Absolute magnitude, M (A-level only) Flashcards – AQA A-level Physics (7408)

What is a light-year?

The distance light travels in a vacuum in one year.

How is a parsec defined using an astronomical unit and an angle?

The distance at which one astronomical unit subtends an angle of one arcsecond.

How is a parsec defined using stellar parallax?

The distance of an object with a stellar parallax angle of one arcsecond.

Approximately how many light-years are in one parsec?

$3.26$ light-years.

What is the absolute magnitude of an astronomical object?

The apparent magnitude it would have at a distance of 10 parsecs.

What does an object's apparent magnitude describe?

How bright it appears at its actual distance.

On the magnitude scale, which numerical value corresponds to greater brightness?

A lower numerical value.

What is the distance modulus equation, with distance in parsecs?

$m-M = 5\log_{10}\left(\frac{d}{10}\right)$

How do apparent and absolute magnitude compare at distances of 10 parsecs, greater than 10 parsecs, and less than 10 parsecs?

• At 10 parsecs: $m=M$
• Greater than 10 parsecs: $m>M$; the object appears dimmer.
• Less than 10 parsecs: $m<M$; the object appears brighter.