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Comet Viscara
The Great Comet of 1901, sometimes known as Comet Viscara, formally designated C/1901 G1 (and in the older nomenclature as 1901 I and 1901a), was a comet which became bright in the spring of 1901. Visible exclusively (or almost exclusively) from the southern hemisphere, it was discovered on the morning of April 12, 1901 as a naked-eye object of second magnitude with a short tail. On the day of perihelion passage, the comet's head was reported as deep yellowish in color, trailing a 10-degree tail. It was last seen by the naked eye on May 23.
==Discovery and observations==
In the pre-dawn of 12 April 1901 there was a naked-eye discovery of the comet by Viscara, the manager of an estancia in the Departamento de Paysandú, Uruguay. In the pre-dawn of April 23 the comet was observed in Queenstown, South Africa and on April 24 by David Gill and Robert Innes at the Royal Observatory, Cape of Good Hope; the tail was then about 10° long. On April 24 the comet was also observed at Cape Leeuwin in Western Australia. At the Sydney Observatory on April 25, H. C. Russell found the tail to be about 2° long.
When the comet's brightness reached a maximum on May 5, the tail had fanned out with a weak plasma tail about 45° long and a curved dust tail about 15° long.〔 On May 5 the comet's brightness reached magnitude 1 or perhaps brighter.〔(【引用サイトリンク】title=NASA JPL Solar System Dynamics: Great Comets in History )〕 According to some observers (of the nucleus viewed telescopically following sunrise) the brightness might have reached magnitude −1.5. From naked-eye observations on May 5 there were at least two reports of aurora-like undulations in the tail.
The comet was readily visible to the naked eye until about May 20 and visible by telescope until October.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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