Astro 103 - Lecture 1

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TOUR OF THE UNIVERSE


Outline

1. Dimensions, scales and notation in astronomy

2. The speed of light and some consequences: The Universe as time machine

3. Scale models of Universe

1. Dimensions and scales

Typical dimensions in Astronomy:

length(m, meter)
time(s, second)
mass(g, gram)
temperature(K, degrees Kelvin)

Scale and Scientific Notation: (see Interlude 1-1 and click here)

one1 = 1001 = 100one
ten10 = 1010.1 = 10-1tenth
hundred100 = 1020.01 = 10-2hundredth
thousand1000 = 1030.001 = 10-3thousandth
million1,000,000 = 1060.000001 = 10-6millionth
billion1,000,000,000 = 1090.000000001 = 10-9billionth
etc. ...

bigger

etc. ...

smaller



Other notation for scales:

Trillion Tera (T) 1012
Billion Giga (G) 109
Million Mega (M) 106
Thousand Kilo (K) 103
...
thousandth mili (m) 10-3
millionth micro (mu) 10-6
billionth nano (n) 10-9
trillionth pico (p) 10-12



Simple examples of notation:

thousand = 1,000
103 = 10 x 10 x 10 = 101 x 101 x 101 = 101+1+1

million = 1,000,000
106 = 103+3 = 103 x 103
"a million" = "a thousand thousand"


Scale + dimension -> unit


Time (dimension) +

seconds (scale) -> s (unit)
year (scale) -> yr (unit)
Examples:

1 yr = 3.15 x 107 s
1 Gyr = 109 yr = 3.15 x 1016 s

your age (roughly) = 20 yr = 6.3 x 108 s
Age of Universe = 20 Gyr = 6.3 x 1017 s

Space (dimension of length) +

meters (scale) -> m (unit)

Examples ("very round numbers"):

atomic nucleus 10-15 m
Hydrogen atom 10-10 m
your height 100 m
earth radius 107 m
earth-sun distance 1011 m
solar system 1013 m
nearest star 1016 m

~ one light year (lyr)

sun to galactic center 1020 m
nearest galaxy 1022 m

106 lyr, or 1,000,000 lyr, or "million" lyr



2. The Speed of Light


speed = distance / time = meters / seconds = m / s


c = speed of light = 3 x 108 m/s


c is :
constant,
finite,
fastest speed there is.
Consequences:

It takes time for light to travel over distance

time = distance / speed


Light travel times:

Distance Light Travel Times
earth to sun 1.5x1011 m 5x102s 8.3 minutes
nearest star ~1016 m 3x107s 1 year
nearest galaxy ~1022 m 3x1013s 1 million, or 106 years
"Event Horizon" 2x1026 m 6x1017s 20 billion, 2x1010 years, or 20 Gyr

Event Horizon -

- looking back to Big Bang, the creation of the Universe
- looking back over the age of the Universe
... and the consequence:



3. Scale Models of the Universe

Scale model #1
Sun - a basketball in my hand

Earth - at the back of the room

Pluto - at the State Capital Building (edge of solar system)

Nearest star - Hawaii


-- now, even smaller --

Scale model #2
Sun - a speck of dust in my hand

Nearest star - at the back of the room

Center of Milky Way - Chicago

Nearest galaxy - opposite side of the Earth


Lectures Lecture page Astro103 page
Last updated: Aug 23, 2011 Matthew A. Bershady