The Annular Eclipse of May 20 2012

Being the second major solar eclipse event of 2012, the annular eclipse of May 20, 2012 is sure to bring about some impressive photographs as the moon passes in front of the sun. Unlike typical solar eclipses, annulars constitute a niche in astronomical classification for eclipse not only because of their rarity, but mostly because of their peculiarity. An eclipse, loosely defined, occurs when the moon passes in front of the sun, leaving a certain place on earth with no or some part of the sun, as seen by inhabitants of a region. The moon literally blocks out part of the sun for observers. However, depending whether the moon is at apogee and perigee can help define whether such an event will be annular or not. As defined in Matthew Winter's Astronomical Events: Eclipses, Transits, Occultations and Conjunctions, we get a good picture on the elements of an annular eclipse.

It [an annular solar eclipse] is defined as ‘a solar eclipse in which the Moon's antumbral shadow traverses Earth (the Moon is too far from Earth to completely cover the Sun). During the maximum phase of an annular eclipse, the Sun appears as a blindingly bright ring surrounding the Moon,’ from NASA’s Glossary of Solar Eclipse Terms. Annular eclipses are straightforward as well; the moon is fully inside the Sun’s disk, but does not cover it. This is because the moon is at perigee. The closer the earth to the moon, the more frequent the annular eclipse. The sun appears as a great ring, because the moon’s orbit is not completely circular, rather it’s an ellipse that travels in an oval. Unfortunately, the Sun’s corona is lost, but a few phenomena occur; annular eclipses only produce shadow bands, but are usually hard to see, even if any occur. It cannot produce Baily’s beads or the diamond-ring affect, because those can only happen under complete totality. So, on occasions, shadow bands will come into view, but don’t count on it. They’re blurry and difficult to relate to if you see any.

In short, annular eclipses have only one important criterion that must be met in order to form such an event: the moon must be at perigee, or farthest from the sun; only then can the sun be seen as a complete ring, which was named accordingly. (Annulus is the Latin word for "ring"). 

Visibility for the May 20, 2012 eclipse

Statistics for this eclipse, the visibility and frequency of others of its kind, are great. Visibility entails where the event will be able to be seen: from Eastern China across the Pacific Ocean to the Southwestern States are among the multitude of places that spectators will be able to witness the eclipse. "In the United States, the eclipse begins at 5:30 pm PDT and lasts for two hours. Around 6:30 pm PDT, the afternoon sun will become a luminous ring in places such as Medford, Oregon; Chico, California; Reno, Nevada; St. George, Utah; Albuquerque, New Mexico, and Lubbock, Texas. Outside the narrow center line, the eclipse will be partial. Observers almost everywhere west of the Mississippi will see a crescent-shaped sun as the Moon passes by off-center," Spaceweather.com comments. The point of greatest visibility will take place just south of the Aleutian Islands in the North Pacific for five minutes and forty-six seconds. This will be the place where the ring, or annulus, will be seen the greatest.

Taking part in Saros Cycle 128, the annular eclipse of May 20 2012 repeats every eighteen years and eleven days, altogether containing 73 events. "Solar eclipses of Saros 128 all occur at the Moon’s descending node and the Moon moves northward with each eclipse. The series began with a partial eclipse in the southern hemisphere on 0984 Aug 29. The series will end with a partial eclipse in the northern hemisphere on 2282 Nov 01. The total duration of Saros series 128 is 1298.17 years," NASA's eclipse website propagates. For more about Saros 128, NASA's eclipse website's database is superb. More information about Saros can be found there as well. 

When viewing this annular eclipse, like any other solar eclipse, it is important that one realizes the safety precautions that need to be made known. Do NOT attempt to look at the sun without the appropriate filter (or even sunglasses), because of the high risk for blindness. Many astronomical websites have stores where you can buy the appropriate equipment for viewing the sun.

