As the centre of gravity of the sun and Jupiter lies at a distance of about 460,000 miles from the sun’s centre, and the sun’s radius is only 433,000 miles, it follows that the centre of gravity of the sun and planet is about 27,000 miles outside the sun’s surface. The attractions of the other planets perpetually change the position of the centre of gravity of the solar system; but in some books on astronomy it is erroneously stated that the centre of gravity of the system is always within the sun’s surface. If all the planets lay on the same side of the sun at the same time (as might possibly happen), then the centre of gravity of the whole system would lie considerably more than 27,000 miles outside the sun’s surface.
With reference to the sun’s great size, Carl Snyder has well said, “It was as if in Vulcan’s smithy the gods had moulded one giant ball, and the planets were but bits and small shot which had spattered off as the glowing ingot was cast and set in space. Little man on a little part of a little earth—a minor planet, a million of which might be tumbled into the shell of the central sun—was growing very small; his wars, the convulsions of a state, were losing consequence. Human endeavour, human ambitions could now scarce possess the significance they had when men could regard the earth as the central fact of the universe.”[12]
With reference to the late Prof. C. A. Young (U.S.A.)—a great authority on the sun—an American writer has written the following lines:—
“The destined course of whirling worlds to trace,
To plot the highways of the universe,
And hear the morning stars their song rehearse,
And find the wandering comet in his place;
This is the triumph written in his face,
And in the gleaming eye that read the sun
Like open book, and from the spectrum won
The secrets of immeasurable space.”[13]
CHAPTER II
Mercury
As the elongation of Mercury from the sun seldom exceeds 18°, it is a difficult object, at least in this country, to see without a telescope. As the poet says, the planet—
“Can scarce be caught by philosophic eye
Lost in the near effulgence of its blaze.”