Halo (fenomena optis)

Halo (dari bahasa Yunani ἅλως^[1]^[2]) adalah fenomena optis berupa lingkaran cahaya di sekitar matahari dan bulan, dan kadang-kadang pada sumber cahaya lain seperti lampu penerangan jalan. Ada berbagai macam halo, tetapi umumnya halo muncul disebabkan oleh kristal es pada awan cirrus (biasanya cirrostratus) yang dingin yang berada 5–10 km atau 3–6 mil di lapisan atas troposfer. Fenomena ini bergantung pada bentuk dan arah kristal es, cahaya matahari direfleksikan dan dibiaskan oleh permukaan es yang berbentuk batang atau prisma sehingga sinar matahari menjadi terpecah kedalam beberapa warna karena efek dispersi udara dan dipantulkan ke arah tertentu, sama seperti pada pelangi.

Halo juga kadang-kadang dapat muncul di dekat permukaan bumi, ketika ada kristal es yang disebut debu berlian. Kejadian ini dapat terjadi pada cuaca yang sangat dingin, ketika kristal es terbentuk di dekat permukaan dan memantulkan cahaya.

Sebelum ilmu meteorologi dikembangkan, Fenomena atmosfer Halo digunakan sebagai sarana untuk prakiraan cuaca.^[3]

Sejarah

Patung Penglihatan Konstantin

Penampakan halo telah tercatat sejak zaman dahulu. Penduduk asli Amerika menggambarkan halo dalam petroglif. Di Tiongkok kuno, seorang kaisar menulis sebuah buku bergambar tentang halo. Sekarang, diyakini bahwa yang disebut sebagai 'penglihatan pagan' yang diyakini Konstantin sebagai tanda dari dewa^[4] disebabkan oleh halo matahari spektakuler yang dia saksikan pada tahun 330 M.^[5]

Aristoteles telah meneliti halo dan fenomena langit lain di zamannya.^[6] Penggambaran halo yang rumit pertama kali di Eropa ditulis oleh Christoph Scheiner di Roma (sekitar 1630), Hevelius di Danzig (1661), dan Tobias Lowitz di St Petersburg (sekitar 1794). Pengamat Tiongkok telah mencatat penampakan halo selama berabad-abad. Dalam catatan "Sejarah Resmi Dinasti Chin" (Chin Shu) tahun 637 bab Astronomi, terdapat bagian berjudul 'Sepuluh Halo' (shih yün). Dalam bab tersebut, tercatat 26 istilah-sitilah yang berkaitan dengan penampakan halo di Tata Surya.^[7]

Rujukan

^ "Henry George Liddell, Robert Scott, A Greek-English Lexicon, ἅλως". www.perseus.tufts.edu. Diarsipkan dari versi asli tanggal 2023-03-22. Diakses tanggal 6 Oktober 2020.
^ Johnson (2009), hlm. 325a, "The Greeks called such things the ‘halo’ (ή άλως), perhaps because of their resemblance to a circular threshing floor (άλως).
^ "Weather Forecasting Through the Ages". earthobservatory.nasa.gov (dalam bahasa Inggris). 2002-02-25. Diarsipkan dari versi asli tanggal 2009-01-22. Diakses tanggal 6 Oktober 2020.
^ Saylor Rodgers, Barbara (1980). "CONSTANTINE'S PAGAN VISION". Byzantion. 50 (1): ;261. ISSN 0378-2506. When Constantine approached the temple to thank the gods for his good fortune, he saw that the gods were awaiting his arrival (...) The panegyric contains a specific message, symbolized and summarized in the account of the vision, which the orator, presumably with the emperor's approval, wanted to his audience.
^ Zinkova, Mila (2018). "Ice halos in weather lore and meteorology, and a rare halo display in San Francisco". Weather (dalam bahasa Inggris). 73 (8): 239. doi:10.1002/wea.3237. ISSN 1477-8696. Diarsipkan dari versi asli tanggal 2023-08-13. Diakses tanggal 2020-10-06. Native Americans depicted halos in petroglyphs (Sassen, 1994). Ice halos were known to the ancient Chinese, where the emperor himself wrote an illustrated book about halos (Ping-Yü and Needham, 1959). It is now widely believed that the so-called ‘pagan vision’ of Constantine was caused by a spectacular solar halo he observed in AD 330 (Weiss, 2003).
^ Johnson (2009), hlm. 325b, "Aristotle tried to explain why halos always appear to form a complete circle, unlike related meteorological phenomena such as rainbows, parhelia, and ‘rods’."
^ Ping‐Yü, Ho; Needham, Joseph (1959). "Ancient Chinese Observations of Solar Haloes and Parhelia". Weather (dalam bahasa Inggris). 14 (4): 124–134. doi:10.1002/j.1477-8696.1959.tb02450.x. ISSN 1477-8696. Diarsipkan dari versi asli tanggal 2020-10-08. Diakses tanggal 2020-10-06. THE first European description of a complex display of haloes and mock suns was that of Christopher Scheiner in +1630, who saw one at the rather southerly latitude of Rome ; the next was that of Hevelius at Danzig in + 1661, but the most elaborate and complicated effect ever seen was probably that described by Tobias Lowitz at St. Petersburg in +1794. (...) The section on the ' Ten Haloes ' (shih yün) in one of the astronomical chapters of the Chin Shu (Official History of the Chin Dynasty), completed about +635, contains some twenty-six technical terms which can be identified with almost every component of the solar halo system.

