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Absolute Magnitude

Physics: AQA A Level, topic 9.2.2

Absolute Magnitude

Absolute magnitude is a measure of the inherent intensity of a source of light.

Light year

Light year

  • 1 light-year is the distance travelled in a vacuum by light in one year.
  • This is equal to 9.46 × 1015 m.
Parsec

Parsec

  • 1 parsec is the distance an object is away from the sun when it has an annual parallax of 1 arc second (as shown in the diagram).
Absolute magnitude

Absolute magnitude

  • The absolute magnitude of an object is the magnitude an object would have if it were 10 parsecs away from Earth.
  • The formula relating the absolute magnitude, M, and the apparent magnitude, m, for an object at a distance of d parsecs is:
  • m−M=5log⁡10(d10)m-M=5\log_{10}(\frac{d}{10})

Test yourself on Absolute Magnitude

  • What is the equation for the absolute magnitude of a star?

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