TRANSIT OF MERCURY.

Shannon News, 27 May 1924, Page 1

TRANSIT OF MERCURY.

Those who have telescopes or good binoculars may, if the sky is clear todav, take part, in observing an as- • tronomical event of considerable'. Interest —a transit of Mercury. Mercury is the smallest of ,thc. planets, aiid is also the nearest to, the sun, fronh which its average distance is 36 million miles. Being between us and 11m sun, it will be about 57 million miles away when seen, and as it is only 3000 miles in diameter, its appearance is not impressive. It will appear as large as a half-penny , a litiUe over 500 yards away, .or ns a large dinner pla'te four miles off. Owing to this fact it cannot he seen, with the unaided eye. Observers should take care to,use a proper dark or smoked glass to protect their eyes if they view the. transit directly ■Anolher way to view the transit, is to tit a small screen of white paper some inches behind the telescope eye-piece and to view the sun’s image projected on the screen. With this method no dark glass is required. The planet takes some eight hours ( to cross the sun. and the transit be- ' gins about Ohr l.Bmin a m., according to the predicted time. Observers should be on watch' before this time. Mercury will cross the sun almost centrally, and may be distinguished from any sun spots by its rapid motion. If we assume the. sun to bo marked like the face of a clock, Mercury will be seen to enter near the 5-hour mark. The transit of’Mercury in November 1914, was well observed at the Royal Observatory at Greenwich. when none of the observer's saw the "black drop,” a halo round Mercury, or a bright spot on the planet. All oi these had been reported at former transits. The phenomenon appeared just as might have been expected from geometrical considerations. A sharp- black spot was seen to cross the sun’s disc. Astronomers are invited to repot t their observations to the New Zealand Astronomical Society,. A transit of Mercury was observed

in Wellington on 10th -May, 1891, when the late Mr C. P. Powles, an enthusiastic astronomer, made a careful drawing of the phenomenon.'This drawing, with a number of others of solar appearances, he presented to the New Zealand Atronomieal Society shortly before death, and it is kept as a valuable item in the society’s archives.