Measuring astronomical distancesEdexcel International A Level Physics: Flashcards

What these 12 flashcards ask

What is the parallax angle?
Why are observations made six months apart?
What is a parsec?
How do you find a distance in parsecs from parallax?
Why does parallax fail for distant stars?
What is a standard candle?
Give one example of a standard candle.
State the equation relating intensity, luminosity and distance.
What happens to intensity if the distance is doubled?
How is a distance found from a standard candle?
How does dust affect a standard candle distance?
How are standard candles calibrated?

Exam questions on Measuring astronomical distances

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
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
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

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).