  EUSO-TA is a ground-based experiment, placed at Black Rock Mesa of the
Telescope Array site as a part of the JEM-EUSO (Joint Experiment Missions for
the Extreme Universe Space Observatory) program. The UV fluorescence imaging
telescope with a field of view of about 10.6 deg x 10.6 deg consisting of 2304
pixels (36 Multi-Anode Photomultipliers, 64 pixels each) works with
2.5-microsecond time resolution. An experimental setup with two Fresnel lenses
allows for measurements of Ultra High Energy Cosmic Rays in parallel with the
TA experiment as well as the other sources like flashes of lightning,
artificial signals from UV calibration lasers, meteors and stars. Stars
increase counts on pixels while crossing the field of view as the point-like
sources. In this work, we discuss the method for calibration of EUSO
fluorescence detectors based on signals from stars registered by the EUSO-TA
experiment during several campaigns. As the star position is known, the
analysis of signals gives an opportunity to determine the pointing accuracy of
the detector. This can be applied to space-borne or balloon-borne EUSO
missions. We describe in details the method of the analysis which provides
information about detector parameters like the shape of the point spread
function and is the way to perform absolute calibration of EUSO cameras.
