ASTONISHING STAR REVELATIONS.

Lake Wakatip Mail, Issue 2789, 18 October 1910, Page 7

ASTONISHING STAR REVELATIONS.

STELLAR LIGHT : 5,000,000 YEARS

TO REACH US

The problem which astronomers have to solve in ascertaining the distances of the stars is one of the most stupendous difficulty, and not until now have any satisfactory results been attained to reward the careful observations of centuries. Of all the thousands of stars that have

been studied astronomers know the di.staaces of about 100, and even these are known only approximately, being the supposed distances within which they cannot be, but beyond which they must be, though the exact limits cannot at present be determined owing to the immense intervals which separate them from our earth. The nearest star is so remote that its light requires four and one-third years to reach us, while the light of the pole star is forty-five years in travelling to us from that distant orb, so that if the light of this star was suddenly extinguished to-day nearly half a century would have to elapse before we should be aware of the fact and miss the familiar orb from its prominent position in the Northern heavens.

The mathematical principles involved in determining the distance of a star are essentially > the same as those employed by a surveyor when he wishes to measure the width of a stream which he cannot cross, only with the astronomer the problem is rendered much more difficult from the fact that he is unable to procure a base line of sufficient length to meet his requirements, and even the diameter of the earth's orbit is not great enough to use in measuring the distances of the stars, with very few exceptions.

WHAT A SPIDER'S WEB CAN DO. To learn the distances of the stars it is first necessary to determine what is known as a star's parallax, in other words, its angle of direction when viewed from two opposite points in the earth's orbit (i.e., its path round the sun), and this is what renders the problem so extremely difficult; for nearly every star that has been examined for the purpose of learning its distance has failed to show any parallax whatever, and in the few instances where a parallax has been recognised the angle is found to be exceedingly small. No star in the heavens at present known to astronomers has a parallax equal to one second of arc, but all thus far determined are below even this small angle. The "annual parallax" of a star is an angle under which the semidiameter of the earth's orbit would appear as viewed from the star.

The value of a second (a 60th part of a minute, which is the GOth part of a degree, which is the 360 th part of a circumference of a circle) is so small that a spider's web placed in the field of view of a telescope completely hides the portion of the celestial sphere where the apparent movements of the stars are effected—a portion at most equal to not quite one second. The reader will therefore be able to realise the diffi- . culty of the problem which is preI sented to astronomers for solution. ! A parallax of one second means that jthe celestial object is 206,265 times i further away than we are from the sun, the sun's distance being onehalf of the base line, or about 93,000,000 miles. If, then a star's parallax be less than one second, the star must be further away than 206,265 times 93,000,000 miles, and this we find to be the case with every star in the heavens that has been studied in this way.

By the orbital motion of the earth around the sun our position with respect to the stars is changed proportionately less than would be that of a grain of dust placed in the middle of the dome of St. Paul's Cathedral, if it were made to whirl round in a circle having a diameter of 1-100 th of an inch. Investigations are now in progress which promise greatly to extend the list of stars having a measurable parallax, and it is possible that the distances of most of the naked-eye stars may be ascertained before many years have elapsed.

The star which gives the greatest parallax of any, and is believed to be the nearest to our earth, is Alpha Centauri, a bright, first-magni-tude star, in the southern heavens. But even this star's parallax is only 75-100ths of a second, which corresponds to a distance of 275,000 times the sun's distance from our earth,

or nearly 25,000,000,000,000 miles

ALL STARS ARE MOVING : WONDERFUL VELOCITY.

The angle or parallax of Alpha Centauri is equal only to the 400 th part of a second space on the face of a watch, and this, it should be remembered, is the nearest star at present known to astronomers, excepting, of course, sun, which is also a s, the thousands that adorn jMHfrijjament. The nearest stars exbi«K|§|ie.'farpest parallax, but no case been found in which this quantity is as great as a foot rule seen at a distance of fifty miles, and only for comparatively few stars is it certainly appreciable. There are some stars so remote that their light, though travelling; with a velocity of 186,000 miles per second, cannot reach us in less than 10,000 years. To traverse the milky way, of which our own solar swWm forms a part, light requireJHKjM years ; and to reach us frosKlome of the distant nebulae, which tftijpear like faint clouds, and hardly visible through the largest telescopes, it must travel for nearly 5,000,000 years.

To ordinary vision all the stars appear at rest in our heavens ; nor can the astronomer himself recognise any signs of motion, except by patient and long continued observation, extending, in some instances,

over a period of many years, and

even centuries, when succeeding astronomers complete the work which their predecessors had begun. But every star in the firmament is on its journey, and moving through space with wonderful velocity. Absolute rest is unknown throughout the material universe.

If we look up to the sky on a calm, bright night, when the stars shine in all their glory, we are usually impressed with the feeling that a solemn stillness reigns in those infinite regions of space. In reality, those amazing star depths above us, which appear so steadfast and unchangeable from year to year, are astir with life, energy and activity, and there is a remarkable process of changes taking place all around us. It is believed by some astronomers that the sun, with its entire family of planets and comets, is moving with great velocity towards the constellation Lyra; and quite recently it has been announced that the immense nebulae, or "star clouds," have also been found to be in motion.—"Popular Science Sittings."