... 12c. Venus transit (1) . 12d. Venus transit (2) . 12e. Venus transit (3) . ... 1 The 2004 Venus transit . ... Kepler's third law allows one to evaluate the dimensions of the solar system in relative units, e.g. in " astronomical units " (AUs), where 1 AU is the mean Sun-Earth distance. ... Edmond Halley suggested using the transit of Venus across the Sun's disk, when it appears as a dark round spot --or to quote one observer of the 2004 transit, "like a blueberry in front of an orange." ...