Observing the Transit of Mercury

Nov. 10, 2019: What will tomorrow’s transit of Mercury look like? Marek Nikodem has the answer. He watched the previous transit of Mercury (May 9, 2016) from Kcynia, Poland, and photographed the event at sunset:

Mercury is the black dot near the bottom of the sun. It’s pretty tiny. Mercury is only 1/194th of the sun’s apparent diameter. That’s why looking at the sun through ordinary eclipse glasses won’t work. You need magnification–50x or more is recommended.

A safe way to view a magnified image of the sun is the projection method. This illustration from the European Space Agency says it all:

Any telescope with a stabilizing tripod can be used to project an image of the sun onto a wall, screen or sidewalk. It’s perfectly safe as long as you don’t look into the eyepiece. Binoculars work, too, with the same precautions.

Or, just stare at your computer screen! Transit of Mercury webcasts: (1) Royal Observatory Greenwich, UK on Facebook; (2) Timeanddate.com from Stavanger, Norway; (3) Griffiths Observatory TV from Los Angeles

Get Ready for the Transit of Mercury

Nov. 8, 2019: One of the biggest astronomy events of the year is only days away: The Transit on Mercury. On Monday, Nov 11th, Mercury will pass directly in front the sun. The rare transit begins at 12:35 UT (7:35 am EST) and lasts for almost six hours. Mercury’s tiny form—jet black and perfectly round—will glide slowly across the solar disk, like this:

Tom-Polakis-mercury_transit_4_1462995969_lg

Credit: Tom Polakis of Tempe AZ made this movie of a previous Mercury transit on May 9, 2016. [more]


People in every continent except Australia can see at least a portion of the crossing. In the USA, the best place to be is on the Atlantic coast, where the entire transit will be visible. On the Pacific coast the transit will already be in progress at sunrise.

Warning! Do not stare at the sun during the transit. Mercury covers only a tiny fraction of the solar disk, so the sun remains as bright as ever. Eye damage can occur.

Ordinary eclipse glasses will keep your eyes safe, but they won’t do much to help you see tiny Mercury. The planet is only 1/194th of the sun’s apparent diameter. To watch this event, a safely-filtered telescope with a magnification of 50x or more is recommended. Don’t have a filter? No problem. Images of the transit may be easily projected onto a wall or screen through an unfiltered telescope. Just do not look through the eye piece.

Nothing beats a telescope equipped with an H-alpha filter. H-alpha filters are narrowly tuned to the red glow of solar hydrogen. They reveal the sun as a boiling inferno cross-crossed by dark seething magnetic filaments. On Nov. 11th, the tiny form of Mercury will navigate this starscape. Here’s a sample H-alpha image taken during the last transit of Mercury on May 9, 2016:

Paul Andrew took the picture from his backyard observatory in St. Margarets at Cliffe, Dover, UK. “The background prominence made Mercury look like it had a comet’s tail,” he says. More images may be found here and here.

Transits of Mercury occur only 13 times each century. The next one won’t occur until Nov. 13, 2032. Don’t miss this unusual event!

Solar Cycle 25 is Slowly Coming to Life

Nov. 1, 2019: Breaking a string of 28 spotless days, a new sunspot (AR2750) is emerging in the sun’s southern hemisphere–and it’s a member of the next solar cycle. A picture of the sunspot is inset in this magnetic map of the sun’s surface from NASA’s Solar Dynamics Observatory:

newspot_crop2

How do we know AR2750 belongs to the next solar cycle? Its magnetic polarity tells us so. Southern sunspots from old Solar Cycle 24 have a -/+ polarity. This sunspot is the opposite: +/-. According to Hale’s Law, sunspots switch polarities from one solar cycle to the next. AR2750 is therefore a member of Solar Cycle 25.

Shortlived sunspots belonging to Solar Cycle 25 have already been reported on Dec. 20, 2016; April 8, 2018; Nov. 17, 2018; May 28, 2019; July 1, 2019; and July 8, 2019. The one on July 8, 2019, was significant because it lasted long enough to receive a number: AR2744. Record-keepers will likely mark it as the first official sunspot of Solar Cycle 25. If so, AR2750 would be the second.

The increasing frequency of new cycle sunspots does not mean Solar Minimum is finished. On the contrary, low solar activity will probably continue for at least another year as Solar Cycle 24 decays and Solar Cycle 25 slowly sputters to life. If forecasters are correct, Solar Cycle 25 sunspots will eventually dominate the solar disk, bringing a new Solar Maximum as early as 2023.