Accurate Measurements of the Brightness of the White-Light Corona at the Total Solar Eclipses on 1 August 2008 and 22 July 2009

摘要

We measured the brightness of the white light corona at the total solar eclipses on 1 August 2008 and 22 July 2009, when solar activity was at its lowest in one hundred years. After careful calibration, the brightness of the corona in both eclipses was evaluated to be approximately 0.4×10−6 of the total brightness of the Sun, which is the lowest level ever observed. Furthermore, the total brightness of the K+F-corona beyond 3R ⊙ in both eclipses is lower than some of the previous measurements of the brightness of the F-corona only. Our accurate measurements of the coronal brightness provide not only the K-corona brightness during a period of very low solar activity but also a reliable upper limit of the brightness of the F-corona.