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On Wednesday, July 22, 2009, there will be a very long total solar eclipse that will be visible from parts of India to China as well as through Japan’s Ryukyu Islands and to the Pacific Ocean where maximum eclipse duration will reach 6mins 39 sec. The Astronomical League of the Philippines, Inc. (ALP) will be sending an eclipse expedition team headed by James Kevin Ty, a veteran eclipse chaser, to observe this event at Wuhan, China. Since the eclipse team will be heading to Wuhan, majority of the data that I will include in this article will be that of Wuhan. Aside from Wuhan, I will also touch on what we can expect to see in this eclipse here in our country, the Philippines. Since all of China, as well as the Philippines, use the same time zone of UT+8, there is no need for the readers to convert the times that I will relate in this article. Hubei province’s capital Wuhan, with a population of more than 9.7 million people, is the fourth largest city in China. It lies just 20 kms south of the center line and thus enjoys a good duration of 5 minutes 25 seconds at 01:27 UT (9:27 a.m. China Standard Time).
During totality, the Sun’s altitude is 48 degrees, the path’s width is 244 km and the umbral velocity is 1 km/sec. The Yangtze River meanders through the eclipse track as the shadow proceeds east.
SAROS CYCLE The periodicity and recurrence of solar (and lunar) eclipses is governed by the Saros cycle. It is a period of approximately 6,585.3 days (about 18 years 11 days 8 hours.) When two eclipses are separated by a period of one Saros, they almost share the same geometry. The eclipses occur at the same node with the Moon at nearly the same distance from Earth and at the same time of the year, except that the eclipse’s path will moves a third of the way west and a little north, on the Earth’s surface from the last eclipse occurrence. Thus, the Saros is useful for organizing eclipses into families or series. Each series typically last about 12 to 13 centuries and contains 70 or more eclipses. The total solar eclipse of July 22, 2009 is the 37th member of Saros 136. The first eclipse of this cycle began with a small partial eclipse on June 14, 1360 off the coast of Antarctica. Throughout the 20th century, Saros 136 continued to produce exceptionally long duration total solar eclipse, with tracks passing across the equator. The eclipse of May 29, 1919 was particularly noteworthy and interesting because it was the first solar eclipse used to measure the gravitational deflection of starlight by the Sun as predicted by Einstein’s general theory of relativity. The June 20, 1955 total solar eclipse was particularly interesting to all of us here because it is the longest duration of all total solar eclipses belonging to the Saros 136 with a maximum duration of 7 minutes 8 seconds, and which passed over the Philippines, including Manila. This eclipse is the longest recorded total solar eclipse. The 2009 eclipse has a maximum duration of 6 minutes 39 seconds although it will occur in the Pacific Ocean. So I have decided to lead the ALP team to Wuhan, China as I think this is the best area to observe this eclipse although at the expense of a much shorter duration but with a better chance of clear sky during the eclipse duration.
WEATHER OUTLOOK Space-based cloud observations show that Wuhan has a sunshine prospect slightly lower than in Chongqing, but surface-based observations give it the best and promising inland site in China. Average cloud cover derived from local weather records is discouraging at 61%, one of the best in China, but it can be considered high nevertheless when compared to cloud amounts at recent eclipses in other parts of the world. Wuhan’s biggest advantage over sunnier sites near the coast is the lower amount of haze and pollution. The city is relatively compact, but open sites in the country-side have to be sought out, as the area is extensively agricultural and sites for large groups are at a premium. The centerline of the eclipse will pass through the airport, so the sites within the city proper may be quite suitable and Wuhan has an assortment of public parks and waterside enclaves. It is an area well worth exploring for cleaner skies compared to sites near Shanghai, and this will allow the distant corona to stand out clearly against the sky.
SKY AT TOTALITY As the partial eclipse progress, the temperature drops noticeably. This can also affect the focus of cameras and telescopes which should be checked once in a while as totality approaches. The total phase of an eclipse is accompanied by the onset of a rapidly darkening sky whose appearance resembles evening twilight about half an hour after sunset. It gives an observer an excellent opportunity to view some planets as well as bright stars in the daytime sky.
