POPULAR ASTRONOMY

Otago Witness, Issue 2817, 4 March 1908, Page 69

POPULAR ASTRONOMY

NOTES FOR MARCH. By Rev. D. Dutton, F.R.A.S., F.G.S. The Sun enters Aries (the Ram) on the 21st, and parses thiough that constellation from Ap.il 16 to May 13. Aries is called the first sign of the Zodiac, and when the constellations were named was the point of j the Vernal Equinox in the Northern Hemi- ] sphere, called the "First point of Aries" — that is, the point where the Sun cro=ses the celestial equator from 6outh to north. Owing to the precession of the equinoxes this point is now in Pisces (the Fishes), which is designated the " Leaders of the celestial host." As explained in previous notes, the Sun will be in this constellation from the middle of this month till the middle of April. Most people know that the word equinox means equal night, and that twice in the year— about March 21 and September 22, at the vernal and autumnal equinoxes respeethely — the days and nights are equal in all place 6. .*■ The Moon will be new on the 3rd, first quarter on the 10th, full on the 18th, last quarter on the 26th. I The Planet*. — Mercury is a morning ' star. Venus is an evening star, and may , be seen in the west as soon as the twilight ! has sufficiently faded to allow it to become visible. Mars and "Saturn are evening stars, but set too early to be of interest to the observer. Jupiter is in Cancer, and is the most, brilliant object in the sky at present except the Moon. The Constellations. — The Southern Cross and Centaurus are in the south-east. Below Centaurus is a group of small stars formthe constellation Lupus (the Wolf). The Triangle is a well-defined figure, and can easily be recognised to the right of Alpha and Beta Ccntauri. Below the Triangle, , between south and south-east, Ara (the Altar) may be noticed. South of Ara is , Pavo (the Peacock), and between south and south-west Hydrus (the Water Snake) apl pears. This constellation iis near, and ; partly between, the Magellanic clouds, ! while Us tail almost reaches the bright star Achernar, the principal star in Eridamus. From Achernar a stream of small stars, forming the River, may be traced from south-west through west to the neigh- ' bourhood of Orion ; hence it is called Orion's River. Argo (the Ship) is partly i at the zenith, and Canopus is overhead. Canis-major, with Sirius, is at a high altitude, and is not easily mistaken for any other group. Orion is lower down, a little tn the west. Above Orion is Lepus j (the Hffc). and west of Canisj major is' Columba (the Dove). Canisminor. with Pro<*vn, is below and to the right of Canis-major. There is a | glorious procession of zodiacal constellaj tions visible at present, beginning with j Taurus (the Bull), rather low down in the ; north-western direction, followed by Oemini (the Twins), between north and north-west. Cancer, (the Crab) tho present location of Jupiter, is to the right of I Gemini. Leo (the Lion) is in the north- ' east, and is easly found by its sickle group !of stars. Virgo (the Virgin), with its brisrht star Spica.. is in the oas{ ; while between east and south-east Libra (the Balance) is coining into view, though at present too near the horizon to bo well j sepn. Above Spica is Corvus (the Crow), and near by Corvus is a small group of stars called Crater (the Cup). This con- j stellation was known in England three j centuries aero as the Two-handed pot. In the Warwick collection there is a small ancient vase bearing an inscription which is translated thus: — "Wise ancients knew when crater rose to sight. Nile's fertile deluge had attained its height. This is rather curious, as no Egyptian remains so far discovered make any allusion to this constellation. The positions of the stare given in these, notes is as they appear about 9 o'clock in the evening. Towards the end of the month they will occupy the positions indicated at an earlier hour of the evening. ITEMS OF INTEREST. In the constellation Leo. near the star Gamma, the radiant point of the famous November star-shower is located. Need- j less to say, the meteors Lave no connection ' with that star or any of the other stars, j These objects, called "shooting stars," do i not become visible until they actually j enter the Earth's atmosphere and are set on fire by its resistance. But when they are carefully observed their direction across the sky is such that if the line of their advance is carried back to what appears as the starting-point, they fewn to radiate from the position in Leo indicated above; hence Loo is called the radient of a pai Ocular group of meteors that appear about the middle of November. It is as though thaie were a hole in the sky where the star Gamma Lconis is placed, through which the meteors are introduced and from winch they flow away in various directions. These meteors are therefore known as Leonides. Every year meteors more or lees numerous are seen flashing from this point about the middle of No\ ember, when the Earth arrives at a certain point of its orbit, while at inter-

