It is rare for Mercury to pass directly in front of the Sun when viewed from Earth. This type of event is called a solar transit of Mercury. One might think that a transit could be seen anytime that Mercury and the Earth were on the same side of the Sun, but because their orbits are at an angle, Mercury is often above or below the Sun's visible disk. The only two locations in Mercury's orbit where a transit can occur lie along or near a line called the line of nodes. If Earth also lies along or near this line, then a transit can occur. Created by Jeff Bryant (jeffb@wolfram.com)