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Astronomy -the study of stars Stars • Huge spheres of hot, glowing gas – Example = sun • Stars give off energy---how do we know this? Energy = waves Electromagnetic spectrum • Huge spheres of hot, glowing gas – Example = sun • Stars give off energy---how do we know this? – Visible light = we can see lots of stars in the sky – Radiant energy from the sun heats the earth – Also, some stars give off radio waves Telescopes • Use lenses or mirrors to collect and focus light from distant objects • Three different types: – Refracting telescope – Reflecting telescope – Radio telescope Both of these are visible light telescopes Refracting telescope • Consists of 2 convex lenses – First lens (objective lens) gathers the light and focuses it – Second lens (eyepiece lens) magnifies it Reflecting Telescope • Uses a concave mirror to gather and focus light • A smaller mirror inside reflects this image to the eyepiece lens which magnifies it Radio Telescope • Detects radio waves given off by objects in space • Most have curved reflecting surfaces that are several hundred meters in diameter • The bigger the radio telescope, the more radio waves it can collect Telescopes: Similarities and Differences Traits which are only true of reflecting telescopes Traits which are only true of refracting telescopes Traits which are only true of radio telescopes Spectroscopes • Also called a spectrograph – Breaks the light from an object into its color spectrum – Astronomers use this to get information about stars including their chemical compositions and temperatures Spectroscopes: star’s chemical composition • What elements is a star made up of? • Astronomers compare the banding patterns of known elements to those of the stars. What elements does this star contain? What makes up the universe? • On the right side of your paper, list as many things as you can come up with in one minute. • Stars, galaxies, star systems, nebulae, etc. • Universe = space and everything in it! Review: What is a star? • A star is a huge sphere of hot, glowing gas. • Can you think of any examples of stars? – The sun is a star! Stars • What pieces of equipment can be used to gain information about stars? – Reflecting telescope – Refracting telescope – Radio telescope – SPECTROSCOPE!! What is a galaxy? • A galaxy is a cluster of stars. • Billions of stars make up a galaxy. Can you think of the name of our galaxy? – Milky Way galaxy How do we measure distance to stars and other galaxies? • We have to use a unit called a light year. • A light year is the distance light can travel in one year….HUGE! • light year is a unit of distance, not time!!!! • 1 light year= ~9.5 million million kilometers Parallax • Parallax is the apparent change in position of an object when you look at it from different places. What characteristics classify stars? • All stars are huge spheres of glowing gas (mostly hydrogen). • Stars are classified based on 3 main physical characteristics: – Temperature – Brightness – size LAB: Color vs. Temperature • You will record the data for your lab in your Cornell notes on the RIGHT side. Summary of Lab Findings • On the right side, place the order of star color by increasing temperature For example: Coolest colornext colordsfsjsdhfjkhottest color Temperature of stars • Color of a star reveals its temperature. • Remember the color vs. temperature lab? – Red stars = relatively cool stars (still hot ~3200 degrees Celsius) – Yellow- white = medium temperature (~5500 degrees Celsius) – Blue-white stars = hottest stars (>10,000 degrees Celsius) Brightness of stars • Brightness = the amount of light stars give off – This depends on its size and temperature – How bright it looks from Earth depends on distance and actual brightness • Apparent magnitude • Absolute magnitude Apparent Magnitude • Brightness as seen from Earth • Example: the sun looks very bright to us on Earth, but it is not the brightest star – It looks brighter because it is closer to earth than other stars. Absolute Magnitude • Brightness of a star if it were a standard distance from the earth Review • What characteristics are used to classify stars? • Now, we will look at graphs that show these characteristics of stars…they are called HR diagrams Hertzsprung – Russell Diagram