Research Highlight
June 15, 2005
From 6th Grade to the CMB
by Sarah Hansen
From 6th Grade to the CMB
The Space Explorers Program is a multi-year extracurricular enrichment program for middle- and high-school minority students from Chicago's South Side who are interested in math and science. The goal for the 2003/2004 academic year was to have students measure the temperature of the Cosmic Microwave Background and understand the cosmological significance of that measurement. Students first investigated what temperature is and explored ways to measure temperatures of remote objects. After detailed discussions about cosmology, students determined the CMB temperature using state-of-the-art instruments. The results of the students' experiment are consistent with professional determinations, and represent the first time that such measurements have been made by pre-college students.
Learning the Background. Students in the program had little experience with the physics of temperature, so we began the year with the basics. Students performed hands-on activities that explored the temperature-volume relationship, how household thermometers work, and the calibration of unlabeled thermometers. Students next investigated remote detection, using the light emitted by hot objects as an indicator of temperature. We discussed measuring the temperature of an electric stove burner, the filament of a light bulb, and the Sun in this manner. Students then used photometric data from the Sloan Digital Sky Survey to estimate the temperatures of other stars, and were challenged to find the closest star of the same temperature as the Sun.
Measuring the CMB Temperature. We spent several class periods discussing the evolution of the universe, and ‘reenacted’ the experience of a photon at the time of recombination. We explored the characteristics of the light from that time, and what must have happened to that light as the universe expanded. Students recognized that the current temperature of the CMB is an important cosmological indicator.
Microwaves are emitted by the atmosphere as well as by the CMB. Consequently, we must correct the measured power in our ground-based, 30 GHz experiment for the contribution from the atmosphere to our signal. This atmospheric foreground can be removed by measuring the total power received at different zenith angles. Most students in the program have not had trigonometry, so before doing the experiment we made physical models of the atmosphere. This hands-on learning helped students gain an intuitive understanding of the geometric relationship between zenith angle and atmospheric thickness.
Collecting Data. Our experiment employed a 30 GHz receiver from the BIMA array that we set up especially for student use. Students measured the total power collected by the instrument at several different zenith angles, and calibrated carefully each time to convert the measured power into temperature. By measuring the power received at different zenith angles, the CMB temperature can be determined.
Applying graphing skills they had strengthened during the year, students extrapolated their data to determine the temperature of the Comic Microwave Background. This plot shows student data determining the CMB temperature to be ~3K.
Summary. The middle- and high-school students in the Space Explorers program spent a year developing the skills and conceptual foundation necessary to measure the temperature of the Cosmic Microwave Background. They strengthened their graphing skills, learned to make careful measurements, and analyzed complicated data. Along the way, they gained an understanding of the physics of how thermometers work, explored measuring temperatures of stars, and learned about cosmology. With professional instruments made available by the Carlstrom group at the KICP, the students successfully measured the 3K temperature of the Cosmic Microwave Background.
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KICP Students: Sarah M. Hansen