Plan your dark-sky gazing around the deep nights shown on this page: The calendar at right displays the hours of "deep night" --  the time between astronomical twilights without the Moon in the sky -- for the night beginning on the date indicated. Please note: asterisk * indicates Friday evenings, and [  ] = New moon, ) = First Quarter, (--) = Full Moon and ( = Last Quarter. These circumstances are calculated for Tuckahoe State Park, MD, located at 38° 59' N and 75° 56' W.

Graphic shading reflects the number of hours of deepnight. At the start of this year, dark nights runs are split between the first and last weeks of the months. As the Moon's phases gradually advance, deepnight runs shift ahead towards the end of the month by year's end. For example, the March column shows that Friday and Saturday nights, the 28th and 29th, will have 8.5 and 8.4 hours of deepnight, respectively, with the next New Moon on the evening of April Fool's Day. This year, Messier Marathon-ers will have to work around the Full Moon (on the night of the 17th) and the bright gibbous phases during the following week. As a result, the weekend of Friday - Saturday, the 28th and 29th is the primary weekend for this annual astronomical endurance event. Good Luck and Clear Skies!

At Tuckahoe: Latest sunrise, 5 and 6 January; Latest beginning of twilight, 8 and 9 January; Shortest twilight, 1.5 h on 4 - 6 March; Earliest sunrise 14 June; Earliest beginning of twilight 17 June; Shortest nights: 15 - 27 June at 5.1 h; Longest twilight, 2.0 h on 20 to 22 June; Latest end of twilight, 25 June; Latest sunset, 27 and 28 June; Shortest twilight (again), 1.5 h on  7 - 9 October; Earliest end of twilight, 4 December; Earliest sunset, 7 December; Longest nights, 15 - 28 December at 11.4 h; Longest deep nights, 21- 24 December at 11.4 h. Eastern Standard Time is 5 hours behind Universal Time; Daylight Time, between 6 April and 26 October 2003, is 4 hours behind.

This deep night calendar is based on the “dark of the moon table” published more or less annually by Guy Ottewell in his Astronomical Calendar. Most planetarium and ephemeris programs will do the necessary calculations for a specified night (twilight times, and moon rise and set), but none that I’m aware of summarize a whole year in an easy to use format for a given location. It was relatively straightforward to modify some old Quattro spreadsheets (based on Jean Meeus’s Astronomical Algorithms) for calculating observing circumstances for Messier objects in order to tabulate the hours of each night without the moon in the sky. These calculated values are now reformatted with VBA in Excel and rendered as a graphic for inclusion in a Moondark web page highlighting astronomical events of the upcoming year. Now, if we could just come up with a formula for hours of clear sky... In the meantime, try Attilla Danko's Clear Sky Clock linked directly from the Delmarva Star Gazers home page.

Moondark is written by Doug Miller and published on the web and in the Delmarva Star Gazers'Star Gazer News. This document was last revised on 25 January '02. All text and images copyright © 2003 Douglas C. Miller, All Rights Reserved. This material may not be reproduced in any form without prior permission.