ASTRONOMICAL NOTES FOR DECEMBER.

Wairarapa Age, Volume XXXI, Issue 3059, 2 December 1908, Page 6

ASTRONOMICAL NOTES FOR DECEMBER.

(By the Rev. P. W. Fairclough, F.R.A.S.)

Saturn will be found due north early in the evening. Jupiter is in Leo, and can be seen rising in the small hours. The grandest region of the heavens, that containing the Pleiades, Orion, and the Dog star, can also be seen eastward "soon as the evening shades prevail." There are two phenomena of some interest this month, a penumbral eclipse of the moon and an annular eclipse of the sun. The former occurs on the 7th, and will not be visible in New Zealand. Indeed, it will scarcely be visible at all to ordinary observers. The moon does not enter the real shadow cone of k the earth. Everywhere within the cone of darkness that the earth throws into space on the side opposite to the sun, the great luminary is entirely hidden. Any part of the moon that enters this dense shadow has the sun totally eclipsed. Outside this cone, however, there is a much larger space in which, seen from the moon, the sun is par- . tially eclipsed. This larger space is the penumbra or partial shade. When the moon enters this region part of the sun's light is obstructed by the earth, and consequently the moon is somewhat bedimmed,. especially on t the.edge nearest to the shadow. On thjs occasion the moon will miss the shadow by only twelve seconds o arc.

The second phenomenon is another annular eclipse of the sun. There "was one on June 28th; there will be another on December 28rd. It will 1 -waste itself in the Altantic Ocean, being seen in South Africa and the Mauritius Islands as a partial eclipse. The sun will be almost at its nearest point to the earth, and hence its apparent diameter will be too much for the moon to cover. Therefore, a ring, or annular, of light will be se.en all around the moon's dark orb. We presume once more our consideration of Partial Impact, and we hasten to escape from the realms of theory and speculation to those of observation. If a collision such as we have discussed, took place, it would produce a tremendous blaze of light. Has any such sudden blaze ever been seen?

Yes, a considerable number of ■ "Novae," or New Stars, "Blaze Stars" or "Temporary Stars" have been observed. Tycho's Star in 1572 was as bright as t Venus at her best. It was seen in daylight, and yet within 16 months faded from sight. There were no telescopes then. In 1604, Kepler saw a blaze star equal to Jupiter, which faded away in two years. Several others have been seen by persons now living. In 1866, an Bth Mag. Star increased more than one hundredfold—that is to Mag 2. v In a few months it lost this sudden splendour. In 1876 a star in Cygnus rose from invisibility to the 2nd Mag. within four hours. It retained its maximum only a few' hours, and was invisible to the naked eye within a month. Its spectrum changed rapidly, and at last <vas like that of a in nebula of Andromeda. In 1892 one appeared in Auriga. It did not rise above the 4th Mag., and faded from the naked eye in a month. It was carefully studied, , and its spectrum appeared to indicate two bodies, one approaching and the other receding. The relative velocity was at least 550 miles per second. Lord Kelvin suggested that if there had been a collision the motion observed might arise |from flying fragments, "spattered off." The spectrum turned to that of a nebula, but subsequently resumed that of a'star. On February 21st, 1901, Nova Persei was discovered. It was as bright as the pole-star—2nd Mag. The region had been photographed on February 19th, and no star was there. It must have increased'at' least 25,000-fold in two days. For a few hours it was brighter than any star save Sirius. Yet at the end of March it [was lost to the naked eye. The spectrum varied and became nebular, tin September, 1901, it became possible w ; th reflecting telescopes to photograph the invisible surroundings of the star. | A roughly circular nebula was found, about half the diameter of the moon. At the most moderate estimate of the distance of the object, its diameter must have, been 3,000 times the distance of the earth from the sun, or, say, 280,000 million miles Probably the object is tens or hundreds of times larger than this estimate. In this object several well-marked knots of condensation are observed, and, by comparing photographs, these are found to be moving away from - the centre at the rate of about one minute of arc in six weeks. If the nebula were as near as Alpha Centauri, this would mean a velocity of 2,000 miles a second. But if the nebula is, as it may well be, nine- - ty times as far away as Alpha, then the velocity is that of light. Kapteyn suggestsjthat this is the true explanation.! The light of the original - outburst is travelling outward over continents of nebulous matter that were there before. It is impossible to suppose that the nebulous mass described above could have originated from the impact of two bodies and have expanded in less than seven months. The mass of such a nebula would be enormous. Supposing it to be as near as the nearest star, it is-fifty times broader than the orbit of Neptune. But, as neither parallax nor proper motion are discoverable, it is more probably at Kupleyn's distance, and 90 or 100 times broader than the estimate. Xn any case the mass is exceedingly great,- and would oppose a tremendous pull to the explosive force. Can it, then, be believed that for, say, '2OB days it expanded at the average rate of 28,000,000 miles an hour, or 7,777 miles a sscond in all directions? It seems incredible, and yet this is the lowest possible estimate. Hence .it seems that this particular nebula not produced / by the same cause as the outburst of the Nova. . The sudden 'appearance of a luminary, possibly exceeding the sun hundreds or even thousands of times!, is a stupendous phenomenon. We know of no explanation of it half as good as impact. More marvellous, however, than the rise of the light is . its rapid decay. While suns are admitted to shine for millions of years, these fade in a few days or weeks. We know of no explanation of this

to be compared "with Professor Bickerton's ingenious theory of swift expansion and selective molecular escape. We refer our readers to Bickerton's "Romance of the Heavens" for full explanations. —Christchurch "Press."