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Stars and galaxies l.jpg

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

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Welcome l.jpg

  • 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

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What are we going to cover?

  • Our Place in the Universe

  • The Electromagnetic Spectrum

  • Classifying Stars

  • Classifying Galaxies

  • History of the Universe

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First up…

  • Our Place in the Universe

    • What is our Universe made of?

    • How big are things? How far away?

    • How do we know?

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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…

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Examining the Components

  • Stars

  • Gas and dust (Nebulae)

  • Star clusters

  • Galaxies

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Different types of stars

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Types of Stars

  • Big

  • Small

  • Red

  • Blue

  • Yellow

  • In groups

  • Alone

    • More later

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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

  • 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

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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”?

  • 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

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Large, massive, bright nebulae

  • Emission Nebula

  • The hot gas is emitting light

Orion image at

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Colder, darker nebulae

Dark dust blocking the hot gas behind it

NOAO/AURA/NSF Image from

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Leftovers from an Explosion

Supernova remnant

(smaller, less gas)

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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

NOAO/AURA/NSF Images at and

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Elliptical Galaxies

Images at

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Irregular Galaxies

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

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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

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The Milky Way

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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

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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.

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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.

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Time for a Break! Next Up

  • Our Place in the Universe

  • The Electromagnetic Spectrum

  • Classifying Stars

  • Classifying Galaxies

  • History of the Universe

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Let’s check your knowledge

  • Please draw an electromagnetic spectrum on a sheet of paper, and label the parts.

  • You can work in groups.

Radiation l.jpg

  • There are lots of types of light (radiation), including visible and invisible

Electromagnetic spectrum


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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.

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  • 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


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Using a Star’s Spectrum

  • We can use a star’s spectrum to classify it.

NOAO/AURA/NSF image at

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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.

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Hertzsprung-Russell Diagram

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Young stars form in nebulaefrom Small Magellanic Cloud

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Star-forming region in the Large Magellanic Cloud:

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Orion image at

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Interstellar “eggs”

Movie at

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Our Sun is a Regular/ Small Star

On the “Main Sequence”

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In a few Billion years… Red Giant

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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 l.jpg
    By 5 billion years… White Dwarf

    Small, but very hot

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    Massive Stars are different

    On the “Main Sequence” but

    not for long

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    Betelgeuse—Red Supergiant

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    Supernova—Massive Star Explodes

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    Neutron Star or Pulsar

    Image at

    Black hole l.jpg
    Black Hole

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    Galaxies l.jpg

    • 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 l.jpg
    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

    Galaxies55 l.jpg

    Image at

    Spiral galaxy andromeda56 l.jpg
    Spiral galaxy--Andromeda

    NOAO/AURA/NSF Images at and

    Spiral galaxy on edge l.jpg
    Spiral Galaxy on Edge

    Image at

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    Image at

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    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 l.jpg
    Elliptical Galaxies

    Images at

    Lenticular l.jpg

    • have a disk but no arms

    • have little or no excess gas and dust

    Image at

    Irregular galaxies62 l.jpg
    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 l.jpg
    Irregular Galaxies

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

    Collisions l.jpg

    • 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

    Interacting l.jpg

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    the Antennae or Mice

    Information at

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    The occasional results of two galaxies colliding: ringed galaxies

    Images from and

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    Various galaxies galaxies (can you identify types?)

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    Supermassive black holes galaxies

    • 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 l.jpg
    Active galaxy galaxies

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    at the center of a large galaxy galaxies

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    Galaxy Clusters galaxies

    • 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!

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    Coma Cluster galaxies

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    Superclusters! galaxies

    • 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 l.jpg
    Evolution of Galaxies galaxies

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    Origin of the Universe galaxies

    • 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 l.jpg

    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 time

    • 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 l.jpg
    History of the Universe time

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    Later History time

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    Big Bang Theory time

    • 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 time

    • 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 time

    • 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 l.jpg
    Predictions for the Big Bang Model time

    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 l.jpg
    Evidence for Big Bang time

    • 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

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    When Did the Universe Form? time

    • ~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

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    Feedback, Questions time

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