# (Practical)Calculating the time of day with angles relative to the position of thesun

• Jun 8th 2013, 02:53 AM
Greymalkin
(Practical)Calculating the time of day with angles relative to the position of thesun
Hey guys, I havent posted in some time and have recently taken a lot of my spare time to enjoy the great outdoors.
My inquisitive nature has lead me to try to figure out a way to tell time using only a cammenga military compass, for those of you who dont know what it is it allows you to see angles(or azimuth)to navigate using your relative position to magnetic north.
Attachment 28549

I am certain it is possible to tell time with a fair amount of accuracy using only the compass given your latitude and time of year.
What I am not certain of is how to go about calculating this, I think this has more to do with physics than calculus, but basic calculus is the highest level of math I am capable of at the moment.

If someone could point me in the right direction that would be great. Ultimately I was wondering if there were some kind of function, or better yet an online calculator to create such a function given a set latitude.
• Jun 17th 2013, 12:31 PM
Greymalkin
Re: (Practical)Calculating the time of day with angles relative to the position of th
anyone?
• Jun 17th 2013, 12:55 PM
ebaines
Re: (Practical)Calculating the time of day with angles relative to the position of th
If you're willing to live with an accuracy of plus or minus about 30 minutes, you can calculate time by considering the angle between the sun's azimuth position and due south. Assuming you are in the northern hemisphere - at noon the sun is due south, and it moves along the ecliptic at a rate of 15 degrees per hour. So the time is 12:00 noon + (Az degrees)/15, where Az degrees is positive for west and negative for east. So if you can measure the sun's azimuth (degrees east or west of due south, regardless of its altitude) you can get a rough estimate of time. You would need to throw in a correction for your position east-or-west within your time zone, and you would need to add one hour in the summer to account for Daylight Savings Time. Finally, there's a very complicated correction that you could add based on the "equation of time" which takes into account the effects of the earth's orbital path throughout the year. When the earth is near apogee (furthest from the sun, around the first week in July) the sun takes less than 24 hours to go from zenith on day 1 to zenith on day 2, and therefore your clock using this method will run a bit fast, and when the earth is as perigee (the first week of December) this clock runs slow. These corrections may account for up to 1/2 hour error plus or minus. If you're interested in details on the equation of time post back, or try a google search.