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stars and galaxies

Stars and Galaxies

Created by the

Lunar and Planetary Institute

For Educational Use Only

LPI is not responsible for the ways

in which this powerpoint may be used or altered.

Space Science for Middle School at HCDE

February 20, 2009

Image at

  • Please complete the pre-assessment
  • It’s for us—it’s not about you
  • Please let us know how much YOU know, not how much your friends sitting next to you know
what are we going to cover
What are we going to cover?
  • Our Place in the Universe
  • The Electromagnetic Spectrum
  • Classifying Stars
  • Classifying Galaxies
  • History of the Universe
first up
First up…
  • Our Place in the Universe
    • What is our Universe made of?
    • How big are things? How far away?
    • How do we know?
what is our universe made of
What is our Universe made of?
  • Stars and planets
  • Gas and dust
  • Organized into star clusters
  • Organized into nebulae
  • Organized into galaxies
  • Other things:
    • Black holes
    • Dark matter
    • Dark energy

What was in your drawing?

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  • Use the Venn diagrams to place the stickers—where does everything go?
  • After you’re finished, let’s discuss…
examining the components
Examining the Components
  • Stars
  • Gas and dust (Nebulae)
  • Star clusters
  • Galaxies
different types of stars
Different types of stars

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types of stars
Types of Stars
  • Big
  • Small
  • Red
  • Blue
  • Yellow
  • In groups
  • Alone
    • More later
what is a star cluster
What is a “star cluster”?
  • stars formed together at same time
  • stars may be gravitationally bound together
  • two types: open (galactic) and globular

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open clusters
Open Clusters
  • dozens to thousands of stars
  • young stars! only a few million years old
  • may still be surrounded by nebula from which they formed
  • located in the spiral arms of a galaxy
  • example: Pleiades

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more open star clusters
More open star clusters

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globular clusters
Globular Clusters
  • millions to hundreds of millions of stars
  • old! 6 to 13 billion years
  • mostly red giants and dwarfs
  • stars are clumped closely together, especially near the center of the cluster (densely)
  • surround our disk as a halo

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what is a nebula
What is a “nebula”?
  • A cloud in space
  • Made of gas and dust
    • Can have stars inside
  • Most of the ones we see are inside our Milky Way Galaxy
  • Different types

Orion image at

large massive bright nebulae
Large, massive, bright nebulae
  • Emission Nebula
  • The hot gas is emitting light

Orion image at

colder darker nebulae
Colder, darker nebulae

Dark dust blocking the hot gas behind it

NOAO/AURA/NSF Image from

leftovers from an explosion
Leftovers from an Explosion

Supernova remnant

(smaller, less gas)

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what is a galaxy
What is a “galaxy”?
  • A large group of stars outside of our own Milky Way
  • Made of billions to trillions of stars
    • Also may have gas and dust
  • Spiral, or elliptical, or irregular shaped

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spiral galaxy andromeda
Spiral galaxy--Andromeda

NOAO/AURA/NSF Images at and

elliptical galaxies
Elliptical Galaxies

Images at

irregular galaxies
Irregular Galaxies

NASA and NOAO/AURA/NSF Images at , , and

our galaxy the milky way
Our Galaxy: the Milky Way
  • has about 200 billion stars, and lots of gas and dust
  • is a barred-spiral (we think)
  • about 100,000 light-years wide
  • our Sun is halfway to the edge, revolving at half a million miles per hour around the center of the Galaxy
  • takes our Solar System about 200 million years to revolve once around our galaxy
the milky way
The Milky Way

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mapping the milky way
Mapping the Milky Way

How do we know what our Galaxy looks like?

We can see stars

  • star clusters
  • nebulae
  • Galaxies
  • Let’s try to Map our Galaxy
measuring distances
Measuring Distances
  • Parallax (let’s model it)
    • As Earth orbits the Sun, we see nearby stars move relative to more distant stars
    • How many degrees did the plate move, relative to the background?
    • Can you calculate the distance to the plate?
    • Sine of the parallax (angle) x Earth’s distance to the Sun = Distance to the star
    • The angles involved for strellar observations are very small and difficult to measure. Proxima Centauri, has a parallax of 0.77 arcsec. This angle is approximately the angle subtended by an object about 2 centimeters in diameter located about 5.3 kilometers away.
measuring distances26
Measuring Distances
  • What is a Light Year?
    • A light year is the distance light travels in a year. Light moves at a velocity of about 300,000 kilometers (km) each second; how far would it move in a year?
    • About 10 trillion km (or about 6 trillion miles).
  • Why do we use light years?
    • Show me how far 5 centimeters is.
    • Now show me 50 centimeters.
    • Now tell me (without thinking about it, or calculating it in meters) how far 500 centemeters is. 2000? 20,000?
    • We need numbers that make sense to us in relationship to objects; we scale up and use meters and kilometers for large numbers.
time for a break next up
Time for a Break! Next Up
  • Our Place in the Universe
  • The Electromagnetic Spectrum
  • Classifying Stars
  • Classifying Galaxies
  • History of the Universe
let s check your knowledge
Let’s check your knowledge
  • Please draw an electromagnetic spectrum on a sheet of paper, and label the parts.
  • You can work in groups.
  • There are lots of types of light (radiation), including visible and invisible

