If you know any backyard astronomers, you’ve heard them rant and rave about the upcoming transit of Mercury. It is purportedly the biggest celestial event of the year. It’s when the smallest, speediest planet partially eclipses the Sun. And it’s kind of rare. The last happened ten years ago. The next two will occur in November 2019 and then November 2032.
Honestly, I’m not at all sure that this will pan out for the vast majority of people. So let’s look at the positives and negatives of Monday’s transit.
First, the positives: It’s cool that a planet can partially eclipse the Sun. And the whole concept is understandable. In our modern era of esoteric celestial happenings, we hear words like exo-planets and dark energy, yet here we have an event whose only terms are planet and Sun. A planet passes in front of the Sun: easy. Who doesn’t like easy?
Moreover, this will be visible from our neck of the woods. It lasts over seven hours, with the middle of the transit happening at around 11 a.m., when the Sun is high. By contrast, the last one (in 2006) was only seen around the Pacific Ocean.
Negatives: You can’t look at the Sun – at least, not if you value your eyesight. So you need eye protection. But even that is not enough. Unlike the transits of Venus in 2004 and 2012, a Mercury transit cannot be seen without a telescope. And it can’t be an ordinary telescope; it has to be equipped with a safe solar filter. Do you own such a thing? I didn’t think so.
Unless you have a friend who has one, and he or she’s not working or at school during the day on Monday, your best bet is to phone your local astronomy club. Around here, the Mid-Hudson Astronomy Association will set up the correct instruments on the promenade in front of the Coykendall Science Building at SUNY-New Paltz, starting at 10 a.m. on Monday, May 9.
As for spectacle, this is a bit esoteric. Mercury is only 12 arc-seconds wide. It will look like a dot. But it will slowly change position during the transit, starting in the early morning and continuing until late afternoon.
Mercury transits have an interesting pattern. They usually happen in November, but occasionally in May, and during no other month. On average, there are 13 Mercury transits per century. This one is a bit unusual because Mercury will cross the Sun’s face not near its edge, but almost centrally. Also, this time around, Mercury is about as close to Earth as it is possible. So although it’s still tiny, it’s about as large as it ever gets.
A May Mercury transit is always followed in three-and-a-half years by a November one. So if it’s cloudy on Monday and you really are itching to see Mercury cross the face of the Sun, you won’t have particularly long to wait.
Want to know more? To read Bob’s previous “Night Sky” columns, visit our Almanac Weekly website at HudsonValleyAlmanacWeekly.com.