On certain radiometric effects during the partial solar eclipse of February 25, 1952

Summary

In this paper we discuss some interesting results of radiometric measurements carried out with a thermopile pyrheliometer and direct reading Gorczynski solarimeter during the eclipse of February 25, 1952, which was partial in Greece, as compared to similar measurements made on the two days preceding the eclipse, under identical meteorological conditions and with a sky of uniform and exceptional purity. These data were assumed to be comparable between themselves, and from the discussion it results:

• a) That on eclipse day the values of the radiation measurements began to dropoff well before first contact, and persisted to remain lower than those of the preceding days at the same hours, well after last contact. We attribute this phenomenon to the entrance before first contact and the lagging after last contact in the field of the instrument which posseses a fieldangle of 3°, of the intersection of the lunar penumbra with the optically important higher atmosphere.

• b) After first contact and before last contact the fractional radiative obscuration is by a factor of the order of ten larger than the fractional covered area; this is probably due to the penumbra in the atmosphere.