Editing Astronomical transit (section)

== Contacts ==
During a transit there are four "contacts", when the [[circumference]] of the small circle (small body disk) touches the circumference of the large circle (large body disk) [[tangent|at a single point]].  Historically, measuring the precise time of each point of contact was one of the most accurate ways to determine the positions of astronomical bodies.  The contacts happen in the following order:

*'''First contact''': the smaller body is entirely outside the larger body, moving inward ("exterior ingress")
*'''Second contact''': the smaller body is entirely inside the larger body, moving further inward ("interior ingress")
*'''Third contact''': the smaller body is entirely inside the larger body, moving outward ("interior egress")
*'''Fourth contact''': the smaller body is entirely outside the larger body, moving outward ("exterior egress")<ref name="UCLsafety">{{cite web|url=http://www.transit-of-venus.org.uk/safety.htm|title=Transit of Venus&nbsp;– Safety|publisher=University of Central Lancashire|access-date=21 September 2006|url-status=dead|archive-url=https://web.archive.org/web/20060925140910/http://www.transit-of-venus.org.uk/safety.htm|archive-date=25 September 2006}}</ref>

A fifth named point is that of greatest transit, when the apparent centers of the two bodies are nearest to each other, halfway through the transit.<ref name="UCLsafety" />