The scale of the universe How did the Millennium Falcon make the Kessel Run in less than 12 parsecs? This Photo by Unknown Author is licensed under CC BY-NC-ND

What is a light year? A light year is the distance that light can travel in one year 9.5 X 1015 m Space is so big that we use light years to describe distances in light years The Sun is less than one light year away, in fact, it is 7 or 8 light minutes away This means that is takes light 7 ish minutes to get to us from the surface of the sun This Photo by Unknown Author is licensed under CC BY-SA-NC

So, what is a parsec? A parsec is 3.26 light years Assuming we could travel the speed of light… The way that the Millennium falcon traveled that far, that fast, is by using the gravity of the black holes to propel itself faster and faster It was quite dangerous as you can see in this scene… https://www.youtube.com/ watch?v=41vELuUbDPM This Photo by Unknown Author is licensed under CC BY-SA-NC So, what is a parsec?

Parallax Astronomers often use parallax to determine how far away close stars are Hold out your thumb, close one eye, now put your thumb over my face Now, switch eyes Notice your thumb is no longer over my face, you have to move it to cover my face again. This is parallax, you can use it and geometry to determine distances to nearby stars This Photo by Unknown Author is licensed under CC BY-NC-ND

How are stars classified? Characteristics used to classify stars include color, temperature, size, composition, and brightness Remember mass and size are not the same The mass of the star determines its color, its size does not matter This Photo by Unknown Author is licensed under CC BY-SA-NC

Brightness Apparent brightness is the brightness of a star seen from earth Absolute brightness is the brightness you would see if all of the stars were lined up the same distance from the Earth Absolute brightness also takes into consideration the atmosphere and removes distortion This Photo by Unknown Author is licensed under CC BY-NC-ND

How to we keep track of how stars change over time? The HR diagram, or Hertzsprung-Russell diagram, allows us to classify stars and understand how they change over time The y-axis is where the brightness is plotted The x-axis is where the temperature is plotted The main sequence is where stars once they have gained their mass, live out most of their lives Once they move out of the main sequence, they are dying, or are already dead This Photo by Unknown Author is licensed under CC BY-NC-ND

What is a galaxy? A galaxy is a huge group of stars, star systems, and star clusters, gas and dust, bound together by gravity Astronomers classify most galaxies into the following types: spiral, elliptical, and irregular This Photo by Unknown Author is licensed under CC BY-SA

Spiral galaxies Disk shaped Bulge in the middle Arms that spiral outward like pinwheels The arms contain dust and many stars The sun is located on the edge of an arm of the spiral galaxy the Milky Way This Photo by Unknown Author is licensed under CC BY-SA Spiral galaxies

Elliptical galaxies Not all galaxies have spiral arms Elliptical galaxies look like flattened balls They have millions of stars, but very little gas and dust between the stars Most elliptical galaxies contain only old stars This Photo by Unknown Author is licensed under CC BY-SA-NC

Irregular galaxies Typically smaller than other types of galaxies Generally have many bright young stars Lots of gas and dust to form new stars This Photo by Unknown Author is licensed under CC BY-SA