Student's Component

Electromagnetic Radiation

 

(1) Electromagnetic Spectrum

It may be helpful to see a diagram depicting basic properties of waves. You can then combine all electromagnetic waves to form a spectrum. The main goal is to see the different options for such a spectrum: according to the wavelength or frequency of radiation. It is very important to compare different types of electromagnetic spectrum charts taken from different sources (textbooks, encyclopedia, etc.).

You may want to see an example of one way to represent the different types of electromagnetic radiation.


(1)(a) The Incan Quipu

A very interesting and non-traditional way to identify each type of radiation in a spectrum is to create a Quipu that contains complete information about this spectrum. Quipu, a so-called knotted-rope-artifact, is a mysterious way of coding and decoding any type of data in a very compact and unusual manner. This method was used by the ancient Incas. Using knots of different shapes (single, figure eight, and long knots) and strings of various lengths and thicknesses, students not only can arrange electromagnetic waves in a spectrum, but also insert any other type of information (wavelength, frequency, energy, etc.).

After quipus are constructed, you can exchange them with other students and try to decipher the coded information by analyzing how the strings are grouped together, how many strings there are in each group, and according to what pattern the knots are arranged. Here is an example of an electromagnetic spectrum quipu based on frequency. First string represents the speed of light. It is considered to be a key string that gives the idea of how to insert numbers with scientific notations using different types of knots. Other six strings represent six types of electromagnetic waves ( from radio waves to gamma rays.)


(2) Types of Radiation: sources and properties

The next, and perhaps, central part of this unit is a detailed description of each type of radiation and how astronomers use electromagnetic radiation as a probe to study different objects in our Universe. Some key concepts include how radiation interacts with matter, being "dispersed," absorbed and emitted by atoms.

Here is a diagram that shows how an hydrogen atom absorbs and emits radiation . You may want to see how continuum, emission, and absorption spectra are produced by the interaction of electromagnetic radiation with a gas such as hydrogen.

Once you understand how the different types of spectra can be produced, you may be ready to make your own model of a star (most of which are sources of absorption spectra) such as the one shown in this diagram.


(3) Examples of Real Data: Continuum, Emission, and Absorption Spectra

Here is an example of a continuum spectrum from a white dwarf star called HZ43, taken with the EUVE satellite. In this example we see extreme ultraviolet electromagnetic photons from the white dwarf HZ43 at wavelengths ranging from 80 to 700 Angstroms.

You may be interested in this example of an emission spectrum from a molecular cloud of gas called W51, located in our Milky Way galaxy. In this example we see radio electromagnetic photons from the W51 molecular cloud at a frequency of 113 Giga Hertz.

Or, try this example of an absorption spectrum from a star called Arcturus, located in our Milky Way galaxy. In this example we see visible electromagnetic photons from Arcturus centered at a wavelength of 4300 Angstroms.


This Lesson's Objectives

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