Magnitudes in Astronomy

Flashcards covering key vocabulary related to magnitudes, apparent brightness, luminosity, and the distance modulus in astronomy, based on the provided lecture notes.

Magnitude

An antiquated, backwards system of measurement that astronomers use to refer to the brightness of stars, relating to luminosity.

Hipparchus

An ancient Greek credited with developing the original magnitude scale, ranking stars from brightest (first class) to faintest (sixth class).

Apparent Visual Magnitude (mV)

How bright a star appears from Earth at visual wavelengths. The brighter the star, the lower its numerical magnitude.

Magnitude Scale Brightness Factor

A decrease in magnitude of 5 corresponds to an increase in apparent brightness by a factor of 100.

Absolute Visual Magnitude (MV)

A measurement of the 'intrinsic' visual magnitude or luminosity of a star, defined as its apparent magnitude if it were located exactly 10 parsecs away.

Distance Modulus (m – Mv)

The difference between a star's apparent visual magnitude (m) and its absolute visual magnitude (Mv), a value used to calculate the star's distance.

Distance Modulus (star at 10 pc)

If a star is located exactly 10 parsecs away, its distance modulus (m – Mv) is zero, as its apparent magnitude equals its absolute magnitude.

Distance Modulus (star closer than 10 pc)

If a star is located closer than 10 parsecs, its apparent magnitude (m) will be lower than its absolute magnitude (Mv), resulting in a negative distance modulus.

Distance Modulus (star farther than 10 pc)

If a star is located farther than 10 parsecs, its apparent magnitude (m) will be higher than its absolute magnitude (Mv), resulting in a positive distance modulus.

Formula for Magnitudes and Distance

The relationship between apparent magnitude (m), absolute magnitude (Mv), and distance in parsecs (d) is given by: m – Mv = – 5 + 5log(d).