What is a large star of high luminosity?

Answer 1

A good example of a medium size star is the Sun, which is very average. Luminosity is measured by the star's absolute magnitude, which is the magnitude seen from a standard distance of ten parsecs (32.6 light-years), and the Sun's absolute magnitude is +4.7. A factor of 100 increase in luminosity corresponds to 5 magnitudes less (larger magnitudes mean dimmer stars). The brightest stars have absolute magnitudes around -7.

Answer 2

The luminosity for any star is given by the luminosity equation:

L=4*pi*sigma*R2*(Teff)4

where sigma is the Stefan-Boltzmann constant (approx. 5.6704x10-8 W m-2 K-4), R is the radius of the star, and Teff is the effective temperature of the star (aka the temperature we observe).

Note: Make sure all of your units match up when calculating this! I.e. if given a radius in km, make sure to convert to m before plugging in, so it matches the Stefan-Boltzmann constant which has units of meters.

Answer 3

The apparent magnitude of a star is a number which tells you how bright it seems compared to others. A first magnitude star looks 100 times as bright as a sixth magnitude star, which latter is the dimmest you can see with the naked eye.

Of course the magnitude depends on two things, how bright the star is and how far away it is. To compare stars fairly a scale called absolute magnitude is used. This is the magnitude the star would have if it were 10 parsecs away. Thus absolute magnitude needs to be used if you are to compare two stars fairly.

Answer 4

A star named Betelgeuse.