Our Solar System doesn’t care about the local weather. When something rare and interesting like today’s transit of Mercury across the solar disk takes place, it happens and there are no “rain checks.” And so it was this morning when the day dawned clear to partly-cloudy allowing us to glimpse the beginning of Mercury’s trek only to have the show stopped by rapidly encroaching clouds progressing to solid overcast!
At the predicted hour Mercury appeared as a tiny dot, silhouetted in the lower left-hand quadrant of the Sun’s bright disk. Using special protective filters, observers on the ground watched as the small dot slowly moved inward from Sol’s limb. Here in Northern Ohio, transit watchers were treated to the beginning of the show. Much of the nation missed out entirely, cloud cover already in place at dawn!
NASA’s Solar Dynamics Observatory, a spacecraft, is unaffected by Earth’s pesky atmospherics and its technology produces some very dramatic images. One of my favorites shows Mercury about to cross between the satellite (us) and the Sun’s glowing photosphere; the planet has the active solar atmosphere as backdrop. Planet Mercury is 3,030 miles in diameter, not much bigger than Earth’s Moon, and looked every bit as tiny as it is compared with our nearest star!
Today’s transit of Mercury took place over several hours. For us in Northern Ohio, the transit began at about 7:12 AM Eastern Daylight Time with the Sun barely up. Midpoint of Mercury’s passage was at 10:57 AM, and the transit ended at 2:42 PM. Because of the orbital inclinations of the inner planets, the alignment needed to produce a transit of Mercury happens only about 13 times per century making even a glimpse of the event something special. After today’s, the next transits of Mercury will take place in November 2019, November 2032, and November 2049.
At least we won’t have to wait for so long as we must for the next transit of Venus — that happens in December 2117.