The brightest planet will be Venus, which shines at around magnitude -3.9. It will be located in Taurus about 41 degrees west of the Sun and is almost nearly overhead from this geographical location. Mercury, which shines at magnitude -1.4, is located about 9 degrees east of the Sun. Mars, at magnitude +1.1, is 12 degrees west of Venus and 52 degrees west of the Sun. Saturn is low in the eastern horizon and located 49 degrees east of the Sun and can be considered hard or impossible to view in China but probably be visible if one is located at the Pacific section of the eclipse track. Some bright stars are also visible during totality and some of them such as Pollux (mag +1.14), Castor (mag +1.94) and Procyon (mag+0.38) are fairly close to the Sun while Sirius (mag -1.44), Betelguese (mag +0.5), Rigel (mag +0.12), Aldebaran (mag +0.87), Capella (mag +0.08) and Regulus (mag +1.35) are visible further away from the Sun. OBSERVING THE ECLIPSE A total solar eclipse is probably the best and most spectacular astronomical event that many people will experience in their lifetime! There is a great deal of interest in observing solar eclipses, and thousands of astronomers (both amateur and professional) travel around the world just to observe and photograph them. A solar eclipse can offer us an opportunity to see a natural phenomenon that illustrates the basic principles of science and mathematics. Some examples are the use of pinhole cameras as well as telescopes or binoculars leads to an understanding of how optics work in these devices; the rise and fall of environmental light levels during an eclipse illustrate the principles of radiometry and photometry; the observation of how plants and animals behave during the eclipse’s entire duration; and, the monitoring of the rise and fall of temperature during the entire eclipse period, etc. Observing the Sun, however, can be dangerous if proper precautions are not taken into account. The solar radiation that reaches the Earth’s surface ranges from ultraviolet (UV) radiation at wavelengths longer than 290nm to radio waves in the meter range. The tissues in the eye transmit a substantial part of the radiation in between 380-400nm to the light sensitive retina at the back of our eye. While environmental exposure to UV radiation is known to cause accelerated aging of the outer layers of the eye and the development of cataracts, the primary concern over improper viewing of the Sun during an eclipse is the development of eclipse blindness or retinal burns. The result can be temporary or permanent, depending on the severity of the damage. When one looks repeatedly, or for a long duration of time, at the Sun without proper eye protection, this can cause retinal damage accompanied by thermal injury - the high level of visible and near-infrared radiation causes heating that literally cooks the exposed tissue. This thermal injury destroys the rods and cones, creating a small blind area! The great danger to vision is significant because of the fact that the injuries occur without nay feeling of pain (the retina doesn’t have any pain receptors) and the visual effects do not become obvious for at least several hours after the damage is done! Viewing through the telescope and binoculars without proper filtration can result in immediate or instant eye damage because of the high irradiance level in the magnified image. The only time that the Sun can be viewed safely with the naked eye is during TOTALITY only. It is NEVER SAFE TO LOOK AT THE SUN DURING PARTIAL OR ANNULAR ECLIPSES, OR PARTIAL PHASES OF A TOTAL SOLAR ECLIPSE!!!! So what are the safe ways or techniques to observe the solar eclipse? Projection method – this is one of the most popular and inexpensive methods. A pinhole or small opening is used to form an image of the Sun on a screen placed about a meter behind the opening. Multiple solar pinhole images can also be made by letting the sunlight pass through broad-leaf tree, loosely woven straw hat, etc. Binoculars or telescope mounted on a tripod or telescope mount can also be used to project a magnified image of the Sun onto a white paper or board. An advantage of this method is that no one is looking at the Sun directly. Aperture Filter method – this is also very popular for those who are using a telescope or binocular in observing the eclipse. The filter is placed at the front part of the telescope or binoculars where the objective lens is located. Among the popular solar filters in the market are Baader Astro Solar Filter, Thousand Oaks Glass Filters, etc. A safe solar filter for viewing should transmit less than 0.003% (density 4.5) of visible light and no more than 0.5% (density 2.3). Another, more -economical, and easier-to-find solar filter for viewing is the Welder’s glass #14 which can be bought at welding supply outlets. Another easy-to-find and safe filter material for visual observation is black-and-white film that has been fully exposed to light and developed to maximum density. But take note that not all lack and white film is considered safe to use. The safe type must have silver halide in it as it acts as a protective layer. Unsafe filters include color film, black and white film that contains no silver (chromogenic film), film negatives with images, smoked glass, sunglasses, photographic neutral density filters, and polarizing filters. Most of these transmit high levels of invisible infrared radiation, which can cause a thermal retinal burn. Solar filters designed to be threaded into the eyepieces