AST101H5 Lecture Notes - Ancient Greek Astronomy, Astronomical Object, Deep Time
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Chapter One - Our Place in the Universe (Sept. 9)
- Only concentrate on the relevant topics discussed in lectures
- Glossary: G1-G14 at the end of textbook
Where is Earth?
- Earth is not the centre of the Universe, Universe is not “geocentric”
- geo = Earth; centric = centered on
- Believed that the Earth was the centre of the universe from the time of Greek
astronomy (2200 years ago) until about the year 1500
- HOW have we learned the correct view?
- Earth is insigniﬁcant, except that we live here
What is the Solar System?
- The Sun and all objects orbiting around the Sun
- The whole system formed billions of years ago
- There are many other “solar systems”, far beyond our system
Members of the Solar System
- Sun = heart of the Solar System, but it is just an ordinary star, like billions of others
- Plants (Earth, Mars, Jupiter, . . .)
- Dwarf planets (Pluto, Eris, . . .)
- Natural satellites (moons) orbiting planets
- Minor planets = asteroids
- Meteoroids = rocks, ice, dust
How “big” is the Solar System?
- Words like “big” do not have enough information, we need to use numbers (no
memorization required... learn HOW we know the number and what it means)
- We use numbers to connect and characterize the objects we study
How “big” is Earth?
- Diameter = 12,756 km; Radius = 6,378
- Include units in numbers
- How did we learn Earth’s diameter? What would change if the numbers were different?
Numbers in ratios
- Ratios compare numbers - more informative than the “pure” number
- D moon/D earth = 3,476km/12,756km = 0.272 OR D moon = 0.272 x D earth
- Ratios have no units
Scientiﬁc Notation - Appendix C
- Huge/tiny numbers are more accurate in scientiﬁc notation
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