Astronomy 1

Terms

Astronomy – The study of the universeUniverse – Everything known that exists, including space, time and matterSolar System – the Sun and its family of orbiting planets, moons, asteroids, meteoroids, and cometsStar - A luminous ball of gas that produces energy through the nuclear fusion of hydrogen

Planet -A body that does not give off light, can be made of solids, liquids, or gases

Moons - an object made mostly of rock that orbits a larger body, usually a planet (also called satellites)

Light year

Light – the fastest thing in the universe.Light year (LY) – the distance light travels in one year– Speed - 186,282 miles per second– Distance light travels in one year

5,870,000,000,000 miles

Astronomical Unit

Astronomical Unit (AU) - the average distance from the Earth to the Sun– 1 AU = about 92,960,000 miles

Interesting Fact

For every grain of sand on earth there are a million stars in our universe!

The Big Bang Theory

The whole universe was believed to be packed into a very dense sphere of hydrogen called a singularity.

About 13 billion years ago it formed a gigantic cloud of gas that expanded.

It has been expanding and cooling ever since.

Some parts moved quicker than others.

Parts of the cloud clumped into billions of stars forming galaxies.

We live in one of those galaxies.

Our galaxy is called the MILKY WAY.

More Interesting Facts

The Universe is not expanding into something. Everything that is, is expanding.

The further away from us a galaxy is, the faster it is moving.

Steady State Theory

Alternate theory for the beginning of the Universe (not many people believe it now)

Says Universe is expanding, but new matter is constantly being created so the overall density stays the same

Galaxies

Galaxies - systems of millions or billions of starsGalaxies contain dust, gases, and starsThe material (dust, asteroids, meteoroids, comets, planets, etc.) that orbits around a star is called a Solar System

3 Types of Galaxies

Spiral Galaxy

Has a central lens-shaped, bright nucleus made of millions of stars (and possibly a super-massive black hole)

Around the nucleus is a fainter, flat disk of stars, gas and dust

This disk is in the shape of spiral arms

Elliptical galaxySystem of stars made mainly of only stars, very little dust and gas– Thought to be older than spiral galaxies

Lens-shaped or sphericalNo spiral armsMost of the stars are close to the center

Irregular galaxy

Small, faint, and less common type of galaxy made up of stars

Have an irregular shape

Irregular GalaxyNGC 1427A

Milky WayOur Galaxy

Over 100 billion stars make up our galaxy

Our sun lies in one of the arms of this galaxy.

The diameter is about 140,000 light years across.

It is about 20,000 light years thick.

The sun is about 23,000 light years away from the center.

Top view

Top ViewSide view

What we see from Earth(with a good camera)

Andromeda Galaxy

Spiral Galaxy

Much larger than the Milky Way

About 2 million light years away

Much like our own Galaxy, that is why it is studied so greatly

Andromeda Galaxy

Magellanic Clouds

Two irregular galaxies that satellite the Milky Way

Can be seen from the southern hemisphere with the naked eye

Looks like…a large cloud and a small cloud

Magellanic Clouds

Local Group

The Milky Way belongs to a cluster of more than 17 galaxies called the Local Group.

The Magellanic Clouds and the Andromeda are part of this Local Group.

* Galaxies usually form in clumps such as our own Local Group.

Nebula

Nebula - cloud of dust and gasA Nebular cloud is made up of:– 99% gas (mostly hydrogen)– 1% dust

Most nebula are invisible.The only way we can see them is by light from a star.AKA: “Stellar Nurseries”

Nebulas

Orion Nebula Eagle Nebula Crab Nebula

Horse head Nebula Bubble Nebula North American Nebula

How a star is born

1. A nebula contains star forming gases.

2. Something disturbs the gases (i.e. shockwave from a supernova) and the gases begin to come together and compress into a ball of hot gases.

3. The ball of gases starts to glow. It is now called a protostar (“baby star”).

Main sequence Star

4. A protostar becomes a star once it becomes hot enough to begin fusing hydrogen into helium. About 10,000,000 K

5. A main sequence star is an “adult star.”– A main sequence star is in a stable state.– This means that the energy produced by a

star equals the gravity acting on the star.

