In the infrared, as in the optical, the means of reporting
source brightnesses and the units employed have varied
considerably. In recent years, however, magnitude systems have
been used less frequently, and the most popular unit for
expressing brightnesses, both for point source fluxes and
surface brightnesses, is steadily becoming the Jansky. We have
adopted the Jansky as the standard flux unit (and Jansky/arcsec2
for surface brightness measurements) for NICMOS in our
documentation and in observer-oriented software. Here we provide
some simple formulae and tables to facilitate the conversion
from other units into Jy . A Unit Conversion Tool is also
available on the NICMOS WWW site, at the following URL: Infrared
astronomy really began in the 1960s, when the vast majority of
astronomy was still carried out in the visual region. Flux
measurements were routinely reported in the UBV magnitude
system, and to attempt to integrate IR astronomy into this
system, Johnson (Ap.J., 134 , 69) defined the first IR magnit