Gerhana matahari
Daripada Wikipedia, ensiklopedia bebas.
Gerhana matahari boleh dibahagi kepada 3 iaitu gerhana penuh, gerhana separuh, dan gerhana analus. Gerhana penuh apabila matahari ditutup sepenuhnya oleh bulan disebabkan bulan berada dekat ke bumi dalam orbit bujurnya, gerhana separuh apabila bulan hanya menutup sebahagian daripada matahari, dan gerhana analus yang terjadi apabila bulan hanya menutup sebahagian daripada matahari dan cahaya matahari selebihnya membentuk cincin bercahaya sekeliling bayangan bulan yang dikenali sebagai 'corona'.
Gerhana matahari berlaku selama 7 minit 30 saat pada tempat yang paling lama. Ketika gerhana matahari, orang ramai dilarang melihat ke arah matahari secara langsung kerana ini boleh merosakkan mata dan mengakibatkan buta.
Bagi mereka yang beragama Islam, mereka digalakkan untuk melakukan Solat Sunat Gerhana ketika berlakunya gerhana.
Pada 26 Januari 2009 berlaku lagi kekuasaan Allah pada alam ini iaitu fenomena Gerhana Matahari. Waktu berlaku pada waktu 16:20 waktu Malaysia dan berakhir dijangka 19:00. Adalah sebaik-baiknya memulakan solat gerhana matahari berjemaah di surau atau masjid di tempat anda kerana dapat mendengar khutbah yang bakal dibacakan oleh khatib. Hukum khutbah dan solat gerhana adalah sunat muakad(yang dituntut) , jadi meninggalkannya hukumnya makruh(dibenci) tanpa uzur syari'e.
There are four types of solar eclipses:
- A total eclipse occurs when the Sun is completely obscured by the Moon. The intensely bright disk of the Sun is replaced by the dark silhouette of the Moon, and the much fainter corona is visible. During any one eclipse, totality is visible only from at most a narrow track on the surface of the Earth.
- An annular eclipse occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon.
- A hybrid eclipse (also called annular/total eclipse) transitions between a total and annular eclipse. At some points on the surface of the Earth it is visible as a total eclipse, whereas at others it is annular. Hybrid eclipses are comparatively rare.
- A partial eclipse occurs when the Sun and Moon are not exactly in line and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can only be seen as a partial eclipse, because the umbra never intersects the Earth's surface, passing above the Earth's polar regions.
The Moon's orbit around the Earth is an ellipse, as is the Earth's orbit around the Sun; the apparent sizes of the Sun and Moon therefore vary.[2][3] The magnitude of an eclipse is the ratio of the apparent size of the Moon to the apparent size of the Sun during an eclipse. An eclipse when the Moon is near its closest distance from the Earth (i.e., near its perigee) can be a total eclipse because the Moon will appear to be large enough to cover completely the Sun's bright disk, or photosphere; a total eclipse has a magnitude greater than 1. Conversely, an eclipse when the Moon is near its farthest distance from the Earth (i.e., near its apogee) can only be an annular eclipse because the Moon will appear to be slightly smaller than the Sun; the magnitude of an annular eclipse is less than 1. Slightly more solar eclipses are annular than total because, on average, the Moon lies too far from Earth to cover the Sun completely. A hybrid eclipse occurs when the magnitude of an eclipse transitions during the event from smaller than one to larger than one—or vice versa—so the eclipse appears to be total at some locations on Earth and annular at other locations.[4]
The Earth's orbit around the Sun is also elliptical, so the Earth's distance from the Sun varies throughout the year. This also affects the apparent sizes of the Sun and Moon, but not so much as the Moon's varying distance from the Earth. When the Earth approaches its farthest distance from the Sun (the aphelion) in July, this tends to favor a total eclipse. As the Earth approaches its closest distance from the Sun (the perihelion) in January, this tends to favor an annular eclipse
Istilah bagi gerhana pusat
Gerhana Pusat "Central eclipse" swering kali digunakan sebagai istilah umum bagi gerhana penuh, gerhana anular, atau gerhana kacukan. Ini bagaimanapun, tidak tepat: istilah bagi gerhana pusat merupakan di mana garis tengah umbra menyentuh permukaan bumi. Ia adalah mungkin, sungguhpun amat jarang, sebahagian umbra melintasi Bumi (dengan itu menghasilkan gerhana anular atau gerhana penuh), tetapi tidak garis tengahnya. Ini sering kali dikenali sebagai gerhana penuh tidak tengah atau gerhana anular.[5] The next non-central solar eclipse will be on April 29, 2014. This will be an annular eclipse. The next non-central total solar eclipse will be on April 9, 2043.[6]
Fasa yang dilihat semasa gerhana penuh dikenali sebagai:
- First Contact — when the moon's shadow first becomes visible on the solar disk. Some also name individual phases between First and Second Contact e.g. Pac-Man phase.
