GLORY OF THE STARS

New Zealand Herald, Volume LXXV, Issue 23157, 1 October 1938, Page 12

GLORY OF THE STARS

HEAVENS IN OCTOBER display of mock suns NATURE OF PHENOMENON BY CRUX AUSTRALIS .fi Refraction and reflection of light among the water vapour and ice ' crystals of the atmosphere can play, •>' many strange tricks upon our eyes providing us with the deep blue of "the ' midday sky, the glorious tints of the 1 ' sunset, rainbows, haloes cud parhelia or mock suns, and the occurrence of mock Suns and Moons in latitudes as close to the equator as Auckland deserves more than passing notice. Those who witnessed the recent dis- ' ' play in Auckland probably saw only a halo surrounding the real Sun, while upon its circumference, level with the * Sun, were two hazy, dim patches of . light—the mock Suns. A phenomenon of fairly frequent occurrence in Arctic and Antarctic regions, the display in A those places can assume an intricate i and complex pattern. Features of Complete Form In its complete form the parhelia, or paraselenae, if the display is centred upon the Moon, consists of two complete haloes surrounding the Sun or Moon at distances of 22 degrees and 46 degrees respectively, and exhibiting the colours of the spectrum in a confused manner, the only decided tint being the red on the inside. - Passing through the luminary and running parallel to the horizon is -a white luminous ray, the parhelic circle, Tjehich extends completely around the slcy. On this circle a. number of images of the luminary appear. The most brilliant are those situated at the intersections of the parhelic circle with the inner hald. On . the outer halo less > brilliant mock Suns or Moons may appear. The mock Suns are most promin- • ent when the Sun is on the horizon. As it rises they pass ,a little beyond the halo and exhibit flaming tails. The Final Mock Sun .... Other images of the Sun may appear * on the parhelic circle. At a spot be- : tween 90 and 140 degrees removed from the Sun the paranthelia are dtuated, while directly opposite the luminary is the anthelion, the seventh and final l mock Sun, often exceeding in size the apparent diameter of the Sun itself. Secondary arcs make up the remainder of the display. A vertical circle passing through the Sun may be witnessed, while, intersecting the mock Suns of the inner halo, two arcs curve * • in the opposite direction to the trend of the halo itself. Above the Sun • further tangential arcs may; be seen touching the inner and outer haloes. The whole of the phenomenon may not be visible at any one display. A _ display of mock Moons visible in Auckland on August 17, 1929, for example, consisted of a single halo and three ? mock images, two level with tbvs Moon possessing tapering tails, while an t > other image without appendage lay directly above the Moon. - Phenomenon in 1930 A year later, on November 9, 1930, i - the phenomenon consisted of a celestial cross, no halo being visible." A vertical r. bar of light passing through the Moon ' was- about twice the length of a second horizontal bar. The explanation of the phenomenon of parhelia is due to Rene Descartes, • who suggested that the display arose by refraction and reflection of light. ice crystals in the upper atmosphere, some 20,000 feet high. Ice crystals have the usual form in clouds of right hexagonal prisms, and one of the prop-, erties of such prisms is that they have three possible refracting angles. The various refractions and reflections. of the light of the luminary in these crystals can be shown mathematically to account for all the various arcs and circles composing the display. Phenomena for October v

The Sun will remain-in the constelljg j tion Virgo during the month, its noon , altitude at Auckland increasing from , 56 degrees to 67 degrees in that time. The Moon will be in conjunction with , the various naked eye planets as fol- . lows: —Jupiter, sth, 11 p.m.; Saturn, 9th, midnight; Mars, 21st, 4 p.m.; ? Venus, 26th, midday. Mercury will be in conjunction with * the Sun on October 10, then passing » from the morning to the evening sky. Venus, the evening star, will attain its greatest brilliance on the 16th. It is by far the most prominent object in 1 fciie western evening sky at present. 1 Mars, in the morning * sky, will be in conjunction with Neptuno on October 12. Jupiter remains a prominent ob- ; ject in the constellation Capricornus, being above the horizon until the early hours of the morning. The planet, Saturn, is also favourably placed for observation, being in opposition- to • the Sun on October 8, and remaining - above the horizon all night.