Sun Position Glossary

Magnetic Direction: The direction a magnetic compass points. It can be the magnetic pole of the earth, your light meter, steel eyeglasses, a local electrical cable, or any local magnetic object. The most common scale is a 360-degree circle with north at 360-0

Magnetic Compasses read magnetic direction.

True Direction: The world is mapped using true north as a guide. A line pointed at the North Pole is true north.

Altitude, Elevation, or Height above the horizon: objects such as the sun, a tree or building can be measured in degrees above a true horizon as viewed by an observer. Objects at the true horizon are 0 degrees and straight overhead are 90 degrees.

True Horizon: At sea or on level ground the horizon is where the sky touches the sea or ground.

False Horizon. If there is a mountain or obstruction between you and the true horizon you can't see the true horizon. The sun would come up later and set earlier over a false horizon.

Clinometer: An instrument for measuring the elevation/altitude/height above the horizon of an object. Abney Levels are a version. Estes makes a plastic large model available in hobby shops. They can be improvised with an Angle Finder found in hardware stores and a small mirror to read the numbers. In England there is a plastic Clinometer made by Invicta. You can make your own if handy with tools. See "Home Made Clinometer". If you can afford it a Suunto Tandum is a great tool that will double as a long lens viewfinder and range finder. See "Sun and Map Suppliers".

Sun Time / Sundial time: The time determined by the position of the sun in the sky. It rarely agrees with clock time. Sun time varies with your position on earth and the date. Fortunately sun position computer programs make all the corrections needed for you.

Clock time: Average time for our convenience. What your watch says.

Latitude: Your position on earth measured from the poles (90 degrees) or equator (0 degrees). Your latitude determines the apparent path of the sun.

Longitude: Your position on earth measured east or west from Greenwich England.

Time Zones: For our convenience clocks are synchronized to read the same time for every 15 degrees of longitude. These lines are adjusted along convenient geographical boundaries. If you are standing between two time zones, one foot is earlier or later by an hour than the other. But sun time is the same for that position.


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