Download Chapter 30.1

Chapter 30.1:
Characteristics of Stars
Characteristics of Stars
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A star is a body of gases that gives off
energy in the form of light & heat.
Size varies
Color varies based on temperature
Our sun is an average star
Composition
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Star composition observed through a spectrometer
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Separates light into its individual colors
Each color represents a different wavelength
Three types of spectra
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Emission or bright-line
Absorption or dark-line
Continuous
Since different elements absorb different
wavelengths of light , elements can be determined.
Composition Continued
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Hydrogen is the most common element.
Surface temperature of a star is indicated
by the color
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Red stars are the coolest and blue are the
hottest (Figure 2 on page 776).
Motion
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Two kinds of motion associated with
stars:
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Actual motion --- just like it sounds!
Apparent motion --- This is motions visible
to the unaided eye in a dark sky; due to
movement of Earth.
Motion Continued
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Some stars create circular trails around a
central star (Polaris aka the North Star)
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Circumpolar: stars that never go below the
horizon. (Circling stars).
Different stars become visible during different
seasons.
Three actual motions:
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Rotate on an axis
2.
Revolve around another star – binary systems
3.
Move away or toward the Earth.
Distance
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Distance
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Light Year = 9.5x1012km; Distance that light
travels in one year.
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Astronomical Unit (AU) --A unit of length used to
measure distances in solar system.
Stellar Magnitude
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Magnitude: a way to measure the brightness of a
body in the sky
Apparent magnitude = brightness of a star as it
appears to us on Earth
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Measure light from star using telescopes
Measurement is then assigned a number
Brightest stars have lowest numbers
Dimmest stars have highest numbers
Absolute: the true brightness of the object