You can measure some important times of though Venus transit on 8th June 2004. It is the first contact (T1), the second contact (T2), the third contact (T3) and the fourth contact (T4). If you know times, you will calculate a distance between the Sun and the Earth. This distance is called the Astronomical Unit (AU). It is on of the most important scales of the Solar system.
The first contact will be visible in 5:19 UT (universal time) in Prague and this time Venus will start to go over the Sun disk. . This time will be difficult to determine time for many amateurs, because Venus couldn’t be seen before this contact. The place of Venus entry on the Sun disk is defined by positional angle of the first contact. This angle measured from the Sun northern pole against direction of clock needle.
The second contact will be visible in 5:39 UT (universal time) in Prague. It is time when Venus will be whole in the Sun disc. Time difference between the first and the second contact is 20 minutes. You will have a lot of time to find Venus on the Sun disc.
The third contact will be visible in 11:03 UT in Prague. Venus will begin to go out of the Sun disc. The second and the third contacts are important to calculate AU.
The fourth contact will be visible in 11:23 UT. It is end of the Venus transit.
You have to determine this times with accuracy one second. You can adjust your watch according to Czech TV or Czech Radio. If you will join the project Venus Transit 2004 of European Southern Observatory, European Association for Astronomy Education, Observatoire de Paris, Institut de Mécanique Céleste et de Calcul des Éphémérides and Astronomical Institute of the Academy of Sciences of the Czech Republic, you will be able to give your observered data to form of ESO websites and they will calculate your AU automatically.
