just as our sun is the centre of gravity for its 
planet. These planets are masses thrown off from 
the "parent" sun. These planets, in addition, have 
often thrown off smaller planets, which we call sat- 
elites, or moons. These revolve round the planet 
to which they belong. Most of the stars we see are 
in our own galaxy, that is, a system of stars re¬ 
volving round a common centre. The milky way is 
the rim of our galaxy. There are many other 
galaxies which appear to us to he nebulae, but which 
powerful modern telescopes have proved to be masses 
of stars. 
Stars are grouped: (a) according to brightness; 
(b) in constellations. The brightest stars are 1st 
magnitude, the next brightest 2nd magnitude, and so 
on. We see only up to 6th magnitude with the naked 
eye, but photographs have revealed up to 20th magni¬ 
tude . The ancient Chaldeans grouped them into 
constellations, and named them after heroes, an¬ 
imals, etc. Many have been named in modern times. 
The age of a star is determined by its colour. They 
start by being red-hot, and then become white-hot, 
and fade away, being yellow, orange, bright red, dull 
red, and then they fade out. 
Some stars are much more distant than others. 
Distance is measured in light years. Light travels 
at the rate of 186,000 miles per second, and 6 
million million miles per year, so that a star that 
is 6 million million miles from the earth is said to 
be 1 light year away. Our Sun’s distance from 
the earth is 8 light minutes, or 93 million miles 
away, and is the nearest star to us. The next 
nearest is Alpha Gentauri (the brightest of the two 
pointers of the Southern Cross) which is 4 light 
years away - the light from it taking 4 years to 
reach us. The most distant of bright stars is 
Canopus in Argo (in the Southern sky) which is 650 
light years away, which means that light that left 
