Virgil ObservatoryClear Sky ChartHistory
This sumarizes the distribution of each different forecast outcome for the Virgil Observatory clear sky chart from 2005-11-06 to 2024-01-13.
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.
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
| Planetary | Data Pts | Deep Sky Max 60% | Data Pts | Both Planetary and Deep Sky Max 60% | Data Pts | Either Planetary or Deep Sky | Data Pts | CCD Imaging | Data Pts |
---|
Night | | 22919 | | 74764 | | 22875 | | 22875 | | 55399 |
By Month
Month | Days of Month | | Planetary | Data Pts | Deep Sky Max 60% | Data Pts | Both Planetary and Deep Sky Max 60% | Data Pts | Either Planetary or Deep Sky | Data Pts | CCD Imaging | Data Pts |
---|
January | 1st to 10th | Night | | 760 | | 2649 | | 757 | | 757 | | 2191 |
January | 11th to 20th | Night | | 732 | | 2556 | | 732 | | 732 | | 2150 |
January | 21st to end | Night | | 792 | | 2574 | | 792 | | 792 | | 2122 |
February | 1st to 10th | Night | | 720 | | 2340 | | 720 | | 720 | | 1937 |
February | 11th to 20th | Night | | 703 | | 2239 | | 700 | | 700 | | 1841 |
February | 21st to end | Night | | 592 | | 1776 | | 592 | | 592 | | 1403 |
March | 1st to 10th | Night | | 720 | | 2115 | | 720 | | 720 | | 1641 |
March | 11th to 20th | Night | | 720 | | 1980 | | 720 | | 720 | | 1528 |
March | 21st to end | Night | | 792 | | 2087 | | 792 | | 792 | | 1593 |
April | 1st to 10th | Night | | 720 | | 1800 | | 720 | | 720 | | 1382 |
April | 11th to 20th | Night | | 711 | | 1775 | | 711 | | 711 | | 1322 |
April | 21st to end | Night | | 720 | | 1800 | | 720 | | 720 | | 1322 |
May | 1st to 10th | Night | | 412 | | 1492 | | 412 | | 412 | | 1050 |
May | 11th to 20th | Night | | 354 | | 1416 | | 354 | | 354 | | 896 |
May | 21st to end | Night | | 388 | | 1551 | | 388 | | 388 | | 969 |
June | 1st to 10th | Night | | 360 | | 1440 | | 360 | | 360 | | 899 |
June | 11th to 20th | Night | | 360 | | 1440 | | 360 | | 360 | | 889 |
June | 21st to end | Night | | 360 | | 1440 | | 360 | | 360 | | 876 |
July | 1st to 10th | Night | | 350 | | 1400 | | 350 | | 350 | | 827 |
July | 11th to 20th | Night | | 348 | | 1392 | | 348 | | 348 | | 804 |
July | 21st to end | Night | | 394 | | 1486 | | 372 | | 372 | | 904 |
August | 1st to 10th | Night | | 537 | | 1600 | | 534 | | 534 | | 1017 |
August | 11th to 20th | Night | | 581 | | 1645 | | 581 | | 581 | | 1130 |
August | 21st to end | Night | | 792 | | 1980 | | 792 | | 792 | | 1339 |
September | 1st to 10th | Night | | 720 | | 1800 | | 720 | | 720 | | 1245 |
September | 11th to 20th | Night | | 720 | | 1800 | | 720 | | 720 | | 1198 |
September | 21st to end | Night | | 720 | | 2038 | | 720 | | 720 | | 1415 |
October | 1st to 10th | Night | | 720 | | 2160 | | 720 | | 720 | | 1558 |
October | 11th to 20th | Night | | 720 | | 2160 | | 720 | | 720 | | 1560 |
October | 21st to end | Night | | 792 | | 2439 | | 792 | | 792 | | 1923 |
November | 1st to 10th | Night | | 740 | | 2407 | | 740 | | 740 | | 1675 |
November | 11th to 20th | Night | | 760 | | 2565 | | 760 | | 760 | | 1898 |
November | 21st to end | Night | | 760 | | 2660 | | 760 | | 760 | | 2039 |
December | 1st to 10th | Night | | 760 | | 2660 | | 760 | | 760 | | 2192 |
December | 11th to 20th | Night | | 759 | | 3249 | | 759 | | 759 | | 2639 |
December | 21st to end | Night | | 830 | | 4853 | | 817 | | 817 | | 4025 |
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 |
| 74723 |
Night |
| 75006 |
|
Transparency | Day |
| 74429 |
Night |
| 74834 |
|
Seeing | Day |
| 13572 |
Night |
| 22927 |
|
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 | 12% | 16% | 10% | 13% | 9% | 4 | 6% | 4 | 5% | 5% | 15% |
| 1517 |
11th to 20th | Day |
| 1456 |
21st to end | Day | 11% | 16% | 9% | 14% | 11% | 6% | 5% | 4 | 5% | 5% | 15% |
| 1782 |
