Method of E.S. King and its variants

The method of E.S. King is based on the measurement of one star and and the reduction of the movement in both directions, the declination and th rightascension. The three variants only distinguish from the orientation of the measurement field. At this place I describe only the variants A and B1.

Where in the sky

All three variants have to be carried out in the close vicinity of the pole, e.g. with Polaris.

Alignment of the measurement filed and orientation of the axes

E.S. King variant A

The alignment of the measurement field is equatorial.

The positive x-axis points in the direction of the positive declination. The positive y-axis points in the direction of the positive rightascension.

E.S. King variant B1

The alignment of the measurement field is azimuthal.

The positive x-axis points in the direction of the positive elevation, that means in the direction of the zenith. The positive y-axis points in the direction of the positive azimuth, that means in principle to the West.

It was A.A. Rambaut who defined in his article the azimuthal coordinate system in that peculiar way.

E.S. King variant B2

Compared to the variant B1 the measurement field has to be rotated by the angle which corresponds to the half of the measuring duration. With this rotation the calculation of the corrections is made simpler.

This variant is mentioned for the sake of completeness and is based on an idea of H.H. Schaefer.

Duration of the measurement

The duration varies between 10 and 130 minutes.

Zero point

The zero point is the apparent (refracted) pole.

Procedure

After the star has been centered it is time to track the star without any intervention. Read the position after about 30 minutes on the measurement field. Enter both values X and Y in the fields X direction and Y direction in units of the grid. Enter the measurement duration in seconds into the field Observing period. Enter into the field Resolution per unit the grid unit in arc seconds and hit submit.

Example variant A

With the following parameters

Latitude: +47
Longitude: -7.601
Height: 550
Temperature: 10
Date: 2001:09:30
Time: 22:04:21
Time zone: cest
Rightascension: 37.9529
Correction star Declination: -20
X direction: -2.51
Y direction: -1.305
Resolution per unit: 5

you obtain the following results

King h : 221.60 degree
King lambda : 107.76 arcsec
King A : -105.91 arcsec
King k : -80.58 arcsec
Move the north end of the hour axis 21.18 units to the WEST
with star at declination -20.00 degree 19.57 units to the WEST
Increase elevation of the hour axis 16.12 units

Comments, questions, corrections: markus.wildi@one-arcsec.org

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