4 7% 10% 59%	1520
	21st to end	Night	3 3 1 4 4 3 3 3 7% 9% 59%	1520
July	1st to 10th	Night	7% 4 2 5% 4 4 4 4 7% 10% 50%	2737
	11th to 20th	Night	4 3 1 4 3 3 4 3 6% 9% 61%	2850
	21st to end	Night	6% 7% 3 7% 5% 5% 6% 4 7% 10% 40%	3098
August	1st to 10th	Night	3 3 1 3 2 3 4 4 5% 8% 64%	2836
	11th to 20th	Night	5% 4 2 5% 4 5% 5% 4 7% 9% 52%	3060
	21st to end	Night	5% 2 1 4 3 3 4 3 5% 9% 61%	3476
September	1st to 10th	Night	8% 4 2 4 4 3 3 3 5% 8% 56%	1900
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 6% 7% 49%	1900
	21st to end	Night	6% 5% 2 5% 3 3 3 3 5% 6% 59%	2156
October	1st to 10th	Night	7% 3 1 3 3 2 3 3 6% 6% 63%	2280
	11th to 20th	Night	12% 5% 1 3 3 3 2 2 4 6% 60%	2280
	21st to end	Night	18% 5% 2 4 2 2 4 3 4 4 53%	2508
November	1st to 10th	Night	13% 5% 2 4 3 3 3 2 4 6% 56%	2340
	11th to 20th	Night	11% 5% 1 4 3 2 3 3 5% 6% 56%	2580
	21st to end	Night	14% 6% 2 4 4 4 3 3 5% 6% 50%	2679
December	1st to 10th	Night	16% 8% 2 5% 4 2 3 3 4 5% 49%	2737
	11th to 20th	Night	15% 7% 3 6% 4 4 4 3 4 5% 46%	3279
	21st to end	Night	15% 11% 4 8% 5% 5% 5% 4 4 6% 34%	4838

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	41% 3 6% 27% 18% 3	2848
	11th to 20th	Day	36% 5% 9% 28% 20% 3	2850
	21st to end	Day	44% 3 9% 20% 20% 5%	3135
February	1st to 10th	Day	45% 4 11% 23% 15% 3	1710
	11th to 20th	Day	44% 4 9% 20% 18% 5%	1789
	21st to end	Day	47% 4 9% 18% 15% 8%	1570
March	1st to 10th	Day	46% 5% 7% 18% 15% 10%	3436
	11th to 20th	Day	36% 5% 8% 26% 19% 6%	3480
	21st to end	Day	43% 5% 10% 24% 17% 1	3863
April	1st to 10th	Day	39% 5% 8% 24% 21% 3	2280
	11th to 20th	Day	41% 5% 11% 21% 15% 6%	2254
	21st to end	Day	45% 6% 9% 21% 16% 2	2280
May	1st to 10th	Day	44% 7% 12% 21% 15% 1	3814
	11th to 20th	Day	39% 9% 14% 24% 12% 1	4086
	21st to end	Day	44% 7% 11% 21% 14% 2	4761
June	1st to 10th	Day	36% 9% 14% 24% 17% 1	2660
	11th to 20th	Day	28% 8% 15% 28% 17% 3	2660
	21st to end	Day	28% 7% 16% 26% 20% 4	2660
July	1st to 10th	Day	37% 6% 17% 26% 13% 2	4163
	11th to 20th	Day	25% 6% 10% 34% 22% 3	4051
	21st to end	Day	44% 6% 16% 25% 8% 1	4325
August	1st to 10th	Day	21% 5% 17% 32% 21% 4	4090
	11th to 20th	Day	37% 5% 14% 29% 14% 1	3804
	21st to end	Day	27% 5% 13% 35% 17% 3	4179
September	1st to 10th	Day	35% 5% 11% 24% 18% 6%	2280
	11th to 20th	Day	36% 6% 10% 20% 25% 3	2280
	21st to end	Day	30% 5% 8% 26% 28% 4	1999
October	1st to 10th	Day	16% 3 6% 17% 44% 15%	3160
	11th to 20th	Day	21% 2 3 22% 41% 11%	3140
	21st to end	Day	31% 3 6% 32% 23% 4	3428
November	1st to 10th	Day	32% 3 8% 26% 24% 7%	1958
	11th to 20th	Day	33% 4 7% 23% 24% 8%	1816
	21st to end	Day	42% 3 8% 20% 23% 4	1718