Daftar Pustaka

Johnson, Monte Ransome (2009-01-01). "The Aristotelian Explanation of the Halo". Apeiron. 42 (4). doi:10.1515/apeiron.2009.42.4.325. ISSN 2156-7093. Diarsipkan dari versi asli tanggal 2023-08-13. Diakses tanggal 2020-10-06.

Pranala luar

Halo explanations and image galleries Diarsipkan 2013-07-28 di Wayback Machine. at Atmospheric Optics Diarsipkan 2012-01-17 di Wayback Machine.
Meteoros AKM - Halo explanations and image galleries Diarsipkan 2013-12-17 di Wayback Machine.
Halo reports of interesting halo observations around the World Diarsipkan 2020-09-25 di Wayback Machine.
Southern Hemisphere Halo and other atmospheric phenomena Diarsipkan 2019-01-19 di Wayback Machine.
Moon Halo Gallery Diarsipkan 2008-02-20 di Wayback Machine.
Halo in Chisinau Moldova (photo and video Diarsipkan 2007-09-28 di Wayback Machine.
Sun Halo appeared in Padang after the earthquake Diarsipkan 2009-10-05 di Wayback Machine.

[1] "Henry George Liddell, Robert Scott, A Greek-English Lexicon, ἅλως". www.perseus.tufts.edu. Diarsipkan dari versi asli tanggal 2023-03-22. Diakses tanggal 6 Oktober 2020.

[FOOTNOTEJohnson(2009)325a-2] Johnson (2009), hlm. 325a, "The Greeks called such things the ‘halo’ (ή άλως), perhaps because of their resemblance to a circular threshing floor (άλως).

[3] "Weather Forecasting Through the Ages". earthobservatory.nasa.gov (dalam bahasa Inggris). 2002-02-25. Diarsipkan dari versi asli tanggal 2009-01-22. Diakses tanggal 6 Oktober 2020.

[4] Saylor Rodgers, Barbara (1980). "CONSTANTINE'S PAGAN VISION". Byzantion. 50 (1): ;261. ISSN 0378-2506. When Constantine approached the temple to thank the gods for his good fortune, he saw that the gods were awaiting his arrival (...) The panegyric contains a specific message, symbolized and summarized in the account of the vision, which the orator, presumably with the emperor's approval, wanted to his audience.

[5] Zinkova, Mila (2018). "Ice halos in weather lore and meteorology, and a rare halo display in San Francisco". Weather (dalam bahasa Inggris). 73 (8): 239. doi:10.1002/wea.3237. ISSN 1477-8696. Diarsipkan dari versi asli tanggal 2023-08-13. Diakses tanggal 2020-10-06. Native Americans depicted halos in petroglyphs (Sassen, 1994). Ice halos were known to the ancient Chinese, where the emperor himself wrote an illustrated book about halos (Ping-Yü and Needham, 1959). It is now widely believed that the so-called ‘pagan vision’ of Constantine was caused by a spectacular solar halo he observed in AD 330 (Weiss, 2003).

[FOOTNOTEJohnson(2009)325b-6] Johnson (2009), hlm. 325b, "Aristotle tried to explain why halos always appear to form a complete circle, unlike related meteorological phenomena such as rainbows, parhelia, and ‘rods’."

[7] Ping‐Yü, Ho; Needham, Joseph (1959). "Ancient Chinese Observations of Solar Haloes and Parhelia". Weather (dalam bahasa Inggris). 14 (4): 124–134. doi:10.1002/j.1477-8696.1959.tb02450.x. ISSN 1477-8696. Diarsipkan dari versi asli tanggal 2020-10-08. Diakses tanggal 2020-10-06. THE first European description of a complex display of haloes and mock suns was that of Christopher Scheiner in +1630, who saw one at the rather southerly latitude of Rome ; the next was that of Hevelius at Danzig in + 1661, but the most elaborate and complicated effect ever seen was probably that described by Tobias Lowitz at St. Petersburg in +1794. (...) The section on the ' Ten Haloes ' (shih yün) in one of the astronomical chapters of the Chin Shu (Official History of the Chin Dynasty), completed about +635, contains some twenty-six technical terms which can be identified with almost every component of the solar halo system.

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