Lecture Notes: The Planets and Days of the Week

Introduction

• Discussion about planets and their historical significance.
• Exploration of how planets are linked to the days of the week.

The Planets in Order

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune

Historical Perspective

• Ancient understanding: 7 planets, including the Sun and Moon.
• Definition of a planet: Anything moving against the fixed background stars.

Etymology of "Planet"

• Derived from Greek word "planus" meaning "wanderer".

7 Planets and 7 Days

• Each day of the week named after one of the seven planets known to the ancients.
• Sunday: Named after the Sun.
• Monday: Named after the Moon.

Norse and Roman/Greek Influences

• Tuesday: Mars (Norse God Tiw or Tyr, a God of War).
• Wednesday: Mercury (Norse God Odin, often linked to journeys and knowledge).
• Thursday: Jupiter (Norse God Thor, God of Thunder, similar to Jupiter in Roman mythology).
• Friday: Venus (Norse Goddess Frigg, associated with love and beauty).
• Saturday: Saturn.

Changes in Planetary Count

• Shift from 7 to 5: Copernicus (mid-1500s) redefined, removing the Sun and Moon.
• Introduced Earth as a planet.

Discovery of Uranus

• Originally named "Planet George" by William Herschel after King George.
• Later changed to Uranus to fit with classical naming conventions.

Conclusion

• Discussion highlights the blending of cultural influences in naming conventions.
• Encouragement to continue exploring and understanding the cosmos.