In the constellation CYGNUS you can find the fine double star Albireo.
It is the head of the flying swan on his long craned neck. Even with a
small telescope you will see a double star with a wonderful contrast
of colour. The brighter star gleams orange, the dimmer in a beautiful
light blue.
CYGNUS
Albireo
What is the reason for the different colours? You may find a similar
phenomenon at home if you have an electric light bulb with a dimmer. If
you dim your lamp down you will see the filament glowing dark
orange. At full power the lamp is more yellow or white. But the light
bulb is not really white. Comparing the light bulb with the sun we
will find the bulb shines orange and the sun in a light yellow.
Hence we have two sequenzes:
Colour
dark orange
orange
yellow
Temperature
2000 K
3500 K
6000 K
The colour of the integral light of the stars tells us about the
temperatures of the stars!
Now, if we break up the light into the colours of the rainbow we might
even learn more about the physical properties of the stars.
(And if you think about your lamps, the colours of the
stars and their brightness, you might learn something about the radii
of these stars :-)
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