ASTRONOMICAL NOTES

Evening Star, Issue 23695, 1 October 1940, Page 2

ASTRONOMICAL NOTES

THE SKIES IN OCTOBER [Written by A. G. C. Crust, M.Sc., for tho ‘ Evening Star.’] POSITIONS OF THE STARS Local sidereal time 24 hours, latitude 46deg S. The following positions of the stars hold good locally four minutes earlier cadi evening—e.g., at midnight, October 2-3, at 11.00 p.m. on October 17 and at 10.00 p.m, on November 1. ’ All times are given in New Zealand summer time. Duo south - shines Alpha Crucis, the brightest star in the Southern Cross, | 18deg above the horizon. Our nearest stellar neighbour, Alpha Centauri, is S.S.W., 21deg, while Antares, in the Scorpion, is S.W. by W., 4deg. Altaic is W.N.W., 12deg, and Fomalhant NAV., 70deg. At this, the impressive “ zero hour ” of sidereal time, we begin to see the brilliant stars of summer rising in tho cast. Thus the orange giant Aldebaran is placed E.N.E., 2dog, and tho bluish Rigel, in Orion, E., 14deg; but most striking of all is the “dog star” Sinus, sparkling brilliantly sdeg abovo the horizon in the E.S.E. In the S.E. are Canopus, at an altitude of 33deg, and Achernar, now the highest bright star, at 72dog. , Nautical twilight ends at Dunedin at 7.52 p.m. on October 2, at 8.21 p.m. on October 17, and at 8.41 p.m. on November 1. New Moon occurs at midnight, October 1-2, and is tho occasion of a solar eclipse on tho other side of the world. On the forenoon of October 3 the Moon will pass 3deg N. of the planet Mercury, on the evening of the oth 9deg N. of Antares, and at 11.40 p.m. on October 7 her position in the sky will bo W. -by S., ICdeg. First quarter falls on tho afternoon of the Bth, at--11 20 p.m., on the 12th our satellite will fie placed N.W. by N., 46deg, on tho forenoon of tho 13tli she will pass 25deg N. of Fomalhaut, and Full Moon will occur on the evening of October 16. At 11.00 p.m. on the Irth the Moon’s position will be N.E. by N., 25deg, on the next day about midday she will pass Ideg S. of the planet Jupiter, and O.ldeg S. of tho Pj a het Saturn, while the afternoon of October 20 will find her Ideg N. of Aldebaran. Last quarter occurs on the afternoon of the 24th, and on the afternoon o:t October 28 she will pass 3deg S. of the brilliant planet Venus. At midnight, October 29-30, she will pass o.sdeg b. of the planet Mars, and New Moon occurs for the second time this montn, on the forenoon of the 31st. Tho planet Mercury will be at greatest elongation east, 24deg from the Sun on October 20. He must be looked for early in the evenings. _ . • The bright planet Venus is visible in the morning sky shortly before sunrise On the afternoon of October 3 she will pass O.Sdog S. of Regullus, and on the forenoon of the 30th, o.2deg N. of the faint and distant planet Neptune. The bright planet Jupiter is now visible at 24 hours S.T., his position being N.E., 18 to 20deg, during the month. A little above him is Saturn, about Ideg distant, position 19 to 21deg in tho N.E. On the forenoon of October 12 these two planets will ho in conjunction, but for a long time they will appear close together in tho sky and afford a good opportunity for all sorts of comparisons. Saturn looks rather dull in comparison with Jupiter, but both are always prominent planets. From the Queen’s Gardens, Dunedin, at 24 hours S.T., Alpha Crucis will appear low in the direction opposite to tliat of First Church, Fomalhaut very bio'll over the Garrison Hall, Canopus moderately low, and Achernar very high in the opposite direction. The planets Jupiter and Saturn will be low and rather low over Anzac Square. The Moon will be low over Customhouse Square at 11.40 p.m. on October 7, at a moderate altitude over Burlington street at 11.20 p.m. on October 12, and rather low over Anzac Square at 11.00 p.m. on the 17th. THE NEW ECLIPSING VARIABLES IN OCTOBER Tau Orion is, close to Rigel, will commence colour maxima 15 minutes earlier daily—e.g., October 2:00:16 to 11:21:43 —while the terminal changes of these maxima occur 2h 17iuin later e.g., October 2:03:33, 12:00:00, and 21:21:27. For 32 Orionis, maxima commence 20 minutes earlier every fifth morning, from October 5:04:22 to 80:02:39, their terminal changes similarly, from October 2:01:37 to 31:23:33. A mixiinuin of Delta Orionis will occur on October 21:00:18, the terminal change commencing on October 21:23 :47. This star seems to be subject to many fluctuations, but minima are predicted to begin on October 7:02:46 and 30:01:02, terminating on October 9 :01:18 and 31 ;23:37. For 37 (Phi 1) Orionis, minima win commence 40 minutes earlier every ninth day, from October 1:01:27 to 27:23:25. As 32 and 37- Orionis are rather far north and are visible during our short summer nights, it is important that they should bo observed in New Zealand if possible. Meantime they aro omitted from the Ephemeris for 1941. Minima of Alpha Pavoms, observable with very small telescopes, aro predicted for October. One will commence on October 13:10:15, and the next on October 26:21:52. The terminal changes of two maxima fall on October 8:0- :-7 and 21:04:04. Alpha Pavonis is a triple system, which may bo roughly illustrated by using an egg in the following manner: —Draw,a line, as straight as possible, from one elongated end of the egg to the other, on its shell, continuing this back to the starting point on the other side. This represents the oval orbit of the eclipsing companion of Alpha Pavonis, while the yolk of the egg represents the principal star. Now draw a line on the shell at right angles to the former line, making a circle around the egg, just as does the rim of the egg cup, rather bellow the widest part of "tho egg. This represents the circular orbit of the companion star found by Curtis by means of the spectroscope, if wo now look at the egg with one end pointing almost directly towards us wo have the same point of view as is presented by Alpha Pavonis itself. Imagine the shell and white of the egg removed, and we have tho_ yolk representing the large star, while two tiny “ sparks ” traverse the two pencil lines, one in 13.07 days and the other, on the circular track, in 11.75 days. Actually, on our model, a collision would bo inevitable, but the circular orbit is really inside the oval one, and actually tho tiny companions only pass very close to each other. There aro times at which they must eclipse each other, and so far we can predict the times when the one on the oval orbit passes in front of. or behind, the other track. On rare occasions eclipses will occur at these times, b.ut it. must bo clearlv understood that usually “ nothing happens.” In October those su- ■ called “ nodal epochs fall on October

,1:1.". 3:21, 16:17. 16:22. 29:18, and 30 ;00, The predictions are given only to the nearest hour, but the chances of eclipses taking place are increased hv the fact that the star on the oral orbit is travelling nearly in the line of sightdirectly aivay from us.