How do properties of stars allow us to organize them? SC.8.E.5.5 Describe and classify specific physical properties of stars: apparent magnitude (brightness), temperature (color), size, and luminosity (absolute brightness). Essential Questions: What is a star? How do properties of stars allow us to organize them?

Bell ringer (write the questions) What characteristics do all terrestrial planets have? Gas giants are mostly made out of what type of gas? Explain how centripetal forces help maintain planets in orbit

“I Do” Electromagnetic Radiation Review Most of the celestial information that we receive is in the form of light. The form of electromagnetic radiation that our eyes can detect is visible light. Light can travel through empty space and does not need a medium to move through. The speed of light is constant in space so it is a consistent tool for measuring distance Scientists have developed techniques to decode information sent to us in rays of light no matter how faint. One technique is spectroscopy which splits light into its different colors or wavelengths and so scientists can analyze the spectrum. The temperature of a stars affects the wavelength of light emitted from them causing them to appear different colors.

What is a Star? Celestial body composed of gas and emits light Mostly hydrogen & helium Sun = Star They form inside a nebula (cloud of dust, hydrogen, helium, and other gases) due to gravity pulling matter into a dense mass that causes increased pressure and raises the temperature. This Photo by Unknown Author is licensed under CC BY-NC-ND

Color and temperature Stars vary in brightness, temperature, and size. Cooler stars are red, hotter stars are blue Stars can range in size from 1/100th the size of the Sun to 1,000 times larger. The temperature and color of a star depends directly on its size. Bigger=hotter, more gravity makes it burn faster raising its temperature Larger stars have a shorter life than smaller stars due to the faster burning of hydrogen fuel

Measuring Temperature Stars have different colors because they have different temperatures. Stars with the coolest temperatures are red. Stars with the highest surface temperatures are blue. Color Surface Temperature °C Blue Above 25,000 Blue-white 10,000 – 25,000 White 7,500 – 10,000 Yellow-white 6,000 – 7,500 Yellow 5,000 – 6,000 Orange 3,500 – 5,000 Red Below 3,500

STAR’S Brightness Stars vary in brightness Apparent Brightness Measurement of a star’s brightness as it APPEARS from Earth The brightness appears different in comparison to other’s because of a star’s distance from the Earth. We use a magnitude system to measure brightness: Faint stars have positive (larger) numbers Bright stars have negative (smaller) numbers

BELL RINGER How would you define apparent brightness? How are the stars organized by color? How do stars form? List the different types of galaxies.

Measuring Temperature Stars have different colors because they have different temperatures. Stars with the coolest temperatures are red. Stars with the highest surface temperatures are blue. Color Surface Temperature °C Blue Above 25,000 Blue-white 10,000 – 25,000 White 7,500 – 10,000 Yellow-white 6,000 – 7,500 Yellow 5,000 – 6,000 Orange 3,500 – 5,000 Red Below 3,500

STAR’S Brightness Stars vary in brightness Apparent Brightness Measurement of a star’s brightness as it APPEARS from Earth The brightness appears different in comparison to other’s because of a star’s distance from the Earth. We use a magnitude system to measure brightness: Faint stars have positive (larger) numbers Bright stars have negative (smaller) numbers

Star’s Brightness (absolute Brightness) Absolute Brightness (LUMINOSITY) Actual Brightness Measurement of a star’s brightness if they were all located at a standard distance Need to know distance from Earth We compare the brightness to a star whose distance from Earth we know.

These all have the same absolute brightness But, they have different apparent magnitudes Comprehension Check: Compare and contrast absolute magnitude and apparent magnitude.

Stars BrainPOP Click Picture to Start Video

Stars SIZE SOLAR Radii: unit of measurement Our Sun is a medium-sized star. It is used as the measuring stick for measuring other stars. The Sun= 1 solar radius To measure a stars size scientist use the SUN (1 Solar Radaii) Some stars are small then the Sun > Some stars are larger then the Sun < Dwarf stars can be 0.001 Super Giants can be 10 to 1,000 times the Sun

Hertzsprung-Russell Diagram (H-R) Diagram named after two astronomers. Used to help us understand stars. The x-axis plots the star’s temperature. The y-axis plots absolute magnitude. http://www.spacetelescope.org/videos/heic1017b/ Click Diagram for Animation

Main Sequence Stars Most stars you see are main sequence stars. Main sequence stars are in their main life cycle. Two forces keep these stars balanced: gravity pulling the atoms toward the center and fusion’s heat pushing atoms outward. When the hydrogen fuel runs out they get bigger and become super giants.

Fun facts about Stars Most of the stars in the universe are red dwarfs. They twinkle because of movement in the Earth's atmosphere. Many stars come in pairs called binary stars. There are some groupings with up to 4 stars. The smaller they are the longer they live. Giant stars are bright, but tend to burn out fast. The nearest star to Earth is Proxima Centauri. It is 4.2 light-years away, meaning you would have to travel at the speed of light for 4.2 years to get there. The Sun is around 4.5 billion years old.

“Independent You Do” Left-hand Side What makes a star different than a planet? How is it possible for Sirius, which is a white dwarf star, to be the brightest star we see in the night sky? How is it possible for two stars with the same absolute magnitude to have different apparent magnitudes? How is it possible for a white star to have the same absolute magnitude as a red star? What factors would allow a red supergiant star to have the same apparent magnitude as a white dwarf star?

Quiz Time!

Bell ringer (write the questions) What is the difference between apparent brightness and absolute brightness? What is the unit of measure that we use to measure the sizes of stars? Using the main sequence image, what stage is our star in?

Formation and development of stars All stars start off as a nebula A contracting cloud of gas and dust with enough mass to form a star is called a protostar Nebula

Main Sequence Stars Most stars you see are main sequence stars. Main sequence stars are in their main life cycle. Two forces keep these stars balanced: gravity pulling the atoms toward the center and fusion’s heat pushing atoms outward. When the hydrogen fuel runs out they get bigger and become super giants.

What unit of measure do we use to measure the solar system? Distances between objects in the solar system are so large that they are not easy to measure using m or Km. Astronomical Unit One astronomical unit = the average distance measured from the center of the sun to the center of earth about 150,000,000 Kilometers.

What unit of measure do we use to measure Galaxies? Distances to stars are so large that meters are not practical. Light year The distance that light travels in one year. About 9.46 trillion kilometers

Exit Ticket: Essential Questions What is a star? How do properties of stars allow us to organize them?