The EM Spectrum

Light is a very mysterious thing, and it took scientists many generations to completely understand its subtle features. In many ways, light behaves like a wave. Watch the teacher video Light Waves for an introduction to wave terminology and light waves. If you like, you can also play around with the Wave on a String Simulator
Read 5.1 The Behavior of Light to understand the dual nature of light as both waves and particles, the relationship between wavelength, frequency, and speed of light, and the principles governing the apparent brightness of light sources.
The electromagnetic spectrum is one of the most amazing concepts in all of physics and astronomy. It connects seemingly different phenomena like radio communication and x-ray imaging into a single framework. You’ve probably learned about the EM Spectrum before, but it’s critical that you have a solid understanding of the full spectrum of light - from the longest wavelengths to the shortest. NASA created an excellent introduction to the EM Spectrum. While the videos look like they came from the 1990’s, they are concise, well-made, and interesting. I encourage you to watch each of the following brief, 3-5 min videos: Introduction, Radio, Microwave, Infrared, Visible, Ultraviolet, X-Ray, and Gamma.
Think back to a time when you have watched something get hot (maybe a stove top turned up to high heat). If it starts slowly, it may begin by glowing a deep red. Then gradually, it becomes more orange and possibly even yellow. We know, intuitively, that the color of an object relates to its temperature. Let’s explore this relationship in greater depth. Watch the video Melted Nail showing a nail heated to its breaking point and then cooling off again. This kind of spectrum, emitted due to an object’s temperature, is called “blackbody radiation.”
Watch the video Blackbody Radiation which examines the blackbody spectrum in greater detail. If you like, you can play with the interactive Blackbody Curves and Filters Explorer yourself.
Just because an object is blue does not mean that it is super hot. A blue t-shirt (at ordinary room temperature), for example, is blue to our eyes because it reflects more blue light than other colors. Objects at ordinary room temperatures (like you and I) are still giving off blackbody radiation, but we are shining at much longer wavelengths - in the infrared, far from what our eyes can see. Make no mistake, though, we are shining - here’s video proof!
If you want to see blackbody radiation with your own eyes - you need to look at something really hot, like the Sun, an incandescent light bulb, or a furnace at a glassblowing studio. In the video from the glassblowing studio, you can see that a reduction in temperature of just 12 degrees causes the blackbody radiation from the furnace to change in two ways. First, the peak wavelength increases (making the furnace look slightly more orange). Second, the brightness of the furnace decreases (which means less total energy is given off as light).
Read 5.2 The Electromagnetic Spectrum for a summary of the various types of electromagnetic radiation, their sources, and how temperature affects the emitted radiation.