Abstract
THE satellite Interkosmos-1, a joint project of the Soviet Union, the German Democratic Republic and Czechoslovakia, was launched on October 14, 1969, into an orbit with perigee height 260 km, apogee height 640 km and an inclination of 48.4 degrees. A Lyman-α photometer, designed at this institute, was mounted on the observing platform of the satellite, and directed towards the Sun with an accuracy of ±1 degree. The photometer consisted of a modified ionization chamber of Forsterite ceramics with an LiF window and a filling of NO gas1, followed by a d.c. amplifier with a time constant of 0.14 s and two output channels with different sensitivities. The spectral range of the photometer was from 1050 Å to 1350 Å2. Its absolute calibration, carried out at the Physical Institute of the Academy of Sciences of the USSR, yielded a scale value of Kphot = 0.780 × 1011 photons cm−2 s−1 V−1 at 1216 Å in the high-sensitivity channel, with an error of ± 3 per cent. During the period of observation, October 15–23, 1969, the measured absolute values of solar Lyman-α flux varied between 3.7 and 4.7 ergs cm−2 s−1, with a mean value of 4.1 ergs cm−2 s−1. One purpose of the experiment was to measure the height-dependent absorption of Lyman-α in the upper atmosphere when the satellite entered the Earth's shadow (“satellite sunset”). The most reliable data of this kind were obtained on October 15 at 1409 UT, when the line-of-sight between the satellite and the Sun touched the Earth's surface at a geographic latitude of about 40° N. For this case, Lyman-α absorption, expressed in terms of optical thickness of the atmosphere as a function of the “grazing height” above the Earth's surface, is presented in Fig. 1. The orientation of the satellite towards the Sun was guaranteed for all grazing heights greater than 10 km.
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FELSKE, D., MARTINI, L., STARK, B. et al. Molecular Oxygen Absorption of Solar Lyman-α observed by Interkosmos-1. Nature 228, 1298 (1970). https://doi.org/10.1038/2281298a0
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DOI: https://doi.org/10.1038/2281298a0
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