Beyond our Solar System

The Milky Way Our solar system is part of a galaxy called the Milky Way Our solar system is part of a galaxy called the Milky Way The Milky Way contains about 400 billion stars! The Milky Way contains about 400 billion stars! It appears as a hazy white band spanning from the southern horizon across the sky overhead It appears as a hazy white band spanning from the southern horizon across the sky overhead It is approximately light years across It is approximately light years across

What is a Galaxy?

A Galaxy is… A huge collection of gas, dust, and hundreds of billions of stars A huge collection of gas, dust, and hundreds of billions of stars They are held together by gravity They are held together by gravity Galaxies have been moving away from each other since the BIG BANG! Galaxies have been moving away from each other since the BIG BANG! Three Types: Spiral, Elliptical or irregular Three Types: Spiral, Elliptical or irregular

Spiral Galaxies The milky way The milky way Arms spiral outwards Arms spiral outwards Nuclear bulge at centre Nuclear bulge at centre

Elliptical Galaxies These are the most common galaxies These are the most common galaxies Most are shaped like a football Most are shaped like a football Stars wrap around the centre in all directions Stars wrap around the centre in all directions “Giant Elliptical” Galaxies can hold 1 trillion stars and are 1 million light yrs across “Giant Elliptical” Galaxies can hold 1 trillion stars and are 1 million light yrs across

Irregular Galaxies These galaxies have no fixed shape These galaxies have no fixed shape Stars, gas and dust are spread randomly Stars, gas and dust are spread randomly They are the smallest and are seen as building blocks for larger galaxies They are the smallest and are seen as building blocks for larger galaxies

What is a Nebula? Suns and planets are still forming within galaxies in areas called nebulas Suns and planets are still forming within galaxies in areas called nebulas Nebulas are vast clouds of gas and dust (more on this later!) Nebulas are vast clouds of gas and dust (more on this later!) The Famous Eagle Nebula

The Orion Nebula The Horse Head Nebula

How many galaxies are out there? In 1925, Edwin Hubble realized a “nebula” he was looking at was actually an entire galaxy! In 1925, Edwin Hubble realized a “nebula” he was looking at was actually an entire galaxy! We now believe that there are about 400 billion galaxies! We now believe that there are about 400 billion galaxies! The Hubble Space Telescope (HST) was named in his honour. The Hubble Space Telescope (HST) was named in his honour.

Hubble ST Deep Space Field This image covers a speck of sky equivalent to the width of a dime held 75 feet away This image covers a speck of sky equivalent to the width of a dime held 75 feet away There are galaxies visible in this photo! There are galaxies visible in this photo! You do the math! You do the math!

The Formation of the Universe The Big Bang Theory

The Big Bang This is the most widely accepted scientific explanation for the origin of the universe. According to this theory… This is the most widely accepted scientific explanation for the origin of the universe. According to this theory… The universe began in an instantaneous event that occurred ~15 billion years ago The universe began in an instantaneous event that occurred ~15 billion years ago When the “clock started”, there were no galaxies at time zero, not even atoms! When the “clock started”, there were no galaxies at time zero, not even atoms!

The Big Bang The universe started out very small and dense, and is expanding as it cools The universe started out very small and dense, and is expanding as it cools As the universe cooled, quarks combined to form the sub-atomic particles (p+, e-, n) As the universe cooled, quarks combined to form the sub-atomic particles (p+, e-, n) Atoms were then formed Atoms were then formed

The Big Bang “Light’ atoms (He, H, Li, Deuterium) were produced by the young, hot universe. “Light’ atoms (He, H, Li, Deuterium) were produced by the young, hot universe. Later, “heavy” atoms were formed by the nuclear reactions that power stars. Later, “heavy” atoms were formed by the nuclear reactions that power stars.

The Big Bang

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

Polaris – The North Star

The axis of the earth is in line with the North star, so this star does not appear to move at all. The axis of the earth is in line with the North star, so this star does not appear to move at all. All other constellations near it appear to revolve around the “pole” star All other constellations near it appear to revolve around the “pole” star

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

Is it a Star or a Planet? Stars “Twinkle” and “move” through the sky as part of a constellation Stars “Twinkle” and “move” through the sky as part of a constellation Planets emit steady light (reflected from the sun) Planets emit steady light (reflected from the sun) They “wander” through the constellations near the “Ecliptic Line” They “wander” through the constellations near the “Ecliptic Line”