Clear Sky Clock Homepage

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 forecast data comes froma numerical weather model run by those very cool guys at the Canadian Meteorological Centre.

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 ishere, 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 showhis bosses at CMC that his astronomy forecasts are actually being used. Feel free to copy me.

Are there Charts for other locations?Yes, hundreds. the coverage area is Canada, USA and parts of Mexico. May I get my own Chart?

If you observe at a site more than 24km or 15 miles from and existing chart site, feel free to request a chartfor it. you can find the closest chart site to a latitude/longitudehere.

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 heavens-above.com. 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 maximallyaccurate forecasts.

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

Clear Sky Clock Homepage


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