December	1st to 10th	Day	39% 5% 8% 28% 16% 3	1560
	11th to 20th	Day	43% 4 6% 22% 23% 2	1915
	21st to end	Day	48% 6% 11% 17% 13% 5%	2824
January	1st to 10th	Night	41% 4 8% 24% 20% 2	4108
	11th to 20th	Night	37% 4 11% 25% 20% 3	4120
	21st to end	Night	46% 3 10% 20% 18% 2	4532
February	1st to 10th	Night	45% 4 9% 23% 16% 3	2470
	11th to 20th	Night	41% 3 9% 23% 19% 5%	2286
	21st to end	Night	40% 4 9% 21% 18% 8%	1884
March	1st to 10th	Night	45% 5% 8% 16% 17% 10%	3433
	11th to 20th	Night	35% 5% 8% 28% 20% 4	3480
	21st to end	Night	40% 6% 9% 28% 16% 1	3768
April	1st to 10th	Night	34% 5% 11% 22% 22% 6%	1900
	11th to 20th	Night	36% 4 9% 24% 20% 7%	1875
	21st to end	Night	39% 5% 11% 25% 17% 3	1900
May	1st to 10th	Night	40% 6% 15% 23% 13% 2	3143
	11th to 20th	Night	37% 8% 15% 25% 13% 2	2824
	21st to end	Night	37% 8% 13% 27% 14% 1	2825
June	1st to 10th	Night	25% 7% 14% 31% 21% 2	1520
	11th to 20th	Night	19% 6% 14% 36% 21% 4	1520
	21st to end	Night	20% 6% 16% 30% 20% 7%	1520
July	1st to 10th	Night	29% 6% 20% 25% 18% 2	2692
	11th to 20th	Night	20% 5% 12% 37% 24% 3	2796
	21st to end	Night	38% 6% 16% 27% 13%	2999
August	1st to 10th	Night	17% 6% 16% 37% 24% 1	2826
	11th to 20th	Night	28% 5% 20% 29% 16% 1	3090
	21st to end	Night	21% 5% 14% 33% 23% 3	3476
September	1st to 10th	Night	27% 5% 11% 29% 19% 9%	1900
	11th to 20th	Night	34% 6% 9% 20% 25% 5%	1900
	21st to end	Night	27% 4 9% 24% 31% 6%	2156
October	1st to 10th	Night	13% 3 7% 16% 40% 22%	3800
	11th to 20th	Night	18% 2 4 17% 39% 20%	3779
	21st to end	Night	28% 3 5% 28% 29% 8%	4120
November	1st to 10th	Night	30% 4 8% 25% 25% 7%	2340
	11th to 20th	Night	29% 3 7% 25% 26% 9%	2580
	21st to end	Night	35% 4 9% 24% 25% 4	2679
December	1st to 10th	Night	39% 3 9% 25% 20% 4	2737
	11th to 20th	Night	42% 3 7% 24% 21% 3	3281
	21st to end	Night	48% 6% 12% 19% 14% 2	4838

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	30% 18% 33% 14% 4	270
	11th to 20th	Day	30% 20% 34% 13% 3	270
	21st to end	Day	28% 19% 34% 16% 3	297
February	1st to 10th	Day	29% 14% 38% 12% 6%	270
	11th to 20th	Day	30% 21% 31% 12% 5% 1	270
	21st to end	Day	36% 20% 32% 8% 3	225
March	1st to 10th	Day	30% 17% 33% 15% 4 1	270
	11th to 20th	Day	33% 19% 33% 13% 3	270
	21st to end	Day	27% 22% 33% 15% 2	321
April	1st to 10th	Day	23% 17% 30% 18% 10% 1	460
	11th to 20th	Day	23% 17% 33% 20% 7% 1	452
	21st to end	Day	24% 14% 33% 21% 6% 2	460
May	1st to 10th	Day	23% 13% 30% 25% 7% 1	464
	11th to 20th	Day	18% 9% 32% 24% 13% 4	675
	21st to end	Day	13% 7% 32% 27% 16% 5%	734
June	1st to 10th	Day	10% 4 21% 29% 26% 9%	680
