# Astro 1 - Lecture 1

## Penn State University

Fall 1996

### © 1995 Matthew A. Bershady

 Lectures Lecture page Astro1 page

# TOUR OF THE UNIVERSE

## Outline

1. Dimensions and scales in astronomy
- space (length), and time
powers of 10
scientific notation
- astronomical examples
2. The speed of light and some consequences:

The Universe as time machine
3. The universe on different scales and their inter-relation
- movie: Powers of 10
- scale models of Universe

## 1. Dimensions and scales

Typical dimensions in Astronomy (see Interlude 1-2)

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

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

 one 1 = 100 1 = 100 one ten 10 = 101 0.1 = 10-1 tenth hundred 100 = 102 0.01 = 10-2 hundredth thousand 1000 = 103 0.001 = 10-3 thousandth million 1,000,000 = 106 0.000001 = 10-6 millionth billion 1,000,000,000 = 109 0.000000001 = 10-9 billionth etc. ... bigger etc. ... smaller

Names for scales:

 Trillion Tera (T) 1012 Billion Giga (T) 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

Examples:

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 10-16 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 6x1018s 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 Beaver Stadium (edge of solar system)

Nearest star - Hawaii

-- now, even smaller --

Scale model #2
Sun - a ball-bearing in my hand

Nearest star - at the back of the room

Center of Milky Way - Baltimore, Pittsburgh, Philly, NYC

Nearest galaxy - opposite side of the Earth

 Lectures Lecture page Astro1 page

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Last updated: Aug 21, 1996 Matthew A. Bershady