This is when the planet Mercury passes in front of the Sun as seen from earth, rather than just above or below the line of sight as is usually the case. These do not occur often, the last one was in 2006 and the next two will be in 2019 and 2032. It is an opportunity to see this usually difficult to see planet.
The event started at 12:12 pm and lasted 7½ hours to 7:42 pm just before sunset. Whilst the event was wholly visible from Kenley, cloud obscured all but 2 hours, limiting the viewing from 12:45 to 3 pm. It appeared as a small circular silhouette and is visible in the image to the right, just below and to the left of centre, which was one of several taken on the day at Kenley.
Our observatory at Kenley was opened on Mon 9th from at least 10 am, and also to the public; where everyone was welcome, and asked to observe all safety precautions and instructions if agreed to join us to avoid permanent eye damage.
Please see this page for information about visiting, especially on facilities and parking.
More information about this astronomical event can be found here: Wikipedia