Sparta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sparta clear sky chart from 2005-11-06 to 2026-08-30.

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	15% 8% 3 7% 4 4 5% 4 6% 7% 36%	143420
	Night	16% 9% 3 6% 4 4 4 3 5% 7% 39%	138832
Transparency	Day	44% 6% 11% 21% 15% 3	147132
	Night	43% 6% 11% 21% 16% 4	143180
Seeing	Day	19% 11% 23% 22% 16% 8%	17037
	Night	18% 9% 20% 30% 19% 3	26999

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	20% 14% 6% 10% 3 3 4 3 4 5% 29%	5258
	11th to 20th	Day	16% 10% 6% 10% 3 2 3 2 3 4 41%	5280
	21st to end	Day	23% 10% 5% 7% 5% 3 3 3 4 5% 33%	6061
February	1st to 10th	Day	21% 12% 4 7% 4 4 3 3 5% 4 33%	2100
	11th to 20th	Day	23% 10% 4 8% 5% 4 3 3 4 5% 30%	2048
	21st to end	Day	22% 10% 4 7% 4 4 3 3 4 5% 35%	1730
March	1st to 10th	Day	21% 10% 4 7% 4 4 4 3 4 5% 34%	4580
	11th to 20th	Day	14% 8% 3 6% 4 4 3 3 4 5% 45%	5038
	21st to end	Day	15% 8% 2 6% 4 4 4 4 5% 6% 42%	5617
April	1st to 10th	Day	15% 5% 2 6% 5% 4 4 3 5% 7% 41%	2520
	11th to 20th	Day	15% 7% 2 5% 4 4 4 3 5% 7% 44%	2494
	21st to end	Day	17% 6% 2 5% 5% 4 5% 4 6% 7% 38%	2651
May	1st to 10th	Day	20% 8% 3 7% 4 4 5% 4 7% 8% 32%	7616
	11th to 20th	Day	14% 8% 3 9% 5% 5% 5% 4 6% 7% 34%	7626
	21st to end	Day	20% 9% 4 10% 6% 5% 5% 3 5% 6% 28%	8391
June	1st to 10th	Day	12% 6% 3 6% 5% 5% 5% 5% 6% 9% 39%	2730
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	2730
	21st to end	Day	8% 5% 2 5% 5% 6% 5% 6% 8% 12% 38%	2730
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 6% 9% 11% 36%	7680
	11th to 20th	Day	12% 7% 3 8% 6% 6% 7% 6% 9% 10% 26%	7680
	21st to end	Day	14% 7% 3 8% 6% 6% 6% 5% 8% 12% 26%	8340
August	1st to 10th	Day	8% 4 2 6% 4 5% 5% 5% 7% 11% 43%	4364
	11th to 20th	Day	8% 4 2 6% 5% 6% 6% 5% 7% 12% 37%	3969
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 6% 9% 47%	4420
September	1st to 10th	Day	14% 5% 2 6% 5% 5% 5% 4 6% 7% 40%	2297
	11th to 20th	Day	14% 6% 3 6% 5% 4 5% 4 5% 7% 42%	2200
	21st to end	Day	15% 6% 2 5% 5% 4 3 4 5% 6% 46%	2200
October	1st to 10th	Day	11% 4 2 5% 3 4 4 3 5% 6% 53%	2200
	11th to 20th	Day	14% 5% 2 3 3 3 3 3 4 6% 54%	2135
	21st to end	Day	17% 6% 1 5% 3 4 3 4 5% 6% 46%	2055
November	1st to 10th	Day	12% 6% 1 5% 2 3 4 3 4 5% 53%	1852
	11th to 20th	Day	14% 7% 2 6% 3 3 4 3 4 6% 47%	1890
	21st to end	Day	17% 9% 3 5% 3 3 4 3 5% 5% 42%	1890
December	1st to 10th	Day	18% 9% 3 7% 5% 4 4 3 4 4 40%	3020
	11th to 20th	Day	21% 14% 5% 8% 4 3 3 3 5% 4 28%	3463
	21st to end	Day	19% 13% 5% 8% 3 4 4 3 5% 7% 28%	4565
January	1st to 10th	Night	18% 13% 4 7% 3 3 3 2 4 5% 38%	7635
	11th to 20th	Night	19% 11% 3 6% 4 4 3 2 3 4 42%	7680
	21st to end	Night	21% 12% 4 8% 4 3 3 2 3 4 36%	8102
February	1st to 10th	Night	21% 10% 3 8% 5% 4 4 3 4 6% 32%	2520
	11th to 20th	Night	25% 10% 4 8% 4 4 4 2 3 4 32%	2458
	21st to end	Night	24% 11% 3 7% 4 3 3 3 5% 5% 32%	2076
