Photometric measurements (2)
	• Aperture magnitudes: pixel values are integrated within a circular aperture § Fast and simple § Unbiased against faint or low surface brightness sources § Contamination by close neighbours can be strong § Rather inefficient in terms of S/N § Can be used whenever the data are meant to be compared with external measurements •  Photometric calibration of standard stars (e.g. Landolt) •  Colour measurements