Electromagnetic spectrum


let s observe a spectrum
Let’s Observe A Spectrum
  • What will the spectrum look like with a red filter in front of your eyes? A blue filter?
  • Hypothesize and test your hypothesis.
  • Now let’s examine the invisible parts—using our cell phones and a solar cell.
There are different types of spectra
    • Continuous
    • Emission or Bright Line (from ionized gas, like a nebula or a neon sign)
    • Absorption or dark line (from stars)

Illustration at

  • All stars emit radiation
    • Radio, infrared, visible, ultraviolet, x-ray and even some gamma rays
    • Most sunlight is yellow-green visible light or close to it

The Sun at X-ray wavelengths

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Image and info at


using a star s spectrum
Using a Star’s Spectrum
  • We can use a star’s spectrum to classify it.

NOAO/AURA/NSF image at

time to create a stellar graph
Time to Create a Stellar Graph
  • Everyone will receive several “stars”
  • Place them on the large paper, according to their color and their brightness
  • This is a version of the Hertzsprung-Russell diagram.
hertzsprung russell diagram
Hertzsprung-Russell Diagram

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young stars form in nebulae from small magellanic cloud
Young stars form in nebulaefrom Small Magellanic Cloud

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Star-forming region in the Large Magellanic Cloud:


Orion image at

interstellar eggs
Interstellar “eggs”

Movie at

our sun is a regular small star
Our Sun is a Regular/ Small Star

On the “Main Sequence”

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in a few billion years red giant
In a few Billion years… Red Giant

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our sun s habitable zone
Our Sun’s Habitable Zone

Billions of years ago, things may have been different

    • The Sun was cooler (by up to 30%!)
    • Earth’s atmosphere was different (thicker, carbon dioxide)
  • Conditions will be different in the future
    • By many accounts, increases in the Sun’s temperature will make Earth uninhabitable in 1 billion years or less
    • These changes will also affect other planets… Mars?

Animation at

by 5 billion years white dwarf
By 5 billion years… White Dwarf

Small, but very hot

Image at


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massive stars are different
Massive Stars are different

On the “Main Sequence” but

not for long

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betelgeuse red supergiant
Betelgeuse—Red Supergiant

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supernova massive star explodes
Supernova—Massive Star Explodes

Images at

neutron star or pulsar
Neutron Star or Pulsar

Image at

black hole
Black Hole

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  • come in different sizes (dwarf, large, giant)
  • come in different shapes and classifications
    • Spirals
    • Ellipticals
    • Lenticulars
    • Irregulars
  • are fairly close together, relative to their sizes
spiral galaxies
Spiral Galaxies
  • have flat disk, spiral arms, central bulge, and a surrounding halo
  • some have a “barred” bulge
  • are fairly large (no dwarf spirals)
  • have lots of gas and dust and younger stars in their arms, but older stars and little gas or dust in their halos and central bulges

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spiral galaxy andromeda56
Spiral galaxy--Andromeda

NOAO/AURA/NSF Images at and

spiral galaxy on edge
Spiral Galaxy on Edge

Image at


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elliptical galaxies59
Elliptical galaxies
  • range from spherical to football shaped
  • range from very small to giant
  • have very little gas or dust
  • mostly old stars
  • similar to the central bulge of a spiral galaxy
elliptical galaxies60
Elliptical Galaxies

Images at

  • have a disk but no arms
  • have little or no excess gas and dust

Image at

irregular galaxies62
Irregular Galaxies
  • any galaxy that isn’t a Spiral, Elliptical, or Lenticular
  • usually have lots of gas and dust and young stars
  • may have a distorted shape from interaction with another galaxy
irregular galaxies63
Irregular Galaxies

NASA and NOAO/AURA/NSF Images at , , and

  • We now think that galaxies in groups and clusters often collide
  • The Milky Way is moving at 300,000 mph toward the Andromeda Galaxy
  • They may collide in about 5 billion years
  • Stars don’t usually collide
  • New orbits, gas piles up to form new stars

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the antennae or mice
the Antennae or Mice

Information at


The occasional results of two galaxies colliding: ringed galaxies

Images from and

various galaxies can you identify types
Various galaxies (can you identify types?)

