Astronomy and Cosmology
Definitions: Astronomy and Cosmology
Exam question
State what is meant by the luminosity of a star.
9702/42 · Feb/Mar 2025 · Q10(a)(i)
Model answer
The total power of electromagnetic radiation emitted by the star.
Exam question
State what is meant by a standard candle.
9702/42 · Oct/Nov 2023 · Q10(b)(i)
Model answer
An astronomical object of known luminosity.
Exam question
State Wien’s displacement law.
9702/41 · Oct/Nov 2025 · Q9(a)
Model answer
The wavelength at which the emission rate is greatest is inversely proportional to the thermodynamic temperature of the star's surface.
Exam question
State Hubble’s law.
9702/41 · May/Jun 2025 · Q10(a)
Model answer
The recession speed of a galaxy from an observer is directly proportional to its distance from that observer.
Exam question
State what is meant by redshift.
9702/41 · May/Jun 2022 · Q10(c)(i)
Model answer
The observed wavelength is greater than the wavelength emitted by the source because the source is moving away from the observer.