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Phases of Venus
Galileo saw Venus go through full set of phases, including gibbous. That only works if Venus orbits the Sun, not Earth.
Elongation 46° · crescent
Before you start
Galileo’s telescope showed Venus going through gibbous phases. That is a heliocentric result.
Key idea
If Venus orbits the Sun, it can pass behind the Sun and look nearly full. Ptolemy’s layout forbids that.
What you see
- Sun-centred orbits
- Elongation readout
- Venus disk
Try this
- Play until elongation is large — Venus is an evening or morning star
- Compare with Ptolemaic Phases of Venus
Common mistakes
- Thinking Venus phases work like Moon phases for the same geometric reason without changing the centre
Glossary
- Gibbous
- More than half illuminated.