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Size and Scale
Attendance Quiz II
Are you here today?
(a) yes
(b) no
(c) are we still here?
Here!
Today’s Topics
• “How do we know?” exercise
• Size and Scale
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•
•
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What is the Universe made of?
How big are these things?
How do they compare to each other?
How can we organize objects to make
sense of them?
What is the Universe made of?
Stars
• Stars make up the vast
majority of the visible mass
of the Universe
• A star is a large, glowing
ball of gas that generates
heat and light through
nuclear fusion
• Our Sun is a star
Planets
•
According to the IAU, a planet is
an object that
1. orbits a star
2. has sufficient self-gravity to make it
round
3. has a mass below the minimum mass
to trigger nuclear fusion
4. has cleared the neighborhood around
its orbit
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A dwarf planet (such as Pluto)
fulfills all these definitions except 4
Planets shine by reflected light
Planets may be rocky, icy, or
gaseous in composition.
Moons, Asteroids, and Comets
• Moons (or satellites) are
objects that orbit a planet
• An asteroid is a relatively
small and rocky object that
orbits a star
• A comet is a relatively small
and icy object that orbits a star
Solar (Star) System
•
A solar (star) system consists of a star and all the material
that orbits it, including its planets and their moons
Star Clusters
• Most stars are found in clusters; there are two main types
• Open clusters consist of a few thousand stars and are young
(1-10 million years old)
• Globular clusters are denser collections of 10s-100s of
thousand stars, and are older (10-14 billion years old)
Nebula
• A nebula is an interstellar cloud of gas and/or dust
• Nebulae are where stars are born and are also created
when they die
Galaxy
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A galaxy is a great island of stars in space, all held together
by gravity and orbiting a common center
In addition, there is gas and dust between the stars, some in
the form of visible nebulae
Cluster of Galaxies
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A collection of galaxies all held together by gravity
Universe
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The Universe is the name for the sum total of all matter and energy; that is,
everything within and between all galaxies
How big are these things?
Object
Size (km)
Moons, asteroids, comets
1-1,000 (100-103)
Planets
1,000-100,000 (103-105); Earth ≈ 104
Stars (middle-aged)
100,000-10,000,000 (105-107); Sun ≈ 106
Stars (extreme)
10 (101) - neutron stars
1,000,000,000 (109) - red giants
Solar (Star) System
10,000,000,000 (1010)
Stellar Clusters
100,000,000,000,000 (1014) - open clusters
1,000,000,000,000,000 (1015) - globular clusters
Nebulae
1,000,000,000,000-1,000,000,000,000,000
(1012-1015)
Galaxies
1,000,000,000,000,000,000 (1018)
Clusters of Galaxies
100,000,000,000,000,000,000 (1020)
Universe
?
Scientific Notation
• In order to write these very big numbers, it is convenient to
use a shorthand known as Scientific Notation
• A number such as 100 can be written as 102, where the 2 in the
exponent means multiply 10 two times, i.e, 100=10x10
• Likewise, 10,000 = 104 and 100,000,000,000 = 1011 and so on
• To multiply two such numbers, we simply add the exponents;
to divide we subract the exponent in the denominator from the
exponent in the numerator
103 x 107 = 10(3+7) = 1010
109 / 104 = 10(9-4) = 105
• Thus, to figure out how many times larger than the Solar
System is the Milky Way: 1018 km / 1010 km = 108; thus, the
Milky Way is 100 million times larger than the Solar System
Astronomical measures of distance
• Since astronomical distances are so large, it is
convenient to define some other measures of size and
distance
1 astronomical unit (AU) = the average distance from the Earth to the Sun
= 150,000,000 km
= 1.5 × 10 8 km
1 light - year = (speed of light) × (1 year)
⎛
km ⎞ ⎛ 365 days 24 hr 60 min 60 s ⎞
= ⎜ 300,000 ⎟ × ⎜
×
×
×
⎟
⎝
s ⎠ ⎝ 1 yr
1 day
1 hr
1 min ⎠
How far is a light-year?
1 light-year = (speed of light) × (1 year)
km ⎞ ⎛ 365 days 24 hr 60 min 60 s ⎞
⎛
= ⎜ 300,000
×⎜
×
×
×
⎟
⎝
s ⎠ ⎝ 1 yr
1 day
1 hr
1 min ⎟⎠
=9,460,000,000,000 km
≈ 10,000,000,000,000 km
≈ 1013 km ≈ 10 5 AU
How big are these things?
Object
Size (km, AU, or light years)
Moons, asteroids, comets
1-1,000 (100-103) km
Planets
1,000-100,000 (103-105) km; Earth ≈ 104 km
Stars (middle-aged)
100,000-10,000,000 (105-107) km; Sun ≈ 106 km
Stars (extreme)
10 (101) km - neutron stars
1,000,000,000 (109) km or 10 AU - red giants
Solar (Star) System
100 AU
Stellar Clusters
30 light years - open clusters
30-150 light years - globular clusters
Nebulae
0.1-100 light years (ly)
Galaxies
100,000 light years (ly)
Clusters of Galaxies
10 million light years (Mly)
Universe
?
How big are these different sizes?
What is our place in the universe?
https://youtu.be/17jymDn0W6U
Organizing Things
What is the correct order from smallest to largest, of
the following objects?
Tree, Continent, Chloroplast, Forest, Earth, Leaf
(a) Earth, Continent, Tree, Forest, Leaf, Chloroplast
(b) Earth, Continent, Forest, Tree, Leaf, Chloroplast
(c) Chloroplast, Leaf, Tree, Forest, Continent, Earth
(d) Leaf, Tree, Chloroplast, Forest, Continent, Earth
(e) Leaf, Chloroplast, Tree, Forest, Continent, Earth
How can we organize astronomical objects?
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Smaller objects often orbit larger objects (planets,
asteroids, comets orbit stars; moons orbit planets)
Some things are contained within other objects
1. Stars, planets, asteroids, comets are part of solar (star)
systems)
2. Stars are part of stellar clusters
3. Stars and stellar clusters form from nebulae
4. Stars, solar (star) systems, stellar clusters, nebulae are part
of galaxies
5. Galaxies are part of galaxy clusters
6. Everything is part of the Universe
•
Most types of objects come in a range of sizes
In-class group activities
•
Important to remember when doing in-class activities
1.
Work as a group. Each of you should have agreed to answer and written
it down, with explanations, before moving on. Don’t let your group
move ahead until you understand each part!
Get right to work! You typically have 10-15 minutes to complete these
activities. That is plenty of time, if you start right in.
These activities are your textbook - write good clear explanations for all
your answers. You will be grateful you did later.
2.
3.
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Get into your groups of 3-4
Complete the two ranking tasks
1.
2.
Size & Scale - Exercise #1
Size & Scale - Exercise #2
(10 minutes)
Pluto v. the Moon
Ordering by Size
What is the correct order from smallest to largest, of the following
objects? Andromeda Galaxy, Jupiter, Galaxy Cluster, Asteroid, Sun,
Solar System
(a) Jupiter, Asteroid, Sun, Solar System, Andromeda Galaxy, Galaxy
Cluster
(b) Asteroid, Jupiter, Sun, Solar System, Andromeda Galaxy, Galaxy
Cluster
(c) Asteroid, Jupiter, Solar System, Sun, Andromeda Galaxy, Galaxy
Cluster
(d) Asteroid, Sun, Jupiter, Solar System, Andromeda Galaxy, Galaxy
Cluster
(e) Asteroid, Jupiter, Sun, Andromeda Galaxy, Galaxy Cluster, Solar
System