Here are two transit images that have been scaled so that the Sun is about the same size in each. The first image show a solar telescope (Halpha) view of Mercury crossing the Sun (still happening as I write this). The second shows Venus crossing the Sun back on 8th June 2004. It is interesting to see how the sizes of the two planets compare.
H alpha image from Hawaii of Mercury during transit on 8th November 2006 CREDIT: Haleakala Amateur Astronomers, Mauna Kea Visitor Information Station and Institute of Astronomy