Download Chapter 28 Stars and Galaxies Reading Guide

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Chapter 28 Stars and Galaxies Reading Guide
Pages 612 – 630
Before you read:
1. Think about a fire you may have seen before. What color are the hottest flames?
Blue
2. Why do you think some objects in the sky are brighter than others?
Hotter, closer
While you read:
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1. What is the electromagnetic spectrum? List the types of electromagnetic radiation in
order from longest of the left to shortest on the right.
Radiation arranged in a continuum.
Radio waves, Microwaves, Infrared, Visible Light, Ultra Violet, X-Rays, Gamma Rays
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2. What is a spectroscope and what does it tell us about stars?
Separates visible white light into its colors, like a prism or rainbow
Tells astronomer the composition of a star (elements and proportions)
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3. What is the Doppler Effect?
Tendency for light and sound waves to become longer when moving away and shorter when moving
towards an observer. For example, you hear the high pitch of the siren of the approaching
ambulance, and notice that its pitch drops suddenly as the ambulance passes you.
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2. Why is Hipparchus important to astronomers?
He devised a system to classify stars based on their brightness from Earth.
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3. What is the apparent magnitude of a star?
Measure of how bright a star appears from Earth
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3. Explain the difference between the two stars listed below:
Star #1 – apparent magnitude = 1.67
Star #2 – apparent magnitude = -1.67
#2 is brighter as seen from Earth because it has a lower apparent magnitude
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4. How do we measure distances to stars?
Light Years
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5. What is the closest star to Earth (besides the Sun)?
Proxima Centauri
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6. Why are light-years used to measure distances in space?
Because of the vast distances
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7. What is parallax? (Use your thumb to demonstrate it to yourself)
Apparent shift in position due to the location of the observer. Used to measure the distance of stars
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8. Why do astronomers call star spectra the “fingerprints of stars”?
Each star has a unique spectrum
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9. What color are the hottest stars?
Blue
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10. What color is our Sun? (make sure you read, it is NOT yellow!)
White with a twinge of yellow
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11. Luminosity is the actual brightness of a star. What two factors determine luminosity?
Size and temperature
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12. A star’s absolute magnitude is how bright it would be if all stars were the same
distance (10 parsecs) from Earth. If the apparent magnitude of Sirius is –1.44 and the
absolute magnitude is +1.42, what does this tell you about the distance of Sirius from
the Earth?
Sirius is closer to Earth than 10 parsecs. Even though it is the brightest star in the sky as seen from
Earth, it is close to earth, but relatively dim.
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13. What is the H-R diagram?
Plots luminosity and temperature of stars.
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14. Look at the H-R diagram. What is unusual about labeling of the x- and y-axes?
(Think about how we normally number an axis.)
The hotter temperatures are to the left of the X-axis and the cooler temperatures are towards the
right.
After you read:
15. The Sun has an apparent magnitude of –26.7. A friend tells you about a star that also has a
magnitude of –26.7. How could this be true?
The friend can be referring to absolute magnitude and not apparent magnitude
16. We are not able to visit distant stars, yet we can determine how far away they are. How do
parallax and math help us do this?
A nearby star's apparent movement against the background of more distant stars as the Earth
revolves around the Sun is referred to as stellar parallax. Nearby objects have a larger parallax than
more distant objects when observed from different positions, so parallax can be used to determine
distances. By observing parallax, measuring angles, and using geometry, one can determine
distance.