On Monday, May 9 solar observers in North America will be able to see the silhouette of planet Mercury as it passes between Earth and our Sun. The event, called a transit, is relatively rare — though not so rare as a transit of Venus — and may cause interest in viewing the Sun. WARNING: Looking at the Sun, especially through optical instruments, requires extreme caution! Permanent vision damage can result if proper precautions are not taken! Click here for a good article on safely observing the Sun.
At present we DO NOT plan to open Stephens Observatory for the transit but if plans change, the announcement will be made here — check back later. If conditions are clear, we hope to post images made via telescope at a remote location.
Tiny planet Mercury will appear as a correspondingly tiny black dot against the Sun’s brilliant disk. If any sunspots are present on Sol’s face, compare them with Mercury: the planet will be distinctly round and noticeably darker than sunspots, and from minute to minute it will move — sunspot motion takes days!
Viewed from Earth, transits occur when one of the inner planets crosses the line of sight between our world and the Sun; only Venus and Mercury are ever able to do that. A transit, then, is a bit like a solar eclipse only viewed at a greater distance and blocking only a small amount of the Sun’s light.
Transits would occur more often but for the fact that the orbits of Mercury and Venus are “tipped” so that they do not align along the same plane as Earth’s path. Only when the planets are in the right position where the line of sight passes straight through to the Sun do we see transits and with Mercury, that happens only about 13 times per century. After May 9, the next transits of Mercury will take place in November 2019, November 2032, and November 2049. The most recent transit of Venus took place in June 2012 and will not be seen again until December 2117.
Monday’s transit of Mercury will take place over several hours. For us in Northern Ohio, the transit begins at about 7:12 AM Eastern Daylight Time with the Sun low in the east. Midpoint of Mercury’s passage will be at 10:57 AM, and the transit ends at 2:42 PM.
Cloudy skies? Don’t have proper gear to view the Sun? Fret not! There will be “live” webcasts of the event from various sources during Mercury’s passage. Use your favorite web search engine to find good sources and check for a planned broadcast via NASA TV. NASA will stream a live program on NASA TV and the agency’s Facebook page from 10:30 to 11:30 AM — an informal roundtable during which experts representing planetary, heliophysics and astrophysics will discuss the science behind the Mercury transit. Viewers can ask questions via Facebook and Twitter using #AskNASA.
We hope to post a few links here later.