Clear Sky Chart

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The Clear Sky Chart Home page

What is it?

It's the astronomers forecast. It shows at a glance when, in the next 48 hours, we might expect clear and dark skies for one specific observing site. There are many, but the example above is for ().

It's is specifically intended for amateur astronomers. The data comes a forecast model developed by Allan Rahill of the Canadian Meteorological Center.

Read from left to right. Locate a column of blue blocks. That's when the sky will likely to be clear and dark. A more detailed explanation is here, but the short version is: the clear sky chart predicts hourly cloud cover, atmospheric transparency and seeing. (Good "seeing" occurs when the air is steady enough to allow you to see fine detail on planets through a telescope.) That means you can plan whether to observe galaxies or planets or stay home and process image data.

If you find this image, or the underlying forecast maps, useful please email Allan Rahill. He needs to show his bosses at CMC that his astronomy forecasts are actually being used. Feel free to copy me.

Are there Charts for other locations?

Yes, thousands. The coverage area is Canada, USA and parts of Mexico.
By Keyword
Ex: "lick observatory" finds the Mount Hamilton chart.

By Position
Display distance in:Kms Miles
Coverage Map

Clickable map
Charts on Google Maps

Clickable and zoomable map
By popular keyword

2017 Solar Eclipse
Astronomy Clubs
Astronomy Villages
Dark-Sky Preserves
Parks: Provincial State National
RASC Centres
Star Parties
Wildlife center/area
Want a more powerful search, try:

Newest charts
All 5139 charts: By Region (912Kb)
Alberta (105)
British Columbia (102)
Manitoba (28)
New Brunswick (34)
Newfoundland (14)
Northwest Territories (5)
Nova Scotia (31)
Nunavut (4)
Ontario (306)
Prince Edward Island (2)
Quebec (195)
Saskatchewan (33)
Yukon (10)

Baja California (8)
Chihuahua (2)
Sonora (9)
Cat Island (1)
Grand Bahama (1)
New Providence (1)
Alabama (54)
Alaska (17)
Arizona (141)
Arkansas (43)
California (437)
Colorado (137)
Connecticut (38)
DC (4)
Delaware (11)
Florida (188)
Georgia (97)
Idaho (48)
Illinois (105)
Indiana (67)
Iowa (50)
Kansas (62)
Kentucky (51)
Louisiana (31)
Maine (48)
Maryland (51)
Massachusetts (69)
Michigan (145)
Minnesota (80)
Mississippi (46)
Missouri (86)
Montana (30)
Nebraska (51)
Nevada (47)
New Hampshire (45)
New Jersey (50)
New Mexico (116)
New York (153)
North Carolina (120)
North Dakota (15)
Ohio (125)
Oklahoma (59)
Oregon (96)
Pennsylvania (158)
Rhode Island (14)
South Carolina (66)
South Dakota (26)
Tennessee (84)
Texas (375)
Utah (62)
Vermont (34)
Virginia (119)
Washington (119)
West Virginia (35)
Wisconsin (102)
Wyoming (41)

May I get my own Chart?

If you observe at a site more than 24km or 15 miles from an existing chart site, feel free to request a chart for it. You can find the closest chart site to a latitude/longitude here.

I can generate charts for almost anywhere in Canada and US. See the coverage map.

To ask for a CSC, email me with:

  • Latitude and longitude accurate to at least 0.01 degree or 1 arcminute. Also elevation, if you know it. Within 300m or 1000ft is good.
    For towns, use For other sites, use Google Maps: zoom in on your site, then click on "link to this page" and email me the resulting url.
  • Timezone and whether you use daylight savings time during summer.
  • Province or State, so I can list it correctly in the directories.
  • Name, or what you'd like to see in the title. Like "Starhill Observatory" or "Saskatoon". Please choose the name of a place. But star party names are good too.
  • Whether the site is public or private, or has any affiliations with astronomy clubs or organizations.
  • URL of a web page related to the site, if you have one. Club or observatory web pages, or web pages about public places at the location of the chart are welcome.
  • Check the privacy policy and let me know if you'd like to keep confidential your site's precise location.

I reserve the right to offer you a different chart that is still close enough to give maximally accurate forecasts.

There is no cost. But you're welcome to sponsor.

Danko's Homepage Ottawa Astronomy Weather

Copyright 2015 A. Danko. Page updated 2015-10-09 01:00:36UT on server2.