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. Heres the link to download Moonrise
and Moonset calculator
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:
• Azimuth. As read from a compass, the number of degrees from due north
where the moon will rise
• Altitude. The highest point in the sky the moon will reach, due south
• Moon Rise. The time of moon rise.
As you click on various dates the plot gets cluttered;
the buttons 'Clear' and 'Draw' do what they say, to
redraw the screen with the curent days plot.
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. "
Download
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
timholland@f2s.com
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