A level Physics · Edexcel 9PH0 · Topic 10C
Distances in space
Key points
- Trigonometric parallax: a nearby star appears to shift against distant stars as Earth orbits the Sun. Measure the parallax angle six months apart; , where is the Earth–Sun distance.
- Parallax only works for relatively near stars because the angles become too small to measure.
- Units: the light-year (distance light travels in a year) and the parsec (distance giving a parallax angle of one arcsecond); 1 pc ≈ 3.26 ly ≈ m.
- A standard candle is an object of known luminosity, such as a Cepheid variable or type Ia supernova.
- Measure the intensity received, then use to calculate the distance.
- Uncertainties grow with distance, so astronomers build a distance ladder of overlapping methods.
Topic notesPremium
Measuring distances is one of the hardest problems in astronomy. Nearby stars can be ranged with geometry; further objects need a known luminosity and a measured intensity.
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