Astron. Astrophys. 325, 1174-1178 (1997)

4. The corrected measurements

Values of R1 and the derived results for Rc are given in Table 1 (column 10) for the 30 series, which in total contain 71000 measurements. Fig. 1 shows the values of R1 corrected only for refraction; it is evident that the results in the 17th and 18th centuries exceed the conventional value 959".63 due to Auwers (1891) - represented by a broken line in the diagram - by 5" at the beginning of this period and 2" at the end. The solid line () represents the effect of applying a diffraction correction to the mean semi- diameter of of form (where D is in cm) up to 1870 and later . It is evident that there is a close correlation between the values of and for the whole of the period between 1660 and 1995. Fig. 2 plots the values of Rc listed in Table 1. It also shows two solid lines corresponding to a semi-diameter of . This uncertainty of 1".5 includes certain of the quantities given in Table 2: personal equation (1" to 2") and seeing (1") - both relative to the solar diameter. It can be seen that this zone of width 3" embraces nearly all of the individual values Rc in Table 1; the only exceptions are the results from the observations by Mouton (ref no. 1), Bouguer (no. 10) and Mayer (no. 11), for which the following comments are relevant. Mouton (1670) had an unusually large personal equation; Bouguer (1753) was not satisfied with his 14 measurements made using the recently designed heliometer; perhaps Mayer (1826) had already applied a correction for irradiation of approximately -2" to his results (Rc actually being instead of ).

Fig. 1. Representation of from 1650 to 1995 (from Table 1). The solid line () represents the effect of applying a diffraction correction to the mean semi-diameter of of form (where D is in cm) up to 1870 and later

Fig. 2. Representation of . Horizontal lines correspond to

© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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