Astronomy transformed: the emergence of radio astronomy in Britain

Abstract

Spectrograms of the 1-micron carbon dioxide bands on Venus at a dispersion of 5.4 Å/mm were obtained on January 24, 1965, March 5, 1966, and March 9, 1966. All exposures were made with an 80-cm focal length (“B”) camera of the newly improved coude spectrograph of the Struve reflector.On the basis of our measured equivalent widths, we derived rotational temperatures of 200–250°K. This is somewhat lower than the rotational temperature found by Chamberlain and Kuiper, but about the same as the radiometric temprature obtained by Sinton and Strong. We find little variation of temperature with phase. As a check on our method of analysis we applied it to the laboratory carbon dioxide spectra of Burch et al. (1965), and found that our ability to measure rotational temperatures was more accurate than our ability to measure the absolute value of the equivalent width of an individual rotational line.All three 1-micron bands are found to lie on the same curve of growth and to follow the square-root law of absorption, as suggested by Chamberlain and Kuiper. Comparison with Spinrad's data indicates a noticeable change in the scattering coefficient between 7820 Å and 10 500 Å. The bands show the same general phase variation as that found by Chamberlain and Kuiper but with substantially more scatter, much as Spinrad found in the case of the 7820 Å band.Using a simple reflecting layer model of the Venus atmosphere, we derived an upper limit to the carbon dioxide abundance of about 1.5 km-atm. This amount is, curiously, about the same as that derived by Kuiper and Spinrad from the weaker 8689 Å and 7820 Å carbon dioxide bands.The high dispersion of our spectra has enabled us to begin a quantitative analysis of the (20°3–04°3)II hot band of carbon dioxide. The results agree with those obtained from the other three bands, but more observations are needed.We are now in a position to combine our results with a more realistic model of the Venus atmosphere, developed by McClatchey, in order to obtain estimates of the Venus atmospheres, developed by McClatchey, in order to obtain esimates of the carbon dioxide mixing ratio.