Student Ideas and Questions
Common Student Ideas
When astronomers use a telescope and camera to take an image, a color image automatically appears.
Bridge to learning:
The investigation leads students through the process of how certain filters are selected and placed in front of a detector (camera), in order to make greyscale images of the light produced from each filter. Each image is then assigned a color and combined to create a color image. As students use the color mixing tools in the investigation, they will develop an understanding of how astronomers select, colorize, and combine the light from different filters, then adjust levels to create a color balanced image.
Filters change the color of light.
Bridge to learning:
The investigation leads students through a tutorial using an interactive filter changer. This helps them visualize that certain wavelengths of white light are blocked by a filter while other wavelengths are permitted to pass.
Common Student Questions
Students may not feel confident about how to construct a color image. You may hear questions like, “What should it look like?” or, “How many colors should I use?”
Reassure students that there is no one “right way” for the image to look, since human eyes only use three colors and the Rubin Observatory camera has the superhuman ability to see in six colors. However, there are wrong ways to construct an image. Colors should be assigned to filters by using chromatic ordering. Sliders should be adjusted for each filter so that the image shows the contributions of each color used. In the end students should attempt to make an image that’s aesthetically pleasing and communicates the desired science information.
Students may question why the practice image is constructed using red, green and blue colors. Some may have had prior classes or experiences working with ink or pigments, where the (3) primary colors are yellow, cyan and magenta.
Mixing pigments or dyes uses a subtractive process to produce color, whereas mixing light (which is what this investigation is about) relies on an additive process to mix colors.
The human eye has three types of color receptors (cone cells) that work together using an additive process to mix light so that any color can be interpreted by the brain, in the same way that red, green, and blue light can be added together to produce any color of light. Since cameras use and mix light to produce images, red, green, and blue filters.
Some students may notice that the figure showing the color filter pattern over the image sensor on page 5 contains twice as many green filters as red or blue.
This common arrangement is known as a Bayer filter and is designed to mimic the physiological response of the human eye, which is most sensitive to green light.