164.78 | 34800 | 1 |
| SUN | ------ | ------ | 866400 | -- |
| MOON | ------ | ------ | 2163 | -- |
|_________|_______________|____________|____________|____________|

FIG. 27]

[Illustration:

______________________________________
| |
| STAR DISTANCES |
|______________________________________|
| |
| DISTANCE IN |
| STAR LIGHT-YEARS |
| |
| POLARIS 76 |
| CAPELLA 49.4 |
| RIGEL 466 |
| SIRIUS 8.7 |
| PROCYON 10.5 |
| REGULUS 98.8 |
| ARCTURUS 43.4 |
| [ALPHA] CENTAURI 4.29 |
| VEGA 34.7 |
|______________________________________|
| |
| SMALLER MAGELLANIC CLOUD 32,600[A] |
| GREAT CLUSTER IN HERCULES 108,600[A] |
|______________________________________|

[A] ESTIMATED

FIG. 28

The above distances are merely approximate and are subject to further
revision. A "light-year" is the distance that light, travelling at the
rate of 186,000 miles per second, would cover in one year.]

In this simple outline we have not touched on some of the more debatable
questions that engage the attention of modern astronomers. Many of these
questions have not yet passed the controversial stage; out of these will
emerge the astronomy of the future. But we have seen enough to convince
us that, whatever advances the future holds in store, the science of the
heavens constitutes one of the most important stones in the wonderful
fabric of human knowledge.

ASTRONOMICAL INSTRUMENTS

Sec. 1

The Telescope

The instruments used in modern astronomy are amongst the finest triumphs
of mechanical skill in the world. In a great modern observatory the
different instruments are to be counted by the score, but there are two
which stand out pre-eminent as the fundamental instruments of modern
astronomy. These instruments are the telescope and the spectroscope, and
without them astronomy, as we know it, could not exist.

There is still some dispute as to where and when the first telescope was
constructed; as an