March	1st to 10th	Night	22% 12% 3 6% 3 3 4 3 4 6% 33%	5493
	11th to 20th	Night	15% 6% 2 4 3 3 4 4 6% 6% 48%	5142
	21st to end	Night	16% 8% 3 7% 4 4 4 3 5% 6% 40%	5588
April	1st to 10th	Night	15% 6% 2 5% 4 4 4 4 6% 7% 44%	2109
	11th to 20th	Night	16% 6% 2 5% 4 3 3 3 4 7% 48%	2075
	21st to end	Night	14% 7% 2 6% 4 4 3 3 6% 7% 43%	1969
May	1st to 10th	Night	18% 8% 3 7% 5% 5% 5% 4 6% 8% 31%	5237
	11th to 20th	Night	15% 8% 3 8% 5% 5% 4 4 5% 7% 35%	5234
	21st to end	Night	19% 8% 3 8% 5% 5% 5% 4 6% 7% 29%	5761
June	1st to 10th	Night	9% 6% 2 7% 5% 5% 4 4 6% 9% 43%	1890
	11th to 20th	Night	5% 4 2 4 3 3 4 4 7% 13% 49%	1890
	21st to end	Night	6% 4 2 5% 5% 6% 5% 6% 8% 11% 43%	1890
July	1st to 10th	Night	8% 5% 2 6% 5% 5% 6% 5% 7% 11% 39%	5278
	11th to 20th	Night	12% 6% 3 8% 5% 6% 6% 5% 7% 12% 32%	5277
	21st to end	Night	10% 7% 3 9% 6% 6% 6% 5% 7% 11% 30%	5736
August	1st to 10th	Night	6% 4 1 5% 4 4 5% 4 6% 9% 50%	3005
	11th to 20th	Night	9% 4 2 6% 4 4 5% 5% 6% 10% 45%	3295
	21st to end	Night	5% 3 2 3 3 4 4 4 6% 9% 56%	3676
September	1st to 10th	Night	11% 5% 3 7% 4 4 4 4 5% 6% 47%	2081
	11th to 20th	Night	10% 6% 2 5% 5% 4 5% 3 5% 7% 46%	2200
	21st to end	Night	12% 5% 2 6% 3 3 3 3 5% 6% 52%	2200
October	1st to 10th	Night	11% 5% 1 4 3 3 3 3 4 6% 58%	2200
	11th to 20th	Night	17% 5% 2 5% 2 3 3 3 4 5% 52%	2264
	21st to end	Night	16% 7% 2 4 2 3 3 3 4 5% 49%	2780
November	1st to 10th	Night	14% 7% 2 4 3 3 3 3 4 5% 51%	2666
	11th to 20th	Night	14% 9% 2 4 3 2 3 3 5% 7% 48%	2730
	21st to end	Night	19% 9% 3 5% 3 2 3 3 4 5% 42%	2730
December	1st to 10th	Night	22% 11% 3 7% 3 3 4 3 4 4 36%	4380
	11th to 20th	Night	25% 12% 4 7% 3 3 2 2 3 4 35%	4952
	21st to end	Night	17% 15% 5% 7% 5% 5% 4 3 5% 6% 27%	6633

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	57% 4 9% 18% 11% 1	5259
	11th to 20th	Day	49% 3 3 15% 27% 2	5280
	21st to end	Day	54% 3 7% 21% 12% 3	6061
February	1st to 10th	Day	55% 4 6% 16% 17% 2	2100
	11th to 20th	Day	56% 4 7% 17% 13% 3	2058
	21st to end	Day	52% 4 8% 14% 17% 5%	1730
March	1st to 10th	Day	52% 5% 6% 14% 16% 8%	4580
	11th to 20th	Day	42% 3 7% 19% 20% 9%	5038
	21st to end	Day	44% 4 9% 27% 15% 1	5619
April	1st to 10th	Day	41% 6% 11% 23% 16% 3	2520
	11th to 20th	Day	40% 4 8% 21% 23% 3	2494
	21st to end	Day	44% 5% 10% 25% 14% 1	2651
May	1st to 10th	Day	48% 7% 12% 22% 11% 1	7651
	11th to 20th	Day	48% 6% 14% 21% 10%	7630
	21st to end	Day	57% 6% 8% 16% 10% 2	8405
June	1st to 10th	Day	40% 9% 14% 22% 14% 2	2730
	11th to 20th	Day	34% 9% 18% 22% 15% 2	2730
	21st to end	Day	36% 10% 19% 20% 13% 3	2730
July	1st to 10th	Day	37% 12% 20% 21% 9% 1	7615
	11th to 20th	Day	46% 13% 20% 17% 4 1	7611
	21st to end	Day	47% 10% 18% 18% 6% 1	8156
August	1st to 10th	Day	32% 9% 16% 31% 11% 1	4351
	11th to 20th	Day	36% 8% 18% 24% 13% 1	4005
	21st to end	Day	32% 8% 13% 31% 15% 1	4419
