A Fabry-Perot Spectrometer for Auroral and AIrglow Observations

A 1-in. Fabry-Perot interferometric spectrometer employing mechanical scanning has been constructed to operate at low order. Such an instrument gives a resolution similar to that of a grating spectrometer but has, at that resolution, a much higher light gathering power. The spectrometer is capable of resolving the sodium D lines in the twilight airglow, scanning once per minute. Some preliminary results on the variation of D2/D1 ratio during twilight are presented. This type of spectrometer should be useful for a number of other applications.