Northern Cross Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northern Cross Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	14% 10% 3 8% 5% 5% 5% 4 5% 7% 34%	100751
	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 35%	98225
Transparency	Day	48% 6% 12% 21% 12% 1	104364
	Night	48% 5% 11% 21% 12% 1	102752
Seeing	Day	18% 12% 29% 23% 14% 5%	15506
	Night	19% 10% 29% 29% 11% 1	25470

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% 21% 7% 12% 5% 4 4 3 4 4 21%	2527
	11th to 20th	Day	15% 21% 6% 13% 9% 7% 5% 3 4 4 13%	2530
	21st to end	Day	28% 21% 7% 12% 4 4 3 2 3 3 14%	3000
February	1st to 10th	Day	13% 15% 6% 12% 8% 5% 5% 3 4 5% 23%	1710
	11th to 20th	Day	14% 14% 6% 13% 7% 5% 4 2 5% 4 24%	1808
	21st to end	Day	14% 16% 6% 12% 5% 4 4 3 4 6% 24%	1570
March	1st to 10th	Day	17% 16% 5% 8% 5% 4 3 3 4 6% 28%	3171
	11th to 20th	Day	12% 13% 6% 9% 5% 5% 4 3 5% 6% 31%	3480
	21st to end	Day	18% 15% 4 9% 5% 4 4 3 4 5% 29%	3815
April	1st to 10th	Day	16% 13% 4 7% 6% 5% 5% 3 5% 6% 30%	2233
	11th to 20th	Day	17% 10% 3 7% 4 5% 4 4 5% 6% 35%	2394
	21st to end	Day	17% 9% 3 8% 5% 4 4 3 5% 6% 34%	2470
May	1st to 10th	Day	18% 8% 3 6% 4 5% 5% 4 5% 6% 35%	4082
	11th to 20th	Day	17% 7% 2 6% 4 4 5% 4 6% 8% 37%	4081
	21st to end	Day	12% 6% 2 6% 4 3 4 4 6% 8% 46%	4536
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 9% 41%	2660
	11th to 20th	Day	11% 6% 2 7% 4 4 5% 4 6% 8% 41%	2660
	21st to end	Day	12% 5% 2 6% 6% 5% 5% 5% 7% 10% 37%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 6% 6% 5% 7% 9% 37%	4440
	11th to 20th	Day	9% 4 1 5% 4 4 5% 5% 6% 9% 49%	4440
	21st to end	Day	9% 5% 2 6% 5% 6% 6% 5% 6% 9% 42%	4602
August	1st to 10th	Day	14% 4 2 6% 5% 4 5% 4 6% 8% 42%	4104
	11th to 20th	Day	13% 5% 2 6% 4 5% 5% 5% 6% 9% 41%	4044
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 5% 6% 9% 41%	4448
September	1st to 10th	Day	11% 6% 2 7% 5% 5% 4 4 7% 8% 40%	2165
	11th to 20th	Day	10% 6% 2 5% 4 3 5% 4 6% 8% 48%	2090
	21st to end	Day	14% 7% 3 7% 5% 4 5% 4 7% 8% 35%	2090
October	1st to 10th	Day	15% 7% 2 7% 5% 4 4 4 5% 6% 42%	2052
	11th to 20th	Day	18% 11% 2 8% 5% 4 4 3 4 7% 33%	1900
	21st to end	Day	21% 12% 3 6% 5% 4 4 4 5% 7% 29%	1910
November	1st to 10th	Day	13% 10% 2 7% 6% 4 4 4 6% 7% 36%	1708
	11th to 20th	Day	14% 14% 5% 8% 5% 4 4 3 4 7% 29%	1710
	21st to end	Day	19% 15% 5% 9% 5% 4 4 3 4 6% 27%	1645
December	1st to 10th	Day	14% 17% 8% 12% 7% 4 4 2 4 5% 22%	1520
	11th to 20th	Day	16% 17% 5% 11% 6% 4 5% 4 5% 5% 22%	1713
	21st to end	Day	24% 23% 7% 13% 5% 4 3 2 3 4 11%	2783
January	1st to 10th	Night	16% 16% 8% 12% 6% 4 4 3 4 5% 22%	4428
	11th to 20th	Night	14% 17% 9% 15% 6% 7% 6% 3 5% 4 14%	4440
	21st to end	Night	23% 17% 9% 12% 5% 3 3 3 4 4 17%	4657
February	1st to 10th	Night	16% 17% 6% 10% 7% 4 5% 3 4 4 23%	2470
	11th to 20th	Night	14% 15% 5% 12% 7% 5% 5% 3 5% 5% 26%	2256
