Part 9

CALENDARS, ETC.

Our year is a little more than 365 days in length--in fact, nearly 365¼. Because of this fact, an extra day accumulates every four years; and to include this we add this extra day to February every “leap year.” In this way, our celestial bookkeeping is kept fairly accurate. Twelve months of 30 days each would give 360 days, with five days over. It was, however, found that five days was not enough, while five and a quarter was too much. It is interesting to note that Hipparchus, who flourished in the 2nd century B. C., worked on this problem, and fixed 5 days and 55 m., as the time required--a truly remarkable achievement, since it has since been found to be accurate to within less than six minutes.

CURVED SPACE

This, and various other problems connected with the Einstein theories may be found treated in No. 408 of the present series, “An Introduction to Einstein,” by William F. Hudgings.

THE TEMPERATURE OF SPACE

The Earth is warmed by the sun’s rays, some of which are absorbed, while some are reflected. But these rays themselves possess no “heat”; they are merely minute vibrations in the ether. Heat is only present when they strike some solid body. Consequently the vast inter-stellar spaces are tremendously cold--probably at or about absolute zero (-273.10°C). Our earth is not heated directly, as a man is heated by standing in front of a blazing fire; but only by means of electro-magnetic undulations, which traverse millions of miles of space, colder than death, without heating them!

LIGHT IN SPACE

Space is also intensely dark; no light exists there save the faint twinklings of distant stars. The sun illumines our earth, because its rays are reflected from its surface; but space itself is intensely black, just as it is intensely cold It is a “cold world” indeed, once we have stepped off the little planet on which we dwell!

LIFE IN SPACE

All this being so, life in any form cannot very well exist in space--since the conditions for its existence are altogether absent. Arrhenius has, however, suggested, that the “germs of life” might possibly be carried across millions of miles of space on dust particles, propelled by the energy of light. This, however, is a pure theory, which has so far received no official proof.

THE CAUSES OF AN ICE AGE

We know that our Earth has passed through several ice ages, in the past, and various astronomical theories have been advanced in order to explain this fact. Perhaps the most ingenious of these is that advanced by Sir Robert Ball (see his “The Cause of An Ice Age”). Very briefly, it is that the eccentricity of the earth’s orbit and the tilting of the polar axis causes an ice age, or the reverse. If the northern axis is tilted towards the sun, when nearest to it (so to say), then the northern hemisphere will enjoy a genial climate, and if the southern axis be thus tilted, the reverse conditions will prevail. This, and various other theories have, however, been discussed by Finger in his book on “The Ice Age,” in the present series, No. 327.

WHY DO STARS “TWINKLE”?

When we look at a star near the horizon, we at once notice that it twinkles, or “scintillates,” especially in the winter time. The phenomenon is purely atmospheric, and is due to waves of air of unequal density sweeping across the line of sight. When viewed through a telescope, this is sometimes magnified into actual dancing.

WHY DOES THE MOON SOMETIMES APPEAR LARGER?

It is well known that the moon often appears larger when rising or setting--i. e., near the horizon, than when it is overhead. The same is true of the Sun. It is hardly necessary to say that these celestial bodies have not actually increased or decreased in size! Why, then, should we perceive them larger at some times than at others?

The reason for this is two-fold; psychological and optical. In the first place, the Heavens do not appear to us quite round, but somewhat flattened out, like a watch-glass. Hence the moon appears to be much further away when it rises than it does when it is overhead, with nothing between. The moon near the horizon is apparently larger because it seems further away. The second reason is that the refraction of the earth’s atmosphere gives this illusion of increased size.

ARE THE PLANETS INHABITED?

This is a much-disputed point! Various astronomers (Schiaparelli, Lowell, etc.) have contended that they have almost indubitable evidence that Mars is inhabited by living beings like ourselves; other equally competent astronomers assert the contrary. Certainly, none of the planets of our own solar system, with the possible exceptions of Mars and Venus, could possibly be inhabited. That is universally granted. And we have no direct evidence of any other inhabited worlds throughout space. Analogy, however, forces us to believe that, of the millions of suns blazing in the heavens, many of them must be attended by a planetary system such as ours; and if such be the case, there is no reason why life should not originate and thrive thereon as well as upon our own planet. We have, however, no means of proving or disproving this directly.

In our own system, Venus and particularly Mars offer possibilities. Venus probably always turns one face towards the sun, so that this side would be tremendously hot, while the other side would be frozen in perpetual ice. Mars is a possibility; and, as we know, great controversy has raged regarding the habitability of this planet, and as to its “Canals.” The interested reader may refer to Lowell’s “Mars as the Abode of Life,” and “Mars and Its Canals” for the affirmative, and to Maunder’s “Are the Planets Inhabited?” for the negative, side of this question.

A FEW DEFINITIONS

What “Parallax” means. Since the earth revolves round the sun, the stars are apparently in slightly different directions from it at different times of the year. The difference in direction of a star as seen from two points on the earth’s orbit which are separated by the mean distance to the sun is the parallax of the star. In other words, the parallax of a star is the angle subtended by the major semi-axis of the earth’s orbit, as seen from the star.

The “Orbit” of a moving body is its more or less circular passage through space, usually around another larger body, as our earth revolves round the sun. The “eccentricity” of the orbit consists in the fluctuations or variations from its exact path.

The “Ecliptic” System. If we could see the stars near the sun, we should find that the Sun apparently moves eastward among them, completing one revolution in a year. Tracing such a path, it will be found that it more or less coincides with the celestial equator. The equator and the ecliptic intersect at two points; these points are the “equinoxes” the vernal equinox being the one at which the sun crosses the equator from south to north, and the autumnal equinox the other one.

“Satellites.” These are smaller bodies which revolve round large ones, and, so to say, attend them. All except two of the planets are known to have satellites revolving round them, just as they revolve round the sun. Mercury and Venus have none; the earth has the moon; Mars has two little moons, only a few miles in diameter; Jupiter has four large satellites and four small ones; Saturn has ten, one of which is larger than Mercury; Uranus has four satellites, and Neptune one.

The “Planetoids.” Between Mars and Jupiter a number of small bodies have been discovered, moving in a regular orbit; these have been called planetoids. If some planet has once occupied this mid-way position, and subsequently exploded, the fragments would occupy the position occupied by the planetoids. Whether or not this is their origin is a disputed point, which it would take us too far afield to consider here. They suggest the possibility.

“Planets.” These are the bodies revolving round a central sun. Aside from those constituting our own solar system, we see no planets in space; we see suns, or stars; but if the latter have planets attendant upon them, we cannot see them.

The point of the moon’s orbit nearest the earth is called the perigee; the furthest point, the apogee.