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Home · IGCSE 0625 · Space physics · Galaxies and light-years · Practice
Core · Practice questions · Galaxies and light-years

Across the cosmos.

Six original Cambridge-style questions on galaxies, the Milky Way, and using light-years.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
What the examiner wants

A distance, not a time.

01
Recall
[1 mark]

State what a galaxy is.

  • A huge collection of stars held together by gravity. ✓
02
Recall
[2 marks]

Name our galaxy and state one object it contains.

  • The Milky Way. ✓
  • It contains the Sun (and billions of other stars). ✓
03
Recall
[2 marks]

State what a light-year is, and give its approximate value in metres.

  • The distance light travels in one year. ✓
  • About 9.5 x 10 to the 15 m. ✓
04
Calculation
[2 marks]

A galaxy is 12 light-years away (for this question). Calculate this distance in metres. (1 light-year = 9.5 x 10 to the 15 m.)

distance = 12 x 9.5 x 10 to the 15 m

distance = 1.1 x 10 to the 17 m

05
Analysis
[2 marks]

A star is 50 light-years from Earth. Explain what we are really seeing when we look at it tonight.

  • The light we see left the star 50 years ago. ✓
  • So we see the star as it was 50 years ago, not as it is now. ✓
06
Application
[1 mark]

A student says a light-year is a measure of time. State the correction.

  • A light-year is a measure of distance, not time. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.