Michael Maunder & Patrick Moore 
Transit When Planets Cross the Sun [PDF ebook] 
When Planets Cross the Sun

Although transits of planets across the Sun are rare (only Mercury and Venus orbit the Sun closer than us, and so can transit the Sun’s disc) amateur astronomers can observe, record and image other kinds of transit, which are very much more frequent. Transit is in two parts, the first telling the fascinating story of the early scientific expeditions to observe transits. The second part is for practical observers, and explains how to observe transits of all sorts — even transits of aircraft as they fly between the observer and the Sun!