AT THE ANTARCTIC.

Dominion, Volume 5, Issue 1529, 27 August 1912, Page 6

AT THE ANTARCTIC.

♦ INTERESTING ASTRONOMICAL FACTS. "PERPETUAL DAY" AND "PERPETUAL NIGHT." (By Commander Hooper of the Amokura.) It will bo interesting to know that the termination of tho "perpetual night" at Captain Scott's base look place last Sunday week, August 18. On that day at noon, given hue weather conditions," tho sun would probably be just visible above the horizon to the northward, and on the lollowing day a space ,of about one half the diameter of tho sun Oiould bo seen between the sun and the horizon; whilst on the second day tho gap would be increased to a liltlo moro than tile sun's diameter. Tho sun would then continue to rise earlier and more to the eastward, and to set later and more to the westward until the spring equinox, September 23, at which time it will rise at the cast point and set at the west point; the day and night being of equal duration, and tho sun being about 12\ degrees above tho horizon to the northward at noon. After this period it will rise to tho southward of tho east point, and set to tho southward of tho west point, daily increasing its height at noon and its dis: tance from this east and west points at rising and setting, and thereby increasing the length of day until October 25. On. this date the sun will reach tho south point of tho horizon without setting, at midnight. Instead of disappearing below the horizon, it will only grazo it, and will continue its progress towards the eastward. The sun.will rise gradually as it proceeds onwards past tho east point until- mid-day; when it will again |>erforiu the round of the compass. This is the commencement.of■ tho.period of "perpetual day." From this date onwards until ;tho; summer solstice, December- 22; the sun will Ire rising higher daily until tho latter date, at which time it will have reached its highest point, about 36 degrees- above: the. northern horizon at noon, and about 10 degrees above the southern horizon at'midnight; it will after (hat date gradually appear lower in the heavens each day until about February 17, at which date, the sun will set near tho southern horizon'at midnight. The phenomena will now take place in the reverse order to the foregoing, the period-of "perpetual day" terminating on February 17. The sun will then appear to riseand set more to the east and west of south every day, eventually risinj and setting at those points on March 21 (Autumnal equinox) at which time tho day and night are again of equal length. After this period its daily appearance abovo the horizon becomes less and less, until April '22, at which tine if (he weather is clear at the northern horizon, the sun's disc will just be seen on the horizon at noon. After this period it will not be seen again until tho following August 18. This is the period of "perpetual night.'" It mini: not be thought that tho whole of the period of the "perpetual night" is a period of absolute darkness from its commencement to its termination, as the sun is not far below tho horizon, for a considerable number of days after the commencement; the darkness first commencing in tho form of a lengthy twilight, which is brightest at noon, gradually becoming less bright towards about 10 p.m., when it will be dark; provided that thero is-no moon. .Tie termination of the dark period is. also _ greatly shortened owiiig to tho very bright twilight visible for a considerable number of- days before the sun's actual appearance on the northern horizon. The length of the "perpetual' day" ' at • Captain Scott's base in M'Murdo Strait is about 116 days, and the length of the-"perpetual. night" about four days less. The darkness of the "perpetual night" is considerably lessened by frequent long moonlight nights, the moon remaining above the horizon frequently for a period of ten days without setting. In fine weather, with the moon at her full near the centre of one of- these periods, the light diffused on the bright surroundings is very bright, and is quite a welcome change during the "perpetual night." At Captain Scoffs base during the present month the moon has 'not been below the horizon during the • period between August 17 and 27, and durine which time she has increased in size' from tho fourth day to full moon; so that it may bo assumed that the nights during that period were very well lighted. Quite the opposite will occur during the period between September 1 and 10, when the moon will not be visible at all in that locality.