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 Post subject: Calculating the Moonrise
PostPosted: Sat May 21, 2011 4:45 pm 
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Joined: Sat Feb 26, 2011 8:44 pm
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Is there an equation that you can use to calculate when the Moon will rise and set :?:


Last edited by Fincle1 on Sat May 21, 2011 5:00 pm, edited 1 time in total.

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PostPosted: Sat May 21, 2011 4:57 pm 
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Location: 55° 57'N: 03° 08'W
You can find your local circumstances using either Websurf or Heavens-Above websites.

Other sources are available.


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PostPosted: Sat May 21, 2011 5:01 pm 
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I know about websites that I can find out when the Moon rises but I really want to be able to do it myself.


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PostPosted: Sat May 21, 2011 5:13 pm 
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There are probably programmes or equations that allow you to do this.
However, I have for the last ten years had a LCD mounted panel that gives sunrise, sunset, moonrise, moonset, pressure, weather outside, inside temperature, outside temperature. Also radio controlled highly accurate time, auto summer time changes etc. A wonderful device.
It was about £40, but it is worth it as I just glance at this information which is instantly available. The batteries last for years and the device has been faultless.
It has towns possibly world wide or maybe own setings when you start it up.
Regards, David

It also gives me the temperature in my fridge, all radio controlled.


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PostPosted: Sun May 22, 2011 8:38 am 
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There used to be tables used by mariners for moonrise and monset and I think 7 figure log book tables for all this to be calculated by hand. I think these were used for getting positions at sea and also used mechanical chronometres on gimbals for accurate time.
How far back do you want to go to calculate it yourself. You cannot really do it from scratch. You have to have accurate time and the position of the Moon.
To do it from scratch you would actually have to measure the elevation of the Moon and azimuth against accurate time and spend years making observations.
Regards, David


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PostPosted: Sun May 22, 2011 10:04 am 
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Location: 55° 57'N: 03° 08'W
You might like to look at Wikipedia entries for George William Hill,
and Ernest William Brown.


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PostPosted: Sun May 22, 2011 11:28 am 
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Thank you, I read those two entries.
My point is that to calculate moonrise you have to use the work of others, either for time keeping or positional work or to get the elements needed to do the calculations.
You then have to decide whether to do these calculations long hand which might take a hundred years or with mechanical calculating engines or with electronic calculators or with computers of varying capacity.
I suppose if you were on a desert island perhaps with lots of pencils or paper or maybe you could make these you might find rough ideas on sunrise, sunset, moonrise and moonset.
I have always thought of being stranded in such a place. I would quickly try to establish latitude and if I had a working accurate watch I would try to establish longitude.
Depending how long the watch battery lasted or if high quality mechanical I might have a go at estimating other things.
For the moment I just glance at the small LCD panel that gives me everything I need every time I am in the hall.

I enjoyed the film with Tom Hanks I think called Castaway.
And the series Lost is a bit ridiculous. With so many survivors and so many watches they could establish latitude and Longitude in a couple of days.
In addition in one episode of 'Numbers' they calculauted the position of a place to pinpoint accuracy from the shadows of the Sun on some photos. It would be impossible from the photos shown to achieve such accuracy.
There are also many other such claims in different episodes, which on close examination could not achieve the claimed accuracy.
Regards, David


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PostPosted: Sun May 22, 2011 4:45 pm 
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Joined: Sun Aug 13, 2006 12:29 pm
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Location: Goosnargh, north of Preston, UK
Fincle1 wrote:
I know about websites that I can find out when the Moon rises but I really want to be able to do it myself.


Chapter 47 of Jean Meuus's classic Astronomical Algorithms explains how to calculate the position of the Moon for a given location and instant. From this you can use an iterative process to derive the Moon's rise and set times. However, Meuus does say that to calculate the position accurately:

Quote:
...it is necessary to take into account hundreds of periodic terms in the Moons longitude, latitude and distance...


Meuus therefore gives a simplified method providing accuracy of 10" longitude and 4" latitude. For readers requiring greater accuracy, Meuus refers them to Chapront's Lunar Tables and Programs.

Chapter 70 of the third edition of Peter Duffett-Smith's Practical astronomy With Your Calculator covered this too. This book appears to have been superseded by Practical Astronomy with your Calculator or Spreadsheet, which I haven't read, but according to the index, covers Moon rise and set on pages 178 - 180.

The state of the art in describing the Moon's position is possibly described by The lunar ephemeris ELP 2000 by Chapront-Touze, M. and Chapront, J. For the greatest accuracy you'd want to implement that complete with its 37862 periodic terms...

_________________
David Entwistle


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PostPosted: Sun May 22, 2011 6:07 pm 
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Location: 55° 57'N: 03° 08'W
It's "Meeus" not "Meuus".


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