	21st to end	Night	17% 13% 4 10% 6% 4 4 3 5% 6% 27%	1884
March	1st to 10th	Night	15% 12% 3 9% 4 4 4 3 4 6% 35%	3681
	11th to 20th	Night	9% 10% 3 7% 5% 4 5% 4 5% 7% 42%	3480
	21st to end	Night	17% 10% 3 8% 5% 4 5% 3 4 6% 35%	3817
April	1st to 10th	Night	16% 12% 3 7% 4 4 4 4 5% 6% 35%	1962
	11th to 20th	Night	19% 9% 2 6% 4 3 5% 4 5% 6% 36%	1735
	21st to end	Night	17% 9% 2 6% 5% 4 4 3 5% 7% 38%	1710
May	1st to 10th	Night	16% 10% 2 6% 4 4 4 3 5% 8% 36%	2813
	11th to 20th	Night	17% 7% 3 6% 4 4 3 3 4 7% 43%	2812
	21st to end	Night	10% 6% 2 5% 5% 4 4 3 4 8% 48%	3017
June	1st to 10th	Night	12% 5% 2 6% 5% 3 3 3 5% 9% 47%	1520
	11th to 20th	Night	10% 6% 2 7% 4 3 4 4 7% 8% 45%	1444
	21st to end	Night	10% 6% 2 6% 4 3 4 3 5% 9% 48%	1520
July	1st to 10th	Night	9% 4 2 5% 4 4 5% 4 7% 10% 46%	2530
	11th to 20th	Night	11% 3 2 4 3 3 4 3 5% 7% 55%	2530
	21st to end	Night	7% 4 2 6% 4 4 5% 4 6% 9% 48%	2952
August	1st to 10th	Night	12% 5% 2 6% 3 4 4 4 6% 8% 48%	2825
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 5% 8% 49%	2785
	21st to end	Night	9% 6% 2 6% 4 4 4 3 5% 7% 49%	3206
September	1st to 10th	Night	10% 7% 2 5% 4 4 4 3 6% 7% 48%	1995
	11th to 20th	Night	11% 5% 1 4 4 3 4 3 4 6% 55%	2090
	21st to end	Night	14% 7% 3 6% 4 3 4 4 5% 6% 43%	2090
October	1st to 10th	Night	15% 7% 2 6% 5% 3 3 3 4 6% 46%	2128
	11th to 20th	Night	19% 11% 3 8% 4 4 4 3 5% 6% 34%	2280
	21st to end	Night	21% 11% 2 7% 6% 4 4 3 5% 6% 32%	2684
November	1st to 10th	Night	14% 9% 3 6% 5% 3 3 3 5% 6% 41%	2470
	11th to 20th	Night	16% 13% 3 8% 5% 5% 5% 4 6% 5% 30%	2470
	21st to end	Night	21% 14% 4 7% 4 4 3 4 4 6% 28%	2530
December	1st to 10th	Night	17% 17% 7% 12% 5% 5% 5% 3 4 5% 20%	2660
	11th to 20th	Night	14% 17% 6% 12% 6% 5% 4 4 5% 6% 22%	3470
	21st to end	Night	26% 24% 7% 10% 5% 4 3 2 3 4 12%	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	66% 6% 10% 13% 5%	2528
	11th to 20th	Day	74% 6% 11% 6% 3	2530
	21st to end	Day	77% 5% 8% 7% 3 1	3000
February	1st to 10th	Day	63% 6% 9% 14% 8%	1710
	11th to 20th	Day	63% 4 8% 14% 9% 1	1818
	21st to end	Day	61% 5% 11% 15% 6% 2	1570
March	1st to 10th	Day	57% 6% 11% 19% 6%	3171
	11th to 20th	Day	53% 5% 13% 19% 8% 1	3480
	21st to end	Day	57% 6% 11% 14% 10% 2	3815
April	1st to 10th	Day	54% 5% 11% 18% 11%	2233
	11th to 20th	Day	49% 6% 11% 20% 12% 2	2394
	21st to end	Day	49% 6% 13% 16% 14% 1	2470
May	1st to 10th	Day	47% 6% 11% 22% 11% 2	4120
	11th to 20th	Day	43% 9% 14% 24% 9% 1	4085
	21st to end	Day	36% 6% 11% 19% 24% 4	4549
June	1st to 10th	Day	38% 8% 12% 27% 14% 2	2660
	11th to 20th	Day	40% 7% 11% 23% 17% 2	2660
	21st to end	Day	39% 9% 13% 22% 16% 1	2660
July	1st to 10th	Day	42% 6% 14% 20% 16% 2	4371
	11th to 20th	Day	31% 6% 12% 34% 16% 2	4365
	21st to end	Day	37% 7% 14% 19% 22% 2	4456
August	1st to 10th	Day	39% 7% 12% 24% 16% 1	4091
