August 29, 2016

AstroEvent: A Pacific-Spanning Annular Eclipse!

(Credit: NASA/A.T. Sinclair).

Live on the west coast of the United States? This weekend, you will get to witness a rare astronomical spectacle, the likes of which the continental U.S. has not seen since 1994.  On May 20th (21st across the International Date Line) an annular solar eclipse graces our fair planet. This eclipse is “annular” in the aspect that the Moon will be only 31 hours from an apogee of 406,450 kilometers around the time it passes between the Earth and the Sun, and thus will appear too small to cover the disk of our nearest star, as it normally does during a total solar eclipse. This is one of the two big ticket solar eclipses of 2012. Although not as dramatic visually, annular or hybrid eclipses (an eclipse that is total along a portion of the track and annular along another portion) are unique in the “ring of fire” effect that they create.

Contrary to what we first thought starting research for this post, annular eclipses are actually slightly more common than total solar eclipses… perhaps they just don’t get the press that total eclipses seem to garner. In fact, a look at our current five millennium epoch from 1999 B.C. to  3000 A.D. shows that of 11898 solar eclipses, 3956 were annular while 3173 were total, a difference of 33.2% versus 26.7%. The rest were partials or hybrid eclipses. Thanks to Jean Meeus and Fred Espenak for helping us out with this bit of info.

As we’ve discussed before, the trend is for total eclipses to become even rarer as the Moon recedes from the Earth. A little less than a billion years ago, the first annular eclipse occurred during the Tonian period in the Neoproterozoic era, and on some  far off date about 1.4 billion years from now, total solar eclipses will cease to be visible from Earth!

But back to our fortunate century. This particular eclipse has a magnitude rating of 0.9439, meaning that 94.39% of the Sun will be blocked for observers along the centerline. And although that seems like a lot, a 5% annulus is still dazzlingly bright, bringing the overall light intensity of the Sun down by only a little over 3 magnitudes of brightness… eye protection and proper precautions will be needed throughout all phases of this eclipse.

Maps courtesy of Michael Zieler at Eclipse Maps. (Click to enlarge).

The action begins as the partial phases touchdown in the Far East at 20:56 Universal Time (UT). The “annulus” of the eclipse then makes its appearance over southeastern China at sunrise on 22:06 UT, crossing over Hong Kong, Taipei, Osaka and Tokyo before headed out to sea. The path width is a maximum of 236.9 kilometers and reaches a maximum duration of 5 minutes and 46.3 seconds just south of the Aleutian Islands right around the time it crosses the International Date Line. Annularity then crosses the California/Oregon coastline just minutes before 0:130UT on May 21st, (the evening of the 20th locally) providing a stunning sunset eclipse across Nevada, Utah, Arizona, New Mexico, Wyoming and Texas. Areas as far east as western New York and Quebec may see the partial phases if clear.

The January 2011 annular eclipse as seen from Hinode. (Credit: NASA/JAXA).

So, what can YOU, the seasoned eclipse-chaser, or just the plain old apprentice, expect to see? Well, intriguingly, areas such as Bryce and the Grand Canyons, Four Corners, and the Very Large Array in Socorro, New Mexico all lie along the path of annularity. Eclipses such as this one aways bring out the time honored debate of “center vs graze-line”; a graze-line view allows for the elusive Baily’s Beads to shine down through the lunar valleys, while a centerline vantage point allows for maximum annularity. I would also point out that a centerline view gives you maximum flexibility in the event that you have to make a quick judgement call to race after clear skies!

And speaking of which, the US southwest also has something else going for it; said clear skies. While the monsoon flow is about to make the wet season wetter in the Far East, and the US Northwest is perennially cloudy, May generally makes for clear (if hot) climes for the US desert southwest. The University of Manitoba maintains a fine forecast site, complete with the latest satellite imagery and links to such essentials as the National Weather Service and Skippy Sky. As this goes to cyber-press on May 14th, it looks like those predictions may come to pass, with long range forecasts for clear skies over the US southwest and clouds over the Asian Far East. Follow us on Twitter for all of the late breaking updates, eclipse facts, lore, pics from the field and more!

A properly filtered Schmidt-Cassegrain telescope… (Photo by Author).

A low to the horizon eclipse can provide the background for some unforgettable shots. On the horizon, a DSLR with a 400mm lens set to 1/500th of a second or faster will help bring out the shadow outline of the horizon as well as the solar annulus; DSLRs allow you to play around a bit with the exposure prior to the event to judge which settings are best… but I wouldn’t slow down the exposure more than 1/200th of a second or so for risk of damaging the camera sensor!

