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Lecture 2

# AS101 Lecture Notes - Lecture 2: Spiral Galaxy, Observable Universe, Googol

Department
Astronomy
Course Code
AS101
Professor
Victor Arora
Lecture
2

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Lecture 2 – January 7, 2015
Models in Science
- In general, a model is something that represents reality
- A scientific model is an idea that can be used to describe an aspect of reality and has
withstood observational or experimental tests
- We can also develop conceptual models to help us think about how nature works
Scale Model: The Solar System
- How do we setup a scale model?
oScale = actual size/desired scale size
- To resize the Sun so it fits in this room, the scale would be a factor of about 80,000
- If we compressed distances by the same factor, the planets would be well off-campus
oObservations
Rocky planets are close together than Jovian (gas planets)
Sizes of planets are puny compared to distances between them
The Astronomical Unit
- We can specify distances in the Solar System by comparing them to the average Earth-
Sun distance
- 1 AU = 150 000 000 km = 150 000 000 000 m
- A planet twice as far from the Sun would be 2 AU away
Scientific Notation
- Specifying how many zeroes a number has is known as scientific notation
o10 = 10^1
o100 = 10^2
o1000 = 10^3
o1 Googol = 10^100
- i.e. the Earth is on average 150 000 000 000 meters from the Sun
oWould be written as a coefficient between one and ten, multiple by the
appropriate power of 10
oAnswer: 1.5 x 10^11 meters
- To multiply two or more numbers written in scientific notation just;
oMultiply the coefficients
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