An astronomer observes a nearby star whose motion relative to the Earth repeats every 20 days.
An absorption line produced by an element in the star has a laboratory wavelength of 589.0 nm589.0\ \mathrm{nm}589.0 nm.
| Time in days | Observed wavelength in nm\mathrm{nm}nm |
|---|---|
| 0 | 589.1 |
| 5 | 589.0 |
| 10 | 588.9 |
Explain how the motion of the star along the line of sight changes from day 0 to day 10.
Predict how the observed frequency of this absorption line on day 30 compares with its laboratory frequency.
Explain your answer.
94 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift, covering 7.2.1 Big Bang and Steady State theories, 7.2.2 Evidence for the Big Bang, 7.2.3 The Doppler effect and red-shift, 7.2.4 Red-shift as evidence for an expanding Universe, and 7.2.5 The CMB and the accepted model. Each one has a worked solution and a mark scheme showing where the marks go.