September	1st to 10th	Day	42% 9% 11% 18% 16% 5%	2297
	11th to 20th	Day	41% 6% 12% 22% 17% 2	2200
	21st to end	Day	39% 6% 12% 21% 19% 4	2200
October	1st to 10th	Day	24% 5% 6% 20% 34% 11%	3590
	11th to 20th	Day	23% 3 6% 24% 31% 12%	3453
	21st to end	Day	30% 4 9% 23% 25% 9%	3292
November	1st to 10th	Day	33% 4 9% 23% 27% 4	1852
	11th to 20th	Day	39% 4 6% 24% 22% 6%	1890
	21st to end	Day	44% 3 6% 22% 20% 4	1890
December	1st to 10th	Day	48% 5% 4 20% 22% 2	3020
	11th to 20th	Day	58% 4 8% 16% 12% 2	3460
	21st to end	Day	54% 4 12% 19% 10% 2	4565
January	1st to 10th	Night	49% 3 14% 19% 13% 1	7636
	11th to 20th	Night	48% 3 5% 16% 24% 4	7680
	21st to end	Night	54% 2 7% 15% 16% 6%	8102
February	1st to 10th	Night	53% 4 8% 17% 15% 2	2520
	11th to 20th	Night	58% 3 6% 17% 12% 4	2459
	21st to end	Night	54% 5% 6% 16% 15% 4	2076
March	1st to 10th	Night	53% 4 7% 15% 17% 4	5493
	11th to 20th	Night	35% 4 7% 22% 20% 12%	5142
	21st to end	Night	46% 4 8% 27% 13% 2	5588
April	1st to 10th	Night	38% 6% 11% 23% 19% 3	2109
	11th to 20th	Night	36% 4 9% 23% 22% 6%	2075
	21st to end	Night	40% 5% 11% 28% 15% 1	1969
May	1st to 10th	Night	48% 8% 12% 22% 10% 1	5264
	11th to 20th	Night	47% 7% 14% 17% 14% 1	5235
	21st to end	Night	51% 9% 12% 17% 9% 1	5771
June	1st to 10th	Night	37% 7% 15% 26% 13% 2	1890
	11th to 20th	Night	25% 9% 21% 28% 15% 2	1890
	21st to end	Night	31% 12% 15% 26% 13% 3	1890
July	1st to 10th	Night	35% 11% 21% 22% 10% 1	5235
	11th to 20th	Night	42% 12% 20% 20% 4 1	5226
	21st to end	Night	44% 11% 21% 16% 7% 1	5606
August	1st to 10th	Night	28% 8% 13% 36% 14% 1	2994
	11th to 20th	Night	32% 8% 21% 25% 13% 1	3325
	21st to end	Night	24% 7% 12% 38% 18% 1	3676
September	1st to 10th	Night	36% 8% 13% 20% 18% 5%	2081
	11th to 20th	Night	36% 7% 12% 22% 22% 2	2200
	21st to end	Night	33% 6% 11% 22% 24% 5%	2200
October	1st to 10th	Night	23% 4 5% 24% 31% 13%	3590
	11th to 20th	Night	23% 3 5% 24% 29% 16%	3685
	21st to end	Night	25% 3 7% 25% 29% 11%	4480
November	1st to 10th	Night	36% 3 6% 23% 24% 7%	2666
	11th to 20th	Night	37% 3 7% 21% 25% 7%	2730
	21st to end	Night	45% 4 6% 23% 19% 4	2730
December	1st to 10th	Night	52% 4 5% 15% 22% 2	4380
	11th to 20th	Night	54% 3 5% 19% 16% 2	4954
	21st to end	Night	56% 5% 10% 19% 9% 1	6633

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	29% 22% 32% 13% 3 1	330
	11th to 20th	Day	33% 25% 25% 13% 3	330
	21st to end	Day	26% 25% 36% 10% 3	363
February	1st to 10th	Day	27% 24% 31% 15% 3	330
	11th to 20th	Day	38% 24% 30% 6% 2	330
	21st to end	Day	34% 22% 32% 8% 2 1	273
March	1st to 10th	Day	27% 23% 35% 12% 3	330
	11th to 20th	Day	29% 21% 28% 17% 4 1	514
	21st to end	Day	27% 18% 33% 16% 6%	594
April	1st to 10th	Day	23% 18% 27% 23% 9% 1	540
	11th to 20th	Day	20% 16% 31% 23% 8% 2	532
	21st to end	Day	23% 13% 28% 22% 12% 2	540