that are often provided on inexpensive telescopes are also unsafe. These glass filters often crack unexpectedly from overheating when the telescope is pointed at the Sun! Retinal damage can occur faster than the observer can move the eye away from the eyepiece! If one doesn't have a solar filter, he or she can opt to punch a small hole in a sheet of paper and let the sunlight passed through the small hole and one can see the eclipsed Sun with this method safely and economically :) Another technique is to go under a tree shading and one can see even more eclipsed Sun images through the openings between the leaves. This is commonly called a pinhole observation method. ECLIPSE PHOTOGRAPHY Solar Eclipse photography has become popular among solar eclipse viewers as most everyone wants to have a souvenir image of the eclipse for them to share to fellow amateur astronomers or relatives and friends after they return home. Almost any type of camera can be used to capture this rare event but single lens reflex cameras offer interchangeable lenses and zooms, thus they are more preferred for use by serious astronomers and photographers. Consumer digital cameras have become more affordable in recent years and many of these can be used to image the eclipse as well. The digital single lens reflex camera (DSLR) is now mostly replacing the old SLR systems in the market lately. The primary difference is that the imaging chip in most DSLR is only about 2/3 the area of that of a 35mm film frame which means the Sun’s relative size will be about 1.5x larger in the DSLR so a shorter focal length lens can be used to achieve the same angular coverage compared to a 35-mm SLR camera. For full disk photography, a lens or a telescope that has a focal length between 500-2000 mm in 35 mm format will be suitable for your needs. However, if one plans to image the inner corona of the Sun during totality, focal lengths between 1000 mm-1500 mm is most suitable, while to image the outer corona, a focal length of 1000 mm or less is your best choice to capture the longer coronal streamers. Of course, the use of a solar filter is a MUST during the partial phases and should only be removed a few seconds before second contact and MUST be installed again a few seconds after 3rd contact.
Exposure range to capture the Bailey’s Beads, prominences, chromosphere, inner and outer corona varies widely depending on your lens or telescope f/ratio so the use of the full range of the camera’s shutter speed is highly recommended. With the totality duration of more than 5 minutes, one can have the time to play along various exposures to get the optimal exposure during totality.
The use of point-and-shoot digital cameras can also be used for the eclipse, but the best types should have a manual shutter exposure for you to use, and not that of the cheaper automatic exposure digicams. Video cameras can also be used to capture the entire eclipse in real time than still cameras but the resolution of the frames are not as good as what the still camera can provide you. CONCLUSION Based on the data checking I did on the entire China area as supplied by Fred Espenak, I have decided to set the ALP main expedition team at Wuhan as I think it will be the best site for us to document the eclipse with weather and optimal eclipse duration, as well as my previous eclipse expedition experience, as a gauge in finalizing the best site in the eclipse path. On a separate note, a few of our members have informed me that they will also set alternative sites in Hangzhou , Shanghai and Jiaxing as well. ALP will have a better coverage of the eclipse with a higher chance of success. On separate note, the Shanghai team will do a live webcast through http://www.justin.tv/medlee . They will do the webcasting if they get hold of internet access from their vantage point. The Wuhan team will upload their reports , images and updates at http://www.astroleaguephils.org/archive/news/090722tse_wuhan.html of their daily routine and eclipse day initial reports after the eclipse. Consolidated eclipse full report will be posted at http://www.astroleaguephils.org/archive/news/090722tse.html after all images and reports have been submitted within the week after the eclipse.
CONTACT TIMES OF THE SOLAR ECLIPSE WUHAN , CHINA (30 deg 36’ N, 114 deg 17’ E)
SHANGHAI , CHINA (31 deg 14’ N, 121 deg 28’ E)
PHILIPPINES OBSERVING GUIDE Over here in the Philippines, we will be able to observe a partial solar eclipse. Below are the estimated contact timings of the eclipse in some cities of our country: MANILA , PHILIPPINES (14 deg 35’ N , 121 deg 00’ E)
BAGUIO , PHILIPPINES (16 deg 26' N , 120 deg 34' E)
CEBU , PHILIPPINES (10 deg 18’ N , 123 deg 54’ E)
DAVAO , PHILIPPINES (7 deg 04’ N , 125 deg 36’ E)
Some members of the Astronomical League of the Philippines (ALP) who are not joining the eclipse expedition team in Wuhan , China as well as the alternate sites will set up in various areas in Metro Manila, particularly in UP-PAGASA observatory in UP-Diliman, Quezon City as well as AstroCamp Observatory Services at SM MOA to document and image the partial eclipse as well as let the public view the it. If you intend to join the above 2 ALP-based setup sites, kindly inform ALP Eclipse-Manila coordinator Henry So at +639185215252. For more details on this event or seeking advise on how to observe and image this eclipse safely, you can contact James Kevin Ty at +639178559863 not later than July 18, 2009.
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