... Transits do not happen every time Mercury passes between the Earth and Sun because their orbits are not in exactly the same plane, as we will see in this activity. ... How many times would Mercury pass the Earth each year? ... Can you tell which two months the orbits of Earth and Mercury are in line with the Sun? _____________________ and ________________________ Provided by: Astronomical Society of the Pacific www.astrosociety.org Instructions: Cut these two disks out along the dotted lines. ...