ANNULAR ECLIPSE

Evening Post, Volume CXXII, Issue 68, 17 September 1936, Page 10

ANNULAR ECLIPSE

EVENT IN DECEMBER

MOST EFFECTIVE AREA

KAWHIA TO TAURANGA

(From "The Post's" Representative.)

LONDON, August 12. When the annular eclipse of the sun occurs in the Southern Hemisphere on December 14 its central line will, by an odd chance, pass directly over Pukekohe, the birthplace of Dr. L. J. Comrie, Superintendent of the Nauti-j cal Almanac Office, Greenwich. In his department, the times of .beginning and end of the eclipse, together with the duration of the annular phase, | have been worked out to the nearest second. Naturally more than usual interest has been taken by Dr. Comrie in the computation of the circumstances of this particular eclipse, and it is a matter of regret to him that he cannot be present in Pukekohe to obtain visual confirmation of his calculations. The difference between a total and an annular eclipse, the progress of the moon's shadow on December 14, and the best method of watching the sun were explained in an interview with Dr. Comrie at Greenwich last week. THE RING OR ANNULUS. "During an annular eclipse," said Dr. Comrie, "the moon is about as far away from the earth as it can possibly be. Therefore its apparent diameter is slightly less than that of the sun. Hence, when the moon is projected on the sun there-is still a ring or annulus left. In this particular case the width of the annulus is about one-thirtieth of the diameter of the sun. In a total eclipse the moon is nearer to the earth, and its apparent diameter is slightly greater than that of the sun. "The annular phase of the eclipse on December 14 may be seen from places between two lines known technically as the northern limit and the southern limit. The northern limit runs from the northern part of Kaipara Harbour to Cape Colville. The southern line runs from the centre of Lake Taupo to about 30 miles south of Gisborne. The central line, from which the annulus will be symmetrical at mid-eclipse, stretches approximately from the Waikato Heads through Tauranga Harbour to the East Cape. The best places from which to view the eclipse will be those not too far from the central line, as, for instance, Auckland, Pukekohe, Ngaruawahia, Hamilton, Thames, Te Aroha, Waihi, Rotorua, and Tauranga. "It will not be possible to see the solar corona, the attraction in total eclipses', because of the brightness of the remaining ring of sun. Nevertheless the spectacle will be unusual and attractive, and those who are able to arrange their holidays so that they are in the track of the eclipse will be rewarded with an interesting sight. BEST KIND OF SCREEN. "It is very dangerous to view the sun with the naked eye. Smoked or coloured glasses should be used. The best screen is smoky black celastoid. If this is cut into little strips of five by two inches and about five strips riveted together at one corner, the observer can use one or more strips according to the intensity of the sun. "As a typical example of the progress of the eclipse," continued Dr. Comrie, "the circumstances for Pukekohe, which were specially calculated in the Nautical Almanac Office as an illustration, may be described. The eclipse begins at 9.15 a.m., when the moon first begins to creep on the sun at a point that would correspond to 11 o'clock if ■it were regarded as a clock face. At that time the sun is already 50deg. high—more than halfway from the horizon to the zenith. An hour later more than half of the sun will be covered by the moon and the sun will be lOdeg. higher. "The visible portion of the sun is now gibbous. By 10.50 a.m. only a small crescent will remain, and at 10.51 a.m. this crescent will become a ring. At that moment the ring will be very broad in the direction corresponding to 4 o'clock and very narrow in the direction corresponding to 10 o'clock. SEVEN MINUTES' DURATION. "This ring may be seen for just over seven minutes. It will continually change its shape, but will be most symmetrical at 10.54J a.m. By 10.58 the broad part of the annulus will have moved round to the 10 o'clock position and the annulus will break in the 4 o'clock position. The crescent that remains will broaden gradually, until, by 11.30 a.m., half the sun will again be visible. The eclipse ends at 12.44 a.m. The last portion of the moon will be seen in the position corresponding to 2 o'clock.

"Annular eclipses are rarer than total eclipses," said Dr. Comrie, "but they are not so exciting. The longest possible time for the complete annulus to be visible is eleven minutes. This one will last for seven, which is quite a good proportion. The longest possible duration of a total eclipse is seven minutes."