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LUMINOSITY
LUMINOSITY IS THE TOTAL POWER A
STAR RADIATES.
LUMINOSITY IS DEPENDENT ON BOTH
THE POWER PER SQUARE METRE
AND THE SURFACE AREA OF THE
STAR.
Eg. A cool star that has half the power per
square metre of a hotter star but is twice it'
s size has the same luminosity.…read more

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MAGNITUDE
APPARENT MAGNITUDE ­ HOW BRIGHT A
STAR LOOKS TO AN OBSERVER
ABSOLUTE MAGNITUDE ­ HOW THE POWER
EMITTED BY A STAR COMPARES WITH
OTHER STARS
BRIGHTNESS ­ COMPARISON OF THE
ENERGY PER SECOND THAT FALLS ON THE
PUPIL OF THE EYE
TO MAKE A FAIR COMPARISON, THE
BRIGHTNESS OF EACH STAR IS
CALCULATED AS IF IT WOULD BE IF IT
WERE 10 PARSECS FROM EARTH…read more

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CLASSIFYING STARS BY
TEMPERATURE
Emission spectra from stars fall into three types:
Continuous spectrum ­ comes from hot (incandescent)
bodies. A determination of where the peak of the energy
is in this spectrum gives the temperature of the star.
Line spectrum ­ the result of excitation of atoms.
Wavelengths present in spectrum are characteristic of
elements that produce the light so comparison of the
starlight with a laboratory source reveals the elements in
the star.
Band spectrum ­ produced in the same way as line
spectrum but is produced by molecules and consists of
bands of light produced by a range of wavelengths
separated by gaps.…read more

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Star type Temperature/ K Colour Cause of absorption lines
O 30,000+ Blue Ionised helium
B 11,000 ­ 30,000 Blue-white Helium atoms and hydrogen
A 7500 ­ 11,000 White Hydrogen and some ionised
calcium
F 6000 ­ 7500 Yellowish-white Ionised calcium and metal atoms
G 5000 ­ 6000 Yellow Calcium atoms and metal ions
such as iron
K 3500 ­ 6000 Orange Metal atoms
M Less than 3500 Red Molecules of titanium oxide
producing band spectra…read more

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HERTZPRUNG-RUSSEL
DIAGRAM…read more

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