ASTRONOMY 1021 (General Astronomy)
Unit 1-9 PowerPoint Notes A+ Graded
University of West Ontario.
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ASTRONOMY 1021
UNIT 1 - PART 1
From Moon to Visible Universe
Star: a spherical object that generates energy through nuclear fusion (typically H He)
- Sun is closest star next closest is Proxima Centauri up to 5000 stars visible in the sky
stars twinkle
- Star has orbiting object - planets (a spherical object that orbits a star; dominates its
orbit; reflects light; rock, ice, gas)
Terrestrial Planets = Mercury, Venus, Earth, Mars
Gas Giants = Jupiter, Saturn, Uranus, Neptune
Dwarf Planets = Eris, Pluto
Some plants have moons (a natural satellites of a planet)
- Satellites - natural or artificial object that orbits a larger celestial body
- Biggest moon in solar system is Jupiter’s moon (Ganymede)
Solar System: a star and all material/objects that orbit it; includes planets, dwarf planets,
moons, other small bodies
Galaxy: very big collections of stars (planetary systems), gas, dust, and dark matter; held
together by gravity and orbiting a common centre (example: Milky Way Galaxy)
Nebula (Latin: cloud): huge interstellar clouds of gas and dust; four main varieties
- 4 Types - Pillars of Creation, Eagle, Cat’s eye, Crab
UNIT 1 - PART 2
How to Quantify Numbers, Sizes & Distances?
Scientific Notation for Large Numbers
It is a shorthand way for describing numbers, for example, “1 billion” can be written as “1
followed by 9 zeros”: 1 000 000 000 every time we add three more zeros, we use a special
name
Scientific Notation for Small Numbers
Decimal numbers: For example, “1 millimetre” can be written as 1/1000 metre = 1/(103)
metre = 1 x 10-3 metre
We moved the decimal point by three places
Our moon radius = 1,700km
Ganymede radius = 2,600km (largest moon in solar system)
Nebula = huge range in size, from being tiny just after they form to up to 1015 km, e.g., Orion
Visible Universe = : 9 x 1023 km
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UNIT 1 - PART 3
What Range of Sizes do we Deal with?
A Journey in Steps of Factor 10
UNIT 1 - PART 4
What Range of Ages do we Deal with? An Example
How old is Earth?
- In 1859, Lord Kelvin estimated Earth’s age was 400 millions years or less
- His calculation: assume that the Earth started as molten rock (Proto-Earth with
uniform temperature T = 30000C) and that the temperature below the surface
increases now by 0.03 K/m. How long did the Earth cool to reach the current state?
-
This corresponds to 400 million years
Later massaged it down to 20 million years
Contemporary best estimate:
4.6 billion years = 4600 million years
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1 - rate of heat loss through Earth's surface
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