A new UV-visible spectrometer system that measures the absorption of l
ight from stars and planets by constituents in the Earth's atmosphere
is described. Because it can be used to make measurements at night, th
e system has a significant advantage for measuring polar constituents
in winter, when conditions that might give rise to ozone loss are init
iated. Other advantages arise from the use of a cooled two-dimensional
CCD array as the detector: an array detector avoids spectral noise re
sulting from scintillation of stars or from clouds passing overhead an
d allows for the possibility of measuring several constituents simulta
neously; its second dimension permits auroral light from the atmospher
e adjacent to the star to be measured simultaneously and subtracted fr
om the stellar light, and a modern low-noise CCD allows us to use a te
lescope of modest diameter. The few previous measurements of constitue
nts made by the used of stellar absorption did not have these advantag
es. The instrument was configured for simplicity and ease of use in fi
eld measurements and was deployed outside in winter in Northern Sweden
in 1991. Examples of ozone measurements are shown.