- Second Contact — starting with Baily's Beads {caused by light shining through valleys on the moon's surface} and the Diamond Ring. Almost the entire disk is covered.
- Totality — with the shadow of the moon obscuring the entire disk of the sun and only the corona visible
- Third Contact — when the first bright light becomes visible and the shadow is moving away from the sun. Again a Diamond Ring may be observed
Ramalan
Geometri
The Moon's orbit around the Earth is inclined at an angle of just over 5 degrees to the plane of the Earth's orbit around the Sun (the ecliptic). Because of this, at the time of a new moon, the Moon will usually pass above or below the Sun. A solar eclipse can occur only when the new moon occurs close to one of the points (known as nodes) where the Moon's orbit crosses the ecliptic.
As noted above, the Moon's orbit is also elliptical. The Moon's distance from the Earth can vary by about 6% from its average value. Therefore, the Moon's apparent size varies with its distance from the Earth, and it is this effect that leads to the difference between total and annular eclipses. The distance of the Earth from the Sun also varies during the year, but this is a smaller effect. On average, the Moon appears to be slightly smaller than the Sun, so the majority (about 60%) of central eclipses are annular. It is only when the Moon is closer to the Earth than average (near its perigee) that a total eclipse occurs.[7][8]
The Moon orbits the Earth in approximately 27.3 days, relative to a fixed frame of reference. This is known as the sidereal month. However, during one sidereal month, the Earth has revolved part way around the Sun, making the average time between one new moon and the next longer than the sidereal month: it is approximately 29.5 days. This is known as the synodic month, and corresponds to what is commonly called the lunar month.
B Annular eclipse in the antumbra.
C Partial eclipse in the penumbra
Finally, the Moon's perigee is moving forwards in its orbit, and makes a complete circuit in about 9 years. The time between one perigee and the next is known as the anomalistic month.
The Moon's orbit intersects with the ecliptic at the two nodes that are 180 degrees apart. Therefore, the new moon occurs close to the nodes at two periods of the year approximately six months apart, and there will always be at least one solar eclipse during these periods. Sometimes the new moon occurs close enough to a node during two consecutive months. This means that in any given year, there will always be at least two solar eclipses, and there can be as many as five. However, some are visible only as partial eclipses, because the umbra passes above Earth's north or south pole, and others are central only in remote regions of the Arctic or Antarctic.[9][10]
Path
During a central eclipse, the Moon's umbra (or antumbra, in the case of an annular eclipse) moves rapidly from west to east across the Earth. The Earth is also rotating from west to east, but the umbra always moves faster than any given point on the Earth's surface, so it almost always appears to move in a roughly west-east direction across a map of the Earth (there are some rare exceptions to this which can occur during an eclipse of the midnight sun in Arctic or Antarctic regions).The width of the track of a central eclipse varies according to the relative apparent diameters of the Sun and Moon. In the most favourable circumstances, when a total eclipse occurs very close to perigee, the track can be over 250 km wide and the duration of totality may be over 7 minutes. Outside of the central track, a partial eclipse can usually be seen over a much larger area of the Earth.[11]
Occurrence and cycles
Total solar eclipses are rare events. Although they occur somewhere on Earth every 18 months on average,[13] it has been estimated that they recur at any given place only once every 370 years, on average. The total eclipse only lasts for a few minutes at that location, as the Moon's umbra moves eastward at over 1700 km/h. Totality can never last more than 7 min 31 s, and is usually much shorter: during each millennium there are typically fewer than 10 total solar eclipses exceeding 7 minutes. The last time this happened was June 30, 1973 (7 min 3 sec). Observers aboard a Concorde aircraft were able to stretch totality to about 74 minutes by flying along the path of the Moon's umbra. The next eclipse exceeding seven minutes in duration will not occur until June 25, 2150. The longest total solar eclipse during the 8,000-year period from 3000 BCE to 5000 AD will occur on July 16, 2186, when totality will last 7 min 29 s.[14] For comparison, the longest eclipse of the 21st century occurred on July 22, 2009 and lasted 6 min 39 sec.
If the date and time of any solar eclipse are known, it is possible to predict other eclipses using eclipse cycles. Two such cycles are the Saros and the Inex. The Saros cycle is probably the best known, and one of the most accurate, eclipse cycles. The Inex cycle is itself a poor cycle, but it is very convenient in the classification of eclipse cycles. After a Saros cycle finishes, a new Saros cycle begins one Inex later, hence its name: in-ex. A Saros cycle lasts 6,585.3 days (a little over 18 years), which means that after this period a practically identical eclipse will occur. The most notable difference will be a shift of 120° in longitude (due to the 0.3 days) and a little in latitude. A Saros series always starts with a partial eclipse near one of Earth's polar regions, then shifts over the globe through a series of annular or total eclipses, and ends at the opposite polar region. A Saros (series) lasts 1226 to 1550 years and 69 to 87 eclipses, with about 40 to 60 central.[15]
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