The gray band is the annular eclipse visibility zone. Anyone within it will see the moon completely cross over the sun. If you're on the red line, the moon will pass exactly over the center of the sun leaving a symmetrical ring of sunlight. Other locations in North America will see a partial eclipse except the East Coast. Click map for interactive version. Credit: NASA map / overlays: Bob King
It’s almost here. Time to get ready for Sunday’s annular eclipse of the sun, the first one visible from the U.S. since 1994. Anyone living in the approximately 150-mile-wide band from southern Oregon to northern Texas will see the moon’s black disk silhouetted squarely against the sun’s.
Folks like me, who live outside that band, will witness a partial eclipse. For Duluth, Minn., the moon will cover a maximum of 63% of the sun. Chicago gets a bit more – 69% – and Dallas 94%.
Clicking on Duluth, Minn. on the NASA website map reveals eclipse details. A magnitude of .633 means 63.3% or nearly 2/3 of the sun is covered during maximum eclipse. Click map to read weather prospects for cities located along he eclipse center line. Credit: NASA
To find out circumstances of the eclipse for any town in the U.S., Canada and other regions, click on the map at top. It will take you to NASA’s eclipse website, where you can zoom in to find your town. When you click again on the town name, an info box pops up with times and “eclipse magnitude”. This is the amount of sun covered for your A magnitude of 0.59 means 59% of the sun will be blocked by the moon at maximum eclipse. The times shown in the bubble are Universal Time (UT or Greenwich time). For Eastern Daylight subtract 4 hours, Central 5 hours, Mountain 6 and Pacific 7 hours. In the example, the eclipse starts at 00:17 UT May 21. Subtracting 5 hours we get 7:17 CDT May 20.
94% of the sun will be covered by the moon during this Sunday's eclipse. Illustration: Bob King
Annular eclipses happen when the moon passes directly in front of the sun just as it does during a total solar eclipse – with one difference. Normally the moon is big enough to completely cover the solar disk, but during this eclipse, it happens to be farthest from Earth and hence a bit smaller than usual. Small enough that it leaves an annulus or ring of sunlight remaining at maximum eclipse.
During a total eclipse (left), the moon is close enough to Earth to cover the sun and casts a shadow called the umbra on Earth. An annular eclipse happens when the moon is farther from Earth than normal. The antumbra defines the path of annularity.
Since some portion of the sun remains visible during the entire eclipse, it’s important to use a safe solar filter to protect your eyes if you plan on watching the event. You can find out where to purchase a filter in this recent blog I wrote on the topic.
I’ve seen two annular eclipses in my time and enjoyed them both immensely. Sure, it’s not the same as a total, where you can stare at the sun directly and watch pink flames lick its circumference beneath a quivering corona. But make no mistake, there’s still plenty to see and enjoy during this eclipse.
Here’s what to watch for with naked eye, binoculars and small telescopes. Again, I can’t emphasize enough how important it is to do your looking through a safe solar filter:
* Daylight perception – When about 75% or more of the sun is covered, you’ll notice a change in the quality of daylight. The sky will be darker and a steelier shade of blue than before the eclipse.
* Weird shadows – Again, in places where about 3/4 of the sun will be covered, the quality of your shadow will change from soft and fuzzy-edged to sharp as the disk of the sun narrows to a thin arc.
Simulated view of moon's edge approaching a sunspot group. Background image: NASA
* The serrated edge – For those with small telescopes, take a look at the silhouetted edge of the moon against the sun. If you look closely, you’ll notice it’s irregular in places like a serrated knife. Those are the tops of mountains and crater rims seen in profile. While an interesting sight in itself, it gets even better (see farther down).
* Sunspot hide and seek – If the sun has any sunspots – very likely – it’s fun to watch the moon’s edge approach, slice into and then cover the spots. See if you can tell which is darker – the silhouetted moon or the dark sunspot cores called umbrae.
Mountains "biting" into the edge of the sun (lower left) during annularity. Credit: W. Van Kerkhoff
* Sticky mountains – For anyone within the annular zone or very close to it, the mountains along the moon’s edge will appear to “stretch” and briefly “stick” to the inner circumference of the sun, breaking it into short segments.
This wonderful sight happens for several seconds at second and third contacts and is caused by atmospheric effects on the moon’s bumpy profile.
Second contact occurs the moment the entire moon is visible against the sun. Third contact occurs the moment the leading edge of the moon touches the inner edge of the sun as it exits the disk. During a total solar eclipse, the same mountains create the sparking “diamond ring” effect.
The Ring of Fire seen during maximum eclipse. Credit: Sancho_Panza
* Ring of fire effect -For many this will be the climax of the eclipse when observers in the path of annularity will be able to see the moon surrounded by a fiery ring of sunlight for about 4 minutes. Be sure to look take your eye away from the scope for a minute to appreciate the sight with the (filtered) naked eye. It’s eery to see nothing but a ring up there, almost like you’re living on a planet orbiting a distant sun.
Venus should be easy to see during the eclipse as long as the sky's transparent all along the eclipse path. Albuquerque is shown here. Created with SkyMap
* Planetary bonus – For those in the annular zone or near it, the sky should get dark enough to see Venus high above the moon in the western sky. Those watching from California and especially from Japan and China, where the sun will be much higher, can also look for Jupiter and Mercury below the it.
* Live Webcast – If you’re not able to see the annular eclipse, check out AstronomyLive’s live webcast.
One of the best things about an annular eclipse is seeing how quickly the moon glides from one side of the sun to the other through a telescope. Unless you witness a total eclipse, you’ll probably never feel it move faster. Now let’s just hope it’s clear. Good luck to all of you!