May	1st to 10th	Day	23% 13% 30% 19% 10% 5%	543
	11th to 20th	Day	16% 9% 27% 25% 15% 7%	567
	21st to end	Day	17% 9% 20% 26% 16% 12%	617
June	1st to 10th	Day	14% 6% 19% 26% 22% 13%	570
	11th to 20th	Day	7% 6% 17% 30% 24% 16%	570
	21st to end	Day	10% 4 18% 24% 25% 19%	570
July	1st to 10th	Day	13% 4 10% 23% 27% 22%	565
	11th to 20th	Day	12% 4 9% 23% 28% 24%	564
	21st to end	Day	13% 4 11% 25% 26% 20%	620
August	1st to 10th	Day	15% 5% 11% 23% 28% 18%	566
	11th to 20th	Day	9% 3 13% 30% 31% 13%	559
	21st to end	Day	11% 3 10% 27% 28% 21%	619
September	1st to 10th	Day	14% 4 10% 25% 33% 15%	530
	11th to 20th	Day	14% 4 9% 29% 30% 15%	530
	21st to end	Day	15% 6% 17% 25% 28% 8%	530
October	1st to 10th	Day	12% 5% 18% 32% 24% 8%	530
	11th to 20th	Day	15% 10% 25% 27% 19% 5%	530
	21st to end	Day	22% 11% 27% 25% 12% 2	438
November	1st to 10th	Day	19% 13% 30% 26% 10% 2	330
	11th to 20th	Day	17% 16% 37% 25% 6%	330
	21st to end	Day	22% 15% 38% 16% 8% 2	330
December	1st to 10th	Day	28% 18% 33% 15% 4 1	330
	11th to 20th	Day	30% 16% 29% 17% 7% 1	330
	21st to end	Day	29% 19% 31% 16% 4 1	363
January	1st to 10th	Night	25% 18% 30% 24% 5%	840
	11th to 20th	Night	30% 18% 25% 22% 4	840
	21st to end	Night	23% 15% 32% 27% 2	924
February	1st to 10th	Night	25% 14% 32% 26% 3	840
	11th to 20th	Night	30% 18% 31% 20% 2	823
	21st to end	Night	30% 18% 28% 22% 2	692
March	1st to 10th	Night	25% 14% 31% 26% 4	840
	11th to 20th	Night	25% 14% 29% 25% 7% 1	840
	21st to end	Night	20% 13% 31% 28% 7%	924
April	1st to 10th	Night	19% 10% 28% 32% 10%	639
	11th to 20th	Night	18% 8% 30% 33% 10% 1	623
	21st to end	Night	19% 7% 26% 35% 12% 1	630
May	1st to 10th	Night	16% 7% 25% 34% 16% 2	630
	11th to 20th	Night	14% 5% 19% 36% 22% 4	621
	21st to end	Night	11% 4 14% 35% 30% 6%	683
June	1st to 10th	Night	10% 3 12% 38% 34% 4	630
	11th to 20th	Night	4 3 11% 37% 36% 9%	630
	21st to end	Night	6% 2 8% 37% 38% 8%	630
July	1st to 10th	Night	11% 2 4 25% 47% 11%	615
	11th to 20th	Night	9% 2 7% 26% 43% 12%	612
	21st to end	Night	9% 3 5% 30% 43% 10%	690
August	1st to 10th	Night	9% 1 6% 27% 49% 8%	627
	11th to 20th	Night	9% 1 6% 33% 45% 6%	624
	21st to end	Night	9% 2 5% 29% 47% 8%	687
September	1st to 10th	Night	12% 2 7% 34% 38% 7%	681
	11th to 20th	Night	14% 3 10% 32% 36% 6%	800
	21st to end	Night	13% 4 13% 33% 31% 6%	800
October	1st to 10th	Night	12% 5% 15% 32% 28% 8%	800
	11th to 20th	Night	18% 6% 22% 33% 20% 2	800
	21st to end	Night	19% 9% 22% 32% 16% 2	880
November	1st to 10th	Night	16% 8% 20% 37% 16% 2	820
	11th to 20th	Night	18% 12% 26% 32% 10% 2	840
	21st to end	Night	24% 12% 25% 28% 11% 1	840
December	1st to 10th	Night	29% 13% 25% 26% 7%	840
	11th to 20th	Night	26% 13% 24% 30% 7% 1	840
	21st to end	Night	27% 17% 24% 27% 5%	924

Page generated at 2026-08-27 03:07:11. Version ac07

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