webspotting 33 - dark sky planner

As published (with minor edits) in the Mar 2014 issue of SCOPE, the newsletter of the RASC Toronto Centre. Republished here with permission.

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Are you an imager after faint deep sky objects? To collect as much data as possible, you need long dark nights. Are you planning a public star party? It is always rewarding to show the Moon through the telescope, hearing the oohs and aahs and OMGs. Near the first quarter Moon phase is the best time, with the stark terminator emphasising the devastated surface of our neighbour. And it's not too late for the kids. A visual astronomer working on the Messier certificate or going after elusive Herschel 400 targets? Or steeling yourself to tackle the Messier Marathon? You need to completely avoid that... Moon.

I recently stumbled across the dark sky calculator at the DVAA. A handy site which may prove useful for all kinds of astronomical purposes. In fact, I'm a monthly visitor to Delaware Valley Amateur Astronomers web site. This club site serves the enthusiastic hobbyists near Philadelphia.

I return regularly for Dave Mitsky's Celestial Calendar. This fairly detailed schedule with notes is one of my trusted sources for The Sky This Month presentations.

When I visited the site at the turn of the month, Mr Mitsky had not yet posted his report for the next period. So I wandered the halls. It seems like the DVAA does a lot of the same things we do. Checked out their benefits of membership, their public star parties, their observatory. I noted the Astronomical Data section. Ooh: binary stars! Some Messier Marathon lists. Neat. Then I spotted the Darkest Hours Planner. Interesting.

You must provide your observing site latitude, longitude, and time zone offset. Indicate the first month and year to display. You can make the calculator show up to 12 months of data. A listing appears. Today's date is highlighted. Within each month we see each day noted in a row. The day row includes the Moon rise and set times, the Sun rise and set times, along with the Astronomical Twilight times. Once a week or so, the Moon phase appears. The final phase is properly noted as 3Q; not LQ. Equinoxes and daylight saving time changes are also noted. But the most interesting bit is the Darkest Hours column.

I show [a portion of] the March 2014 listing. March 1st is the longest night, with over 9½ hours of dark. Immediately the Moon begins to interfere. By first quarter, the sky is completely dark only for 2.8 hours. The "none" indicator shows around the full Moon. Clean the eyepieces or camera on those nights. Then on the 18th, darkness returns, briefly, less than 1 hour. The next maximums occur on and after the 27th, with 3 nights of 8 hours of blackie blackness.

Surf into the dark calculator. Add it to your favourite bookmarks.

http://dvaa.org/php/DarkCal.php

Another tool for your planning toolkit.