Astronomy › Section M · Celestial distances › Topic M.1
Fundamental units of distance
Every distance in astronomy, out to the farthest galaxy, is built on a few carefully defined units. This topic shows where the metre, the astronomical unit and the light-year come from, and how radar fixed the size of the solar system.
In this topic
- Why a standard unit matters
- The metre, from Earth to light
- Relative distances are not enough
- Radar ranging
- Worked example: radar sets the scale
- The astronomical unit, pinned down
- Worked example: radar on a passing asteroid
- Light-units link the scales
- Voyager 1 and the gap to the stars
- Common mistakes to avoid
- Key takeaways
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