A Photographic Observation of the Satellite 1957 Beta leaving the Earth's Shadow

Abstract

ON December 15 a photograph of the satellite 1957 Beta was taken at the Warner and Swasey Observatory of the Case Institute of Technology, Cleveland, Ohio, which shows the satellite coming out of the Earth's shadow (Fig. 1). This observation can be used for deriving the distance of the satellite from the Earth's surface. It was concluded from visual observations made the previous morning that the satellite should leave the Earth's shadow in the constellation Ursa Major. An exposure, therefore, was started at 5h. 10m. OOs. E.S.T. with Ursa Major in the centre of the field, although the satellite was not yet visible. The satellite was first observed visually between 5h. 10m. 20s. and 5h. 10m. 30s. It is estimated that it came out of the shadow not earlier than 5h. 10m. 10s. The position where the track is first recorded on the photograph is α = 11h. 53m., δ = + 54.8°. It is possible that the satellite at this position had already left the shadow, but was not recorded earlier because it was at minimum brightness. Nevertheless, since the period of light variation was about 40 sec., the real position should be between the value already given and α = 11h. 37m., δ = + 61°. From these two positions, heights above the surface of 770 and 800 km. respectively were derived, assuming a spherical Earth and a cylindrical shadow with a radius equal to that of the Earth. If refraction isrtaken into account, smaller values of the height result. Assuming a deflexion of the light rays from the Sun of 1°, the corresponding heights are 713 and 739 km. It would appear then that the derived value of 785 ± 15 km. is a maximum one. From predictions of the Smithsonian Institution a height of about 1,000 km. was expected. According to our observations this is too large by at least 200 km.