•cale of between 33 and 34 years the meteor* at this point are so abundant that' they constitute a. groat shower of shoot' ing "tar«. It is obvious from this 1 that the Leonides are pursuing a pathrourd the Sun in a long elliptical orbit, having a period of between 35 and 34 years. The great body of the meteors travels round the Sun in a compact, euarm, which at the above intervals intersects the Earth's orbit at the place to which the Earth always returns on the 13th of November of each year. Hunboldt observed a very brilliant ' shower of Leonides in 1799. There was I another fine display of these celestial fireworks on the 13th and 14th of November, 1833, and again on the same days of the month of November, 1866. A gentleman ! on that occasion, who supposed that shooting stars were the actual stars that twinkle | in the sky, said the stars continued to fall j until none were left, and added. " I am I anxious to see .how the heavens will appear j to-morrow evening, for I believe we s.hall see no more stars in the sky." The Leonides were due to appear again in November, 1899, and an eager and expectant watch was kept for them ; but the ! watchers were doomed to disappointment, as very few of the meteors were seen at that time. In 1900 a small shower was witnessed in some parts of Canada. It is now held that the absence of the meteoric shower in 1899 was due to the influence of the larger planets, chiefly Jupiter, as it is known that these meteors are subject to perturbations caused by the larger planets, which ha%e the effect of slightly changing their orbits, pulling them backward and forward and thus thrusting the swarm inside or outside the orbit of the Earth. It is probable that the perturbations that occurred during the period from 1866 to 1899 deflected the etream to such an extent that it did rrot then, in its more dense part, intersect the orbit of the Earth. Whether the subsequent influence of the outer planets will drag the meteors back to their former position in relation to the Earth's orbit time alone will 6how. There are hundreds of radient points of meteors now known from which year after year at about the same time of the year for each group meteors radiate, showing in these cases an extended distribution of meteors all along the course of their orbits. In the early part of August each year a star-shower comes from a radient point in the constellation Perseus. These meteors are known as the Persides, but, unfortunately, neither Leo nor Perseus are favourably placed in August and November for our seeing in these parts. One of the most interesting of all the metoric showers is that which occurs towards the end of November, called Andromedcs, also the Bielids. This swarm is supposed to be very closely connected with the lost comet known as Biela's comet. This comet, which had a period of about 61 years, has not been seen a3 a comet since 1852, but from near the position where the comet should have been in November, 1872, when the earth was crossing the comet's orbit, there came a great .meteoric shower. There have been several repetitions of this shower, aud as Miss Clerke says, " It became evident that Biela's comet was shedding over the earth the pulverised products of its disintegration." Up to the boginninng of last century meteors were not regarded as celestial objects. They were supposed to be merely vaporous exhalations from the earth which occasiona'ly caught fire in the higher regions of the atmosphere. When, howI ever, their real nature was discovered they became of growing interest to astronomers. 1 and a great deyl of time and study are de- , voted to what has become a specialised branch of astronomy. Attempts have been made to approximately estimate the number ' of meteors that are ordinarily encountered ; by the earth daily, the number has been etaled to be from 18 to 20 millions. On a j citar nigKt a watchful observer will see {on an averaci 1 from 10 to 16 meteors in an hour. The space covered by tho lange of vision of one observer is very limited. When a sufficient number of observer* stationed at different places within a given area ar« employe.!, and observing in every direction, the number of meteors rounted per hour mounts up to 1 several hundreds. Using this as a basis of I calculation, it is estim-ited that during the 24 hours all the world ov«r the number entering the earth's atmosphere is many millions per day. The height at which meteors become visible is about 75 mile*, and is about f>o mile* when they disappear. The £>reat \ekxity with which fhev move through thr> atmosphere is converted into heat by the resistance they meet with, they become incandescent, and ere quickly reduced to impalpable du*t. Most of them are more grains of matter, but sometimes a meteor is so large and compact that it 6uoeeeds in breaking through the earth's atmospherio shield. Thoaeh not without loss, and reaches the surface. These arccalled meteorites, or aerolites, and in some j ca=cis weigh many hundreds of pounds. | The largest single fragment of a meteorite | seen to fall from tho sky .->nd afterwards ) secured weighed about 5001b. Reports of much larger masses being found in various parts of the world aie current. In ISOO the French Academy declared that the reports of stonfts having fallen from the sky were absolutely untrue and absurd. That venerable body of learned men experienced a genuine surprise, and suffered some loss of assurance when, in 1803, at Laigle. in the Department of Ornp. a great stone fell from the &kv and exploded with a fearful noiee. scattering its fragments o^ er ! several miles of country S^mo of the i pieces of this meteorite are to be. found in j various national collections. Where these meteorites originate is an open oueston: they aro supnosed by many to have a different origin from that of meieors. There i« an undoubted connection bet.ween meteors and comets, which seems nlainlv to indicate that meteors are the debris of disrupted comets. Several of the mare important meteoric swarms are moving in orbits which are identically the same a.* those of well-known comets.