Jika anda ternampak muka saya tengah TT (Teh Tarik) ni, bermakna anda telah selamat mengharungi 3 hari bumi tak jadi bergelap, dan tarikh 21hb Dis yang penuh tragis dan huru-hara (kononlah).
Nak ceritanya, Falak Online telah pun berpindah rumah. Bermula sekarang silalah kemaskini link ke WWW.FALAKONLINE.NET , tak perlulah letak apa-apa selepas tu, kerana ia akan redirect ke muka hadapan BARU yang sepatutnya.
Laman lama (yang anda lihat sekarang ni), InsyaAllah akan kekal untuk beberapa bulan mendatang. Ia akan menyenaraikan KESEMUA artikel lama saya di FO, bagi rujukan anda semua. Maka, kalau anda nak masih nak marah-marah kat saya berkenaan artikel "3 hari bergelap tu" , masih boleh berbuat demikian, saya terima dengan hati terbuka! :-)
Apa pun, InsyaAllah 2013 mendatang akan terdapat beberapa pembaharuan yang saya dan rakan-rakan Personaliti Astronomi lain usahakan, demi kemajuan bidang Astronomi di Malaysia.
Jom dan Selamat Datang Ke Tahun Baru 2013.
Jemput masuk ---> WWW.FALAKONLINE.NET
Reader Michael Knowles discovered the glory of a Sun halo while paragliding above the French Alps.
When I planned my trip to La-Plagne, France, this past March, I didn’t foresee mixing paragliding with astronomical imaging — the opportunity arose purely by chance. After prepping meticulously under the tutelage of my paragliding instructor, I descended off Mount La Grande Rochette and managed to capture the image below: a circular halo cast around the Sun behind the frozen Alps.
At the take-off point on top of the summit, I stood at an altitude of 2,505 meters (8,267 feet). The descent can take between 15 and 20 minutes depending on the thermals, the rising columns of warm air heated by the Sun. The drop-zone target lay 535 meters below take-off, at Plagne Centre (altitude: 1970 meters).Solar Ice Halos
Regardless of its position in the sky, a Sun halo is always the same size. Both the Sun and Moon can make a 22° circular halo, though depending on the conditions, sometimes only arcs of the circle will be visible. Smaller, colored rings are sometimes spotted around the Sun or Moon, but these form via diffraction through water droplets rather than ice crystals.
Ice crystals generally don’t form as spheres — their shapes range from solid, hollow columns to plates, bullet rosettes, and aggregates, as large as thousands of microns. Those crystals that create halos are typically suspended in cirrus or cirrostratus clouds high in the upper troposphere. Temperatures at this altitude sink as low as -30° Celsius. During severe cold weather conditions, ice halos dubbed “diamond dust” can even hover near ground level.Elsewhere in the Solar System
As I paraglided above the frozen Alps, I thought of what this might look from elsewhere in the solar system. On other planets, the different atmospheric composition would give the solar halo a different size. Solar halos in Mars’s atmosphere would refract through ice made of water and carbon dioxide, while in the atmospheres of the giant planets, ammonia and methane, as well as other molecules, could form more complex halos.
It was an exhilarating experience to glide high above the pristine Alps, framed by an illuminated backdrop of a solar ice halo.Michael Knowles is a member of the Sherwood Astronomical Observatory in Nottinghamshire, United Kingdom.
Centauri Clube de Astronomia de ItapetiningaADDRESS
Sao Paolo, Brazil
Rodrigo RaffaPHONE EMAIL
https://www.facebook.com/astronomiaitapetiningaNUMBER OF MEMBERS OTHER INFORMATION
O Clube de Astronomia Centauri de Itapetininga foi fundado pelo Professor de Física Rodrigo Raffa, junto a colaboração de professores e estudantes de graduação em Física para divulgar a Astronomia, fazer observações Astronômicas em grupo e compartilhar conhecimentos de Astronomia para todos os níveis. Há a possibilidade do Grupo ser colaborado por um Projeto de Extensão da UFSCar, ampliando os projetos e possibilitando novos horizontes ao Grupo que conta com os alunos e ex alunos do IFSP Campus Itapetininga e com pessoal certificado em Astronomia. Pesquisadores, Astrônomos Amadores, Professores e Alunos são bem vindos ao clube. Ainda em expansão, o projeto prevê melhorias e encontros periódicos.
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In a borderline eclipse of the Moon like last Saturday's, the difference between "total" and "partial" depends on some crucial assumptions.
