ASTRONOMICAL NOTES

Otago Witness, Issue 2842, 2 September 1908, Page 89

ASTRONOMICAL NOTES

FOR SEPTEMBER, 1908* By John Gbigg, F.R.A.S. THE SUN. The Sun's path during the month will be from R.A., 10.41 dec, N. 8.21, in the constellation of Leo to R.A. 12.25 dec. S. 2.4-5 in Virgo, crossing the equator on the 23rd at 10.29 p.m., N.Z. standard time, at which period day and night will be-equal in length. This is usually called the autumnal equinox, but the appellation is inappropriate in the Southern, j Hemisphere, which the Sun is then passing into. We may, however, congratulate our- 1 selves on the passing away of the intensely j cold weather which has recently caused us co much loss and inconvenience. THE MOON | will enter Libra on the Ist, being then 5 days' old. Its periodic phases will occur as under : — First quarter,- 4th, 8h 20m a.m. ; full moon, 10th, llr 53m p.m. ; laet quarter, 17th, lOh 3m p.m. ; new moon, 26th, 2h 30m a.m.; perigee,' 10th; apogee, 23rd» THE PLANETS. Mercury, which passed behind the Sun last month, will be 9 degrees east at the beginning of this month, too near to be visible to us, but as that (angular) distance is increasing, while its actual distance from us is decreasing, we may look for it later on. It will be near the Moon on the 27th, and about 25 degrees from the Sum E.N.E. at the end of the month. Vclnus, rising three hours before the Sun, is increasing its westerly distance, attaining its maximum (46 degrees) on the 15th, after which it will appear to reapproach the Sun, its diminishing diameter showing that it is receding from us in its journey round and behind the Sun. Mars and Jupiter, being also behind ihe Sun, are unfavourably situated for observation. Saturn rises at 8 p.m., and at 'the end of the month 6 p.m. Uranus may be looked for with the telescope 7 degrees north of the star Zeta Sagittarii, its path for the month being from R.A. 18.57 dec. S. 23.13 to 18.56 dec. 23.14, its meridian, passage being from 8 p.m. to 6 p.m. It may be noticed that its position is very slightly changed from that given last month. This is owing to its immense distance, whioh at the present time is 1,804,000,000 of miles (19£ times that of the Sun). By a careful search with a good instrument of 3 or 4 inches aperture it may easily be differentiated from a star by its small, dull disc, as it was by Herschel, who thereby discovered it in 1781. ENCKES COMET. Since writing last month's notes news has come to haotid that this comet was detected at the Cape of. Good Hope Observatory on May 28, not far from its computed place. THE STARS. The following bright stars, as seen from Dunedin, will culminate at the hours named on the. Ist of the month, and 3min 56sec earlier daily afterwards: — Anlares, 5h 51m, altitude 70 N. ; Canopus 7h 49m, altitude 9 S., lower transit; Vega, 8h om, altitude 6 N. ; Altair, 9h 14m, altitude 36 N. ; Fomalhaut 12h 19m, altitude 74 N. These times are oalouated for the meridian of Port Chalmers, and reduced to New Zealand standard time — llhrs 30inin- fast of Greenwich. For inland places on or about the same latitude one minute should be added for every 12 miles westward. If a compass is used for finding the meridian allowance must be made for its variation, which is given as 16.48 east of true north. SUNSPOTS. During August many groups of spots were visible on the Sun, several of them unusually large. It is not unlikely these disturbances may continue for a while, and as they may be seen with the assistance of a very small telescope, we will describe a simple method of viewing them. Cut a hole in a piece of card and fit it on to the draw-tube of the telescope. Then turn the object glass towards the Sun and hold another piece of card before the eyeglass, about a foot distant. The Sun's image will be aeon projected on it. Gradually increase the distance until the disc is sharply defined, then any spots tliat may be present will be distinctly soen. By using a larger instrument and attaching a suitable camera they may be photographed. This is done in many observatories, public and pmate, the records being subsequently measured and registered. t The spots ira\el across tue Sun s discfrom east to west, indicating the rotation of the Sun upon it* axis. They nmv die out in a few da.vs or remain (subject to changes) for several weeks, or even months, occupying 12 or 13 days in crossing, and after an absence of a similar psrion reappearing to repeat the journey. Their motion is somewhat fluctuating, which, ju-u-fies their description as storms in the luminous envelope of the Sun. Several years ago Mr E. W. Maunder, of Greenwich, assisted by his talented wifo, measured 4700 group? as catalogued during the previous 23 years, and, inter alia, deler- ' mined the Sun's actual rotation period to ' be 25i days, its apparent period, as seen from our mowng Earth being two day 3 longer. r Do sunspot= portend change of weather.' Our reply is. Whatever effect changed con- ' ditions in the Sun may have upon our j Earth as a whole, we cannot .conceive of ■ effects limited to certain localities, a c ' "weather" invariably is. But the larger question has long been under consideration. Electrical disturbances are recorded by changes in the direction of magnetic needles, which occur simultaneously all over the world, and are generally coincident with solar outbursts. The probability of these Ij^ing cause and effoct is therefore ! essurned. but is not sufficiently understood i to be adopted as proved. I , .