Diehard eclipse-chasers have been going through withdrawal because there hasn't been a total solar eclipse since July 2010. But they'll be happier this year, thanks to two "central" eclipses of the Sun: an annular in May (widely visible from western U.S. states) and a total eclipse in November that will send them flying off to Australia or the South Pacific.
Interestingly, up to seven eclipses of the Sun and Moon can take place in one year, and the last time that happened was 1982. (The fewest possible is four.) Yet any given year can have only two annular or total solar eclipses, as will be the case in 2012.
A solar eclipse can only happen at new Moon, when the lunar disk passes directly between us and the Sun. Conversely, a lunar eclipse occurs during full Moon, when our satellite passes through Earth's shadow. These alignments don't occur at every new and full Moon because the lunar orbit is tipped about 5° to Earth's orbital plane — only occasionally do the Sun, Earth, and Moon line up exactly enough for an eclipse to occur.
Three types of lunar eclipse are possible (total, partial, and penumbral) depending on how deep the full Moon plunges into or near the umbra, our planet's dark, central shadow. If it goes all the way in, we see a total lunar eclipse that's preceded and followed by partial phases. If the Moon skims part way into the umbra, only the partial phases occur. And if its disk passes just outside the umbra, it still encounters the weak penumbral shadow cast by Earth. Fortunately, no matter which type occurs, a lunar eclipse is observable anywhere on Earth where the Moon is above the horizon. (But there's still an element of luck involved: last December's total lunar eclipse was gorgeous from Los Angeles but completely unobservable from New York.)
Because the Moon casts a smaller shadow than Earth does, eclipses of the Sun require even tighter constraints on where you can see them. If the Moon completely hides the Sun, even for a moment, the eclipse is considered total. With its brilliant disk completely covered, the Sun's ghostly white outer atmosphere is momentarily revealed for anywhere from seconds to several minutes. However, this totality can only be viewed a narrow track or path on Earth's surface that's typically only about 100 miles (160 km) wide. Outside that path, about half the world is able to watch a partial eclipse as the Moon obscures a portion of the Sun.
Occasionally the Moon passes directly in front of the Sun but doesn't completely cover it. This odd-sounding situation is an annular eclipse, so-called because you can see a ring, or annulus, of sunlight surrounding the lunar disk. But an annular's path is likewise narrow, and outside of it observers see only a partial cover-up.
Below are brief descriptions of this year's eclipses of the Sun and Moon. You'll find more details on this website and in Sky & Telescope magazine as the date of each draws near. Times are in Universal Time (UT) except as noted.
May 20: Annular Solar Eclipse
Strange as it might seem, the fist eclipse of 2012 doesn't occur until the year is roughly half over. But it'll be something special: a ring eclipse that's observable from a wide swath of the American West. Read on to get the basics, or click here for a more detailed overview.
Because this event comes just a day after the Moon reaches apogee (the most distant point in its orbit), its black silhouette appears completely surrounded by the Sun's disk from a generously wide path that's at least 150 miles (240 km) across. This will be the first central solar eclipse visible from the United States in nearly two decades.
The event is first seen across Southeast Asia at dawn. Guangzhou in southern China sits within the eclipse track, as do Tokyo, Osaka, and Yokohama in Japan, along with Hong Kong and Taipei. Then the Moon's shadow races eastward across the Pacific, narrowly missing Alaska's Aleutian Islands before making landfall along the California-Oregon border. By then it's already late afternoon locally, and the farther east you are along the track, the more important it becomes to find a clear western horizon.
Many towns in southwest Oregon (such as Medford), northern California (Eureka, Redding), central Nevada (Reno), southern Utah (St. George), northern Arizona (Flagstaff) and New Mexico (Albuquerque), and northern Texas (Lubbock) lie within the annular zone. Sky & Telescope has compiled an list of predicted times for more than 40 communities within the path (12-hour clock or 24-hour clock).
A deep partial eclipse occurs to either side of the path of annularity, and most of North America will see at least a small bit taken out of the Sun that day. Click here for the predicted circumstances in Asia and Canada, and here for major cities across the United States. For weather prospects, see meteorologist Jay Anderson's comprehensive analysis.
June 4: Partial Lunar Eclipse
A central solar eclipse is often followed (or preceded) by a partial lunar eclipse a half lunation later, and so it is that the Americas get to see the full Moon partially engulfed two weeks after May's ringed spectacle. During June 4th's partial cover-up, a bit more than a third of the lunar disk slips across Earth's umbra. The event favors the same general locales as those having experienced annularity: eastern Asia and Australia, the Pacific, and western North and South America. In the U.S., go out before dawn and look low in the west-southwest. Mid-eclipse, at 11:03 UT, corresponds to 6:03 a.m. CDT, 5:03 a.m. MDT, and 4:03 a.m. PDT. Unfortunately, those of us in the Northeast are out of luck. Get more details in this eclipse preview.
November 13: Total Solar Eclipse
Syzygially speaking, the year's big event is a complete blocking of the Sun on November 13th. Once again the Pacific is favored — just as it was for totality in 2009 and 2010. (Don't read anything more into this trifecta than mere luck of the draw!) This time the Moon's shadow makes no landfall except for northern Australia, where thousands of "umbraphiles" plan to converge. Many paln to view from Cairns, a bit south of the path's centerline, where the Sun disk is totally covered for 2 minutes. A few cruise ships are setting sail for locations farther east along the track; at 22:12 UT, someone bobbing about 1,250 miles (2,000 km) east of Auckland, New Zealand, would be treated to the maximum extent of totality, lasting 4 minutes 2 seconds. Weather permitting, residents of eastern Australia and southernmost South America can look forward to seeing a deep partial eclipse.
November 28: Penumbral Lunar Eclipse
The fourth and final eclipse of 2012 is a barely-there affair during which the Moon skirts just south of Earth's umbra but well into its broad penumbra. Mid-eclipse is at 14:33 UT. Observers in eastern Europe and throughout Asia have a chance to see this fairly obvious shading in early evening after moonrise, and the same holds true for those in western North America in the predawn hours before moonset. The best seats run from Alaska down through Japan and China to Australia.
Looking ahead, 2013 will feature an annular eclipse in May (Australia lucks out again!) and a total-annular "hybrid" in November. The three lunar eclipses will be either partial or penumbral.