Get your own valid XHTML YouTube embed code

Recommended links for further information

NASA’s eclipse web site http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2012May20Agoogle.html

Detailed weather reports for this eclipse at Jay Anderson’s web site, http://eclipser.ca/

Descriptions and interactive maps by Bill Kramer at http://www.eclipse-chasers.com/tseNext.php?TSE=ase2012d

Interactive Google map by Xavier Jubier at  http://xjubier.free.fr/en/site_pages/solar_eclipses/ASE_20120520_pg01.html.

National Astronomical Observatory of Japan: http://naojcamp.mtk.nao.ac.jp/phenomena/20120521/summary-en.html

U.S. Naval Observatory and HM Nautical Almanac Office: http://astro.ukho.gov.uk/eclipse/0132012/

Occultation of Mercury: October 28, 2011

The third and final occultation of 2011, Mercury's occultation this October 28, 2011 will be an astronomical treat for those in Australia, New Zealand, & southern Oceania. Although it was a true fact that each of these occultations this year (2011) were poor to view, 2012 brings yet another smorgasbord of events, as listed at the end of this article.

"It will be observable after sunset from French Polynesia," the Transits Page writes in correspondence of the event. From there, the whole southern Oceanic hemisphere, centered in Australia & New Zealand, will see Mercury occult, right through the center of the Moon. This is a "central one," referring that Mercury will pass through the center of the Moon. Basic information is below.

Greatest Occultation = 2011-Oct-28 02:11:32 TT

Occulted Planet = Mercury

Occultation Series = 7560

Member = 1 of 1

Elongation from Sun = 18° E

Moon illuminated fraction = 2 %

Lunar Magnitude = -5.9

Planetary Magnitude = -0.3

Gamma = -0.21966

Gr. Longitude = 158° 31.4' E

Gr. Latitude = 32° 43.0' S

Gr. Duration = 94m 10.3s

ΔT = 66.64s

Credit: the Transits Page

This occultation occurs in the 7560 series (similar to the Saros of eclipses), and will be the best to view. Mars' Tahitian occultation in July, and Venus' Mediterranean occultation in June both occurred with poor lunar conditions, but the moon will only be two percent illuminated this time! Mercury will pass swiftly - starting on the 27th of October at 23:56 UT and ending on the 28th at 04:24 UT - four hours and twenty-eight minutes total. Below is a picture of Mercury's entrance and exit passage at the green dot in the above picture (in between Australia and New Zealand).

Credit: Transits Page

Local Circumstances—Greatest Occutation

Longitude = 160° 42' 51" E

Latitude =  32° 08' 34" S

Elevation = 0m.

Greatest Occultation = 2011-Oct-28 02:16:20.4 UT

Altitude =  77.8°

Azimuth = 353.7°

  

            Calendar Date and Time          Planet           Sun     Limb

                Universal Time         Azi    Alt    PA      Alt      PA

Ingress    2011-Oct-28 01:29:10.9 d   39.2°  74.8°  102.4°   69.7°  290.8°

Egress     2011-Oct-28 03:03:56.2 b  311.7°  72.9°  287.7°   56.0°  290.4°

Duration    94m 45.3s

Mercury's occultation is hoped to be great - so watch the Moon, if you live in the area of occultation!

Welcoming Saros 156: July 1, 2011 Partial Solar Eclipse Pictures

A new Saros began yesterday at 08:39:11 UT. Even though nobody could see the eclipse (after all, 99% of the visibility was suspended over the ocean), nevertheless the moon blocked out 9.7% of the Sun. Taken by the Proba-2 satellite (by European Space Agency (ESA)), the below picture is a real picture of what happened yesterday. Although it does seen fake, it's the eclipse in a never-seen-before perspective.

Surprisingly, this was the only picture I could find on the eclipse. I guess it was the eclipse 'nobody could see!' By now, a few may be asking what Saros is? Starting a new Saros is rare - even though nobody could see the eclipse, it was still significant, but only under academic terms. As defined by a dictionary, Saros is simply:

The period of 223 synodic months, equaling 6585.32 days or 18 years, 11.32 days (or 10.32 days if 5 leap years occur in the interval), after which eclipses repeat but are shifted 120° west.

