Types of Spectrum
When white light falls on a prism, placed in a spectrometer, the waves of different wavelength are deviated to different directions by the prism. The image obtained in the field of view of the telescope consists of the number of coloured images of the slit. Such an image is called a spectrum.
If the slit is illuminated with light from sodium vapour lamp, two images of the slit are obtained in the yellow region of the spectrum. These images are the emission lines of sodium have wave lengths 5896A and 5890A. This is known as spectrum of sodium.
The spectrum obtained from different bodies can be classified into two types
(i) emission spectrum