Transcript lecture2

Scales of the Universe
(and a little refresher)
www.astro.umass.edu/~mauro/astro100
Goals
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to refresh and use scientific notations
to remember how to convert units!
to see the levels of structure in the
Universe
to comprehend the vastness of scales
in the Universe
In order to describe and
understand what you see, you need
numbers and units
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Amherst:
UMass is about 1.5 miles
from the center;
Antonio’s pizza is about 1
pound a slice
The town was founded
about 200 years ago
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The Universe:
The nearest star is 4 light
years away;
The mass of a massive
black hole is about 108
solar mass (1 solar mass
is about 2*1030 Kg)
The age of the Universe is
about 14 billion years
The scales we meet in exploring the Universe are very
big, we must learn how to deal with them
How to say big numbers
Billion
Million
Thousand
thousandth
millionth
billionth
Giga
Mega
Kilo
...
milli
micro
nano
(G)
(M)
(K)
109
106
103
(m)
(m)
(n)
10-3
10-6
10-9
Units Conversion
First of all – Units are good things!
You can say the distance to Boston in miles
(or km) instead of inches (or cm)!
Translating to useful units is a very handy skill.
The key to changing units is remembering to replace
a unit by something equivalent
Converting Units
How many quarters are there in 1000 dollars?
1000 dollars= 1000x 1 dollar
= 1000x 4 quarters
= 4000 quarters
Question: How many cm are there in 3 km?
3 km = 3x 1km
= 3x 1000 m= 3000 m
= 3000x 1m
= 3000x 100 cm
= 300000cm
Light-time=Light traveling time=distance
Car-traveling time as distance: Boston is about 1.5 hours
away (assuming the speed of a car is 60 mph)
The speed of light: c =
Destination
London
Moon
Sun
Jupiter
Nearest Star
Most Distant Galaxy
Distance (km)
6,000
385,000
1.5 x 108
7.8 x 108
4 x 1013
1.4 x 1023
5
3x10
km/s.
Light Travel time
0.02 s
1.3 s
500 s (8.3 min)
43 min
4.3 years
14 billion years
Whenever you see "light-(time)", that means we are talking
about distance, not time.
Examples
1 yr = 3.15 x 107 s (Earth revolves around the Sun once)
1 ly = (3 x 105 km/s) x 3.15 x 107 s = 9.45 x 1012 km
=10 thousand billion km!
Now… on to scales in the
Cosmos...
52 feet across
1 mile across
160 kilometers across
1 mile = 1.61 kilometers
Infrared photo
12,756 km
1,600,000 km
=1.6 x 106 km
Moon
1.6x108 km =1.6x1011m
1AU = 1.5x1011 m
AU is a distance unit
1.6 x 1010 km, or a trillion (1012) times wider than the first picture!
32 AU
100 AU
10,000 AU
Stars are so far apart from each other!
If the Sun is a golf ball in NYC, the nearest star is a golf ball in Chicago!!!
106 AU = 17 ly
1 ly =63,000 AU = 1013 km
1700 ly
170,000 ly
1.7 x 107 ly
The local group of galaxies
1.7 x 109 ly
Basic classes of objects:
Planets:
Earth as one
Stars
Sun as one
Galaxies
Milky Way as one
Their sizes
Earth:
104 km
poppy seed
Sun:
106 km
grape fruit
Milky Way 1018 km
Earth-Sun distance
Universe 1023 km
100,000 Earth-Sun distance
A Sense of Space
1. The Sun would hold 1.3 million Earths.
i.e. the radius of the Sun is about 100 times
that of the Earth.
2. There are ~100 billion "Suns" in a galaxy like our
own Milky Way Galaxy.
3.Astronomers can see billions of galaxies.
Your local address:
So…How Big is the Observable
Universe anyway?
…about 14 billion-billion-billion centimeters in diameter
or
14,000,000,000,000,000,000,000,000,000 cm
or
1.4x1028 cm
or
14 billion ly
or
6000 Mpc
Summary of concepts
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Various units and their conversion
Order of magnitude
Power of 10, exponent
Scientific notation
The speed of light
Various scales of the Universe
Our place in the Universe, both in space
and time
Assigned Reading for Next Class
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Chapter 2, “The Sky”, complete (p.12 to
p.33)
What is our address in the
Universe?
UMass, Amherst, Massachusetts
U.S.A., Earth, Solar System
Milky Way Galaxy, Local Group, Local
Supercluster
Our Universe