In Astronomical Events: Eclipses, Transits, Occultations, and Conjunctions, Matthew Winter writes this about Saros and the synodic (etc) months. Months will never be the same after reading this!

How are eclipsed formed? What are the requirements? There is a whole complex underlying structure that keeps eclipses in balance; where Saros comes into the picture. Saros determines when eclipses occur, where they occur, how they occur, why they occur, and much more. Despite this concept needs a paper for just it itself, Saros is easily understandable. Fred Espanak’s Glossary of Solar Eclipse Terms tells us what Saros is. ‘The periodicity and recurrence of solar (and lunar) eclipses is governed by the Saros cycle, a period of approximately 6585.3 days (18yr 11d 8h). When two eclipses are separated by a period of one Saros, they share a very similar geometry. The eclipses occur at the same node with the Moon at nearly the same distance from Earth and at the same time of year. Thus, the Saros is a useful tool for organizing eclipses into families or series. Each series typically lasts 12 or 13 centuries and contains 70 or more eclipses.’ 

First introduced by van den Bergh in 1955, numbering Saros cycles never appealed to anyone else before him. Currently, there are a total of 204 Saros cycles (thanks to van den Bergh) in use today with more than 20,000 eclipses (both solar and lunar) in a period of five-thousand years. Each of these eclipses happen during an eclipse season and in an eclipse season come types of periods (a fancy term for months). These four types of months (all with different day counts—a few are just by a matter of seconds!) all play their own role in Saros, which is what they are all comprised of. It’s not really mathematics, but numbers play a huge role in computing days and other essential matters. First, nodes and the nodical period play their part for eclipses to occur. A node is a general term which is used to express the intersection of two planes in space. The nodical period is the interval of time it takes the moon to make two successive crossings of either the ascending or descending nodes (ascending node: the moon crosses the ecliptic in the north, descending node is direct opposite—the south). The nodical period is 27.2122 days. After every year, the nodes move westward (which also referred to as lunar regression) on account of orbital motion, and must return to that same node before completing a complete orbit around earth. Nodes regress because the nodes result from the Sun’s gravity trying to pull the orbital plane of the moon into the plane of the ecliptic. As a result, the force causes the moon’s orbit to ‘wobble’ (nodical regression cycle) to the west. One ‘wobble’ takes 18.61 years. 

Secondly, the next month is the sidereal month. Although a strange name, its meaning is simple. A sidereal month is only the period of revolution of the moon around the earth, which is 27.321661 days. It’s not a perfect number of days; that’s why the phases of the moon shift a day on the regular calendar you have at your house. If a full moon’s on a Monday in January, then it will be on a Tuesday in February. Sometimes, two days will pass after the decimals (27.321661) build up to equal one day—every three to four months. 

The synodic period, another type of special astronomical month, is the length of time it takes for the moon to complete all its phases. This is from first quarter to first quarter of another month. Between the years 1600 to 2400 AD, the shortest synodic month is 29.27152 days and the longest, just a few hours later at 29.83262 days. But, on average the moon’s synodic month is 29.53059 days. Note that the synodic month is different from the sidereal month. The sidereal period does not include the time of phases, while synodic period does not determine the moon’s revolution alone. 

Lastly, comes the tropical month. Although seven seconds shorter than the sidereal month (27.32158 days), the tropical month is completely different than a sidereal month. The tropical month is the time taken for the moon to return to the same celestial longitude where it started its orbit. The sidereal month encompasses time of revolution—not the time to return to celestial longitude. So, both periods are totally different, yet so close to each other in time!

