Magnitudes in Astronomy - Flashcards

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

Magnitude

An antiquated, backwards system of measurement related to luminosity that astronomers still use to refer to the brightness of celestial objects.

Hipparchus

An ancient Greek who is credited with developing the original magnitude scale, ranking the brightest stars as first class and the faintest as sixth class.

Magnitude Scale (Historical)

Developed by Hipparchus, it ranked the brightest stars as 'first class' and the faintest stars visible to the eye as 'sixth class'.

Apparent Visual Magnitude (mV)

How bright a star appears (in terms of magnitudes) at visual wavelengths. The brighter the star, the lower (or more negative) the magnitude.

Rule of Magnitude and Brightness

The brighter a star appears, the lower its apparent magnitude. A decrease in magnitude by 5 corresponds to an increase in apparent brightness by a factor of 100.

Absolute Visual Magnitude (MV)

The luminosity of a star (in terms of magnitudes) at visual wavelengths; an intrinsic measure of a star's brightness, analogous to luminosity.

Reference Distance for Absolute Magnitude

Astronomers define the absolute magnitude of a star as equal to its apparent magnitude when the star is located exactly 10 parsecs (pc) away.

Distance Modulus (m  – Mv)

A way of expressing distances on a logarithmic scale based on the astronomical magnitude system, calculated as the difference between apparent magnitude (m) and absolute magnitude (Mv).

Distance Modulus = 0 (m  – Mv = 0)

Indicates that a star is located exactly 10 parsecs (pc) away from Earth.

Distance Modulus is Negative (m  – Mv < 0)

Indicates that a star is closer than 10 parsecs (pc) from Earth.

Distance Modulus is Positive (m  – Mv > 0)

Indicates that a star is farther than 10 parsecs (pc) from Earth.