	11th to 20th	Day	39% 7% 9% 32% 12% 1	4083
	21st to end	Day	39% 5% 14% 28% 13% 1	4447
September	1st to 10th	Day	41% 7% 13% 25% 13% 2	2165
	11th to 20th	Day	33% 7% 13% 32% 15% 1	2090
	21st to end	Day	44% 7% 12% 23% 13%	2090
October	1st to 10th	Day	33% 4 10% 32% 20% 1	3416
	11th to 20th	Day	42% 4 10% 26% 18%	3140
	21st to end	Day	47% 4 13% 24% 11% 1	3122
November	1st to 10th	Day	46% 6% 13% 22% 12% 1	1708
	11th to 20th	Day	54% 5% 13% 19% 8% 1	1710
	21st to end	Day	59% 5% 12% 17% 7% 1	1645
December	1st to 10th	Day	65% 5% 10% 15% 4	1520
	11th to 20th	Day	63% 6% 13% 14% 4	1709
	21st to end	Day	79% 4 9% 6% 3	2783
January	1st to 10th	Night	64% 5% 11% 14% 6% 1	4428
	11th to 20th	Night	71% 6% 10% 9% 4	4440
	21st to end	Night	71% 5% 9% 11% 3	4657
February	1st to 10th	Night	63% 6% 10% 13% 7% 1	2470
	11th to 20th	Night	59% 5% 10% 17% 9% 1	2257
	21st to end	Night	56% 6% 12% 16% 8% 1	1884
March	1st to 10th	Night	50% 5% 13% 24% 7% 1	3681
	11th to 20th	Night	39% 6% 16% 20% 19% 1	3480
	21st to end	Night	50% 5% 12% 21% 11% 1	3817
April	1st to 10th	Night	48% 5% 10% 21% 14% 2	1962
	11th to 20th	Night	47% 6% 10% 17% 18% 2	1735
	21st to end	Night	46% 6% 11% 19% 16% 2	1710
May	1st to 10th	Night	45% 7% 11% 21% 13% 3	2840
	11th to 20th	Night	41% 6% 10% 28% 13% 2	2813
	21st to end	Night	34% 7% 12% 21% 20% 6%	3025
June	1st to 10th	Night	35% 6% 11% 29% 18% 2	1520
	11th to 20th	Night	34% 8% 14% 25% 18% 2	1444
	21st to end	Night	34% 5% 13% 27% 20% 1	1520
July	1st to 10th	Night	32% 5% 12% 28% 16% 6%	2490
	11th to 20th	Night	29% 5% 12% 32% 21% 1	2482
	21st to end	Night	32% 7% 17% 19% 22% 2	2858
August	1st to 10th	Night	34% 6% 13% 28% 17% 1	2814
	11th to 20th	Night	34% 6% 9% 38% 12% 2	2812
	21st to end	Night	35% 5% 12% 32% 15% 1	3206
September	1st to 10th	Night	35% 7% 12% 27% 18% 2	1995
	11th to 20th	Night	30% 6% 10% 30% 22% 2	2090
	21st to end	Night	40% 6% 12% 27% 14% 1	2090
October	1st to 10th	Night	27% 3 10% 33% 26% 1	3544
	11th to 20th	Night	44% 4 10% 23% 18%	3779
	21st to end	Night	42% 4 11% 30% 13% 1	4422
November	1st to 10th	Night	43% 5% 11% 25% 14% 1	2470
	11th to 20th	Night	53% 6% 13% 19% 8% 1	2470
	21st to end	Night	57% 5% 12% 19% 7%	2530
December	1st to 10th	Night	65% 6% 10% 13% 5%	2660
	11th to 20th	Night	61% 7% 12% 13% 6% 1	3473
	21st to end	Night	76% 5% 10% 6% 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	25% 17% 36% 15% 7%	270
	11th to 20th	Day	24% 14% 44% 14% 3 1	270
	21st to end	Day	31% 15% 30% 18% 5% 1	297
February	1st to 10th	Day	26% 20% 38% 13% 2 1	270
	11th to 20th	Day	26% 19% 39% 14% 1	270
	21st to end	Day	27% 28% 33% 9% 2	225
March	1st to 10th	Day	25% 23% 34% 15% 3	295
	11th to 20th	Day	22% 14% 34% 23% 7%	460
	21st to end	Day	28% 14% 31% 21% 6% 1	506
April	1st to 10th	Day	20% 16% 34% 21% 9% 1	460
	11th to 20th	Day	26% 18% 31% 15% 5% 5%	452
	21st to end	Day	25% 13% 30% 20% 9% 2	460
