Scientific reduction of astronomical images

Astronomers use information encoded in light to learn about the universe. After acquiring raw images using telescopes these must be corrected for a range of instrumental effects to ensure that they are of high enough quality to be used for scientific purposes. This process is known as image reduction and in modern astronomy one of the most frequently used tools for this purpose is IRAF. In this work we give an introduction to the essential techniques in image reduction and how to apply them in IRAF. Concepts such as aperture and extended object photometry as well as spectroscopic reduction are discussed using real examples and step-by-step guides for IRAF.