The primary aim of continuum measurements is to obtain the photospheric temperature scale, but numerous other uses range from gravity measurement, chemical composition studies, the detection of companion stars and disks, through properties of broad-band photometric systems, and bolometric corrections. In the hotter stars, the shape of the continuum is molded by the bound–free absorption of neutral hydrogen. From the ground, we can measure only a small part of the Balmer continuum (912–3647 Å) long-ward of the ozone cut-off ∼3400 Å, the complete Paschen continuum (3647–8207 Å), and some of the Brackett continuum (8207–14 588 Å) which is badly cut up by terrestrial molecular absorption. The Balmer and Paschen discontinuities are useful as pressure diagnostics for late A and F stars, but they also depend on temperature. In cooler stars, where the negative hydrogen ion dominates, all continuum characteristics depend almost exclusively on temperature.

The spectrum measured with low resolution, e.g., 10–50 Å, is often called the “energy distribution.” In such situations, the spectral lines are included, and then measurements of the fraction of light removed by spectral lines is needed to regain accurate information on the position of the continuum.