The day before John F. Kennedy’s election, two teenagers played hooky to watch Mercury pass in front of the sun. These were the junior high’s science nuts. Mike already had a fantastic ham radio setup. The other had memorized celestial data as if they were baseball cards: that was me.
Through my small telescope we saw a black dot that looked like a runaway sunspot, moving a hundred times faster than the sun’s rotation. This was Mercury, its nightside facing us. We used a solar filter to keep our eyes from turning to carbon. It was the kind you screwed into the eyepiece to reduce the light at the last moment, just in front of your eyeball. Its dark glass got fiercely hot. Nobody uses those dangerous little filters anymore. Now a large disk sits in front of the tube, blocking the sunlight before it becomes intensified by the telescope. You no longer need to risk frying your eyeballs to see Mercury flitting around the sun like a moth.
This month Mercury will again transit the sun’s face, as it does some 13 times a century. But most of us won’t see it, not this time. Unlike total solar eclipses, visible from just a narrow strip of Earth, everyone sees a Mercury transit as long as the sun is shining at their location. Unfortunately, we’ll be on the wrong side of the planet, facing into the night, just as we were for the last transit, in November 1986. And for the time before, in November 1973. And for the time before that, in May 1970. Come to think of it, the transit Mike and I saw in 1960 was the last one visible from the mainland United States.
The reason? Plain bad luck. But the list of dates does serve to expose Mercury’s pattern: the transits happen exclusively in May or November, when the tilted plane of Mercury’s orbit lines up with ours.
You can see this transit if you live in Hawaii or will be visiting Asia. From Hawaii the Mercurial disk will cross the sun near its southern edge during the hour before sunset on November 5. What you’ll see is exciting--the actual orbital movement of the innermost planet. The sun sets with Mercury still in front of it!
The rest of us might look ahead to the transit of November 1999, but it’ll hardly be worth the effort. Mercury will barely graze the sun. Then our astonishing bad luck continues, with the May 2003 transit hidden as well. All of this means that people in the Eastern Hemisphere have caught every one.
If it’s any consolation, on November 13 and 14 Mercury will make a magnificent conjunction with dazzling Venus. Look low in the southwestern sky after sunset. But if hunting for planets in twilight’s glare sounds too much like work, try the total lunar eclipse on November 28. Seen from the entire United States, Earth’s shadow first invades the moon at 11:40 P.M. Eastern time. Totality begins 80 minutes later.
If your heart is still set on a transit, we’re finally dealt a good hand in November 2006. That event, however, will be overshadowed by a transit the world hasn’t seen since 1882. Every 105 or 122 years, a pair of Venus transits--spaced eight years apart--grace the sky. Bigger and closer to us than Mercury, Venus can be seen crossing the sun with just the naked, albeit protected, eye. Millions will watch on June 8, 2004 (but not us, again), and June 6, 2012 (finally!). And I’ll bet Mike, wherever he is, will be one of them.