Automatic solar image motion measurements

Abstract

The solar seeing image motion has been monitored electronically and absolutely with a 25 cm telescope at three sites along the ridge at the southern end of the Magdalena Mountains west of Socorro, New Mexico. The uncorrelated component of the variations of the optical flux from two points at opposite limbs of the solar disk was continually monitored in 3 frequencies centred at 0.3, 3 and 30 Hz. The frequency band of maximum signal centred at 3 Hz showed the average absolute value of image motion to be somewhat less than 2″ although wide variations from ⩾ 20″ to an extraordinarily quiet day of less than the measurement limit of 1/2″ were observed. The observer estimates of combined blurring and image motion were well correlated with electronically measured image motion, but the observer estimates gave a larger value ≈ × 2 presumable because the electronic measurement gave only the uncorrelated motion of opposite limbs. Approximately 30% of the total solar time would allow spatial position measurements of solar features to a precision ⩽ 2″ and, from the visual estimates, blurring limited measurements to a precision ⩽ 4″.