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STUDY GUIDE FOR CHAP. 4.2 – CHARACTERISTICS OF STARS
I. CLASSIFYING STARS
- All stars are huge spheres of glowing ___.
- They are made up mainly of ________ and produce __________ through nuclear fusion.
- The nuclear energy released from the nuclear fusion is ___________ into electromagnetic radiation.
- This conversion of energy makes stars shine ____________.
- Astronomers classify stars according to their physical characteristics of _______, ___________, _______,
___________, and ____________.
A. COLOR AND TEMPERATURE
- The stars’ colors reveal the ____________________ of the stars.
- Cool stars appear _________ in color with a surface temperature of about 3,200 degrees Celsius.
- Warm stars appear _____________ in color with a surface temperature of about 5,500 degrees Celsius.
- The hottest stars are ____________ in color and have a surface temperature over 20,000 degrees Celsius.
B. SIZE
- Very large stars are called _________ or ______________. These stars are 10X – 100X larger than the Sun.
- Stars like the Sun are considered ______________ stars.
- Stars that are the size of Earth are called _____________ Stars.
- The smallest known stars are called ____________ Stars and are only 20 kilometers in diameter.
C. CHEMICAL COMPOSITION
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The chemical composition of most stars is _____% hydrogen, ______% helium, and ___% other
elements. This is very close to our Sun’s chemical composition.
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Astronomers use a ______________ to determine the elements found in stars.
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A spectrograph is a device that breaks ________ into colors and produces a color-banded image of the
resulting colors.
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The color-banded image is similar to our ___________ – it is a star’s id. It shows what chemicals are
present.
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The black band within the color is a wavelength of that color ___________by a star’s atmosphere.
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II. BRIGHTNESS OF STARS
- The brightness of a star depends upon both its _________ and ____________.
- If a star is very hot or very big, it will be very __________.
- On Earth, the brightness of a star depends upon its _______ from Earth (apparent brightness) and how ______
the star truly is (absolute brightness).
A. APPARENT BRIGHTNESS
- Stars that are _________ to Earth appear brighter to us and stars ____________ from Earth seem dimmer.
B. ABSOLUTE BRIGHTNESS
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Def. of absolute brightness: the true _____________ a star would have if all stars were the same
standard distance from Earth.
III. MEASURING DISTANCES TO STARS
A. THE LIGHT-YEAR
- Astronomers use a unit called the ___________ to measure distances between the stars.
- A light-year is the distance that light travels in _________ year which is about 9.5 million kilometers.
- Light travels in space at a speed of about ____________ kilometers per second.
- It takes the sun’s light __ minutes to travel from the sun to Earth.
B. PARALLAX
- Def. of Parallax: An apparent __________ in position of an object when you look at it from different places.
C. PARALLAX IN ASTRONOMY
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Astromoners are able to measure the parallax of nearby stars to determine their __________.
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Astronomers do this by measuring the distance of the nearby star when it is on ____ side of the sun.
Then, they wait ______ months to measure it again when it is on the other side of the sun.
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The _______________ between the two measurements tells astronomers how far away certain stars.
IV. THE HERTZSPRUNG-RUSSELL DIAGRAM
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Over 100 years ago, two scientists working independently came upon the same discovery.
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Both scientists, __________________ and ____________, made graphs to find out if the surface
temperature of a star and its absolute brightness were related.
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The two scientists concluded from their graphs that the hot ____________ stars are found on the left
side of the diagram while the cooler _______stars are found on the right side of the diagram.
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Also, the absolute brightest stars are located on the _____ of the diagram and the dimmest stars are
located at the _________ of the diagram.
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