Bell Ringer 9/29 What are stars made of?

Stars

Star A star is a body of gases that gives off a tremendous amount of radiant energy in the form of light and heat Appear to be tiny specks of white light Most vary in color and are much larger than Earth

Motion Stars move through the night sky towards the west Stars rotate around the North Star, Polaris –Circumpolar = stars that circle around Polaris Because of the earth’s rotation, some stars are not visible during particular seasons

Constellations Pattern of stars Location changes throughout the year due to Earth’s orbit –Classified by season 3000 years ago, people observed and recorded shifting patterns –Knew when to plant, harvest, and celebrate rituals based on location of constellations

Constellations Astronomers recognize 88 constellations Constellations are named for animals, ancient gods, & legendary heroes –Most do not look like what they are named for

Common Constellations Ursa Major (Big Dipper) Ursa Minor (Little Dipper) Draco the Dragon Orion Zodiac Animals

Constellation stars Astronomers use constellations to locate particular stars Stars within a constellation are named according to apparent magnitude –Brightest star is labeled alpha –Next brightest beta and so on Some constellation stars have individual names –Polaris (North star) in the Little Dipper

Constellation Project Starting September 25, we will being a class project on Constellations You will pair up and pick a constellation Do some research on the constellation Make a visual aid about the constellation

Constellations to choose from Aquarius Aries Cancer Capricornus Gemini Leo Ursa Major (Big Dipper) Ursa Minor (Little Dipper) Draco the Dragon Orion Cassiopeia Libra Pisces Sagittarius Scorpius Taurus Virgo Cygnus Hercules Pegasus Hydra Lyra Centaurus

Star Clusters Stars appear to be close to each other because the human eye cannot distinguish the distance a star is from earth Clusters are stars close to each other due to gravitational attraction

Binary Stars Multiple-star systems –Pairs of stars that revolve around one another –Gravitationally bound & orbiting a common center of mass Used to determine stellar mass Appear as a single star to the human eye

Distance Astronomers use different methods to measure the distance between stars and Earth

Distance to Stars Distance to stars from Earth is measured in Light-years –Light-year = distance light travels in one year –Light-year = x m

Light Light travels 9.5 trillion km in one year –Speed of light = 300,000 km/s –Sun is 8 light-minutes away because it takes 8 minutes for the sunlight to reach Earth Parsec = 3.26 light-year = x10 16 m

Parallax Apparent shift in position caused by motion of observer Change in position of Earth as it orbits –Closer stars have larger change in parallax –Farther stars have smaller change in parallax Distance determined by angle of change

Parallax

Example of Parallax Extend your arm and hold up your left thumb Close your right eye and note location of thumb as compared to classroom wall Now close left eye and note location of thumb

Example of Parallax You will see your thumb appears to move This movement is because your eyes view everything at different angles, since they are a couple centimeters apart on your face If you move your thumb closer to your face you will see a bigger change in thumb location

In-Class Assignment/Homework WKT 29.2

29.2 B Notes

Properties of Stars Mass Diameter Luminosity (Magnitude) Temperature

Magnitude Apparent Magnitude = how bright a star appears System established by Greeks Brightest stars = +1

Magnitude Absolute = how bright a star would appear at 10 parsecs (30 light-years away) Allows for comparison based on how bright stars would appear at equal distances

Magnitude Luminosity = Energy output from surface of stars Measured in watts –Think light bulbs

Temperature Stars are assigned spectral type then further subdivided into numbers –O stars have a temperature of ~50,000 K –M stars have a temperature of ~2000 K Based on temperature and pattern of spectra lines –Sun = G2, temperature = ~5800 K Temperature also related to luminosity and absolute magnitude

Composition All stars have nearly identical compositions ~73% Hydrogen ~25% Helium 2% - other elements

Classification of Stars H-R diagram = graph showing pattern between absolute magnitude and surface temperature of a star –Charts absolute magnitude, temperature & spectral type Brightness of stars increases as surface temperature increases

H-R Diagram

Main-sequence stars = band of stars running through middle of diagram –Sun and most stars in our sky are main- sequence stars Band extends from cool, dim, red in the lower right corner to hot, bright, blue stars in upper left corner

Main Sequence Fusing Hydrogen in core As stars evolve they begin to fuse Helium and burn hydrogen –High mass stars burn Hydrogen faster than low mass stars

H-R Diagram Other types of stars –Giants= very large, cool, bright star –Supergiants = extremely large, giant star –White Dwarfs = small, hot, dim star

In-Class Assignment/Homework