bell ringer 9/29 what are stars made of?. 29.2 - stars
TRANSCRIPT
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 to Stars
• Distance to stars from Earth is measured in Light-years– Light-year = distance light travels in one year– Light-year = 9.461 x 1015 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 = 3.086 x1016 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
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
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
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