We report on an observing campaign in March 2001 to monitor the brightness of the later arriving Q0957+561 B image in order to compare with the previously published brightness observations of the (first arriving) A image. The 12 participating observatories provided 3543 image frames which we have analyzed for brightness fluctuations. From our classical methods for time delay determination, we find a 417.09 ± 0.07 day time delay which should be free of effects due to incomplete sampling. During the campaign period, the quasar brightness was relatively constant and only small fluctuations were found; we compare the struc--3ture function for the new data with structure function estimates for the 1995-6 epoch, and show that the structure function is statistically non-stationary. We also examine the data for any evidence of correlated fluctuations at zero lag. We discuss the limits to our ability to measure the cosmological time delay if the quasar's emitting surface is time resolved, as seems likely.

Abstract. This paper measures the solar radius, using the new Tubitak National Observatory astrolabe as well as data acquisition and reduction procedures. The mean values of the solar radius obtained are slightly lower than the other results to which they are compared. We have compared our results with data obtained since 1981, and show that our results are very homogeneous. We hope to extend these measurements to obtain accurate determinations of solar position.

The results of the solar radius measurements from February 2001 to November 2003 with the solar astrolabe at the TUBITAK National Observatory are presented. The mean semi-diameter for the period, corrected for systematic effects such as the Fried parameter and the zenith distance, is found to be 959.29 ± 0.01 arc sec. A comparison of the monthly averages of the solar radius with the monthly means of sunspot numbers shows that the semi-diameter of the Sun increases with an amplitude of 0.017 arc sec per year in opposite phase with solar cycle 23.