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supermassive black holes
Supermassive black holes
  • almost every medium to large galaxy we’ve check has a supermassive black hole at the center
  • the larger the galaxy, the more massive the black hole
  • we don’t know which comes first, the galaxy or the black hole
  • we think that these black holes are responsible for some of the galaxies with jets and lobes which give off radio waves, x-rays, etc.
active galaxy
Active galaxy

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at the center of a large galaxy
at the center of a large galaxy

Image at and

galaxy clusters
Galaxy Clusters
  • the Local Group
    • includes the Milky Way, the Andromeda, and over 30 other smaller galaxies
  • the Virgo Cluster
    • hundreds to thousands of galaxies, 60 million light-years away
    • giant elliptical at center, formed by galactic cannibalism
    • the Local Group is “falling” toward the Virgo Cluster at 60 to 250 miles per second!
coma cluster
Coma Cluster

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  • clusters are bound together in larger structures, called superclusters
  • these superclusters have been mapped, and are grouped into long strings
    • 300 million to a billion light-years long
    • 100 to 300 million light-years wide
    • and only 10 to 30 million light-years thick
  • in between these strings are huge voids of galaxies, although some astronomers may have detected hot gas
evolution of galaxies
Evolution of Galaxies

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Origin of the Universe

  • Big Bang
    • Dominant scientific theory about the origin of the universe
    • Occurred ~13.7 billion years ago
  • What is the Big Bang?
  • How do we know?
what is the big bang
Infinitely dense point not governed by our physical laws or time

All matter and energy contained in one point

What is the Big Bang?

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history of the universe
History of the Universe
  • 10-43 seconds - gravity separates from other forces
  • 10-35 to 10-32 seconds - fundamental particles - quarks and electrons
  • 10-6 seconds - quarks combine into protons and neutrons
  • 1 second - electromagnetic and weak nuclear forces separate
  • 3 minutes - protons and neutrons combine into atomic nuclei
  • 105 years - electrons join nuclei to make atoms; light is emitted
  • 105-109 years - matter collapses into clouds, making galaxies and stars

Orion Nebula -

history of the universe80
History of the Universe

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later history
Later History

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big bang theory
Big Bang Theory
  • In 1915, Albert Einstein concluded that the universe could not be static based on his recently-discovered theory of relativity and added a "cosmological constant" to the theory of relativity because astronomers assured him that the universe was static
  • Aleksandr Friedmann and Abbe George LeMaitre are credited with developing the basics of the Big Bang model between 1922 and 1927; their calculations suggested that universe is expanding, not static.
  • Years later, Einstein called his cosmological constant the biggest mistake of his career

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expanding universe
Expanding Universe
  • In 1929, Edwin Hubble showed that most galaxies are red-shifted (moving away from us), and that a galaxy’s velocity is proportional to its distance (galaxies that are twice as far from us move twice as fast)

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hubble s evidence
Hubble’s Evidence
  • Doppler shifting - wavelength emitted by something moving away from us is shifted to a lower frequency
  • Sound of a fire truck siren - pitch of the siren is higher as the fire truck moves towards you, and lower as it moves away from you
  • Visible wavelengths emitted by objects moving away from us are shifted towards the red part of the visible spectrum
  • The faster they move away from us, the more they are redshifted. Thus, redshift is a reasonable way to measure the speed of an object.
  • When we observe the redshift of galaxies, almost every galaxy appears to be moving away from us – the Universe is expanding.
predictions for the big bang model
Predictions for the Big Bang Model

The expansion of the Universe

  • Edwin Hubble's 1929 observation that galaxies were generally receding from us provided the first clue that the Big Bang theory might be right.

The abundance of the light elements H, He, Li

  • The Big Bang theory predicts that these light elements should have been fused from protons and neutrons in the first few minutes after the Big Bang.

The cosmic microwave background (CMB) radiation

  • The early universe should have been very hot. The cosmic microwave background radiation is the remnant heat leftover from the Big Bang.
evidence for big bang
Evidence for Big Bang
  • Red shift - as light from distant galaxies approach earth there is an increase of space between earth and the galaxy, which leads to wavelengths being stretched
  • In 1964, Arno Penzias and Robert Wilson, discovered a noise of extraterrestrial origin that came from all directions at once - radiation left over from the Big Bang
  • In June 1995, scientists detected helium in the far reaches of the universe - consistent with an important aspect of the Big Bang theory that a mixture of hydrogen (75%) and helium (25%) was created at the beginning of the universe
when did the universe form
When Did the Universe Form?
  • ~13.7 billion years ago
  • How do we know?
    • Spreading (Red Shift) -know distances, rates of retreat, relative positions
    • Pervasive background radiation of 2.7°C above absolute zero - afterglow of the Big Bang

Cosmic background radiation temperature on celestial sphere

feedback questions
Feedback, Questions

Reach us online at

For more information, contact

Christine ShuplaLunar and Planetary Institute3600 Bay Area BlvdHouston, TX  77058(281)