Once again, another word about solar viewing safety (that’s how important it is!) Only view the annular eclipse via projection or by use of a safe, approved filter MEANT for looking at the Sun. Shoebox projectors are easy to construct, and Sky & Telescope has a great article in their recent June 2012 issue on how to build a “Sun-Gun”. The only thing I would add to this is that such a device is  best suited to a refractor or a Newtonian reflector; a Schmidt-Cassegrain can heat up quickly aimed at the Sun! Be sure and only use said projection method when aiming that DSLR at the setting Sun as well.

Orientation of the planets during mid-eclipse (created by the author in Starry Night).

As stated, many are surprised at just how bright only 5% of the Sun is… a broad blue daylight sky may take on a slightly deeper metallic-looking tone, as we noted observing the May 10th, 1994 annular eclipse from the shores of Lake Erie. Speaking of which, this eclipse is part of the same saros cycle 128, being rotated 120° degrees westward 18 years and 11 days later!

Another interesting phenomenon to watch for is the projection of tiny solar “crescents” along the ground as the sunlight streams through gaps in the leaves, lattice-work, etc. Often overlooked, this can make for a fun and unusual shot as crescents seem to “litter” the ground!

Daytime planet sighting is another possibility, as Venus, Mercury, and Jupiter all lay within 25° degrees of the annular-eclipsed Sun. (See the diagram above) Venus is particularly bright at magnitude -4.3 as it closes in on next month’s transit of the Sun; however, I would only attempt a daytime sighting of it by physically BLOCKING the dazzling Sun with an object (such as a hill or a peak of a house), even during mid-eclipse.

Recent solar activity as of May 12th… unfortunately, sunspot AR1476 will be leaving the solar disk in the day of the eclipse. (Photo by Author).

Another big question mark for eclipse day is the level of solar activity that may be present during the eclipse; we’re heading towards solar maximum, and an active Sun speckled with sunspots makes for an interesting photographic target. With the advent of hydrogen alpha telescopes, it may even be possible for viewers to “nab” the approaching Moon just as the eclipse begins, that is, if a well placed prominence reaches out at an opportune time! Early this May, sunspot active region 1476 came into view on the solar disk. The speed of the rotation of the Sun varies with latitude, with the equator rotating the fastest at about 25 days as seen from the Earth. Thus, anything entering view from the Earth past May 8th stands a good chance of remaining visible until May 20th if it remains active.

A friend of ours, Michael Zeiler over at Eclipse Maps, suggested a unique annular eclipse observation that, to our knowledge, has never been attempted; measuring the effects that the annular eclipse has on the elusive gegenschein at the solar antipodal point. A good place to try for this would be from the region of South Africa, assuming of course, your skies are dark enough to see the gegenschein to begin with! We’d welcome hearing from any takers of this unique photographic challenge!

In the realm of the strange and curious, it’s also worth noting the vantage points in low Earth orbit that will also witness the eclipse, such as the International Space Station and ESA’s Proba-2. Although the ISS will just miss annularity, Proba-2 should catch some deep partial phases. It may even be possible to catch the ISS transit the Sun during the partial phases from a narrow path across north east Asia and Sakhalin Island, Russia; CALSky is a great place to check for the particulars of such an unusual event days prior. It’s worth noting that Space X is planning on launching its Dragon capsule on May 19th headed to the ISS for a rendezvous around May 21st… will it be in the vicinity of the ISS for a “tandem solar transit” over the Siberian tundra during the eclipse?

Finally, stuck on the wrong side of the planet? Hey, we are too, and we expect there to be a wealth of live broadcasts across the web to console us on eclipse day; the following are events known of thus far;

- Panasonic’s live broadcast from the top of Mount Fuji, Japan.

Scotty’s Sky Channel on UStream.

-AstronomyLive and a collection of potential broadcasts.

-SLOOH’s site: (Note that their Canary Island and Chilean facility are out of range of this eclipse; they may will stream from an alternate location).

-TAM001, which may go live from Taipei, Taiwan via UStream,

-And the webcast from Hong Kong Observatory.

-A broadcast from the Central Weather Bureau in Taipei, Taiwan;

-Hydrogen-Alpha and White Light webcast of the eclipse courtesy of Sommers-Bausch Observatory in Boulder, Colorado;

-The SEMS broadcast courtesy of the University of North Dakota;

-A National Park Service broadcast from New Mexico;

-And finally (?) The Night Skies Network in Arizona.

Watch this space, as more webcasts are bound to make themselves known as eclipse day arrives…(broadcasting? Let us know in the comments!)

So, whether you’re in the path of annularity or only nab a portion of the partial phases, be sure to get out there and observe this month’s annular eclipse of the Sun. Consider this a harbinger of the main event on August 21st, 2017, when totality once again graces the continental US for the first time since 1979. With just a little over five years to go, it almost seems real now!


  1. We, Hong Kong Observatory and Hong Kong Space Museum, will provide a webcast from Hong Kong:


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