	11th to 20th	Day	7% 2 19% 40% 26% 6%	680
	21st to end	Day	5% 4 22% 37% 26% 6%	680
July	1st to 10th	Day	8% 1 15% 33% 31% 12%	671
	11th to 20th	Day	5% 2 14% 34% 32% 13%	668
	21st to end	Day	7% 2 12% 30% 33% 15%	739
August	1st to 10th	Day	8% 2 10% 39% 33% 8%	676
	11th to 20th	Day	13% 3 10% 30% 33% 11%	506
	21st to end	Day	9% 2 8% 30% 35% 16%	539
September	1st to 10th	Day	11% 3 9% 32% 33% 11%	490
	11th to 20th	Day	12% 2 11% 32% 29% 14%	490
	21st to end	Day	13% 6% 21% 31% 22% 6%	342
October	1st to 10th	Day	8% 9% 21% 33% 24% 4	300
	11th to 20th	Day	18% 13% 33% 24% 11% 1	300
	21st to end	Day	31% 11% 30% 22% 6% 1	330
November	1st to 10th	Day	19% 10% 34% 23% 12% 3	300
	11th to 20th	Day	19% 15% 34% 23% 9% 1	300
	21st to end	Day	30% 13% 30% 18% 8% 2	300
December	1st to 10th	Day	21% 22% 31% 15% 8% 2	285
	11th to 20th	Day	27% 19% 29% 19% 6%	270
	21st to end	Day	25% 23% 34% 15% 3	297
January	1st to 10th	Night	23% 16% 32% 24% 5%	950
	11th to 20th	Night	24% 17% 32% 21% 5%	950
	21st to end	Night	22% 13% 36% 26% 3	1045
February	1st to 10th	Night	24% 13% 33% 26% 4	950
	11th to 20th	Night	21% 17% 37% 23% 2	810
	21st to end	Night	25% 17% 35% 21% 2	628
March	1st to 10th	Night	23% 12% 32% 30% 4	584
	11th to 20th	Night	24% 11% 31% 29% 5%	570
	21st to end	Night	22% 12% 34% 26% 6%	627
April	1st to 10th	Night	17% 14% 36% 28% 5%	570
	11th to 20th	Night	17% 14% 30% 30% 8%	563
	21st to end	Night	17% 10% 38% 27% 8% 1	570
May	1st to 10th	Night	14% 10% 29% 37% 9% 1	570
	11th to 20th	Night	17% 5% 27% 28% 20% 2	561
	21st to end	Night	11% 4 22% 37% 22% 4	617
June	1st to 10th	Night	9% 2 16% 34% 35% 4	570
	11th to 20th	Night	4 1 15% 44% 33% 3	570
	21st to end	Night	4 1 15% 42% 34% 4	570
July	1st to 10th	Night	7% 2 7% 36% 41% 8%	555
	11th to 20th	Night	5% 1 8% 37% 41% 8%	552
	21st to end	Night	6% 1 5% 40% 38% 10%	624
August	1st to 10th	Night	7% 1 6% 39% 40% 7%	567
	11th to 20th	Night	8% 1 9% 41% 37% 4	564
	21st to end	Night	6% 2 8% 34% 44% 6%	627
September	1st to 10th	Night	9% 9% 35% 41% 4	570
	11th to 20th	Night	13% 2 8% 34% 37% 7%	570
	21st to end	Night	9% 5% 15% 35% 32% 4	683
October	1st to 10th	Night	9% 3 18% 35% 32% 3	760
	11th to 20th	Night	13% 9% 27% 33% 17% 1	760
	21st to end	Night	22% 9% 26% 30% 12% 1	836
November	1st to 10th	Night	15% 8% 30% 33% 14% 1	780
	11th to 20th	Night	16% 9% 32% 33% 10%	800
	21st to end	Night	19% 12% 29% 30% 10%	879
December	1st to 10th	Night	21% 11% 32% 30% 7%	978
	11th to 20th	Night	24% 12% 27% 32% 6%	950
	21st to end	Night	24% 15% 30% 27% 4	1045

Page generated at 2024-12-03 05:45:08. Version ac07

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