OVERVIEW FOR THE TEACHER
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Level: HS Advanced, College
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Objective: In this sequence of activities, using a horn telescope, the students will take measurements of HI spectra along the galactic plane of the Milky Way Galaxy. From their observations of galactic quadrants II & III the students will be able to deduce that the MWG is rotating. From their observations of galactic quadrant I the students will be able to determine a velocity curve of the MWG and compare it to expected curves for different galactic mass distributions.
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Pre-Knowledge of Students:
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The students have been exposed to the horn telescope and understand how to read a spectrum.
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The students understand what radio waves are, and they understand that the spin-flip in hydrogen atoms is the source of the 21-cm waves detected by the horn telescope.
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The students understand how to apply the Doppler shift to the spectrum peaks in order to find the relative velocity of the detected hydrogen.
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The students understand trigonometry.
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The students understand relative velocity.
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The students understand Newton’s law of gravitation and can relate it to the orbital motion of satellites.
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Key Terms: horn telescope, HI spectrum, galactic coordinates, Horizontal Coordinates, Stellarium, Doppler Shift, red shift, blue shift, relative velocity, circular motion, law of gravitation, orbital motion
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Related Videos for Teacher: Galaxy Survey Trailer
- Teacher Preparation:
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This activity can be done with a single horn shared with the class, or with multiple horns assigned to groups of students.
- The students have used a horn telescope before. It is recommended that the following lessons have been completed:
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Intro to the Horn Telescope
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Electromagnetic Spectrum
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The 21 cm Wavelength of Neutral Hydrogen
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Understanding Coordinate Systems
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The teacher should be familiar with the implications of red-shifted and blue-shifted signals, and understand that the general trend of blue-shifted peaks from quadrant II and red-shifted peaks from quadrant III imply that the galaxy rotates in a CW sense in reference to standard galactic coordinates.
- The teacher should be familiar with the tangent method and how the motion of an object toward the sun along a tangent is related to the galactic distances and angles involved. See the Teacher Notes under Part 2: Galactic Quadrant I Observation.
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- Sequence of activities: - The Teacher Notes for each part provide more details.
INTRO: The students can run through this sequence of activities to build a rudimentary understanding of the concepts and exposure to the horn telescope
a. These 4 activities could be grouped together so that smaller groups could work with the horn telescope for the one hands on activity.
b. The students may have had some of these experiences if other lesson modules have been done (Basic Observational Tools)
PART I The students collect spectra at different galactic longitudes along the galactic plane in quadrants II and III.
a. The student analyze the spectra to determine the relative velocity of the detected hydrogen.
b. The students determine that the galaxy is rotating.
PART II The students then collect spectra at different galactic longitudes along the galactic plane in quadrant I.
a. Assuming circular motion of the galaxy, the speed of the tangent point along the observation line is calculated.
b. A graph showing galactic speed vs distance from the galactic center is created using these results.
c. This graph is compared to the graph expected in different models of mass distribution in the galaxy.
Intro Activities for Radio Astronomy
OBJECTIVE: These activities allow this Velocity Curve of the MWG module be able to stand alone from start to finish. There is also some overlap with the Basic Observational Tools module. These basic activities will bring fuller understanding to creating the galactic velocity curve.
Teacher Notes Since there is an activity with “discovering” what the horn telescope can do, it is suggested to assign all 4 activities so that students can be busy while other small groups are working with the scope(s) your have set up. (Most teachers very likely with have only one telescope.)
Part 1: Galactic Quadrants II & III Observation
OBJECTIVE: In this activity, the students collect spectra of the MWG along the galactic plane in quadrants II & III. From these they should be able to deduce that the MWG is rotating and the direction of rotation.
Student Handout for Part 1 Observation
Student Handout for Part 1 Analysis & Interpretation
Part 2: Galactic Quadrant I Observation
OBJECTIVE: In this activity, the students collect spectra of the MWG along the galactic plane in quadrant I. The students will determine the speeds of the most red-shifted part of the spectra, and then apply the tangent method to determine the galaxy’s velocity as a function of distance from the galactic center.
Student Handout for Part 2 Observation
Student Handout for Part 2 Analysis & Interpretation
Velocity Curve Lessons