|
February | 1st to 10th | Day | 17% | 14% | 7% | 15% | 10% | 4 | 6% | 3 | 5% | 5% | 14% |
| 1620 |
11th to 20th | Day | 13% | 15% | 10% | 14% | 10% | 3 | 6% | 4 | 3 | 5% | 16% |
| 1609 |
21st to end | Day |
| 1480 |
|
March | 1st to 10th | Day |
| 1840 |
11th to 20th | Day |
| 1980 |
21st to end | Day |
| 2268 |
|
April | 1st to 10th | Day |
| 2160 |
11th to 20th | Day |
| 2134 |
21st to end | Day |
| 2173 |
|
May | 1st to 10th | Day |
| 2467 |
11th to 20th | Day |
| 2478 |
21st to end | Day |
| 2725 |
|
June | 1st to 10th | Day |
| 2520 |
11th to 20th | Day |
| 2520 |
21st to end | Day |
| 2520 |
|
July | 1st to 10th | Day |
| 2520 |
11th to 20th | Day |
| 2520 |
21st to end | Day |
| 2741 |
|
August | 1st to 10th | Day |
| 2327 |
11th to 20th | Day |
| 2236 |
21st to end | Day |
| 2376 |
|
September | 1st to 10th | Day |
| 2160 |
11th to 20th | Day |
| 2160 |
21st to end | Day |
| 1919 |
|
October | 1st to 10th | Day |
| 1800 |
11th to 20th | Day |
| 1800 |
21st to end | Day |
| 1915 |
|
November | 1st to 10th | Day |
| 1671 |
11th to 20th | Day |
| 1611 |
21st to end | Day |
| 1520 |
|
December | 1st to 10th | Day |
| 1520 |
11th to 20th | Day |
| 1906 |
21st to end | Day |
| 2772 |
|
January | 1st to 10th | Night |
| 2649 |
11th to 20th | Night |
| 2556 |
21st to end | Night | 12% | 14% | 7% | 12% | 12% | 7% | 6% | 5% | 5% | 5% | 15% |
| 2574 |
|
February | 1st to 10th | Night |
| 2340 |
11th to 20th | Night | 14% | 13% | 8% | 14% | 10% | 3 | 6% | 5% | 4 | 5% | 18% |
| 2237 |
21st to end | Night |
| 1776 |
|
March | 1st to 10th | Night |
| 2105 |
11th to 20th | Night |
| 1979 |
21st to end | Night |
| 2087 |
|
April | 1st to 10th | Night |
| 1800 |
11th to 20th | Night |
| 1775 |
21st to end | Night |
| 1800 |
|
May | 1st to 10th | Night |
| 1492 |
11th to 20th | Night |
| 1415 |
21st to end | Night |
| 1550 |
|
June | 1st to 10th | Night |
| 1440 |
11th to 20th | Night |
| 1440 |
21st to end | Night |
| 1440 |
|
July | 1st to 10th | Night |
| 1440 |
11th to 20th | Night |
| 1440 |
21st to end | Night |
| 1574 |
|
August | 1st to 10th | Night |
| 1611 |
11th to 20th | Night |
| 1645 |
21st to end | Night |
| 1980 |
|
September | 1st to 10th | Night |
| 1800 |
11th to 20th | Night |
| 1800 |
21st to end | Night |
| 2038 |
|
October | 1st to 10th | Night |
| 2160 |
11th to 20th | Night |
| 2160 |
21st to end | Night |
| 2439 |
|
November | 1st to 10th | Night |
| 2407 |
11th to 20th | Night |
| 2565 |
21st to end | Night |
| 2660 |
|
December | 1st to 10th | Night |
| 2660 |
11th to 20th | Night |
| 3288 |
21st to end | Night |
| 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 |
| 1518 |
11th to 20th | Day |
| 1456 |
21st to end | Day |
| 1782 |
|
February | 1st to 10th | Day |
| 1620 |
11th to 20th | Day |
| 1618 |
21st to end | Day |
| 1480 |
|
March | 1st to 10th | Day |
| 1843 |
11th to 20th | Day |
| 1980 |
21st to end | Day |
| 2268 |
|
April | 1st to 10th | Day |
| 2160 |
11th to 20th | Day |
| 2134 |
21st to end | Day |
| 2173 |
|
May | 1st to 10th | Day |
| 2467 |
11th to 20th | Day |
| 2482 |
21st to end | Day |
| 2725 |
|
June | 1st to 10th | Day |
| 2520 |
11th to 20th | Day |
| 2520 |
21st to end | Day |
| 2520 |
|
July | 1st to 10th | Day |
| 2450 |
11th to 20th | Day |
| 2445 |
21st to end | Day |
| 2588 |
|
August | 1st to 10th | Day |
| 2314 |
11th to 20th | Day |
| 2236 |
21st to end | Day |
| 2376 |
|
September | 1st to 10th | Day |
| 2160 |
11th to 20th | Day |
| 2160 |
21st to end | Day |
| 1919 |
|
October | 1st to 10th | Day |
| 1800 |
11th to 20th | Day |
| 1800 |
21st to end | Day |
| 1915 |
|
November | 1st to 10th | Day |
| 1671 |
11th to 20th | Day |
| 1611 |
21st to end | Day |
| 1520 |
|
December | 1st to 10th | Day |
| 1520 |
11th to 20th | Day |
| 1906 |
21st to end | Day |
| 2772 |
