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TRANSIT OF MERCURY ACROSS THE CORONA
A transit of Mercury across the solar disk and the corona, as observed by the Yohkoh Soft X-ray Telescope on 6 November 1993. Solar north is up, west to the right. The panel on the left shows the trajectory of Mercury, which grazed the S limb of the Sun as shown. Its path took it across a narrow coronal hole (the notch seen at nearly the S pole). The four panels on the right show the actual silhouette of Mercury in four locations, with times as marked. The diameter of Mercury at this time was approximately 10 arc s.
This rare observation was the first of an occultation of the solar corona by a planetary body. By comparing images with and without Mercury present, we get a direct and reliable measurement of the coronal X-ray brightness as a function of time as Mercury sweeps across different solar features.
Submitted by Sam Freeland and Hugh Hudson, 18 December 1993