Photometry

Photometry, from Greek photo- (“light”) and -metry (“measure”), is a technique used in astronomy that is concerned with measuring the flux or intensity of light radiated by astronomical objects. This light is measured through a telescope using a photometer (often CCD). When calibrated against standard stars (or other light sources) of known intensity and colour, photometers can measure the brightness or apparent magnitude of celestial objects.

Photometry is also used in the observation of variable stars. The technique of surface photometry can also be used with extended objects like planets, comets, nebulae or galaxies that measures the apparent magnitude in terms of magnitudes per square arcsecond.

In this unit, we will cover:

• How various radiometric quantities such as flux, flux density, and spectral radiance are defined
• What are magnitudes and how they relate to flux measurements
• How radiation is produced in nature, and its characteristics
• Telescopes and the use of CCDs
• Radiative Transfer and synchrotron radiation

Recommended Reading

• Chapter 5 and 6 of “Foundations of Astrophysics” by Barbara Ryden and Bradley M. Peterson
• Chapter 3 and 5 of “An Introduction to Modern Astrophysics” by Bradley W. Carroll and Dale A. Ostlie
• Chapter 4, 7 and 8 of “Fundamentals of Astronomy” by Flavio Salvati
• Chapter 3, 4 and 5 of “Fundamental Astronomy” by Hannu Karttunen et al.
• Chapter 15, 16, 17, 18 and 19 of “Astronomy: Principles and Practice” by A. E. Roy and D. Clarke