|
January | 1st to 10th | Night |
| 2649 |
11th to 20th | Night |
| 2556 |
21st to end | Night |
| 2574 |
|
February | 1st to 10th | Night |
| 2340 |
11th to 20th | Night |
| 2239 |
21st to end | Night |
| 1776 |
|
March | 1st to 10th | Night |
| 2115 |
11th to 20th | Night |
| 1980 |
21st to end | Night |
| 2087 |
|
April | 1st to 10th | Night |
| 1800 |
11th to 20th | Night |
| 1775 |
21st to end | Night |
| 1800 |
|
May | 1st to 10th | Night |
| 1492 |
11th to 20th | Night |
| 1416 |
21st to end | Night |
| 1551 |
|
June | 1st to 10th | Night |
| 1440 |
11th to 20th | Night |
| 1440 |
21st to end | Night |
| 1440 |
|
July | 1st to 10th | Night |
| 1400 |
11th to 20th | Night |
| 1392 |
21st to end | Night |
| 1486 |
|
August | 1st to 10th | Night |
| 1600 |
11th to 20th | Night |
| 1645 |
21st to end | Night |
| 1980 |
|
September | 1st to 10th | Night |
| 1800 |
11th to 20th | Night |
| 1800 |
21st to end | Night |
| 2038 |
|
October | 1st to 10th | Night |
| 2160 |
11th to 20th | Night |
| 2160 |
21st to end | Night |
| 2439 |
|
November | 1st to 10th | Night |
| 2407 |
11th to 20th | Night |
| 2565 |
21st to end | Night |
| 2660 |
|
December | 1st to 10th | Night |
| 2660 |
11th to 20th | Night |
| 3288 |
21st to end | Night |
| 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 |
| 180 |
11th to 20th | Day |
| 164 |
21st to end | Day |
| 264 |
|
February | 1st to 10th | Day |
| 240 |
11th to 20th | Day |
| 276 |
21st to end | Day |
| 346 |
|
March | 1st to 10th | Day |
| 420 |
11th to 20th | Day |
| 420 |
21st to end | Day |
| 462 |
|
April | 1st to 10th | Day |
| 420 |
11th to 20th | Day |
| 412 |
21st to end | Day |
| 420 |
|
May | 1st to 10th | Day |
| 423 |
11th to 20th | Day |
| 447 |
21st to end | Day |
| 485 |
|
June | 1st to 10th | Day |
| 450 |
11th to 20th | Day |
| 450 |
21st to end | Day |
| 450 |
|
July | 1st to 10th | Day |
| 445 |
11th to 20th | Day |
| 444 |
21st to end | Day |
| 488 |
|
August | 1st to 10th | Day |
| 446 |
11th to 20th | Day |
| 439 |
21st to end | Day |
| 495 |
|
September | 1st to 10th | Day |
| 450 |
11th to 20th | Day |
| 450 |
21st to end | Day |
| 450 |
|
October | 1st to 10th | Day |
| 450 |
11th to 20th | Day |
| 450 |
21st to end | Day |
| 462 |
|
November | 1st to 10th | Day |
| 365 |
11th to 20th | Day |
| 271 |
21st to end | Day |
| 180 |
|
December | 1st to 10th | Day |
| 180 |
11th to 20th | Day |
| 180 |
21st to end | Day |
| 198 |
|
January | 1st to 10th | Night |
| 760 |
11th to 20th | Night |
| 732 |
21st to end | Night |
| 792 |
|
February | 1st to 10th | Night |
| 720 |
11th to 20th | Night |
| 703 |
21st to end | Night |
| 592 |
|
March | 1st to 10th | Night |
| 720 |
11th to 20th | Night |
| 720 |
21st to end | Night |
| 792 |
|
April | 1st to 10th | Night |
| 720 |
11th to 20th | Night |
| 711 |
21st to end | Night |
| 720 |
|
May | 1st to 10th | Night |
| 412 |
11th to 20th | Night |
| 354 |
21st to end | Night |
| 389 |
|
June | 1st to 10th | Night |
| 360 |
11th to 20th | Night |
| 360 |
21st to end | Night |
| 360 |
|
July | 1st to 10th | Night |
| 350 |
11th to 20th | Night |
| 348 |
21st to end | Night |
| 394 |
|
August | 1st to 10th | Night |
| 537 |
11th to 20th | Night |
| 581 |
21st to end | Night |
| 792 |
|
September | 1st to 10th | Night |
| 720 |
11th to 20th | Night |
| 720 |
21st to end | Night |
| 720 |
|
October | 1st to 10th | Night |
| 720 |
11th to 20th | Night |
| 720 |
21st to end | Night |
| 792 |
|
November | 1st to 10th | Night |
| 740 |
11th to 20th | Night |
| 760 |
21st to end | Night |
| 760 |
|
December | 1st to 10th | Night |
| 760 |
11th to 20th | Night |
| 760 |
21st to end | Night |
| 836 |
Page generated at 2024-01-10 10:16:13. Version ac07Copyright 2024 Attilla Danko
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