Moonrise Calculator

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Programme and article written by Tim Holland.

2006 was the year of the lunar standstill, the peak of the wandering path of the Moon along the horizon. I'm interested in the way the cycle is seen from the Earth, and how it was used to align stones with hills to form a sacred mandala.

My intention was to write a little programme , giving an earth centred view point of the maximum and minimum rising (and setting) points of the moon to show the rising and setting of the moon at any time. To do this, I've written a programme using the Swiss Ephemeris astrological algoithms and thrown this together over the Yule break. Feedback welcome, with the usual disclaimers of user beware! I've tested it on several Windows platforms, 98, 2000, XP and it seems ok.

Assuming you've managed to download it ok, theres only one screen and this is it. The top pane shows a stylised view of the horizon, looking South. The tall vertical line is due South, left and right are the East and West compass points. North is behind. The calendar starts off at the current date, read from your computer, with my home location, Stroud, England Latitude 51 degrees 45 minutes (North) Longitude 2 degrees 12 minutes West.

To change your location, click in the box and type the numbers. There's no error checking so don't be surprised if odd things happen at the north pole!

Changing the date is easy, by clicking on the calendar. Each time you change the day or month or year, the plot of the moons rise and setting is shown, with the moon phase too.

The other important bits of information shown are:

Here's one of the interesting points in time; the 11th June 2006 major standstill, coincident with a full moon, and should be worth staying up for. Here, the moon's path on the horizon gets about as far South as it can get, rising at 139 degrees 53 minutes and only reaching 10 degrees high in the sky.

14 days later, through the solstice on the 21st, she'll be rising higher and higher each day, rising further north.
Note, all times are BST, and don't add anything extra at this time.

For comparison, in 1997, halfway through the 19 year cycle, the moon wanders much less.

Accuracy
Always a tricky one. The Swiss Ephemeris algorithm is as good as you can get, and it takes into account barometic pressure and temperature effects on the rising and setting times, which will cause changes due to refraction. I've used sea level altitude and 'standard' apparent conditions. The horizon is considered to be at sea level. From the US Naval Observatory the following note is given, and their online calculator gives the same result for moonrise. I'd love to see how it compares in real life!

"Moonrise and Moonset conventionally refer to the times when the upper edge of the disk of the Moon is on the horizon, considered unobstructed relative to the location of interest. Atmospheric conditions are assumed to be average, and the location is in a level region on the Earth's surface. "
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As usual, theres no warranty against it messing up your computer, but I've done all the virus checks and tried it on different Windows platforms, with no problems. It can be uninstalled using the usual 'Control Panel / Add remove" tool, where it appears as "Moon" Right click on the Moon below and "Save Target As" the file Moon.zip to a local temporary folder. It's about 3.8MB. Unzip and run the Setup.exe file, and it will create a folder in your c:\programe\ files directory called "Moon". Just run the program moon.exe, and you should see the above! Alternatively, from the "Start" "Programs" menu at the bottom of the screen, find "Moon"

Feedback appreciated! And for more information on my calculator go to
http:/standstill.timholland.co.uk
[email protected]

 

 


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