Classification by luminosity (A-level only) Flashcards – AQA A-level Physics (7408)

What is apparent magnitude?

A numerical measure of how bright a star appears from Earth, based on its received light intensity.

How did Hipparchus classify visible stars by magnitude?

Brighter stars had smaller magnitudes; the dimmest visible stars were assigned magnitude 6.

What is the approximate naked-eye magnitude limit under good observing conditions?

Magnitude 6.

How does apparent magnitude relate to received light intensity?

A lower apparent magnitude means a greater received light intensity.

What received-intensity ratio corresponds to a difference of one apparent magnitude?

Approximately 2.51.

For stars with apparent magnitudes $m_1$ and $m_2$ and received intensities $I_1$ and $I_2$, what is the approximate intensity ratio?

$\frac{I_1}{I_2} \approx 2.51^{m_2-m_1}$

What is the distinction between brightness and received light intensity?

Brightness is a subjective visual perception; received light intensity is a measurable physical quantity.