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Classification of stars (A-level only)

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Question 3

GJ 892 A and GJ 892 B are two stars that appear very close to each other when viewed from Earth.

There are two possible reasons for this:

  • they are an orbiting binary system
  • they are distant from each other and only appear in the same line of sight.

In an orbiting binary system, the difference between the apparent magnitude and the absolute magnitude for each star is similar.

The table below shows data about these two stars.

Temperature / 720072007200Radius of star / 9.5×1099.5 \times 10^99.5×109Apparent magnitude
GJ 892 A7200720072009.5×1099.5 \times 10^99.5×1098.28.28.2
GJ 892 B3800380038004.5×10104.5 \times 10^{10}4.5×10108.98.98.9

Discuss the appearance of the two stars to an astronomer on the Earth. In your answer you should:

  • compare the colour of the stars
  • compare the brightness of the stars
  • deduce, with a calculation, whether the stars form an orbiting binary system.
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Markscheme

Classification of stars (A-level only) Questions

  1. A Level
  2. /Physics
  3. /Classification of stars (A-level only)

18 exam-style questions on AQA A Level Physics Classification of stars (A-level only), covering Classification by luminosity (A-level only), Absolute magnitude, *M* (A-level only), Classification by temperature, black-body radiation (A-level only), Principles of the use of stellar spectral classes (A-level only), The Hertzsprung–Russell (HR) diagram (A-level only), and Supernovae, neutron stars and black holes (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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