Larry McNish's
Dark Sky Calculator Version 1.31
Title:   For:     
Longitude: Deg: Min: WestEast  UTC Offset (Hrs):
Latitude:   Deg: Min: NorthSouth
Include: Sun Moon symbols in bar graph. Remember new values.
Include: Jrts (Jupiter rise, transit, set) and grs (Great Red Spot transit) times.
Include: Minima of Algol times.
Enter your Standard Time offset in "UTC Offset (Hrs)" above.

All times are displayed in Standard Time. If Daylight Savings time is in effect at the designated location, add one hour to all event times.
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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.
  • If the Jrts option is checked, Jupiter's Rise, Transit and Set times are shown as: Jrts xx:xx xx:xx xx:xx and the Great Red Spot transit times are shown as grs xx:xx. If one of the GRS transit times occurs between the times of Jupiter rise and set, and if that time is before sunrise or after sunset, then the Great Red Spot should be visible.
  • If the Minima of Algol times option is checked, and a Minima of Algol occurs on that date, then the local standard time of the minima will be shown as xx:xx.
  • 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.
    Bar graph legend

  • 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 Page Setup margins to 0.25 inch.
  • If the "grayed-out" dates (those before the first of the month and after the last day of the month) 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.
Notes:
  • Copyright © 2003-2013 Larry McNish All Rights Reserved http://members.shaw.ca/rlmcnish/
  • Please link to this page rather than copying it.
  • Disclaimer: I assume no liability for the use of this web page.
  • This page should work on Firefox, Internet Explorer 5 and later and Netscape 7 and later.
  • All the calculations are done on your PC using restricted JavaScript (not JAVA) - the slower your computer, the longer the calendar takes to appear, or to compute a different month.
  • Except for high latitudes, Sun rise/set times are accurate to within a minute or two.
  • Moon rise/set times are accurate to within about 5 minutes.
  • All times are displayed in Standard Time.
  • If Daylight Savings time is in effect at the designated location, ADD one hour to all event times.
  • If Daylight Savings time would be in effect on your PC "at home" for a calendar date then a red "DST" appears on the line under the date, but this is NOT added to the event times since you may have set the parameters for a different location which may or may not observe DST on the same schedule as your PC.
Other astronomy-related web pages you may be interested in that are on this site: