Friday, May 18, 2012

Rare Annular Eclipse

A rare "annular eclipse" of the Sun will occur in our area (northern California) in the late afternoon of May 20, 2012. I encourage you to see it, regardless of whether you can be within the narrow path where the "ring of fire" will be visible. (You will at least see a deep partial eclipse of the Sun, if you are in the western US.)

An annular solar eclipse occurs when the Sun, Moon, and Earth are lined up, but the Moon is farther than average from Earth, so it looks a bit too small to fully cover the Sun. Thus, if you are at one of the right places (see the below map), the Sun will form a ring, or annulus, around the Moon. It's a special form of a partial solar eclipse that's cool to see (though not nearly as dramatic and mind-blowing as a total solar eclipse). You can view a map showing the eclipse path in detail here.

Online, you can zoom in on it and find specific locations from which the eclipse will be visible. Click on the location to find times, etc. Note that "UT" is "Universal Time" (the time in Greenwich, UK), and right now it is 7 hours ahead of PDT. So, for example, I find that in northern CA, the middle of the eclipse will occur around 6:28 pm PDT on May 20 (1:28 am UT on May 21), and the annular phase will last about 4.5 minutes if you are near the "centerline." (Note: the non-annular partial phases will last much longer, a couple hours total: 5:20 pm to 7:34 pm, plus or minus a few minutes, depending on exactly where you are.)

The centerline (from which the Moon will appear perfectly centered on the Sun at mid-eclipse) is the orange curve, and the blue lines mark the northern and southern edges of the path of annularity; outside the blue lines, you'll see a partial solar eclipse but not a complete annulus or ring. So, try to go to a favorable location, within the brown swath. Choose your location wisely! You can find a summary graph that shows the percent cloudiness along the path here.

Oroville in CA (near Chico) has great odds, it seems: just 11% cloudiness. But it isn't super close to the centerline; Redding and Mt. Shasta are closer, but have somewhat worse odds. If you are between the two red lines, you'll see a complete "ring of fire." Outside that band, you'll see a partial eclipse, but not a full ring. You don't have to be right on the centerline, by the way -- just within the swath, if you want to see the "ring of fire," though it will last longer if you are closer to the centerline.

More info about weather patterns is given here at the following websites:

Have fun viewing the annular eclipse, but be sure to view it safely! And if you can't get to the path of annularity (the brown swath in the map), at least view the regular partial eclipse from wherever you happen to be at the time (late afternoon on May 20), if it's visible.

1 comment:

  1. Thank you for providing this helpful and informative page -- I needed some explanatory information yesterday evening (during the 5/20/12 annular eclipse) and found it here. Stunning background you've got going here, too -- is it original? Or perhaps something I should readily recognize and be embarrassed to even be asking about? Anyway, it's beautiful, and your explanations here are clearly and concisely presented.

    I meant to post this last night, but my PC crashed -- kind of its de rigueur thing these days, I guess. Anyway, thanks again for your help.