Two stars of the same spectral class?

Question

Two stars of the same spectral class must have that same
radius
temp
mass
distance
all of the above

Answer 1

Spectral class relates to the temperature, since when something is hot, it gives off visible light, and hence a spectrum. So two stars of the same spectral class have the same temperature.

Proxima Centauri is slightly bigger than Jupiter (88,000 miles) and has the mass of about 1/10 Solar mass. Betelgeuse is slightly bigger than Jupiter's orbit (500,000,000 miles) and has 20 Solar masses. Both are of spectral class M. This shows the answer is not radius or mass. If in addition, the two stars are both Main Sequence stars, then they would have the same radius and mass.


The Sun and Capella are both spectral type G, but they are at widely different distances - the Sun is only millions of miles away, while Capella is trillions. So the answer is not distance.

Answer 2

Temperature.

Answer 3

Radius, temp, mass