To an Astronomer, What Is a "Standard Candle

Multiple Choice

To an astronomer, what is a "standard candle"?

A) standard light source that is placed in a telescope, with which the brightness of stars and other objects can be compared
B) galaxy whose redshift has been measured accurately
C) object whose absolute magnitude or intrinsic brightness is known
D) accurately defined brightness scale for stars and galaxies, such as the magnitude scale