Astronomy.

Progress, Volume VI, Issue 4, 1 February 1911, Page 544

Astronomy.

About the Heavens Generally. Lecture by Mr. C. P. Powles, President of the Astronomical Society. (Continued.) I have spoken of a zodiac, and will now explain what it is. It is so called from a Greek word zodion, meaning an animal, and is applied to the belt in the sky in which the Sun and the planets have their paths, and comprises nine degrees on each side of the ecliptic, or path of the Sun. When I say the path of the Sun I mean the path which the Sun appears to take in consequence of the motion of the Earth round him. As the Earth goes on in its orbit, we see. the Sun in different places with respect to the stars, making him appear to travel through certain constellations. These, constellations are twelve in number and are called the signs of the zodiac. They are Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin), Libra (the Scales), Scorpio (the Scorpion), Sagittarius (the Archer), Capricornus (the Goat), Aquarius (the Water Carrier), Pisces (the Fishes), or as I learnt them years ago— The Ram, the Bull, the Heavenly Twins, and next the Crab The Lion shines, the Virgin, and the Scales, The Scorpion, Archer and He Goat, the man that holds the Water Pot, and Pish with . glittering scales.. There are twelve, one for each month. The Sun enters Aries in March, on the 21st, which in the Northern Hemisphere is the spring, or “vernal equinox” (equal day and night), and during a year passes through the twelve constellations. Professor Newcombe, in a work of his on the stars, gives the following as a. summary of more or less probable conclusions drawn from facts known to astronomers:— 1. The stars differ enormously in their actual luminosity. Some are thousands or tens of thousands of times more luminous than the Sun; others only one hundredth or one thousandth as luminous. 2. The more luminous stars are generally the hotter, the bluer, and the rarer in their constitution. They are, as it were, inflated masses of rare and intensely incandescent gas. Hence the stars do not differ in mass so easily as in luminosity. 3. The bluest and most luminous stars are situate mainly in the region of the Milky Way. There is some reason to suspect, that in this region the more densely the stars are agglomerated the larger and more luminous they are. 4. The collection of stars which we cal] the Universe is limited in extent. The smallest stars that we see with the most powerful telescopes are not, for the most part, more distant than those a grade brighter, but are mostly stars of less luminosity, situate in the same.' regions. This does not preclude the possibility that far outside of our universe there may be other collections of stars of which we know nothing.

5. The boundary of our universe is probably somewhat indefinite and irregular. As we approach it the stars may thin out gradually. 6. The Universe extends further around the girdle of the Milky Way than towards the poles of that girdle. But in every direction it extends beyond the limit within which the proper motions of the stars have yet been determined. 7. It does not yet seem possible to decide whether the agglomerations of the Milky Way lie on the boundary of the Universe or not. 8. The total number of stars is to be counted by hundreds of millions. 9. Outside the galactic region the stars in general show no tendency to collect into systems or clusters, but are mostly scattered through space with some approach to uniformity. Now the Sun, as I have said, is a star and only a second-rate one. It has been estimated that Sirius, the brightest star in the constellation Canis Major (the greater Bog), and the brightest of all the stars, is of more importance than any other star, however large and brilliant it may be. The Sun is the centre, of our system; he gives us light and heat, without which life of any kind would be impossible, and the force of his attraction keeps the Earth and the other planets in their places revolving round him. His diameter is 865,000 miles, his temperature far greater than any heat that can be artificially produced. Our mean , distance from him is about 92,700,000 miles, and yet we can feel his heat, and in some parts of the earth, as we know, his heat is oppressive. It has been found that the Sun revolves on his axis in about 25 days, and this has been done by observing the spots which from time to time appear on his surface. They are seen to pass from one side of the disc to the other, always going the same way, apparently passing across, really being carried round by his motion. These spots are seen to be depressions in the Sun’s surface caused, it is believed, by disturbances in what is called the photosphere, the luminous outside covering of the Sun, which gives us light. The interior of the Sun is supposed to consist of various substances in such a state of heat as to bo resolved into a gaseous state, and at times there are great eruptions of flame from the photosphere which are seen as prominences projected from the edge of the disc. ■ Some of them can be seen when the Sun is totally eclipsed, and now, by recent improvements in the spectroscope, they can be observed, and even photographed, at any time. From the fact that the spectrum of the Sun has in it lines which we can produce by the combustion of various substances, it is found that the sun has three substances in an incandescent state. So we say that in the Sun are iron, nickel, manganese, cobalt, carbon, calcium, palladium, magnesium,

