Beyond our Solar SystemBeyond our Solar System

The Milky WayThe Milky Way Our solar system is part Our solar system is part

of a galaxy called the of a galaxy called the Milky WayMilky Way

The The Milky WayMilky Way contains contains about 400 billion stars!about 400 billion stars!

It appears as a hazy It appears as a hazy white band spanning from white band spanning from the southern horizon the southern horizon across the sky overheadacross the sky overhead

It is approximately It is approximately 100 000 light years 100 000 light years acrossacross

What is a Galaxy?What is a Galaxy?

A Galaxy is…A Galaxy is…

A huge collection of gas, A huge collection of gas, dust, and hundreds of dust, and hundreds of billions of starsbillions of stars

They are held together by They are held together by gravitygravity

Galaxies have been Galaxies have been moving away from each moving away from each other since the other since the BIG BIG BANG!BANG!

Three Types: Spiral, Three Types: Spiral, Elliptical or irregularElliptical or irregular

Spiral GalaxiesSpiral Galaxies

The milky way The milky way

Arms spiral outwardsArms spiral outwards

Nuclear bulge at centreNuclear bulge at centre

Elliptical GalaxiesElliptical Galaxies

These are the most These are the most common galaxiescommon galaxies

Most are shaped like Most are shaped like a footballa football

Stars wrap around the Stars wrap around the centre in all directionscentre in all directions

““Giant Elliptical” Giant Elliptical” Galaxies can hold 1 Galaxies can hold 1 trillion stars and are 1 trillion stars and are 1 million light yrs acrossmillion light yrs across

Irregular GalaxiesIrregular Galaxies

These galaxies have These galaxies have no fixed shapeno fixed shape

Stars, gas and dust Stars, gas and dust are spread randomlyare spread randomly

They are the smallest They are the smallest and are seen as and are seen as building blocks for building blocks for larger galaxieslarger galaxies

What is a Nebula?What is a Nebula?

Suns and planets are Suns and planets are still forming within still forming within galaxies in areas galaxies in areas called nebulas called nebulas

Nebulas are vast Nebulas are vast clouds of gas and clouds of gas and dust (more on this dust (more on this later!)later!)

The Famous Eagle Nebula

The Orion NebulaThe Orion Nebula

The Horse Head Nebula

How many galaxies are out there?How many galaxies are out there?

In 1925, Edwin Hubble In 1925, Edwin Hubble realized a “nebula” he realized a “nebula” he was looking at was was looking at was actually an entire galaxy!actually an entire galaxy!

We now believe that We now believe that there are about 400 there are about 400 billion galaxies!billion galaxies!

The Hubble Space The Hubble Space Telescope (HST) was Telescope (HST) was named in his honour.named in his honour.

Hubble ST Deep Space FieldHubble ST Deep Space Field

This image covers a This image covers a speck of sky speck of sky equivalent to the equivalent to the width of a dime held width of a dime held 75 feet away75 feet away

There are 1 500 There are 1 500 galaxies visible in this galaxies visible in this photo!photo!

You do the math!You do the math!

The Formation of the UniverseThe Formation of the UniverseThe Big Bang TheoryThe Big Bang Theory

The Big BangThe Big Bang

This is the most widely accepted scientific This is the most widely accepted scientific explanation for the origin of the universe. explanation for the origin of the universe. According to this theory…According to this theory…

The universe began in an instantaneous The universe began in an instantaneous event that occurred ~15 billion years agoevent that occurred ~15 billion years ago

When the “clock started”, there were no When the “clock started”, there were no galaxies at time zero, not even atoms!galaxies at time zero, not even atoms!

The Big BangThe Big Bang

The universe started The universe started out very small and out very small and dense, and is dense, and is expanding as it coolsexpanding as it cools

As the universe As the universe cooled, quarks cooled, quarks combined to form the combined to form the sub-atomic particles sub-atomic particles (p+, e-, n)(p+, e-, n)

Atoms were then Atoms were then formedformed

The Big BangThe Big Bang

““Light’ atoms (He, H, Light’ atoms (He, H, Li, Deuterium) were Li, Deuterium) were produced by the produced by the young, hot universe.young, hot universe.

Later, “heavy” atoms Later, “heavy” atoms were formed by the were formed by the nuclear reactions that nuclear reactions that power stars.power stars.

The Big BangThe Big Bang

http://www.youtube.com/watch?v=PV0ACIykxQI

Movement of the StarsMovement of the Stars

The stars do not The stars do not move across our move across our sky…they just appear sky…they just appear to because the earth to because the earth is rotating on it’s axisis rotating on it’s axis

Polaris – The North StarPolaris – The North Star

Polaris – The North StarPolaris – The North Star

The axis of the earth The axis of the earth is in line with the is in line with the North star, so this star North star, so this star does not appear to does not appear to move at all.move at all.

All other All other constellations near it constellations near it appear to revolve appear to revolve around the “pole” stararound the “pole” star

Movement of the StarsMovement of the Stars

Stars are moving Stars are moving however, within their however, within their own galaxies, since own galaxies, since all galaxies are all galaxies are moving away from moving away from each other as the each other as the universe keeps universe keeps expandingexpanding

Is it a Star or a Planet?Is it a Star or a Planet?

Stars “Twinkle” and Stars “Twinkle” and “move” through the sky “move” through the sky as part of a constellationas part of a constellation

Planets emit steady light Planets emit steady light (reflected from the sun)(reflected from the sun)

They “wander” through They “wander” through the constellations near the constellations near the “Ecliptic Line”the “Ecliptic Line”