POLLING LIGHT TO PIECES.

Putaruru Press, Volume IV, Issue 156, 28 October 1926, Page 2

POLLING LIGHT TO PIECES.

WORK OF ASTRONOMERS. The astronomer studies the sun by “taking it to pieces.*’ The instrument employed is called a heliograph, and is really a highly-de-veloped form o>f spectroscope. The spectroscope, as mop* people is an instrument designed to analzse light. It consists of a tube, at the forward, end of which is a fine adjustable slit, to regulate the amount of light entering the Instrument, while at the inner end there is a collecting lens to render the rays of light parallel before l they enter the dispersing system. Now, when the spectroscope is applied to the sun, .instead of an image formed in the usual way, wte see a lovely coloured ribbon of light violet at one; end. and rekl at thej other, witjj every conceivable shade of colour between. This is due to t : he light of the sun having been sorted out into its various constitutent parts and ranged in order of wave-length. This coloured spectrum 'is seen to be crossed, by an enormous number of fine dark lines, indicating the presence of definite chemical elements in the sun. Each element is responsible for a particular lie of set of lines. The spectroheliograph differs from the simple spectroscope in having the slits m-ade. long enough to span the whole disc of the sun. Also, behind, the first slit there is a second | movable slit, .wjrich can be placed to let through the light coming from * any particular linei in the spectrum and exclude the rst. The light passing through the second slit falls on a photographic plate. This is mounted on a moving carriage, the speed of which can regulated so. that the plate keep 3 pace with the diurnal motion of the sun. As jthe son movs slowly in front of the first slit, so d.oes the plate! behind .the second one, and in th/is way a picture of the whole disc of the sun is built up. The picture j really consists of successive narrow j strips side by side. In this way by j choosing successive lines, and suitI ably placing the second slit, we can j obtaiil photographs of the sun by the light of any element we please, 'and, thus study the/ distribution of that element in the sun.