Astrophysics

• Apparent magnitude is the perceived brightness of a star as seen from Earth.
• Luminosity is the total power output of radiation emitted by a star.
• Brightness of a star

  The intensity of radiation received on Earth from a star.
• Factors that the brightness of a star depend on

  -Its luminosity

  -How far away the star is
• What is the difference between luminosity and brightness?

  Luminosity: how bright the star is at its surface

  Brightness: how bright the star is as observed from the Earth
• Define an astronomical unit.

  The mean distance from the centre of the Earth to the centre of the Sun.
• Define a light-year.

  The distance travelled by light in one year.
• Define a Parsec.

  The distance at which the radius of the Earth's orbit around the Sun subtends at an angle of 1 arcsecond.