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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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