sodium, silicon, stoutium, barium, alu minium, zinc, copper, silver, tin, lead, potassium, altogether some 35 substances known on the Earth. The Sun is .being constantly observed by astronomers with specially constructed instruments, and fresh information about its phenomena is being obtained. The Earth and the other planets revolve round the Sun in orbits which are ellipses, some departing more than others from a circle. There are, including the Earth, eight planets. Venus and Mercury between the Earth and the Sun, and Mars, Jupiter, Saturn, Uranus and Neptune beyond the Earth. Mercury’s mean distance from the Sun is 35,392,000 miles, the Earth 92,700,000 miles, and the outermost planet, Neptune, 2,746,271,000 miles. Mercury goes round the Sun in nearly 88 days, the Earth in 365 days, our year, and Neptune in nearly 165 of our years. There is a curious law, known as Bode law, referring to the distances of the planets. Take the series of numbers, 0,3, 6, 12, 24, 48, 96, each of which, after the second, is double the number that precedes it. Add 4 to each number, and we have the series 4,7, 10, 16, 28, 52, 100. With the exception of the fifth number, 28, all these are proportional to the distances of the planets from the Sun. Thus Mercury 3-9, Venus 7-2, Barth 10, Mars 15-2, Jupiter 52-9, Saturn 95-4, Now you will see that there is no planet corresponding to the fifth number 28, and astronomers, seeing this apparent discrepancy, set to work to find a planet to fill the gap. An Italian astronomer, Piaggi, was the first to discover such a body. In January, .1801, after many observations, he detected movement in what looked like one of the small stars in the constellation Taurus. It was named Ceres, and was found to go round the Sun between Mars and Jupiter. It is very small, quite unlike, the eight other planets. Soon astronomers found other small bodies of the same kind, and at the present time more than 600 of these minor planets, or asteroids, as they are called, have been observed, all going round the Sun in separate orbits, between Mars and Jupiter where there was a gap in the sequence of the planets. Are they fragments of a planet which once occupied that position? Venus and Mercury, being between us and the Sun, exhibit phases like those of the Moon: they are both seen alternately as morning and evening stars. Venus is the most brilliant of the planets, and when at its brightest, can be seen with the naked eye in broad daylight. Its very brilliance renders it a difficult telescopic object, and 4.1, „ U„„4. + „ 1 ... •, • • A ’ A Lin- umi Mine m j uuocivd it IS 111 the daytime. Venus is 7510 miles in diameter, nearly equal in size to the Earth. Mercury diameter is only 2962 miles. Mars is small, its diameter being only 4920 miles, but it appears to be the planet that is most like the Earth when if ap-

proaches nearest to the Earth in opposi tion; that is to say, on the other side of the Sun, so that its surface receives the full light of the Sun, it is still more than thirty 'millions of miles from us. Powerful telescopes exhibit markings which are called lakes, and seas, and continents, and canals, and at the poles white caps, which are seen to diminish in size at times and are considered to be snow, which melts as the Sun shines upon it. There is much discussion and controversy as to whether Mars is inhabited, whether markings seen are artificial that is made by its inhabitants. .Last year Mars was in a very favourable position for observation, and I think the result of observations made was against the theory of canals and inhabitants who made them. Jupiter, the giantplanet, more than 80,000 miles in diameter, is a fine object noaiiy approaching Venus in brilliance. It has a number of "dark belts across its disc, with various markings, one of which is known as the large red spot, a large spot of a ruddy hue which varies in appearance from time to time. From the motion of spots and markings on the belts it is found that Jupiter revolves on his axis in a little less than ten hours, the shortest known period of rotation of any of the planets in the solar system. Jupiter, even through a small Sin. telescope, is a beautiful object, the .four largest of his moons being plainly seen, and it is very interesting to see these moons passing over the planet's disc, or being occulted, that is, passing behind him, or being eclipsed by him or causing eclipses on his surface. All these phenomena I have seen with a Sin. telescope, the most interesting being, I think', to see a satellite coming out from eclipse. You see a faint speck of light appear in the dark sky near the planet, which gradually brightens, until the satellite', having passed out of the planet's shadow, shines out with its normal brilliance. But I think the most beautiful object of all is Saturn. He is nearly as large as Jupiter, his diameter being 71,000 miles, and on his disc are seen belts something like those of Jupiter, but what makes him so beautiful is the possession of rings. Round the planet are fiat rings concentric with the planet; there is the outer ring, then a division called Cassini division, from the astronomer who first discovered it. Then the inner ring, which has at its edge next the planet a dusky border called the crape ring, from its appearance. The diameter of the outer ring is 172,600 miles. The orbit of Saturn is not in the same plane as that of the Earth; sometimes, therefore, he appears above our orbit, sometimes below it. and so the rings appear to vary in extent and position. At one time, when Saturn crosses the plane of our orbit, we see the rings edgeways, and as they are very thin, they disappear altogether, as far as small telescopes are concerned; then gradually, as Saturn passes above or below our plane, the rings open out and we look up to or down upon them. Uranus and Neptune are so distant that as telescopic objects they have comparatively little interest; with my Sin. I can see Uranus as a very small disc of a bluish colour. I have been talking chiefly of the planets' and incidentally mentioned some of their satellites, or moons. Mars has two, Jupiter seven, Saturn ten, Uranus four! Neptune one, and the Earth has one, which

