THE SUN AS A VARIABLE STAR III.
Final rept. for 1950-1966,
LOWELL OBSERVATORY FLAGSTAFF ARIZ
Pagination or Media Count:
The observations of Neptune in the years 1950-1962, corrected for the effects of changing distance, indicate a decrease in blue magnitude from 8.26 to 8.23. During the period 1963-1966 the brightness was constant and equal to 8.24 mag. The steady decrease of the instrumental transformation coeffcient A8 in the years 1950-1960 throws some doubt on the reality of the changes in Neptunes brightness. If these changes are real they may be due either to intrinsic changes in Neptunes surface or to solar variability or to both. The observations of Uranus indicate no changes in solar brightness from 1950 to 1966 if 22 percent darkening from the equator towards the pole of the planet is assumed. On this assumption the total range of the intrinsic change of the blue magnitude of Uranus is 0.038 mag., with a period of 42 years. In the authors opinion, this long sequence of photoelectric observations has taught us more about the variations of solar type stars than about the sun itself. The observations of 15 stars of spectral types F and G in the years 1955-1966 indicate that for none of these stars does the standard deviation of the yearly mean magnitude exceed 0.008, and for the stars 40 Leo, beta CVn and eta Boo this deviation is less than 0.004 mag. No evidence of variability in the stars which are similar to the sun has been detected during this program. If we assume the sun acts in similar fashion to each of these stars, its variability over a fifteen-year period probably does not exceed one-half of one percent. Another by-product of this research results from one of the most extensive series of night-time extinction observations ever carried out at a single observatory. Author