Mercury will transit - pass in front of the sun as seen from Earth - on May 9. This is the first time a solar transit of the innermost planet will be visible since 2006.
This transit will be seen over most of the world, including all of North America. One of the few regions of the world where the event will not be visible will be Japan and surrounding regions of eastern Asia.
Looking directly at the sun can cause damage to human eyes and is never recommended. Pointing a telescope at our parent star can cause even more damage and is an act that should never be undertaken.
Many amateur skygazers build simple pinhole cameras to safely view the sun during solar eclipses. However, the planet Mercury is so small, it will not be visible using these simple devices.
Telescopes come in three major designs - refractors, where the main lens is placed in front, reflectors, utilizing a single large mirror in back, and Cassegrains, which bounce light between mirrors. Amateur astronomers using telescopes should never use Cassegrains for solar observations, as sunlight can destroy these instruments.
Refractors and reflectors should be properly fitted with solar filters to protect both eyes and telescopes. The best solar filters are made of Mylar and fit over the front of the observational instrument. If these filters are not available, an image may be projected through an eyepiece onto a piece of paper. However, doing this can occasionally crack eyepieces, so it is important not to use a beloved ocular.
Armchair astronomers who wish to view the transit from the comfort of their own homes may do so through the NASA Web site.
"Mercury will appear as a small black dot as it crosses the edge of the sun and into view at 7:12 a.m. The planet will make a leisurely journey across the face of the sun, reaching mid-point at approximately 10:47 a.m., and exiting the golden disk at 2:42 p.m. The entire 7.5-hour path across the sun will be visible across the Eastern United States - with magnification and proper solar filters - while those in the West can observe the transit in progress after sunrise," NASA officials wrote in a special media advisory on the event.
The national space agency will present images of the transit in an hour-long television special, social media mentions, and in photos on their Web site. Among these will be recordings from the Solar Dynamics Observatory (SDO).
"Transits provide a great opportunity to study the way planets and stars move in space - information that has been used throughout the ages to better understand the solar system and which still helps scientists today calibrate their instruments. Three of NASA's solar telescopes will watch the transit for just that reason," NASA officials report.
Mercury only carries out these transits, as seen from our home planet, roughly 13 times each century. Due to the relative tilts in orbits of the two planets, transits do not occur with each 88-day orbit of Mercury around the sun. The next similar transit of Mercury in front of the sun will be seen in the year 2019.
