Star Properties

Star Distances

Units of Distance for Space:

Astronomical Units (AU): The distance from the earth to the sun (150,000,000 km)

Light Years: Distance light travels in a year. 9.4 trilliion km

Physical Properties of Stars: Size and Density

Color , temperature, size and density vary greatly between stars.

Some are smaller than earth, others are 2000 times wider than the sun

Elements in Stars Stars are mainly 99% Hydrogen (H) and Helium (He)

1-2% may be heavier elements like Oxygen, Carbon, Nitrogen, Calcium

Sun is 70% Hydrogen and 28% Helium

Stars produce energy (heat and light) by fusing hydrogen atoms to make helium

Star Color The color of the star is dependant on its surface

temperature.

Hot stars = Blue or White, ~30,000 K

Cool stars = Red or Orange, ~3,000 K

The Sun = Orange or Yellow, ~5,500 K

Star BrightnessLuminosity How bright a star actually is. Dependant on the size and temperature of the star.

Hotter = Brighter Bigger = Brighter

Star Brightness

Apparent Magnitude: How bright the star appears to be to an observer on Earth.

Ranking 1st to 6th, 1st being brightest A 1st is 100x brighter than a 6th magnitude

Absolute Magnitude: The luminosity of stars if they were all seen from the same distance (32.6 light years from the sun)

Star Types Nebula: a cloud of dust and gas that stars are born

out of; most are invisible

2 Visible types of Nebulas Diffuse Nebula: visible

due to the light provided by close stars

Dark Nebula: A nebula that you can see blocking other stars

Star Types Protostars: “baby stars” that appear as a nebula

contracts and heats up.

Main Sequence/Stable State: Young stars that are still mostly hydrogen that is fusing into helium

Stars in “The prime of their life” The more mass, the hotter

Star Types Giants: Highly luminous due to their overwhelming

size Supergiant: Largest and brightest of all stars Dwarfs: Small, less luminous stars

Can still be very hot, but dim because they are so small

Test Tomorrow (Tuesday 10/19)

1. Stars, Galaxies, Universe

2. Review Sheet Due Tomorrow

Constellations Presentations Start Wednesday

(Laranda@cps.edu)

Star Life Cycle Activity

Diagram and describe YOUNGEST to OLDEST in order.

Nebula, Protostar Main Sequence Giant/Supergiant Dwarf Supernova Neutron Black Hole

High Temp Low Temp

A

B

C

D

Determine Star Color & Type….

Origin of Stars Start as huge clouds of gas and dust (nebulae) Gas & clouds originated from supernovas

Formation of Protostars Something outside the nebula triggers the gravity

between the gasses and dust

As the nebula contracts, spots begin to glow with heat, forming protostars.

Formation of Main Sequence Stars

As protostars continue to contract, they get hotter and brighter until fusion begins.

IMPORTANT: STARS ARE ALWAYS TRYING TO COLLAPSE DUE TO THEIR OWN GRAVITY

Stars release energy equal to the force of gravity, which stops the contracting

It is now a Main Sequence Star

Formation of Giants/Supergiants

When hydrogen is almost depleted, the energy of fusion no longer balances the force of gravity.

Core of the star contracts and increases in heat.

Increased energy causes the outer layers to expand creating a Giant/Supergiant

Formation of Dwarfs With no fuel, no energy is released to support the

outer layers of the star THE STAR COLLAPSES ON ITSELF DUE TO

GRAVITY This squeezes the nuclei together very tightly and it

becomes a dwarf Causing the star to glow for billions of years as they

cool

Massive Star Life Cycle: Supernova

When fusion stops in very MASSIVE STARS, a super dense central iron core is left.

The core’s gravity is so strong that it collapses further, increasing pressure.

All the pressure on the core makes the star explode violently and half its mass is blown away in a great cloud called a supernova

Supernova Before and After

Neutron stars The leftover half of supernova.

Its gravity is so strong that all of the atoms particles are crushed together, leaving only neutrons.

Neutron stars may be 10km wide but are a trillions times as dense as the sun.

Black Holes If the neutron star is massive enough, its gravity

causes it to collapse, creating Black Holes.

Gravity is so great that not even light can escape

Gathering evidence supports the theory that the central core of the galaxy is a black hole

If we can’t see them, how do we know that they are there?

Strong X-Ray emissions from the Cygnus constellation were detected.

Upon observation, we saw a star orbiting around an empty spot in space

When something gets sucked into a black hole, its atoms get ripped apart and it emits x-rays

This was what was happening to the star’s matter It is believed that the center of our galaxy and

many others are massive black holes

Galaxies and Universe

Starting small

Solar system: the sun and its orbiting planets, asteroids, meteors, and comets.

Galaxy: groups of millions or billions of stars held together by gravity.

Universe: contains all the planets, stars, solar systems, and galaxies.

The Milky Way Sun is 1 of 100 billion stars

in the Milky Way galaxy

It is 1 of 17 nearby galaxies that make up the Local Group

Milky Way Facts Diameter: 140,000 light

years 1 light year =9,460,730,472,580.8 km

Width: 20,000 light years

Sun is 23,000 light years from the center

That’s Us!

Galaxy Types: Spiral Galaxies Spiral Galaxies have a central nucleus made of

millions of stars

Have arms extending from the nucleus, (made of clouds of dust & gas)

75% of known galaxies are spiral.

Barred Spiral Galaxies Same as spiral galaxies, except they have a bar that

goes through the middle.

Which is Which?

Elliptical Galaxies Elliptical Galaxies range from spherical to lens

shaped Contain no gas and dust clouds

Irregular Galaxies Irregular Galaxies are smaller, fainter, and less

common; Stars have no pattern

The Origin of the Universe Big-Bang Theory1. Universe started as 1 dense sphere of hydrogen

2. 13.7 bya it exploded, forming an expanding cloud of gas & dust

3. Cloud parts condensed into stars. Stars joined with other stars to become galaxies

Evidence for the Big Bang

1. Edwin Hubble discovered that the light of distant stars is constantly becoming more red.

Red Shift the object producing the light is moving away from us

2. Microwaves coming from all directions in the universe Echoes of the original explosion

What is Dark Matter?