Astrophysics (index)


(studying starlight through bandpass filters)

In astronomy, the term Photometry is used for the study of the brightness (Magnitude) of stars and other bodies, and often implies the use of bandpass Filters (i.e., different Passbands) to measure magnitudes specifically over given spectral ranges, i.e., to determine Color Index. The results of such observation may be called the star's photometry.

This is as opposed to a more complete characterization of the body's light via Spectroscopy, which requires a more specialized instrument. Photometry has the advantage of requiring less light (Apparent Magnitude (m)), thus has a greater range, i.e., can be used with many more stars.

Collected observations and models have associated color magnitudes and color indexes with various physical characteristics of stars. This has been standardized by using conventional filters, e.g., in Photometric Systems.

Filters with different passband widths are used, according to need and light-availability, yielding a number of levels of spectral detail short of using full spectroscopy. These can be of use in Direct Imaging Extra Solar Planets, for which limited light reaches Earth. Some conventional terms:

  • Broad Band Photometry - passband width on the order of 100 nm.
  • Intermediate Band Photometry - on the order of 20 nm.
  • Narrow Band Photometry - on the order of 5 nm.
  • Spectral Photometry - for even narrower passbands.
  • Precision Photometry - (or high-precision or ultra-precision, etc.) producing reliable magnitude measurements in higher precision than typical, e.g., thousandths.


Referenced by:
Aperture Photometry
Catalog of Azzopardi & Vigneau (AzV)
Balmer-Break Galaxy (BBG)
Exoplanet Eclipse Light Curve
Galaxy SED
Hawaii K-Band Galaxy Survey
Bright Star Catalog (HR)
Photometric Redshift
Sloan Digital Sky Survey (SDSS)
SkyMapper Southern Survey (SMSS)
Stellar Parameter Determination
Stellar Temperature Determination
Synthetic Photometry