The sky background can contribute significant Poisson noise in broad and medium band filters, and must be taken into account during noise calculations. The actual sky brightness depends on the heliocentric ecliptic coordinates (latitude and longitude) in a manner summarized in Table 6.3 . ... 22.4 . ... An average sky brightness of V=22.9 mag arcsec -2 is assumed. ... Values for other filters or sky brightnesses can be computed from Table 6.2 , Table 6.1 , Table 6.3 , and Equation 6.2. ...