Fun in the Sun

Posted by Michael Bakich
on Monday, November 20, 2006

On November 8, Mercury crossed the Sun’s disk in an event astronomers call a solar transit. Here at Astronomy magazine, the day was warm and clear, with only a few passing clouds blocking our view for brief periods. In our parking lot, the staff set up four telescopes — three with visual solar filters plus one Hydrogen-alpha scope. We observed from first contact, at 1:12 P.M., until the Sun set behind our building, shortly before 4:30 P.M. And we had a blast!

This event reminded me how much fun solar observing is, and not just during transits. Solar observing has some real advantages. First, it opens up the “other half” of the day. Of course, if it was cloudy last night and the morning is clear, this benefit is easy to see. But many times the real advantage is convenience — often logistics, fatigue, or how busy your day was affects your decision to observe at night or not. During the day, you don’t have to travel to a dark site (as if you could) or any site with “special” characteristics. Your driveway or backyard will do nicely.

Another advantage to solar observing results from the Sun being big and bright. Only have a small telescope? No problem. You’re not hunting a galaxy’s spiral arms at the edge of visual detection here.

I prefer to observe the Sun through a Hydrogen-alpha (Ha) filter. Not only is more detail visible than through a visual filter, but the Sun is dynamic in Ha wavelengths — things happen in real time. I remember many day-long observing sessions in my previous home in El Paso. I’d set up my telescope/filter combination early in the morning and let it track the Sun all day. It always amazed me how the Sun’s appearance could change so dramatically in only 8 or 10 hours. Often, friends would drop by and we’d watch prominences start as spikes, morph into loops, and end up as tree-shaped structures, all in only a few hours.

Ok, so Ha observing is great, but Ha filters also cost more than visual-light filters — in some cases, a hundred times more. Don’t despair. You’ll see lots of features through a visual solar filter as well. In fact, if you’re drawn to sunspots, you’ll see greater spot detail through a visual filter than through an Ha filter. Be sure to crank up the magnification to a point just below where the image really starts to degrade.

One final warning about observing the Sun — no, I’m sure you already know not to look directly at the Sun, especially through a telescope. But if you plan to do lots of solar observing, be sure to take precautions against sunburn.

On a hot July day, we almost can feel our skin crisping under the Sun’s rays. No further warning is necessary. The danger, however, comes on cool late spring or early fall days when the Sun still sits high in the sky, and its warmth feels great. Watch out! Even an hour under the Sun causes harm to skin, and you’re going to be spending a lot more time than that observing.

In El Paso, where I had a roll-off-roof observatory in my backyard, I’d retract the roof until it almost touched the telescope’s tube. This provided the maximum shadow within the observatory. I also fashioned a shading device to slip over the tube. It wasn’t complicated: I bought a large (3' by 3') piece of foam-core at an art supply store and cut out a hole the size of the telescope’s tube. Foam-core board is light, so when I slipped the shade over the tube, the extra weight didn’t affect the motor drive at all.

However you choose to observe the Sun, now’s the time to start. The Sun has been quiet the past few years. It just passed through a time (which happens every 11 years) called solar minimum. Sunspot numbers are down, and observers see fewer prominences and solar flares. On Earth, fewer aurorae (displays of northern or southern lights) occur.

During the next few years, we’ll approach solar maximum. During the last solar maximum, which stretched from the late 1990s to the early 2000s, the Sun was ablaze (pardon the pun) with activity. Some sunspots were so big you could see them through a filter with your naked eyes. Prepare for exhilaration!

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