is a most useful attendant upon our planet. It gives us light at night, and helps largely in the production of the tides of the oceans. Its motion among the stars, too, is useful in navigation. And it is a most interesting object to study with a telescope ; a small one will show a great wealth of detail. Its mountains and craters and plains, can be seen; the plains were first named by astronomers, who thought they were seas; there is Mare Serenitatis, the Sea of Serenity, Mare Tranquilitatis, Mare Vaporum, Mare Nubium, etc., and mountain ranges have names: The Alps, the Appenines, Caucasus, etc. All the craters or objects that appear like craters, are named after well-known astronomers and other noted men, Greek, Roman, French. English, Italian. Some of the craters are also called plains, on account of their size; some of them exceed 100 miles in diameter-, while the largest crater on the Earth does not exceed 7 miles. The mountains, too. are loftier than any on the Earth, some of the highest peaks being 36,000 feet, while Mt. Everest, the highest mountain we have, it but a little over 29,000 feet. How the moon became as we now see her is an unsolved problem. She possesses no atmosphere; at least, if there is any it is so thin that it does not affect the brightness of a star when occulted. The star remains at its normal brightness up to the instant when it disappears through the passage of the Moon over it.

There is another group of heavenly bodies which I have not touched upon, and will only shortly name. I refer to comets. These visitors are marvellous, and bitf little is known or understood about them. Some move in orbits, which bring them back in varying periods; some appear, pass round the sun, and are known no more. Their number is considerable. Early this year we had a visit from a notable comet, Halley's, and we in this Southern Hemisphere were greatly favoured, having a fine view of it as it approached the sun. I have now given a discursive talk about astronomy, which has touched upon a great variety of subjects, in but a poor way, such as an amateur can do. But I hope my remarks may be of some use iu showing to some who would like to study astronomy that there are many objects to observe, many branches of study to take tip, and that in all that comes under the name of astronomy there is so much to interest and instruct the mind. And, I am sure, many, if they once begin to observe and study the sky at night, and to learn something of the constellations and the movements of the planets, would become fascinated by what they learnt, and would continue the study, lifting their eyes to something above, and better than the electric lights of the city. Many things I have mentioned are really beyond our powers to grasp. What do we know of millions; how can we think of a space of 92,700,000 miles which separates us from the Sun, and a lay mind may be forgiven when it hesitates to believe all that astronomers tell us about distances and magnitudes. But we can see and understand many things they tell us and so we should" believe them in those we cannot understand. There is a wonderful book published in England yearly, two years in advance, for the benefit, chiefly, of navigators. I refer to the Nautical Al manaek. Though published two years

beforehand, it gives the position of Jupiter's satellites each day, and the exact moment of their transits, occupations and eclipses, and you must remember that we are moving, Jupiter is moving, and the Satellites are moving. It also tells the exact time of the occupation of a number of stars by the moon. Here, again, we are moving and the Moon is moving. The positions of the planets, right ascension and declination, are also given for each day (except those of Uranus and Neptune, which are given for each fourth day) throughout the year, so that if you have a telescope equatorially mounted' you can set it to the required position by means of the right ascension and declination circles and find the planet in the field. Then, the other day, we had a triumph of mathematical astronomy, when two of the astronomers at the Greenwich Observatory calculated the spot among the stars where Halley's Comet was first to appear, and the first discovery of the comet made by a German astronomer by means of photography, showed it less than the apparent diameter of the Moon from the calculated spot. And this comet was returning from a journey far out beyond our farthest planet Neptune, more than 2,746,271,000 miles from the Sun. It was last seen by us some 76 years ago. and m the calculations of its orbit many things have to be considered and allowed for such as the effect of the attraction of the planets upon it as it passed them on its way out from the Sun and on its iournev back. J

Astronomers are doing their utmost to perfect their knowledge of the heavenly bodies, and are now paying great attention to astrophysics, which means the study of the physics of the stars, their composition, size, weight, whether they have, as so many of them have, a companion star, what is the size, weight and attractive force of this companion, is one star revolving round the other, or are they revolving round a common centre. ( As to our section of the Philosophical Society, there is no reason "why it should not in time develop somewhat on the lines of the British Astronomical Association, which is divided into sections for purposes of observations. Some observers take up variable stars, some the planet some Jupiter, some the Moon, some the Sun. Each section works under a director, and much good work is being done.

There is one thing the study of astronomy does if it is taken up seriously and with intent to learn: it makes man and all the wonders he can achieve appear very, very small. What is the Earth among the millions of bodies which we find out by the aid of telescopes and photography. Any one studying astronomy must surely find his wonder at the marvels spread out before him increasing as he studies. He will find such evidences of majestic law and order governing the movements of the Heavenly bodies, and his very inability to grasp the distances and dimensions of these bodies or the extent of our system must excite in his mind wonder and admiration and lead him to acknowledge the greatness of the Creator and to thank Him for having given us mortals such a measure of understanding as to be able to find out so much about the marvels of creation, •