Final answer:
The astronomer is using the technique of photometry to measure the brightness of the star through different filters in the visual (yellow-green), violet, and ultraviolet regions.
Step-by-step explanation:
The name of the technique being used by the astronomer is photometry. Photometry is the measurement of the brightness of an object, such as a star, using filters to measure the intensity of light at different wavelengths. In this case, the astronomer is using different filters in the visual (yellow-green), violet, and ultraviolet regions to measure the brightness of the star.