Observing Sunspots

If you’ve ever wanted to see sunspots, now’s the time! Our "Daytime Star" is at its long anticipated sunspot maximum this year, with its visible surface peppered much of the time with dark spots of various sizes. Watching them develop and move across the face of the Sun from day-to-day as it slowly rotates is a fascinating activity. But extreme caution is required in doing so due to the overwhelming solar radiance.

Utmost care is necessary in observing the Sun. Even the darkest pair of sunglasses will not protect you. They may filter its visible light, but harmful ultraviolet and infrared rays will still get through. One traditional recommendation is looking through a #14 welder’s filter. Better is an inexpensive and safe pair of "Eclipse Shades" similar in construction (only!) to the 3-D glasses being used in theaters, and available from Scientifics. For up-close views of sunspots, binoculars and telescopes are recommended. These will show that the spots have a dark inner core called the umbra surrounded by a lighter halo known as the penumbra. However (and here especially), proper filters are an absolute must to avoid serious eye damage or blindness! And the filters must be of the type that fit over the front of a telescope or both binocular lenses and NOT over their eyepieces. Many inexpensive small telescopes (especially imported ones) have an eyepiece filter marked "Sun" on it. These are absolutely deadly and often crack due to the intense heat being focused by the telescope itself. Stopping most of the light and heat of the Sun before it enters an instrument is the only safe and sane way to view it directly. There are a number of sources for such optical solar filters, one of the best being Thousand Oaks Optical (click on the “solar filters” icon).

Another safe—though not as effective—way to view sunspots is to project the Sun’s image through a pinhole in a piece of cardboard and onto a white sheet of paper or card stock. The projected image will be quite small depending on the hole size and how far back the screen is placed, but it will show the larger sunspots. A similar scheme called "eyepiece projection" is sometimes used with telescopes themselves but has been known to crack eyepieces from the intense heat if prolonged for too long. And here, as any time a telescope is being used for solar viewing, its finder scope must be capped since it can also cause damage!

Many of the larger active sunspots are now sending flares in our direction as they approach the center of the Sun’s disk, disrupting electronic communications and causing displays of the Aurora Borealis (or Northern Lights). A very valuable web site for monitoring the Sun’s activity and expected auroal displays is SpaceWeather. It shows a daily real-time image of the Sun—which is one way of observing sunspots that’s absolutely safe (and independent of sky conditions)!

—James Mullaney
Former assistant editor at Sky & Telescope magazine & author of nine books on stargazing.