light_LA2
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School
Bucks County Community College *
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Course
102
Subject
Astronomy
Date
Dec 6, 2023
Type
Pages
4
Uploaded by GeneralLyrebird2546
Using Light to Study Stars 1 Background and Purpose: Light is one of the most important tools for astronomers when studying the objects in the universe. By looking at the spectral emissions a star, astronomers can determine amazing things about it: what it is made of; its spectral classification; how fast the star is rotating; a hint about how big the star is; and whether it is moving away from us or toward us. In this brief activity, you will practice spectral analysis for a series of stellar spectra to determine what the stars are made of (Part 1) and apply your understanding of the Doppler Shift and spectral lines to describe how galaxies are moving relative to one another (Part 2). Part 1: The Stuff of Stars On the following page are a series of emission spectra. The top spectra are the emission spectra of individual elements. If the elements’ electrons are in an excited state, they will emit light at particular points along the visible light spectrum (shown as white emission lines on our spectra that follow). Each element emits its own unique set of emission lines, sort of functioning like a spectral fingerprint for each element! This is useful to astronomers when studying stars because they can identify which fingerprints they are seeing and, therefore, determine what the star is made of. Question 1.
Below the elements’ emission spectra are three unknown spectra from three different stars. Using the elements’ emission spectra, you will determine what elements are in the three unknown spectra. To do this, compare the white lines present the spectra with the white lines present in the spectra for the elements. Write out the which elements (full name, not the chemical symbol) you have identified in the space provided above the spectra. (
5 points
) Handy tip
I have found that tracing the spectral lines on a transparency or tracing paper can be helpful. Try different colors for the different elements (e.g., hydrogen lines all red, etc.). Then to the right of your trace indicate the count of how many lines per element there are (e.g., hydrogen has 6 red lines). Then you can move the trace over page 2. If you see 6 red lines visibly, when you lay hydrogen over a mystery spectrum, then you know that spectrum has hydrogen in it. If only 5 of the red lines are visible, then hydrogen is not present in that spectrum, etc.
Using Light to Study Stars 2
Using Light to Study Stars 3 Part 2: Using Doppler Shifts to Identify Galaxy Movement For this second part, we will work with the Doppler Effect (visit our text and the supplemental slides for this week). When an object moves relative to us (or vice-versa), we will still see the same pattern of emission or absorption spectra (because that is the chemical makeup of the star), but we see the entire pattern of lines shifted closer to the blue end of the spectrum (blue-shifting) or toward the red end of the spectrum (red-shifting). When objects red shift, it means they are moving away from us. When they blue-shift, that means they are moving toward us. Both blue-shifting and red-shifting are due to the Doppler Effect. Below we see a spectral set of emission lines. This is our reference spectrum. Below the reference spectrum is a spectrum from the Andromeda galaxy. Reference Spectrum Spectrum from the Andromeda Galaxy Question 2.
Write out two observations about the emission lines in the two spectra directly above (i.e., compare them and contrast them) (
1 points
): 1. 2. Question 3.
What does the spectrum from the Andromeda galaxy tell us about how the galaxy is moving? (
1 point
)
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Using Light to Study Stars 4 Question 4.
A) What is the movement you identified in Question 3 called? B) What phenomenon are we referring to, in general? (
1 points
): A. B. Question 5.
Below are three different spectra from three different galaxies. Note the top spectrum is a reference spectrum and is the same for all three galaxies. Review the spectra and use them to answer the questions (A through C) that follow (
2 points
): Galaxy A Galaxy B Galaxy C A. Which of the galaxies are moving toward us? ____________________ B. Which of the galaxies are moving away from us? ___________________ C. Which galaxy is moving away fastest? ____________________