An especially intriguing eclipse of the Moon delighted observers from western North America to Australia and the Far East last Saturday (April 4th). What still makes it so intriguing, two days later, is the unsettled question of whether the world saw a barely total lunar eclipse — the third in a "tetrad" of four, as almost universally predicted — or a barely partial lunar eclipse, with a hair-thin rim of sunlit lunar surface remaining just outside the umbra of Earth's shadow. Which would spoil the tetrad.
Visual observers are saying it was barely partial.
You'd think astronomers would be awfully embarrassed not to get such a simple prediction right. But the edge of Earth's umbra is fuzzy enough, and the umbra just inside the edge is bright enough — and the effects of Earth's atmosphere on the umbra's precise size are unpredictable enough — that we may never be sure which kind of eclipse we saw on Saturday.
However, the evidence leans toward partial — not just in terms of how people judge what they saw, but also in terms of the most detailed mathematical prediction.Views of the Lunar Eclipse
"I observed the eclipse from San Francisco, naked eye and through mounted 11×56 binoculars," writes Anthony Barreiro in a typical report. "At no time did the eclipse appear total to me. The Moon’s far northern limb remained brightly illuminated throughout. Inside the apparent edge of the umbra the Moon’s surface was bright but obviously reddened. The very edge of the Moon remained much brighter and without any visible reddening."
Scott Bulkley, who has observed lunar eclipses for more than 50 years, used naked-eye observations, 10×50 binoculars, and a 5-inch Schmidt-Cassegrain telescope for this one. "Using all three viewing methods during the critical minutes, I was not able to observe totality at any time," he writes. "There was always at least a very thin ‘sliver’ of brightly illuminated lunar surface on the northern limb of the Moon."
Alastair from New Zealand writes, "I am sure this was not a fully total eclipse. A thin sliver of the limb was still quite brightly illuminated throughout totality."
All the other reports we’ve received so far agree.
But the problem with such reports is that the innermost penumbra — the portion of Earth's shadow just outside the umbra — was not necessarily in view, so there was nothing that the relatively bright umbral rim could definitely be compared against.
Nor does imaging help. Imaging is actually worse for determining the umbra's edge, because the amount of exposure, contrast, dynamic range and so forth can vary far more between different images than between different people's eyes at a telescope. Not to mention tweaking and processing that may happen automatically in the camera or to "correct" an image afterward.Eclipse Theory and Eclipse Observation
Wouldn't the simple geometry of the Earth, Moon, and Sun — known with extreme precision — give an exact answer?
The problem here is that Earth's atmosphere enlarges the size of the globe, for shadow-casting purposes, by a not-quite-exact amount. The U.S. Naval Observatory, in its lunar-eclipse predictions, adds a standard 2% to the umbra's "geometric" radius to account for the effect of the atmosphere. This led the USNO to predict 12.2 minutes of totality. The French national almanac office, and eclipse predictor Fred Espenak, used the supposedly more sophisticated "Danjon method." This gave 4.7 minutes of totality and a much thinner margin for error.
However, in the days before the eclipse, Chicago amateur Curt Renz pointed out that neither method includes Earth's oblateness. Our planet is 1⁄300 less wide from pole to pole than it is across the equator (due to rotation). And Earth's far northern latitudes were the parts that cast the shadow's eclipse-defining northern edge.
Normally Earth's oblateness is insignificant. But Renz pointed out that in such a borderline case, it might tip the eclipse into being technically partial if the Danjon method is assumed to be otherwise right. For more about this see Kelly Beatty's article Saturday’s Lunar Eclipse: Not Total? posted the day before the event.
The umbra does have an edge that is precisely definable, regardless of how the eye and brain might judge it. That edge is the place in the fuzziness where the change in brightness from point to point is steepest. This is the most natural definition of the umbra's edge, the one that visual observers generally try to use when timing when the edge crosses craters and other lunar markings. Astronomers have done many thousands of crater timings during lunar eclipses for more than 1½ centuries, and this work provides the best fix we have on what the umbra actually does.
Roger Sinnott and David Herald recently completed a thorough analysis of the 26,685 known lunar-eclipse timings made from 1842 to 2011, many of them by S&T readers since 1956. As Sinnott will summarize in our June issue, he and Herald found that from one eclipse to the next, the atmosphere's effective eclipsing layer varies in thickness by a scant few kilometers for reasons unknown. Unpredictably.
We don't yet know how many people did good crater timings during this particular eclipse.
So, was it total or partial?
Visual observers seem to agree that it appeared partial. But by the exact, most natural definition of the umbra's edge, we may never know.
For a closer look at our nearest celestial neighbor, check out our Moon globe, pieced together from thousands of Lunar Reconnaissance Orbiter images.
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