Partial Solar Eclipse of April 8, 2005

By Evan H. Zucker

Other eclipses

Click on the images to get a large version.

Alex Zucker looking through Eclipse Shades
Alex Zucker viewing through Coronado Personal Solar Telescope
Mid-eclipse 14:53 UT
Sunspotter solar telescope

My 7-year-old son Alex and I successfully observed what may be the smallest solar eclipse anybody has every seen: 0.0% obscuration according to my sources.

We drove about 30 miles south of our house to San Ysidro, California. We stopped at a dirt pull-out adjacent to the South Bay International Wastewater Treatment Plant, about 1/4 mile north of the Mexican border, at 32-32.7N, 117-4.1W. I had calculated that this was the furthest north any portion of the partial eclipse could be seen on the Pacific Coast. I could have driven 60 miles east of San Diego, where the eclipse would reach a more respectable (and observable) magnitude of 1.0% and obscuration of 0.1%, but I liked the idea of trying to observe a smaller maximum eclipse than anybody has ever before seen.

Normally I would rely upon Fred Espenak's tables for eclipse contact timings and magnitudes, but so little of this eclipse was visible from California that Fred did not include any California locations in his eclipse bulletin.

According to the Javascript Eclipse Calculator v3.2b2 by Chris O'Byrne and Stephen McCann, first contact was scheduled for 14:45:25 PDT (21:45:25 UT), mid-eclipse at 14:50:52, and fourth contact at 14:56:32, with a maximum magnitude of 0.23% and an obscuration of 0.0%.

According to TheSky software, first contact would be at 14:43, mid-eclipse at 14:52, and fourth contact at 15:01, with a maximum magnitude of 0.6% and an obscuration of 0%.

Obviously, for an eclipse to be visible it has to be greater than 0% obscuration, but from our location the eclipse was so small that the percentage of the sun's disc that was obscured must have been smaller than 0.05%, and so it rounded off to 0.0%. Perhaps somebody who is better at math than I can calculate the actual obscuration of an 4eclipse with a magnitude of 0.23% or 0.6%.

I had a Sunspotter solar telescope and a Coronado Personal Solar Telescope. The sky was clear overhead (some clouds on the horizon), and the winds were breezy. (The San Diego Clear Sky Clock, which my company, Totality Software, sponsors, was far more accurate in predicting clear skies than the typically inaccurate National Weather Service, which had forecast partly cloudy.) There was no one in sight except for a couple of workers on the other side of a rather large fence bordering the wastewater treatment plant. A Border Patrol SUV passed by at one point, and the officer honked at us, apparently as a greeting. (I guess we didn't look like illegal aliens.)

I could easily see one sunspot group in both telescopes, although Alex could only see it on the Sunspotter. Through the PST I could discern a large and small component to the group, even more clearly than in this SOHO photo. Through the PST I could easily see a number of prominences, consistent with this far more detailed SOHO photo.

At a normal solar eclipse -- meaning an eclipse where the magnitude would reach some reasonable level, say above 5% or 10% -- I can usually make out first contact within 1 to 2 minutes of the scheduled time. However, it doesn't work that way for 0% eclipses because the moon is approaching the sun at such a slight angle. I was not able to discern first contact through the PST until 14:48 which was 2.5 or 5 minutes after the scheduled time, depending upon which of the two sources you are relying upon.

Mid-eclipse was at 14:51 or 14:52 (3 or 4 minutes after I saw first contact), and the eclipse was most evident at that time. Both Alex and I were able to make out an extremely small notch on the right side of the sun (as viewed through the PST) to the upper right of the sunspot group. It was visible in both the PST and the Sunspotter, but it was definitely easier to see in the PST because of the sharper image. Neither of us could see the notch using with our naked eyes protected by a Mylar filter or No. 14 welding glass. Unfortunately the portion of the photosphere where first contact occurred did not have any visible prominences or else I might have been able to see the moon's edge a little earlier.

By 2:55 PM (3 or 4 minutes after mid-eclipse), I could no longer make out the lunar notch. Thus, based upon our visual observations, our eclipse lasted a total of 7 minutes, as compared with the 11 or 18 minutes theoretically visible from our location.

I haven't done a lot of research, but I would have to imagine that it's relatively rare for the edge of the penumbral path to pass through a major city like San Diego. Consequently, not many people have had the opportunity to observe such a small magnitude eclipse without significant travel, and not many people are going to travel a significant distance just to get to the very edge of the penumbral path. The only person I know who has done so is Glenn Schneider in 1976.

However, Glenn's eclipse was a whopping 0.4% obscuration. I could say it was infinitely larger than our 0.0% eclipse -- after all, 0.4 divided by 0.0 is infinite, or undefined -- but, if I assume for the sake of discussion that my eclipse was 0.049%, then Glenn's eclipse was 8 times larger than mine. Having seen the photos on Glenn's web site, I can definitely say that his eclipse was significantly deeper than ours. Alas, I did not have a camera hooked up to a telescope, and the sun was far too bright to photograph without a strong neutral density filter (in contrast to Glenn's sunrise eclipse, which did not require an artificial filter), and I did not have an ND filter with me. (All my eclipse equipment was destroyed in the October 2003 San Diego wildfire. I bought the Sunspotter on eBay last month and the PST at Scope City two days ago.)

I did take some photos of the solar image on the Sunspotter at mid-eclipse, when Alex and I could just barely discern the lunar disc in the Sunspotter image, but I cannot see it in the photos. (I will post them on my web site shortly.) I suppose that is some degree of evidence of how slight the eclipse was because if it had been a 0.4% eclipse I have no doubt the lunar notch would have been visible in those photos.

Glenn and I (and our observing companions, Craig Small and Alex Zucker) are the charter members of the 1% Eclipse Club. Has anybody else ever seen a solar eclipse with a maximum obscuration of 1% or less?