|Blue light from Sun NASA APOD |
Image Credit & Copyright © Alan Friedman (Averted Imagination)
The image of blue Sun is highly educational example of spectral analysis which is one of the principal tools for studying stars. Photos arriving from the stars and galaxies is the hard evidence that we Earthly observes have. One of the important aspects of information star light carries to us is the chemical composition of stellar objects so crucial in our attempts to understand the making of the Universe.
In order to create the amazing Blue Sun photo Alan Friedman first took an image of the Sun through a highly accurate narrow-band filter that removed all other colors from the light except extreme violet light CaK (393.4 nm) emitted by ionized Calcium. After taking a picture of the Sun he false color-inverted the image to get this stunning result. The captured light is hard evidence about the presence of Calcium in the atmosphere of the Sun.
For a detailed explanation of how to take CaK filtered images and the camera equipment needed see, for eaxmple, the Elizabeth Observatory of Athens project.
Understandably the filtering and spectral analysis of light from more distant suns does not give such an extravaganza of identifiable band-widths. Nevertheless, the principle is similar when dealing even the faintest galaxies with significant Red Shift.
Spectral analysis has allowed stellar astronomers to achieve amazingly detailed information of stars. For example, light from Sirius A bears evidence of the significant traces of metals on its atmosphere. The fact has been explained, or so I have at least understood the explanation, that the heavier then helium metals have been captured from the dusty remnants of Sirius B.