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

• 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 star2. has sufficient self-gravity to make it

round3. has a mass below the minimum mass

to trigger nuclear fusion4. has cleared the neighborhood around

its orbit

• 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• 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

• A collection of galaxies all held together by gravity

Universe• 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 stars1,000,000,000 (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 clustersNebulae 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

�

1 light - year = (speed of light) × (1 year)

= 300,000 kms

⎛ ⎝ ⎜

⎞ ⎠ ⎟ ×

365 days1 yr

× 24 hr1 day

× 60 min1 hr

× 60 s1 min

⎛

⎝ ⎜

⎞

⎠ ⎟

1 astronomical unit (AU) = the average distance from the Earth to the Sun= 150,000,000 km= 1.5 ×108 km

Astronomical measures of distance• Since astronomical distances are so large, it is

convenient to define some other measures of size and distance

How far is a light-year?

1 light-year = (speed of light) × (1 year)

= 300,000 kms

⎛⎝⎜

⎞⎠⎟×

365 days1 yr

×24 hr1 day

×60 min

1 hr×

60 s1 min

⎛⎝⎜

⎞⎠⎟

=9,460,000,000,000 km≈ 10,000,000,000,000 km ≈ 1013 km ≈ 105 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 kmStars (middle-aged) 100,000-10,000,000 (105-107) km; Sun ≈ 106 km

Stars (extreme) 10 (101) km - neutron stars1,000,000,000 (109) km or 10 AU - red giants

Solar (Star) System 100 AUStellar Clusters 30 light years - open clusters

30-150 light years - globular clustersNebulae 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

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

Organizing Things

How can we organize astronomical objects?• 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 clusters3. Stars and stellar clusters form from nebulae4. Stars, solar (star) systems, stellar clusters, nebulae are part

of galaxies5. Galaxies are part of galaxy clusters6. 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 activities1. 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!

2. Get right to work! You typically have 10-15 minutes to complete these activities. That is plenty of time, if you start right in.

3. These activities are your textbook - write good clear explanations for all your answers. You will be grateful you did later.

• Get into your groups of 3-4• Complete the two ranking tasks (10 minutes)

1. Size & Scale - Exercise #12. Size & Scale - Exercise #2

Pluto v. the Moon

What is the correct order from smallest to largest, of the followingobjects? 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

Ordering by Size