Stellar Paparazzi

Last Thursday (23 Oct 2014), North America was treated to a partial solar eclipse. This occurs when the moon passes between the Earth and Sun, casting its shadow onto part of our planet. For observers in the California Bay Area, the moon blocked about 40% of the sun. Partial eclipses are fairly common (2-5 times a year, somewhere on the Earth), but they can still be quite interesting to observe.

The first two eclipses I recall observing were on 11 July 1991 and 10 May 1994. The exact dates are not memorable; they’re just easy to look up as the last eclipses to pass through places I lived ! But I do remember trying to observe them with some lackluster-but-easily-available methods of the time. Pinhole projection seems to be most commonly suggested, but I never got good results from it. Using a commercial audio CD (which uses a thin aluminum coating) had worked a bit better for me, but this is highly variable and can be unsafe.

I got more serious about observing in 2012. For the annular solar eclipse and transit of Venus which occurred that May/June, I made an effort to switch to higher-quality methods. My previous blog post goes into detail, but I first tried a pinhead mirror projection, which gave this better-but-not-awesome result:

(In fairness, the equipment fits into a pocket, and it was a last-minute plan to drive 6 hours, round trip, for better viewing.)

For the transit of Venus a few days later — a very rare event that occurs only once ever 105 years — I switched to using my telescope for even better quality. You don’t look through it, but instead use it to project a bright image of the sun onto another surface for viewing.

I was excited to catch last week’s eclipse because there was an unusually large sunspot (“AR2192”) that was going to be visible. It’s one of the larger sunspots of the last century, so it seemed like a bit of an historic opportunity to catch it.

This time I took the unusual step of observing from indoors, looking out a window. This basically allows for projecting into a darker area (compared to full sunlight), resulting in better image contrast. Here’s a shot of my basic setup — a Celestron C8 telescope, with a right angle adapter and 30mm eyepiece, projecting the full image of the sun (including eclipse and sunspots) onto the wall of my home:

The image was obviously quite large, and made it easy to examine details of the large sunspot AR2192, as well as a number of smaller sunspots that were present.

I also switched to a 12.5mm eyepiece, allowing for a higher magnification, which made the 2-tone details of the main sunspot even more obvious. The image is a little soft, but not too bad — it’s hard to get sharp contrast at high zoom, and the image was noticeably wavering as a result of thermal convection withing the telescope and atmosphere. (Not to mention that a telescope mounted on carpet in a multistory building isn’t the epitome of stability — I had to stand very still or else the image would shake! Not ideal, but workable.)

As with the transit of Venus, it’s fun to compare my picture with that from NASA’s $850-million Solar Dynamics Observatory.

Observing this sunspot wasn’t nearly as exciting as the Carrington Event of 1859, but it was still a beautiful sight to behold. I’m definitely looking forward to the 21 August 2017 eclipse, which should be a fantastic total eclipse visible from a wide swath of the US!

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