# Presentation: 134201

## Azimuth Determination FromSolar Observations

- Azimuth Determination FromSolar Observations

- ALAN M BERARDUCCI
- National Geomagnetism Program - US Geological Survey
- geomag.usgs.gov

## Methods of Azimuth Determination

- Solar or Star Observations
- GPS
- Gyro compass

## Equipment for Solar Observations

- Theodolite with
-     Solar Filter
- Tripod or Pillar
- Watch or Clock
- Map or GPS

## Gurley Transit

## Solar Filter

## Direct Azimuth determination

## Indirect Azimuth Determination

## Azimuth Monument

## Preparation

- Synchronize clock to UTC.
- Obtain Lat and Long from GPS or Map.
- Set theodolite on tripod or pillar.
- Measurements made anytime except near noon.

## Methodology

- Horizontal angles for azimuth and sun.
- Forward and reverse angles to Azimuth before and after sun readings.
- Equal number of forward and reverse readings to sun.
- Time accuracy to within 1 second.
- 2 to 8 sun readings on sun per set.
- 2 morning and 2 afternoon sets.

## Sun in Crosshair - Zeiss

## Sun in Crosshair Right or Left edge

## Solar Observations Step 1-Sight the Azimuth Mark

- Place the vertical circle on the right with the telescope aimed at the azimuth mark.
- Precisely align the cross hairs with the azimuth mark.
- Record the horizontal circle reading on the observation form.
- Rotate the theodolite 180° so that the vertical circle is on the left with the telescope aimed at the azimuth mark.
- Precisely align the cross lines with the azimuth mark.
- Record the horizontal circle reading on the observation form.

## Solar ObservationsStep 2 – Find sun in the telescope

**Caution:  Never look at the sun through the telescope without a solar filter.**
- Orient the horizontal circle so the telescope is facing the sun.  Tip the objective end of the scope downward so that a shadow from the sun shows on the base of the theodolite.
- Do not look through the telescope during this procedure. Orient the shadow so that it is precisely centred on the theodolite base.  Rotate the telescope upward until the bright light of the sun is visible through the telescope.
- Place the solar filter on the telescope.  Look through the telescope and focus the sun so the edges are well defined.  The Zeiss Jena theodolite has a circular hair which is a bit larger than the diameter of the sun.
- The idea is to move the telescope with the sun until it precisely aligned in the circular hair.  At that moment, you stop moving the telescope and get the precise UTC time.

## Solar ObservationsStep 3 – Direct – Vertical Circle Left  

- With the vertical circle on the left, find the sun as described in **Step 2 **above.
- Align the sun in the circular hair.  At the moment it is aligned, note the time and record it on the observation form.
- Record the horizontal circle reading on the observation form.
- Make three more observations on the sun with the vertical circle left.  Record the time and horizontal angle on the observation form.

## Solar ObservationsStep 4 – Reverse – Vertical circle right

- Remove the solar filter and eyepiece, rotate the theodolite 180° so that the vertical circle is on the right and find the sun as described in **Step 2** above.
-  Align the sun in the circular hair.  At the moment it is aligned, note the time and record it on the observation form.
- Make three more observations on the sun with the vertical circle right and record the time and horizontal angle on the observation form.

## Solar ObservationsStep 5 – Sight on the azimuth mark 

- Place the vertical circle on the right with the telescope aimed at the azimuth mark.
- Precisely align the cross hairs with the azimuth mark.
- Record the horizontal circle reading on the observation form.
- Rotate the theodolite 180° so that the vertical circle is on the left with the telescope aimed at the azimuth mark.
- Precisely align the cross lines with the azimuth mark.
- Record the horizontal circle reading on the observation form.

## Computation of the Azimuth

- The simplest computation method is to use a computer program.
- Elgin, Knowles and Senne, Inc. has several products for comuter or HP 48 calculator:  _[http://www.rollanet.org/~eksi/](http://www.rollanet.org/~eksi/)_
- A freeware program is available from:
-    _[http://www3.sympatico.ca/craymer/spade/](http://www3.sympatico.ca/craymer/spade/)_

## Computation (cont.)

- The procedure and formulas are also described in the Sokkia Celestial Observation handbook and Ephemeris, which is printed yearly.
- A Naval Almanac is available from:  _[http://](http://aa.usno.navy.mil/publications/docs/ord_info.php)__[aa.usno.navy.mil/publications/docs/ord_info.php](http://aa.usno.navy.mil/publications/docs/ord_info.php)_

## Azimuth Determination From Solar Observations

- Azimuth Determination From Solar Observations

- ALAN M BERARDUCCI
- National Geomagnetism Program
- US Geological Survey
- geomag.usgs.gov