When will the night sky be dark this Month? This web page will take your longitude, latitude, time zone offset from Universal (Greenwich) time, and display a complete calendar for a month showing graphically as well as numerically what effect the sun and the moon will have on your dark sky observing time. Just enter your parameters and click Submit.

Reading the Calendar:

• The images of the moon are approximations from static images.
• The day of the year is shown between the image of the moon and the calendar date.
• The SunRise and SunSet times are shown as Sun hh:mm-hh:mm followed by the hours of daylight [hh:mm].
  
• The MoonRise and MoonSet times are shown as Moon R:hh:mm and S:hh:mm.
  
• If the Moon sets in the morning hours and rises in the evening hours it will be shown as Moon S:hh:mm R:hh:mm.
  
• If the Moon does not rise or set on a particular day that time is shown as xx:xx.
  
• The Moon Phase in degrees and % illumination at 12h UTC is shown as M12hUTC=ddd° =xxx%.
  
• The Julian Date at 0h UTC is shown as JD 0h UT=xxx.
  
• The Local Mean Sidereal Time at 0h local time is shown as LMST 0h loc=hh:mm:ss.
  
• The Equinoxes and Solstices are shown on appropriate dates in local time.
  
  
• The two lines of characters across the bottom of each day represent the hours from midnight to noon (top line) and noon to midnight (bottom line). Each symbol represents one hour of time on that day.
  
  
  
• Boxes shown as:■■■■■ represent times when the sky is dark.
  
• Boxes shown as:□□□□□ represent times when the sun is up.
  
• Boxes shown as:○○○○○ represent times when the sun is down but the moon is up and of significant brightness to hinder astrophotography (>6% illuminated).
  
• To exclude the Sun symbols from the graphs "uncheck" the Include Sun checkbox.
  
• To exclude the Moon symbols from the graphs "uncheck" the Include Moon checkbox.
  
• To save your settings for the next time you use DarkSky, check the "Remember New Values" checkbox before clicking Submit. This will store the settings on your PC in a small "cookie". Revisiting this site or clicking the The Reset button will then reset any values to the "saved" values. To eliminate the set of saved values click the small button to the right of the Reset button to delete the cookie.
  
  
• To fit the printed calendar on a single page properly, set your Internet Explorer Page Setup margins to 0.25 inch.
  
• If the grayed out dates do not print as gray: Set Internet Explorer as follows: Click on Tools, Internet Options..., Advanced and scroll down to Printing and check Print Background colors and images.
  
  

• Some of the JavaScript used to calculate these values was written by and is Copyright © Peter Hayes 2001-2007. His website can be found at http://www.aphayes.pwp.blueyonder.co.uk/
  
  
• Accurate tables of sunrise/sunset, moonrise/moonset, civil twilight, nautical twilight and astronomical twilight can be generated at the United States Naval Observatory web site at http://aa.usno.navy.mil/.
  
  
• Current weather information for Canadian centres can be obtained from the Environment Canada web site at http://weatheroffice.ec.gc.ca/canada_e.html
  
  
• Current Canadian Clear Sky information can be obtained from the Clear Sky Clock page at http://cleardarksky.com/csk/index.html#clock_list