On Monday May 9, the planet Mercury will be out in front of the sun nearly all day. Instead of hiding in its glare, the innermost planet will pass directly across the sun’s face in an event called a transit. Our sun is big and Mercury is both small and far away (52 million miles / 83.6 million kilometers), so it takes 7 1/2 hours for the little orb to travel from one side of the solar disk to the other.
Mercury is too small to see silhouetted against the sun with the naked eye and sun filter alone, so you’ll need a scope. Anything that magnifies around 30x that’s equipped with a safe solar filter will do the trick. The planet will look like a small black dot similar to a sunspot but perfectly circular and black as midnight. No scope? If you happen to be in the Duluth, Minn. area maybe we can help.
I along with my colleagues from the Arrowhead Astronomical Society will be out in front of the Marshall W. Alworth planetarium on the University of Minnesota-Duluth campus for the transit duration. The forecast is perfect — mostly sunny skies with the temperature in the mid-50s. Some of us will be there as early as 6:15 a.m., but most, including myself, will set up shop between 9 and 10 a.m. Mercury enters the solar stage around 6:15 a.m. CDT and exits at 1:42 p.m.
I’d love it if you stopped by. With all those scopes, you won’t be able to miss us. Stay for 5 minutes or stay for an hour. We’ll be there till transit end.
When you watch the transit, you’re witnessing in real time how professional astronomers discover the majority of extrasolar planets: they measure the drop in light as a planet passes in front of its host star. Measuring the depth in the dip in brightness, scientists can determine the object’s diameter. From the time between successive transits, they measure its orbital period or how long it takes to go around the star. With the orbital period known, Kepler’s Third Law of Planetary motion yields the average distance between planet and star.
The table below lists the times of the event across the four time zones of the continental U.S. If clouds prevent you from viewing this cool and rare event, Italian astronomer Gianluca Masi will live stream it from his telescope starting at 6 a.m. CDT (11:00 UT) Monday. For more detailed information, check out this earlier blog on the topic. And though I’ve said this before, let me caution again never to look directly at the sun without a safe, secure solar filter.
I hope to see you tomorrow!
|Time Zone||Eastern (EDT)||Central (CDT)||Mountain (MDT)||Pacific (PDT)|
|Transit start||7:12 a.m.||6:12 a.m.||5:12 a.m.||Not visible|
|Mid-transit||10:57 a.m.||9:57 a.m.||8:57 a.m.||7:57 a.m.|
|Transit end||2:42 p.m.||1:42 p.m.||12:42 p.m.||11:42 a.m.|