ASTRONOMICAL NOTES FOR OCTOBER.

Lyttelton Times, Volume CXIV, Issue 16358, 30 September 1913, Page 6

ASTRONOMICAL NOTES FOR OCTOBER.

♦ The planets Mars and Jupiter are both in quadrature with the sun on October 3. This means that the distances between them and the sun are each UOdeg, or a quarter- of a circuit of the heavens. When the moon is in a similar position, she is said to be at first or last quarter, and in this case Jupiter is east of the sun, while Mars is west. Jupiter passed through opposition a few months ago, so his present position was to be expected, but the news about Mars is rather a surprise, because this planet has not yet become noticeable. It is only equal to an ordinary star of the first magnitude, and is situated on the boundary of the constellations Taurus and Gemini, where it does not rise until between 1 and 2 a.m.

The motions of Jupiter's four bright satellites are always predicted in _ the Nautical Almanac except at those times when the planet itself is invisible, and on October 22 a very unusual prediction is made concerning them. All four of them will become invisible from 4.28 p.m. to 5.3 p.m. The observation, however, is not one that Nsw_ Zealanders can make, because at that time the sun will still be above the horizon in this longitude. The period of thirty-five minutes mentioned commences with tho disappearance of the first satellite behind Jupiter, and ends with the reappearance of tho thiid after a passage in front of the planet. The second satellite is also rendered invisible by passing in transit across the disc of the planet, and the cause of the fourth satellite's invisibility _ is that it is eclipsed all the time in the shadow of Jupiter. The positions of tho first three—two in front of the planet and one behind it—are due to a. peculiar law by which these littlo moons are controlled. When two of them are in line on one sido of Jupiter, the other is always in the same line on the other side. No explanation of this behaviour seems to have been found, but there must be some natural law in existence, as these satellites always move in obedience to it.

Saturn is stationary on October 1; that is to say, his apparent motion changes from eastward to westward on that date owing to the motion of the earth, which is now overtaking him rapidly. He will be in opposition to tho sun at the beginning of December, and during. October ho becomes visible in the evening sky, rising on the first of tho month at 11.54 p.m., and on the 31st at 9.47 p.m. His position in tho northern part of Taurus is not a favourable one for observers in the southern hemisphere. Tho morning papers during the past month have brought news of two comets, but neither of them_ 6eems to have been seen at all in this country. Tho first one, reported from Adelaide Observatory, and said to bo moving north-west from a position between the stars Beta Cygni and Alpha Vulpeculae, was certainly searched for by a number of amateurs in New Zealand. There is a nebula near this position which looks like a small comet, and this raised hopes at first until it was identified, but nothing whatever was seen of the comet itself. The other comet mentioned in the cable news appears to have been found by Dr Metcalt while searching for WestphaPs comet, and its position was not stated. Several ephemerides for this comet have been published, but tho dates given for its perihelion passage are merely conjectural, so that the comet has been predicted to appear in a good many different places. The identification, of a now comet would bo effected by finding whether its motion shown by a few days' observation corresponded with the predicted comet, and, as no cable came a fow days later to confirm the supposition, it seems probable that Westphal's comet has not been found vet It passed perihelion on October 12 1852 and was found to be moving in'an ellipse instead of ft parabola but the return in sixty-one years deduced is merely a computation result, as a period of such length could not be calculated accurately from the observations of a few weeks. The transactions of the International Conference at Bonn on the subject of solar research have not _ yet been chronicled in any of tho scientific publications, but there is plenty of news about tho doings of tho delegates while nassine through London. Professor Pickering and Miss Cannon, after thenvisit to the Royal Astronomical Society, wero present at the last meeting of tho British Astronomical Association on June 25, and again they delighted all who were present to hear their accounts of the work at Harvard College Observatory. The report of that meeting is one of the many things that make ' amateurs in New Zealand realise- how

much they are missing. Miss Cannon spoke first, and described in detail the methods by which .variable stars are discovered at that observatory, not singly or in dozens, but in hundreds.' Out of 4525 known variables 3731 were found at Harvard. One of the methods, of discovering them is the outcome of tho work done with the prismatio camera described in these notes a month ago. This instrument records the spectra of stars down as low as the ninth magnitude as readily and as plentifully as a common camera would record the stars themselves. Nearly all variable stars of long period show' a spectrum of the third type: that is with broad bands as well as lines, but having also some complications, of which the chief is the presence of a fewbright lines. When a spectrum of this sort is found on the plates, the negatives of tho star-field taken with a common camera at intervals during a. period of more than twenty years can be examined, as all euoh photos taken at Harvard are stored there for ready reference. This has led to the detection of a large number of variable stars, but there is a simpler method still namely, the comparison of plates of the same region taken at different dates- A positive ia made from one of the plates, and then the other negative is placed in contact with it. For some reason not mentioned in the reports the star images are larger on the positive than on the negative, and so when the plates are superposed, the negative images do not cover the whole of the star discs, but produce an effect like an annular eclipse. It does not require a great deal of study to notice a star which has an annulus greater or less than those which surround it, and an exception of this sort can only mean that some variation has taken place in the brightness of the star. A number of specimen plates were handed round for inspection. Professor Pickering also spoke on tha work of the observatory he represents, but he gave a great deal of sound advice to amateurs. Briefly, his oonclu-. sions are that owners or small tele- ! scopes cannot undertake any observa-, tions of planets which are likely to be of permanent value. One of the most valuable kinds of work open to such observers is to watch variable stars and determine their magnitudes on as many nights as possible. Only by such means can the period and range of variation be discovered, as the photographs at Harvard and elsewhere give no information of this kind at all. It may be mentioned here that Professor Bickerton was present at this meeting, and he asked Professor Pickering several questions about the appearance of bright lines and the changes they undergo in tho 6pectra of new stars and variables, from which it is easy to guess' what he had in his mind.