EQUATOR TO POLE

Taranaki Daily News, 1 August 1931, Page 1 (Supplement)

EQUATOR TO POLE

CURIOUS SITUATIONS

(By

Rev. B. Dudley, F.R.A.S.)

To dispose first of simple definitions, it may 'be stated that the equator is an imaginary line drawn round the Earth midway between the poles. Deau Inge (not always gloomy) relates some amusiim- schoolboy stories, one of which is to the effect that a young hopeful, having misheard his teacher in the classroom, wrote that the equator is a “menagerie lion running all the way round the earth.” The text books define the terrestrial equator as “the great circle of the Earth's surface, dividing it into the northern and southern hemispheres.” The length of this imaginary line is about 24,902 miles. Owing to the fact that the Earth is flattened, at the poles, the equator is the longest line that can be drawn in one plane round the globe. Ignoring fractions, the diameter of the Earth at the equator is about 7926 miles, whereas the diameter in a direction at right angles to this, namely from pole to pole, is 7899 miles, which means that the equatorial bulge, caused by the fact that the globe spins upon its axis and throws large masses of matter, so to speak, away from the terrestrial centre, amounts to nearly 27 miles. If we represent the Earth (by a 'ball one yard in diameter, that diameter will make the polar diameter one eighth of an inch too long. There are good reasons for the belief that the-Earth has not always indulged in fier present spinning motion, and that she will not forever continue to epin at the same rate. It, is certain that there is a gradual slowing-down process going on, owing to t.ie tides raised in the ocean by moon and sun, even though the falling off in rotational speed has been so infinitesimal during any time which we have records available to show it, that we cannot be sure it has amounted to a measurable quantity. These tides act as a brake on our ocean shores. The rotation of the Earth on its centre might 'be thought of as a somewhat slow affair, occurring only once in a day of 24 hours. When, however, we take the size of the earth into consideration, our ideas of this speed become somewhat modified. The actual radius of the earth, or the distance from centre to circumference, is so great that the .populations resident on the equator are 'being whirled along constantly at the rate of a thousand miles an hour.

Not only has the Earth this heapedup condition, as it were, at the equator. The same. Obtains in respect to other bodies in the solar system. ,The planets Jupiter and Saturn, for example, are so much bulged that the distortion can 'be seen with the eye. In the case of Jupiter the bulge amounts to about 5000 miles, his poles being 82,500 miles apart, while a line drawn straight across from side to side at the equator would have to be 87,'500‘ miles long. So tliat, could, the population of Borneo ibe suddenly transported to the Jovian world and occupy on its surface a position corresponding with that which they enjoy here, they would have to travel-, not a thousand, but - early eleven thousand miles an hour; although, instead of taking 24 hours to complete one circuit, they would make the curve in 9 hours, 55 minutes, that being the length of Jupiter’s day. It is sometimes asked whether, seeing the Sun rotates on its axis, it too bulges at the equator. We have no measures that show its polar to be less than its equatorial diameter. Nor is this very surprising. For, although the ■Sun is rotating on its axis and there is probably a .protuberance, so slight'is it that it cannot be detected. The Sun takes,' not 24 hours to complete one Totatipn, but 25 days. Therefore the protuberance might well 'be inappreciable.

Every place in the equator of the Earth passes directly 'beneath the Sun at local noon, t so that at this hour one’s 'body will cast ho shadow. And while at noon the -Sun is directly over an observer’s head, at midnight it will be directly beneath his feet. . The “celestial equator” is the great circle in the starry vault which coincides with the Earth’s equator. It may 'be regarded as an extension of the ■plane of the Earth’s equator. In the same way the pole of the heavens is the point among the stars that would be reached were the Earth’s axis extended indefinitely, the south pole of the planet pointing to the south celestial pole. Leaving now the equatorial regions, and taking up our position at the pole of the Earth, let ns see how matters stand. The situation has completely changed. We have now neither east nor west. In whatever direction we move from the north pole, we must perforce go south; while, correspondingly, every step we take from the south pole leads due north. There are no “easterly” winds; ail blow either north or south according to the pole we occupy. The sun does not rise and set day by day. It grazes the horizon—-above it for six months of the year, below it for the six months following, a variation due to the fact that in winter the north pole is tilted slightly away from the sun, while in summer it is tilted slightly towards it. The same changing relations at the south pole give similar results in that region. An observer stationed at, say, the north pole, will turn once every 24 hours on his own axis; and though in turn he faces , all directions, he looks only south! At night, looking overhead at the starry skies, he sees the pole-star gazing directly down upon his head. All other stars move round in larger or smaller circles according to their distance from this o>right object, until those nearest his horizon sweep round him in the largest circles possible. Like the sun, they neither rise nor set daily. In truth, there is neither “daily round nor common task” here. From the north pole the eye can see only the of the northern heavens, just as from the south it can Observe only the southern celestial host; whereas we who live in intermediate latitudes can see a large number of constellations that belong to the opposite hemisphere. Seen’ from the pole the moon would forever play a coquettish game with the ''horizon, never mounting high in the sky. Her monthly behaviour would present some strange appearances, due to the'' fact that her path across the heavens does not coincide with that of the sun. The horns of her silvery crescent would often point in directions quite unfamiliar to us, although they could never do other than turn away from the sun.