DO NOW: Write it down  1. Most of the galaxies in the universe are moving __________ from us. 2. Our evidence to support this is ___ ___________________________. 3. One exception to this is the galaxy ______________ which is moving toward us (it has a ___________). 4. Why?

AIM: How can we characterize stars? Constellations: groups of stars * Human invented Apparent movement caused by Earth’s rotation and revolution Because Earth rotates from WEST to EAST, the sky seems rotate counter clockwise around Polaris! *Sun moon and stars rise in East and set in West. Polaris is stationary http://www.skyviewcafe.com/skyview.php

Why does the sky change? The sky SEEMS to change * NIGHTLY- because of Earth’s ROTATION (spin on axis)- 15°/hr *SEASONALLY- because of Earth’s REVOLUTION (orbit around sun) 360° around slightly elliptical orbit in 365 days. http://www.classzone.com/books/earth_science/terc/content/visualizations/es0408/es0408page01.cfm

Rotation Seasonal Changes Nightly Changes

Apparent Magnitude- How bright a star seems to be to an observer on Earth * DEPENDS ON HOW CLOSE A STAR IS TO EARTH Our next closest star, Proxima Centuri Our Sun VS.

*DISTANCE FROM EARTH IS NOT A FACTOR! Luminosity- a star’s ACTUAL brightness. It depends on the size and temperature. *DISTANCE FROM EARTH IS NOT A FACTOR! Absolute magnitude- measure of how bright stars would be if they were the same distance from Earth Example) What if I held a light bulb in front of your face and then walked across Port Blvd? Would it look the same size? Would it still BE the same size?

Astronomical Unit- the distance from Earth to closest star (sun) 150 million km. Proxima Centuri is the next closest star (260,000 AU)

Pushes outward 2. Gravity – pulls inward FORCES that balance out a star- 1. Nuclear fusion- 1 Hydrogen + 1 Hydrogen = Helium http://www.astronomynotes.com/starsun/s3.htm Pushes outward 2. Gravity – pulls inward

HR DIAGRAM aka stars’ family album http://aspire.cosmic-ray.org/Labs/OldStarLife/hr_interactive.html (Open links in internet Explorer) Have you seen any of these? http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/stars/planetsstarsandgalaxiesact.shtml

~DENEB ~ Now even though it is a massive super-giant, Deneb is actually a very young star, at least compared to the sun. Deneb was born only about 3 million years ago, long after the Dinosaurs died out, and is already approaching the end of its life -- the star can last at most another million years. Compare this to the life of our sun -- it has been around for 5 BILLION years, and has another 5 billion left in it. This is because Deneb is so much more massive than the sun. The greater mass causes greater pressure and forces the star to burn much hotter (shorter wavelength) and faster. With stars, the bigger they are, the harder they fall. NOTE- Deneb is 2,600 light –years away. http://my.execpc.com/60/B3/culp/astronomy/Fall/MilkyWay.html

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