Once these terms are understood, then it is also necessary to understand Saros further by knowing what circumstances are necessary for the repetition of two eclipses; note they may not be similar. For one thing, the moon must be new (for solar eclipses) or full (for solar eclipses), and because the synodic period of the moon takes us about one-twelfth around the Sun; the earth, moon, and sun are not in the same alignment. To repeat the alignment, the moon must continue orbiting for two and one-sixth day. When this interval is added to the sidereal period, it turns out to be the synodic period—which you could also be called ‘the elongated sidereal period.’  While that is occurring, the moon must be at one of its node (either ascending or descending). So the chance that the moon is at one of its nodes and the correct position in the sky is rare. That’s why eclipses happen so rarely (and not every time it is at its nodes). So, 47 synodic months (1387.938 days) equals 51 nodical months (1387.822 days) which equal eclipse repetition! “In order for the repetition of an eclipse to occur, the same number of days must be contained within integral numbers of synodic and nodical months. Integers are whole or counting number such as -2, -1, 0, 1, 2, etc.” Astronomy.org tells us about the repetition of two eclipses. “The numbers 47 and 51 are integers, while the numbers of whole days within 47 synodic months equals the same number of days in 51 nodical months.” The period of that time equals 3.8 years, and represents an eclipse cycle. It does not mean the eclipse will be similar, though. But, because different Saros series are currently running, eclipses occur more than one every 3.8 years! 

Circumstances for the repetition of similar eclipses are another matter. Even though this section is mainly towards solar eclipses, it may apply to lunar eclipses as well. Along with cemented, known facts about the repetition of similar eclipses (the moon must be at one of its nodes, it must be new/full, etc.), to repeat similarly, the moon must be at a similar distance from the earth. This makes an eclipse repeat itself. Then we are introduced to another period: the anomalistic month. The anomalistic month is the time interval between the moon’s apogee (farthest) and perigee (closest); it takes the time of 27.555 days and is longer than the sidereal month, with only 27.321661 days. The line of apsides, ‘which is the major axis of the moon’s elliptical orbit...and...Is the longest line segment that can be placed within the boundary of an elliptical orbit’ as Astronomy.org defines, for the moon, the line of apsides finishes one revolution around the sky in the time interval of 8.85 years. Therefore, because the line of apsides completes one revolution in 8.85 years, the perigee and apogee continuously change their positions, creating uncertainty where the next apogee or perigee will be next, but we know that it will be ahead of its last location. Occasionally, the line of apsides will cause the moon to orbit faster on account of solar tidal forces, but this is not a dramatic effect; it is just thought of as another part of the moon’s orbit.

Finally, Saros enters the picture in full force. In order to meet conditions of similar solar eclipses, these things must occur: integral numbers of the synodic period, integral numbers of the nodical period, and integral numbers of the anomalistic month must all contain the same number of whole days. The result is Saros! Saros is a period of eighteen years, ten or eleven days (depending on whether it’s leap-year) and eight hours. 233 synodic months equal 6586.312 days which equal Saros! 247 nodical months equal 6585.375 days which equal Saros! (And) 239 anomalistic months equal 6585.538 days which equal Saros! So in conclusion, similar eclipses will repeat themselves in approximately 6585 days. However, the occurrence of the eclipse will be one-third day later (which is 0.321 day), shifting the location about 120 degrees west across the globe. That’s why we can get an eclipse in Antarctica in one year, and get another the next year (note that it’s part of another Saros cycle) we can get one over Alaska. More mathematics is required to go fully in-depth, but that is just too advanced for now. Saros is in incredible method!

July 1, 2011: Partial Solar Eclipse

As the month of June passes, the last eclipse of this month's eclipse trifecta comes to a close. You should that that this would be the grandest of all, but actually it will be one of the poorest eclipses viewed in years. The moon's shadow just passes over the South Atlantic Ocean/East Indian Ocean, so that no land is in view (only a tidbit of Antarctica: but who lives there!) Only people in ships or boats will be able to view the moon block out only 9.7% of the Sun's disk - which is nothing. Below is a visibility chart.

 

 

But, on a higher note, This eclipse starts a new Saros! This is incredible! EarthSky.com praises, "The Saros family of eclipses is famous for bringing about a succeeding eclipse every 18 years and 11 and 1/3 days – or sometimes 10 and 1/3 days – depending on the number of intervening leap years. Saros series 156 will present its last eclipse on July 14, 3237."

The greatest eclipse occurs at 08:39:11 UT with a magnitude of 0.096 at latitude -65° 09.5’, longitude +28° 38.9’. You can watch this live here (when the time comes). Below is an image of the moon's shadow passing over the earth.