SURFACE AND ATMOSPHERE OF THE SUN — LINDBLAD 181 



by H. Kristenson and myself to amount to about five magnitudes per 

 second of arc. A certain arbitrary layer may be assumed to define the 

 "photosphere." Wlien the decrease of intensity with height over the 

 photosphere is known, each measurement of the intensity of the con- 

 tinuous spectrum may be converted into height over the photosphere. 

 The measurements on various spectral images on the film therefore 

 give the profile of the lunar contour in relation to the photosphere. 

 In this w^ay each spectral image links together the solar and lunar 

 limbs with extreme accuracy and we may define and measure the con- 

 tact with a mean error of only a few hundredths of a second. As 

 intermediary, when defining the contact, F. Hayn's map of the lunar 

 contour for different degrees of libration may be used with advantage. 



Third contact- 

 PtKtomethc profiles 

 — ~— - Sfcc^J^o/m ere 

 "'^^ Lund eJ^p. 



Figure 5. — The lunar contour determined photometrically from the records of the 

 flash spectrum according to the results from the Stockholm expedition (full- 

 drawn curve) and the Lund expedition (dotted curve). Third contact. 



The comparison of contours with respect to the photosphere for 

 points along the eclipse track enables us to find the difference be- 

 tween the times at which a given contact occurs at different places 

 with a very great accuracy. If Ei and Eo (fig. 6) are two points 

 at which contacts are being observed, and if we know the motion of the 

 moon and the distance between the earth and the moon, the difference 

 in time for the two places will allow us to determine the true distance 

 E1VE2 between the two places. 



At the total eclipse of May 20, 1947, an attempt to apply the 

 cinematographic methods for contact determinations was made by 

 expeditions sent by the Finnish Geodetic Institute and by the Geo- 

 graphical Survey Office in Sweden, in collaboration with the Swedish 

 observatories of Lund, Stockholm, and Uppsala, to Brazil and to 

 French Togoland and the Gold Coast. On account of bad weather 

 at the place of the Swedish Brazil expedition, cinematography of 

 the flash spectrum could only be carried through on the African side. 



The next eclipse that will allow a connection in this way between 

 America and Europe occurs on June 30, 1954. 



