On May 9 at 11:12 UT, Mercury will begin its 7½-hour journey across the face of the Sun as seen from Earth’s vantage point. Observers in eastern North America will be treated to the entire transit while those farther west will need to wait until sunrise to join in.
Mercury’s disk will be very small, only 1/158th that of the Sun. So before you head out, you should familiarize yourself with its contact points along the solar limb, or edge, and its transit path. You can use ephemeris predictors like WinJUPOS. Developed as freeware by Grischa Hahn, WinJUPOS is a valuable planning tool that is dedicated to solar system objects. After entering the pertinent data for your observing location and the viewing orientation of your telescope, you can view a graphic of Mercury’s predicted position relative to the Sun.
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