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Lecture 2

Astronomy 1021 Lecture Notes - Lecture 2: Cosmic Calendar, Big Bang, Observable Universe


Department
Astronomy
Course Code
ASTR 1021
Professor
Robert Cockcroft
Lecture
2

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Our solar system
- Eight planets, moon, pluto (by size):
- Jupiter
- Saturn
- Uranus
- Neptune
- Earth
- Venus
- Mars
- Mercury
- Our moon
- Pluto
- Earth and moon scale: 385000 (3.85 x 10 to the power of 5 km)
Light years:
- Light year is distance
- Distance that light travels in 1 year
- Distance = Speed x Time
- Light year = 3 x 108 m/s x 1 year
- Light year = 3 x 108 m/s x 365d x 24hr x 60min x 60sec
- Light year = 3 x 108 m/s x 3.15 x 107 s
- Light year = 9.5 x 1015 m
- Light-years also gives you the travel time it took light to cross that distance
- Examples:
- 1.5 light-seconds; Moon-Earth
- 8 light-minutes; Sun-Earth
- 4.5 light-hours; Pluto-Earth
- 4.2 light-years; Alpha Centauri-Sun
- 1-2 x 105 light-years; Milky Way diameter
- 2.5 x 106 light-years; Andromeda-Sun
- 9.1 x 1010 light-years; diameter of observable universe
Cosmic calendar:
- Compress history of universe in single year
- If big bang happened in january then everything that has happened on earth is on
december 31st
- February milky way starts forming
- September the solar system forms
- October life starts froming
- December 29th is dinosaurs and december 30th they're extinct
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- First humans would have emerged around 11:54 pm december 31st at 11:59:30 is
recorded history
How do we measure time scales:
- Dendrochronology - tree rings
- Annual glacier layers
- Radiometric dating
Longer time scales:
- Universe’s oldest objects
- Determine Universe’s expansion time
- Abundances of elements
- Use observations (spectra) and simulations/models
“Spaceship” Earth:
- Earth is spinning and revolving around earth
- Sun is moving based on stars
- Stars are moving
- milky way is moving
- Einstein: it's all relative
2D Celestial Sphere:
- Imagine Earth is in a snow globe
- From our perspective on the ground the stars appear tobe on this imaginary surface
- Constellations are in the same line of sight but have no connection at all
Constellations:
- 88 official constellations
- Have an area surrounding them so the entire sky is separated into 88 sections
- Official boundaries set
- Brightest
- alpha
- beta
- gamma
- delta
- and so on.
- Magnitude scale:
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