Rare Alignment

A transit of Venus occurs when Venus passes directly between the sun and earth.  This alignment is rare, coming in pairs that are eight years apart but separated by over a century.  The most recent transits of Venus were a thrilling sight in June 2004 and 2012, with the next transit of Venus pair occurring in December 2117 and 2125. 

Global Expeditions

Observers from two locations on earth see two distinct paths (red and blue) of Venus across the sun.  The slight difference in times Venus takes, moving from edge to edge, can mathematically unlock the distance from earth to the sun, and thus the size of our solar system.  For 17th & 18th century transits, intrepid explorers set out to answer a leading question of mankind.  Not all of them made the voyage back home.

Mystery of "Black Drop"

Just before or after the circular black dot of Venus seems to touch the edge of the sun, a peculiar "black drop effect" sometimes occurs between the contact points.  A ligament of darkness smears the juncture of Venus and the sun.  You can see a similar anomaly if you almost pinch your thumb and forefinger together.  Just before you sense contact, a black feature spans your two digits.

Transits Lead the Hunt

Once again, transits are on the leading edge of new discoveries.  The NASA Kepler mission and others are using the transit method to find habitable planets around distant stars.  The Kepler spacecraft monitors over 150,000 stars, looking for periodic dips in their light curves which reveal the presence of companion planets.  You, too, can join this quest for new worlds.