Bands

Color or frequency bands are standardized systems of filters in astronomy which are very different for different frequency ranges. In the visibile range, the bands are usually called spectral color bands or photometric bands or photometric systems. In radio they are called frequency bands each of which are made of narrower frequency channels.

The most widely used photometric system is the UBV system, created by the American astronomers Harold Johnson and William Wilson Morgan, where the symbols U, B and V are used for the ultraviolet, blue and the visual (yellow-green) filters. The R and I filters were later added to this for read and infrared to create the UBVRI system. The transmission efficiency of the filters are shown below as a function of frequency.

As evident from the figure, the U filter only allows ultraviolet light, the B filter blue light and V yellow-green light. In the Johnson-Cousins-Glass (JCG) system more filters are added. In the following table, we show the effective wavelength $\lambda_e$, effective frequency $\nu_e$, the FWHM passbands $\Delta\lambda$ and $\Delta\nu$, and the spectral flux density at magnitude $m=0$ at $\nu_e$ in units of jansky (Jy) for each of the filters in the JCG system (Bradt, AM).