Precise Determination of the Orientation of the Solar Image |
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Authors: | L Gy?ri |
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Institution: | 1.Debrecen Heliophysical Observatory,Gyula Observing Station,Gyula,Hungary |
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Abstract: | Accurate heliographic coordinates of objects on the Sun have to be known in several fields of solar physics. One of the factors
that affect the accuracy of the measurements of the heliographic coordinates is the accuracy of the orientation of a solar
image. In this paper the well-known drift method for determining the orientation of the solar image is applied to data taken
with a solar telescope equipped with a CCD camera. The factors that influence the accuracy of the method are systematically
discussed, and the necessary corrections are determined. These factors are as follows: the trajectory of the center of the
solar disk on the CCD with the telescope drive turned off, the astronomical refraction, the change of the declination of the
Sun, and the optical distortion of the telescope. The method can be used on any solar telescope that is equipped with a CCD
camera and is capable of taking solar full-disk images. As an example to illustrate the method and its application, the orientation
of solar images taken with the Gyula heliograph is determined. As a byproduct, a new method to determine the optical distortion
of a solar telescope is proposed. |
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