Question

a) Explain what is meant by UBV filters.

b) Explain why astronomers would want to use such filters.

c) Give an example of the usage of UBV filters.

Answer 1

a)UBV system, system of classifying stars by spectral type, based on photometric measurements of the ultraviolet (U), blue (B), and visual (V [yellow]) magnitudes. These magnitudes are measured through filters sensitive to light at wavelengths of 360, 420, and 540 nanometres, respectively. This system was introduced in the early 1950s by the American astronomers Harold Lester Johnson .

b)Most astronomical instruments can only measure the intensity of incident light – they are not able to measure the intensity of light and its wavelength simultaneously. Thus, astronomers make use of filters to control the particular range of wavelengths over which the brightness is measured. A filter is simply a (precisely manufactured) piece of colored glass that is placed in the light beam path between the telescope and the detector. The percentages of each wavelength that are allowed to pass are carefully designed to collect particular pieces of astronomical information.

c)To measure the intensity and wavelength of light emitted by stars,UBV filters are used.