Measuring astronomical distancesEdexcel International A Level Physics: Mind map

Exam questions on Measuring astronomical distances

1. Astronomers measure the position of a nearby star against much more distant background stars on two occasions six months apart. The star appears to shift position, and the observations give a parallax angle of 0.050 arcsecond for the star.
   Calculate the distance to the star in metres. 1 parsec = 3.09 × 10¹⁶ m.2 marks
2. A type Ia supernova in a distant galaxy is used as a standard candle. Its peak luminosity is known to be 2.0 × 10³⁶ W. Telescopes on Earth measure the intensity of its light, and assume that no light is absorbed on the way.
   The intensity received at Earth is 1.6 × 10⁻¹³ W m⁻². Calculate the distance to the supernova in metres.2 marks
3. Astronomers want to find the distance to two objects: a star X about 50 pc from Earth, and a type Ia supernova Y in a galaxy about 5.0 × 10⁷ pc away. Their telescope can measure a parallax angle reliably only if it is at least 1.0 × 10⁻³ arcsecond. A type Ia supernova has a known peak luminosity.
   Use calculations to deduce whether trigonometric parallax can be used to find the distance to each object.3 marks