Summer Research Program for Science Teachers
Rachel Berger, Horace Mann School - 1997
Radio Astronomy: Grades 11 & 12
Introduction:
In teaching astronomy at the high school level, the focus is almost always limited to what we see with our eyes. This area of the electromagnetic (em) spectrum, known as the visible or optical region, is a very tiny part of the entire spectrum that also includes the radio, x-ray, and microwave regions. Students need to understand that the light that they see is only a tiny fraction of the entire energy in the universe and that each region of the em spectrum can provide scientists with different information about an astronomical object. [Content Standard B- Interactions of energy and matter]
Radio astronomy is the second most popular ground-based astronomy used today. Unlike energy waves in the infrared and ultraviolet regions, radio waves pass through a radio window in the atmosphere and are easily detectable on the Earth's surface. And, unlike optical telescopes that have limits on their size, radio telescopes can be linked together in arrays that span from 30 kilometers across up to the size of the Earth. For this reason, today's astronomy student should be familiar with radio astronomy, as well as the traditional optical view of the universe. [Content Standard E- Understandings about science/technology]
The Internet is a crucial source for astronomical data. Almost all of the data from the many different sky surveys is available on the Internet, including images straight from both ground-based and orbiting telescopes. This offers an incredible amount of data that is available to any student who has access to the Internet, and this data can be useful as early as the high school level.
To prepare for a section on radio astronomy, the electromagnetic spectrum as a whole should be first introduced to students. This is done by beginning with what students are most familiar with - visible light. Hand-held spectrometers are used to examine various light sources ranging from white light to gas tubes of hydrogen and helium. Once the concept of light as a form of energy is understood, other forms can be introduced.
Students will already be familiar with the radio region of the spectrum because radios are a source of sound. This idea just needs to be expanded upon to include the concept of energy. What students need to understand is that radio waves are just that, waves that have a certain energy. This energy just happens to be less than that of the visible light they see. When they listen to the radio, their stereo antenna is picking up radio waves and turning them into sound waves that can be heard. In this way the stereo is acting like a very small radio telescope. The difference is that the telescope turns the radio waves into visual and binary data instead of sound waves. It is important to emphasize that radio waves are not what is heard from a stereo, it is the machine itself that turns the radio waves into sound. [Content Standard B- Conservation of energy]
Viewing actual astronomical objects in the different spectral regions can now begin. A few galaxies and nebulae are shown in the visual and radio regions using slides and a Laserdisk. The relationship between temperature and energy is the focus of discussion. The hotter an object is, the more energy it emits. Therefore, a cooler galaxy will emit more in the lower-energy radio region while a hotter star will emit in the visible region. Stars rarely emit in the radio region. So, when a galaxy is viewed in the visible and then the radio region, the pictures are very different. The crux of this lesson is that each region of the em spectrum tells us very different things about an astronomical object. If the students see a bright object in the radio region, it means there is cool dust and nebulae present. That same object, however, could be very dim in a visual picture.
After the classroom section of the lesson is finished, the students will be ready for the lab. It is better to have a computer lab available for class use, but the lab could also be conducted in the classroom with a projector and computer that has Internet access. There are two main Internet sites (see Bibliography) that are sources for radio and optical images of the sky. The first is the Digital Sky Survey, which is optical; and the other is the FIRST survey (Faint Images of the Radio Sky at 20 cm), which is the radio region. [Teaching Standard D- Make accessible technological resources] The instructor should have coordinates of different galaxies, nebulae, Messier objects, and commonly known stars ready so that examples of different types of objects are at hand. The Observer's Handbook is a good source for these. The students will examine the different structures that each type of object displays in the optical and radio regions. Also, the students will learn the names of the objects that are used in the lab. This will be the basis for evaluation at the end of the section.
When the lab has been completed, a test will be given on the concepts of waves, energy, and the different regions of the electromagnetic spectrum. There will be a slide identification portion to the test. On one of the days following the test Dr. Helfand has agreed to visit the class and talk about his research in radio astronomy. [Teaching Standard D- Identify/use resources outside the school] This will conclude the radio astronomy section of the course.
Pre-Lesson:
A. Introduction to the optical region of the electromagnetic spectrum. Spectrometers and light tubes containing various types of gases will be used.
B. Expand the students= concepts of the electromagnetic spectrum from one centered on the visual region to one that includes all the other regions of the spectrum. This will be accomplished through a lecture on waves as carriers of both energy and information from the stars, emphasizing that the information from each region of the spectrum tells us something different about an astronomical object being studied.
C. Using slides and a Laserdisk, I will introduce students to the instruments that astronomers use to study the universe in the various spectral regions. I will also present the role that the Earth=s atmosphere has to play in that study. More specifically, in the radio region, the Very Large Array will be introduced as one of the premiere radio telescopes in the world.
Lesson:
A. The lesson itself involves an Internet tour of raw data collected from telescopes in the optical and radio regions. The focus is on becoming aware of the features that we see in the optical region versus the radio region, and on recognizing specific galaxies and nebulae in both spectral regions.
B. The students are allowed to explore the Hubble Space Telescope Internet site on their own to see some of the most up-to-date images of the optical universe.
Post Lesson:
A. The students will be evaluated with a slide identification test using images of different radio and optical objects.
B. Columbia University professors in both radio and optical astronomy will visit the class and explain how they utilize data from a specific region of the electromagnetic spectrum in their research.
C. The class will visit Columbia University=s Astronomy Department to see how data is collected and where it is analyzed. A trip to the Very Large Array and Kitt Peak is possible for a smaller group of students, most likely the students who comprise the Astronomy Club.
D. The astronomy class will join an astronomy class from another local high school for a combined observing night. It will include a viewing of the moon, planets, and the constellations visible that season. [Teaching Standard D- Identify/use resources outside the school]