Astronomy of To-day

neral view of the solar system-a bir

various planets move around the sun. But we have not yet stated what these distances ac

of an hour's sharp walk, for instance; or yonder village or

ppear very great to us, who find that a walk of a few miles at a time taxes our strength; but they are a me

are called "mean" distances; for, as the orbits are oval, the planets vary in their dista

out 36,000

" 67,2

" 92,9

141,5

" 483,

" 886,0

1,781,9

" 2,791,

of the various bodies of the system. In that case the distances were limited to thousands of miles; in this, however, we have to deal wi

they can picture in their minds such immense distances, they actually can not. In matters like these we unconsciously employ a kind of convention, and we estimate a thing as being two or three or more times the size of another. More than this we are unable to do. Fo

parisons with other and simpler facts, though this is at the best a mere self-cheating device. The analogy which seems most suited

000 miles. At its sixty-miles-an-hour rate of going, this journey will take nearly 17 days. Next let us send it from the earth to the moon. This distance, 240,000 miles, being ten times as great as the last, will of course take ten times as long to cover, namely, 170 days; that is to say, nearly half a year. Again, let us send it still fu

e that our train makes a tour right roun

traight out to the known boundaries of the solar system, that is to say, as far

of space appalling to contemplate, when one realises that a body moving incessantly at such a rate would take so long as 10,000 years to traverse merely the breadth of our solar system? Ten thousand years! J

d dimensions of the solar system, let us next inquire into it

this holds good, no matter what portion of the globe we visit. The same is really true of the sky by day, though in

ged within the midst of a great tangle of stars. What position, by the way, do we occ

comprising planets and satellites, comets and meteors;-or perchance indeed some further variety of attendant bodies of which we have no example in our tiny corner of space. But as to whether one is right in a conjecture of this kind, there is up to the present no proof whatever. No telescope has yet shown a planet in attendance upon one of these distant suns; for such bodies, eve

singly long after the very outposts of the stellar universe has been left behind. Shall we then start our imaginary express train once more, and send it out towards the nearest of the stars? This would, however, be a useless experiment. Our express-train method of gauging space would fail miserably in the attempt to bring home to us the mighty gulf by which we are now faced. Let us therefo

ut from sun to sun is measured in billions. But does the mere stating of this fact convey anything? I fear not. For the word "billion" runs as g

lion of millions. That means a million, each unit of which is again a million. In fact every separate "1" in this million is itself a million. Here is a way of trying t

two years to cover a million miles. To cover a billion miles-that is to say, a million times this distance-would thus take of course nearly two million years. Alp

s in return for billions; and so the mind, driven in upon itself, whirls round and round like a squirrel in its revolving cage. There is, however, a useful illustration st

3,000,000 of miles which separate us from the sun in about eight minutes. It travels from the sun out to Neptune in about four hours, which means that it would cross the s

ld take to pass from them to our earth. They speak of that distance which light takes a year to traverse as a "light year

therefore be always some four years old. Were then this star to be suddenly removed from the universe at any moment, we should continue to see it still in its place in the sky for some four years more, after which it wou

ge in the light of any of these remote stars, we are inclined to ask ourselves when that change did actually occur. Was it in the days of Queen Elizabeth, or at the time of the Norman Conquest; or was it when Rome was at the height of her glory, or perhaps ages before that