Teaching Tips

Teaching Tips: The Galaxy Experiment

Synopsis:
In this module, students use a simulation and database to analyze different electromagnetic waves emitted by astronomical objects. Students view “photographs” of different astronomical objects. Through the use of a database and their observations, the students analyze and identify various astronomical objects.

Big Ideas:
a. Astronomical objects emit different electromagnetic waves with various intensities.
b. Electromagnetic wave emission can be used to identify and categorize astronomical objects.
c. Different astronomical objects are composed of different elements.
d. Elemental spectra can be used to identify astronomical objects.

Misconceptions Addressed:
a. Astronomical objects only emit visible light.
b. All astronomical objects are composed of the same matter.

NSES Grade 5-8 Standards
a. Earth and Space Science
i. Earth in the solar system
b. Physical Science
i. Transfer of energy
ii. Properties and changes of properties in matter

Astronomical Data

The Galaxy PSI Sim™ is designed to help students compare visual data with analytical numeric and textual data. Drawing information from many sources, students try to determine the defining characteristics of various heavenly bodies. The experiment is essentially a database exercise, where the database records contain astronomical data. The astronomical information they encounter helps them understand that different heavenly bodies contain different elements, emit different wavelengths of light, and have different characteristics. The idea of wavelength is discussed, as well as its relationship to frequency.

C, F, and Lamda

In the methodology section of The Galaxy PSI Sim™ students see the relationship between the speed of light, the wavelength of that light, and the frequency of the light. Given by the formula:

Most students learn that wavelength and freqency are inversely proportional. It might be a good time for a math lesson, mentioning that the reason that if one quantity goes up the other must go down because the speed of light is a constant as far as we now know...this is currently being debated. The animation in the methodology section shows two waves with different wavelengths moving at the same speed. It is a good illustration of what we mean by frequency - students can see the wave crests and troughs arriving more frequent-ly.

The Spectrum

In the methodology section, student see multiple drawings of a spectrum chart. In each case, the spectrum has arrows pointing to the left and right of the spectrum shown. This is an important idea to discuss. There are waves longer and shorter than the waves mentioned in the diagrams. For example, audible sound waves are longer than radio waves. Just as we can see only a small part of the electromagnetic spectrum, we can hear only a small part of the audio spectrum. On the other side of the spectrum are gamma rays, that we consider to be the smallest electromagnetic waves, since they are the smallest waves known. In other words, we currently define very short waves to be gamma rays, and until we find a special set of extremely short waves with specific characteristics, all of the smallest waves (< 10¹⁵ meters) will be called gamma-rays. Students may ask about cosmic-rays, which are actually charged particles of various elements and not Gamma-rays. Gamma-rays are useful in medical applications where they may be used to kill cancer cells. In deep space, gamma-ray bursts produce incredible amounts of energy. In ten seconds, a gamma-ray burst can release more energy than the Sun has emitted or will emit in its entire lifespan (about 10 billion years!)

Using the Simulation

Students should be discouraged from guessing in the simulation. They are to deduce the objects identity by comparing information from the graph and spectral scanner along with information they glean from the images to the information found in the database. They will need to identify least on most intense wavelengths on the graph, and so a review of basic graphing may be required with younger students. Unlike most PSI Sims, The Galaxy PSI Sim™, contains a correct response for each scenario and offers positive reinforcement for a correct response.