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Introduction

There are several ways to figure out where the Sun will rise or set on any day of the year. Our Orthographic Projections section is one way. This is done with a pair of compasses, a straight edge, protractor and pencil and paper. Even if you do not plan to use this technique, we encourage you to go through this section, as it will give you a good feel for what is happening between where you are on the Earth and the Sun throughout the year

Thanks to Sig's nephew, Fred VandenBergh, we can now offer you another way to figure out where the Sun will rise on any day of the year at any latitude and any angle of elevation to the horizon. This is useful not only at prehistoric sacred sites to figure out if outlying stones or notches on the horizon have an astronomical orientation, but also in the construction of new sites, to orient them to Sun rises or sets on any day of the year. One of the best aspects of this program is that it is done in JavaScript, so you may download this program to your laptop, and use it out in the field without a connection to the Internet!

To begin with, you will need some tools and information:

I. Latitude and Longitude - Where On Earth Are You? You will need to know this for several reasons - it will allow you to figure out Magnetic Deviation, and you will also need it when you come to figure out where the Sun will rise or set at your location.

a. A good topographic map (Ordnance Survey Map in the UK) of your area will give you these,

b. If you own an iPhone, I use an iTunes App called $0.99. Also, $0.99 - in addition to latitude and longitude, it gives the azimuth of the Sun, its angle of elevation to the horizon (above or below), temperature, and other useful info. (I am using my iPhone more and more for outdoor astronomy and archaeoastronomy.)

c. If you are on a computer, one way to get your latitude is to go to iTouchMap.com.

These sites will give you the Latitude and Longitude for the town you are in. This should be accurate enough for most purposes - though the topographic map will be even more accurate. A Global Positioning System (GPS) is another way to find Latitude and Longitude in the field. It uses satellites to locate you very accurately on the surface of the Earth. Also, Google Earth is an easy way to find it. You can have a free download of this useful program at < http://earth.google.com/>.

II. A Compass - You will need a compass to determine the Azimuth (number of degrees from true North in a clockwise direction) you are shooting. To begin with, any compass will do, but as with all tools and operations here, the more accurate, the better. Orienteering compasses are not what you want. They are useful to begin with, but they really are not accurate enough. Sig uses a Suunto Tandem (page 11). Check out their KB-20 Vista, and their KB-14/360RD, and their Twin – A compact compass and clinometer combination. Silva offers several different less expensive options, the 54LU Combi has a see through lens that gives remarkably accurate azmuth readings, and the Ranger 24 uses a mirror for accuracy, and comes with a clinometer - to measure the angle of elevation to the horizon. See Silva's Swedish web site (see Precision Instruments).

Sun paths

Given a level horizon, on either Equinox, the sun will rise due East, and (North of the Equator) the Summer Solstice Sun will rise North of there and the Winter Solstice Sun will rise in to the South, the exact azimuth depends on your latitude.

With the Sun Finder on the next page, you can find out azimuths for sun rises and sets. There are 360 degrees in a circle. If your azimuth is less that 180°, it could be a sun rise point. If it is over 180°, it could be a sun set point.

III. Magnetic Deviation - At 99% of the places on Earth, your magnetic compass will not point true North. This is due to something called Magnetic Deviation. This deviation (also called magnetic declination, magnetic variation, or compass variation) is the angle between the north compass (magnetic) heading and the heading to true (geographic) north. True north can be determined with a compass reading plus/minus (as appropriate) the location’s magnetic deviation. Geodetic Maps can show you this deviation, but be aware, it changes significantly over time (the map should tell you how much per year)!

There are several web sites that can give this deviation as of today. One is Ricardo's Geo-Orbit Quick Look. It is a visual chart/map of these deviations all over the Earth. Like the Sunfinder program itself, we recommend that you download a copy of these maps, so you can refer to them for magnetic deviation when you are in the field with your lap top computer. Another place to visit is the National Geophysical Data Center World Data Center/Geomagnetism in Colorado USA. This is more accurate, and figures out the deviation at your particular Latitude and Longitude mathematically. The Longitude and Latitude are in degrees and minutes. For the National Geophysical Data Center web site, you will need to convert the minutes, of which there are 60 in a degree into a decimal. (Example: 3° 30'. 30/60 = .5, so 3.5) The answer is - the first number at the top column on the left. Declination is measured positive east and negative west (i.e. D -6 means 6 degrees west of north). If your Magnetic Deviation is a positive number, add it to your magnetic compass reading. If it is a negative number, subtract it from your magnetic reading.

In addtition to magnetic deviation, be aware that a number of sacred sites in the British Isles have magnetic anomalies that pull the needle of your compass away from Magnetic North. At Carn Angli in Wales (just West of the Prescelli Mountains), there is a space about the size of a brick where you can stick your compass in, and the needle turns 180°! In the Grampian region of north-east Scotland, there are a number of recumbent stone rings that also exhibit these anomalies as well, though not necessarily as strongly as Carn Ingli. The point here is that where ever you are, you need to check that this isn't happening where you are needing to take a compass reading. Find Magnetic North, then move to a number of different places on your site to see if the needle continues to point to the same point on the horizon. If it doesn't, you need to wait 'till dark locate Polaris also known as the North Star to find True North. Then you can figure out the azimuth you seek from that.

IV. Clinometer - measures the angle of elevation to the horizon - The Sun doesn't rise vertically. North of the Equator, it rises at an angle to the South - and vice versa in the Southern Hemisphere. If you have a level horizon, you have no problem. It is at the azimuth you have measured. But most horizons are not level. You will need a tool to measure this angle. The most simple one is as D shaped protractor, some fishing line or thread, and a weight. Suunto makes combination compasses and clinometers like the Tandem, and their Twin. In the United States, Forestry Suppliers Inc., PO Box 8397, Jackson, Mississippi 39204 (Phone: 800-647-5368) sell a number of different clinometers by Brunton, Suunto and others. When you get to their home page, type in their Search window.

Two Limitations - We have not included the capability to do latitudes south of the Equator, and we have not yet built in the capability to do dates before the time of Christ (BCE). We intend to rectify these two deficiencies in the near future, but we wanted to get this Sunfinder up because we trust that it will be useful to many. If you have any suggestions or other observations, please contact Sig Lonegren.

You will find the Sunfinder on the next page. To download it to your lap top, so you can take it into the field, go to the next page, then go to on your menu line, and click on . Save it as a . When it is on your computer, just double click on the icon, and enjoy!

Sunfinder Calculator >>