May	1st to 10th	Day	25% 13% 27% 22% 11% 2	463
	11th to 20th	Day	20% 9% 28% 23% 13% 7%	487
	21st to end	Day	15% 6% 24% 28% 19% 8%	563
June	1st to 10th	Day	12% 9% 28% 30% 17% 5%	680
	11th to 20th	Day	14% 8% 30% 27% 17% 4	680
	21st to end	Day	13% 9% 28% 29% 16% 5%	680
July	1st to 10th	Day	9% 6% 22% 28% 23% 11%	671
	11th to 20th	Day	10% 6% 28% 29% 18% 9%	668
	21st to end	Day	9% 3 25% 30% 24% 9%	616
August	1st to 10th	Day	9% 4 21% 26% 24% 15%	486
	11th to 20th	Day	13% 4 18% 28% 23% 13%	479
	21st to end	Day	11% 6% 20% 27% 24% 13%	539
September	1st to 10th	Day	13% 7% 22% 25% 21% 11%	490
	11th to 20th	Day	9% 4 21% 22% 30% 14%	490
	21st to end	Day	19% 9% 23% 22% 21% 7%	490
October	1st to 10th	Day	18% 8% 28% 23% 16% 7%	490
	11th to 20th	Day	21% 16% 28% 26% 8% 2	490
	21st to end	Day	29% 16% 35% 15% 5%	359
November	1st to 10th	Day	17% 21% 35% 16% 10% 1	282
	11th to 20th	Day	21% 22% 33% 18% 5% 1	270
	21st to end	Day	29% 19% 35% 13% 4	239
December	1st to 10th	Day	27% 21% 29% 15% 8%	180
	11th to 20th	Day	25% 21% 41% 10% 2 1	182
	21st to end	Day	28% 25% 33% 14% 1	297
January	1st to 10th	Night	23% 15% 36% 21% 5% 1	950
	11th to 20th	Night	25% 15% 34% 21% 5% 1	950
	21st to end	Night	22% 11% 34% 27% 6%	909
February	1st to 10th	Night	25% 13% 37% 22% 3	760
	11th to 20th	Night	23% 15% 34% 25% 3	743
	21st to end	Night	24% 18% 36% 20% 2	628
March	1st to 10th	Night	22% 13% 35% 24% 6% 1	760
	11th to 20th	Night	17% 16% 36% 26% 5% 1	760
	21st to end	Night	23% 12% 31% 26% 7% 1	836
April	1st to 10th	Night	22% 14% 34% 25% 4 1	632
	11th to 20th	Night	23% 10% 34% 24% 7% 2	563
	21st to end	Night	21% 8% 34% 29% 8%	570
May	1st to 10th	Night	20% 7% 31% 34% 8% 1	570
	11th to 20th	Night	20% 5% 30% 31% 12% 1	561
	21st to end	Night	12% 4 24% 39% 19% 2	617
June	1st to 10th	Night	12% 4 24% 45% 14% 1	570
	11th to 20th	Night	12% 4 25% 42% 16%	494
	21st to end	Night	12% 4 21% 45% 16% 2	570
July	1st to 10th	Night	9% 2 17% 41% 27% 4	555
	11th to 20th	Night	11% 1 21% 41% 23% 3	552
	21st to end	Night	5% 2 20% 47% 23% 2	624
August	1st to 10th	Night	9% 2 15% 44% 27% 3	567
	11th to 20th	Night	10% 1 21% 35% 28% 4	564
	21st to end	Night	11% 3 16% 35% 31% 3	627
September	1st to 10th	Night	12% 4 21% 34% 25% 4	665
	11th to 20th	Night	12% 3 18% 35% 28% 4	760
	21st to end	Night	17% 7% 20% 32% 19% 5%	760
October	1st to 10th	Night	18% 6% 28% 29% 17% 2	760
	11th to 20th	Night	24% 13% 27% 27% 8% 1	760
	21st to end	Night	26% 11% 33% 24% 5%	836
November	1st to 10th	Night	20% 11% 29% 28% 11% 1	760
	11th to 20th	Night	23% 15% 34% 21% 7% 1	760
	21st to end	Night	27% 12% 33% 23% 5%	760
December	1st to 10th	Night	24% 18% 33% 20% 6%	760
	11th to 20th	Night	23% 15% 38% 21% 3 1	912
	21st to end	Night	31% 13% 36% 18% 2	1045

Page generated at 2024-11-03 02:11:14. Version ac07

Copyright © 2024 Attilla Danko.