IN THEIR OWN LIGHT

Bay of Plenty Beacon, Volume 9, Issue 61, 10 April 1946, Page 2

IN THEIR OWN LIGHT

A LESON IN ASTRONOMY You look up at the heavens at night and see the stars shining. Perhaps you know that men are now able to photograph the stars by their own light, even those so distant that the human eye cannot see them through the strongest telescope'; not only can they photograph them, but by the spectroscope can tell what they are made of How wonderful! But, of course, in the photograph that star shows only a little dot of light, and if a speck of dust gets on the glass that makes another dot. How shall they tell the difference—which is dust and which is star?

They do it in "this way. If you have watched the stars a long time you have seen that they move across the heavens—or seem to move; of course it is the earth’s motio'n that changes our position. So when the astronomers photograph stars they have to keep the telescope moving by clockwork just as fast, to keep it pointing at the star. When the photograph is taken the telescope stops, and of course the star mores on, and so makes a tiny trail of light from the dot on the photograph. The dust doesn’t move, so makes no train.