Stable state

GravityGravity

Gravity

Gravity

Energy

H-R Diagram

Hertzsprung - Russell Diagram– Shows how the Luminosity (brightness)

and temperature of a star are related– When a star is on the Main Sequence:

• as temperature increases, so does luminosity• as temperature decreases, so does luminosity

A good thing to remember

Hot stars are blue in color.

Cool stars are red in color.

Our sun is a whitish/yellow color star. It’s temperature is somewhere in the middle of blue and red.

Think of fire: the hottest part of a flame is the blue part, not the orange part!!!

Red Giants

6. A star’s core uses up its hydrogen.

7. The core collapses causing heavier elements to fuse together – Burning: helium, then carbon, oxygen, etc.

8. When it burns heavier elements the star expands to a large size and begins to cool off.

Red Giant

What will happen to a star after it dies?

Prior to this point in the star life cycle, all stars behave the same wayDepending on the star’s mass, when it was a main sequence star it will become one of the following:– White dwarf– White dwarf with a planetary nebula– Neutron star– Pulsar– BLACK HOLE

Important to know…

The more mass a star has, the more gravity is acting upon it. A star must burn a lot of gases to keep it from collapsing in on itself. Therefore, it must exert a lot of energy. – However, gravity always wins!

Massive stars: die quicklyLess massive stars: live for a really long timeAverage Stars: (Our Sun): live about 10 billion years

White DwarfsA low mass adult star turns into a red giant

When it dies, it stops producing its own energy. (No longer being classified as a star)

It collapses in on itself (to about the size of the Earth, but much more massive)

It glows white hot until it cools off. (Never to be seen again - takes a really long time to do this!!!)

A white dwarf is not a star since it is not doing fusion any more!

One tsp. of a white dwarf would weigh several tons!

White Dwarf with a Planetary Nebula

Medium-mass stars, like our Sun, will die the same way as low mass stars EXCEPT:During the last moments of being a star, it will shed its outer layer of gases (instead of exploding) and form a planetary nebula (has nothing to do with planets) The core will collapse into a white dwarf, illuminating the nebulaThis will be the fate of our own sun roughly 5 billion years from now.

White Dwarf with a Planetary Nebula

Supernova

Is an exploding starHappens to stars that are at least 7 times more massive than our own sun right before they die.Is a result of a red giant burning up iron at its core.Iron is too heavy. When iron fusion occurs in the core, it will collapse at an incredible rate. It will then explode, releasing gas and dust, and begin to fuse the gases into heavier elements.

Supernovas viewed from Earth

Supernovae are among the brightest events in the universe ... the bright spot in the lower left is a supernova observed in 1994, and is almost as bright as all the other stars in the centre of the spiral galaxy. This galaxy and supernova are 52 million lights years from Earth.

What Supernovas form…

Neutron Stars

These objects are not really stars at all.After a supernova occurs, half of the star’s material is ejected out into space.The remaining material collects into a small dense sphere. The object is made up of only neutrons. – Protons and electrons are forced together

to form these neutrons.

These objects are extremely small and extremely dense. – It has a mass several times greater than

our own sun– One tsp. of a neutron star would weigh

about a million tons!

it is about the size of a small city.

It rotates very rapidly.

This is how the size of a neutron star matches with the size of the city of Chicago

Pulsars

Are neutron stars that rotate very rapidly and give off light or radio waves

When the waves reach the earth they come in as pulses of waves hence the name pulsars

Pulsar Diagram

Black Holes

Very massive stars become SUPER RED GIANTS

EXPLODE as supernovae

And become Black holes!

VERY DENSE but smaller than the point on your pencil!

Their gravity is so great that even light (the fastest moving thing in our universe) cannot escape it.

Event horizon - the surface of a black hole– Objects won’t get “sucked” into a black hole

unless they are within this boundary

• Singularity- central point of a black hole