Timing the Transit of Venus.

 

Vocabulary

1st Contact- The instant when the planetís disk is externally tangent to the Sun (transit begins).

2nd Contact- The entire disk of the planet is first seen when the planet is internally tangent to the Sun.

3rd Contact- The planet reaches the opposite limb and is once again internally tangent to the Sun.

4th Contact- The planetís disk is externally tangent to the Sun (transit ends).

Ingress- Contacts one and two define Ingress.

Egress- Contacts three and four define Egress.