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Poor mans methods to determine apparent altitude


In this page some poor mans methods to determine the aparent altitude are discussed. The following methods are discussed:

Altitude measurement

One can directly measure apparent altitude with the use of a clinometer, Abney level, SetRise Tool® or theodolite.



Height grid

The height (in [m]) can be determined by: Using the map, the height difference between two points (A and B) can be determined. With this information and the distance between the two points, one can determine the apparent altitude by using a formala given by A. Thom. A web page has been made to calculate the apparent altitude using this method.
An GPS is not so good in providing the height of a point, so the error in the height difference becomes around 25 [m]. More info on GPS accuracy can be found here. With an GPS one can though determine the position and then find on the map the height at that position.
In general the two points must have a height difference of at least 40 [m], otherwise the error in the apparent altitude becomes too big.

If point B is a vast plain, the formula for the apparent altitude becomes different, see this link.

Reference object

One can use a reference object with known position on land (like a top of house, meadow rim, etc.) as a means of providing the apparent altitude. The easiest reference is an object determined by means of a hand level or Abney level through which one can determine the zero apparent altitude level. Using then photometry one can determine the apparent altitude of the horizon.

See a worked out example for Maeshowe (section: Determination of horizon altitude).
 

Remote light source

The shadow of a celestial body can also be used to determine this (certainly when determining the sunniness/mooniness). One has to determine the time (use a clock as precise as possible, like GPS or NTP) the measurements were done. The apparent altitude of the sun/moon can be determined by ephemeris programs (e.g. SkyMap or JPL ephemeris). Remember that these programs determine the middle of the celestial object and normally the shadow is determined by the top or lower rim of the object (for moon and sun this is around 14' difference near the horizon and 16' difference when they are higher than some 5°).

See a worked out example for Maeshowe (section: By using the sun).

Building survey

Use a good ground plan of the building (from literature or made yourself). Remember that an accurate zero altitude must be provided by this ground plan (a good tool here is a hand level, a water hose or Abney level throught which one can look).
Information from ground plan can be input in the sunniness/mooniness page to determine apparent altitude (and azimuth).

See a worked out example for Maeshowe.
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Last major content related changes: July 23, 2000