Accessible Astronomy: Catch the Light! CCD Cameras

So far in this series, we have explored light as a form of electromagnetic (EM) radiation. Different “flavors” of EM radiation are defined by their wavelength and frequency and come to us from many different objects in the universe such as planets, stars, and galaxies. We introduced a tactile telescope as a way of allowing students to explore one type of telescope that gathers and focuses EM radiation. Now it’s time to capture and record that radiation so we can study the objects where our telescope is pointed. This is a challenging topic for everyone, so the IDATA team worked hard to come up with a fun and memorable way of explaining how a telescope camera works.

Imagine the cameras used with telescopes as really fancy versions of cell phone cameras. Your phone camera captures and records visible light. You can zoom in on those pictures, crop them, and color them in many different ways. The part of a telescope camera that is responsible for recording the EM radiation is called a Charge, Coupled Device (CCD) chip. It is similar to the chip in your phone camera but much bigger, and it doesn’t take pictures in color. Astronomers use filters in front of the chip to measure light one color at a time. Imagine sorting pebbles from a pile of sand using a sieve. The sieve allows only the part of the mixture that you want to pass through. A filter in astronomy does the same thing for EM radiation.

Once the EM photon hits the CCD chip, it kicks off an electron. It is those electrons that are counted by the camera in a grid, one box or pixel for each part of the sky where the telescope is pointed. From this grid of numbers, astronomers can learn a lot about what the objects are made of, how old they are, and even their motion. However, as you can tell from this brief description, there are a lot of parts to keep track of. We want students to understand how the CCD camera works so that they can learn to work with numbers instead of pictures to understand the universe.

In the activity attached, students role-play the journey of photons from an object in space through a filter and onto a CCD chip. There is a lot of prep involved, but if you want to teach your students how a camera works and why vision is not essential to studying astronomical objects, it will be well worth your effort. IDATA teachers and leaders are ready to answer your questions and give you encouragement if you need it.  We will use your questions to make our material better, so give it a try.

Download the Filters and CCD Camera - an Interactive Model activity here.

Download the Master Grid (link to the master grid is also in the Filters and CCD Camera activity download).

The images below correspond with the Filters and CCD Camera activity which is written out in the download above.

Image 1: Two students are shown participating in the CCD modeling activity. Three of the four CCD posters described in the activity are sitting on a chalk tray. Each large poster is divided into nine equal sections. The student standing furthest from the poster board is the Filter student. This student is blindfolded and is counting the photons of the type that corresponds with the filter they represent. The Filter student communicates that number to the student nearest the posters. The student nearest the poster is the CCD student. His job is to place map pins into the CCD poster. The push pins represent the electrons that are kicked off the CCD chip when the photons hit the chip. It is the electrons that are counted.

2 students adding pins to 3 3x3 grids boards representing CCD camera filtered images.

Image 2 - A female student wearing a sleep mask is standing in front of the nine small grid pieces that are part of the CCD Model activity. The grid pieces are sitting on a table. Each grid piece has a different number of three types of photons, blue, red and green. The different kinds of photons are designated by color and shape. This Photon-carrying student will pick up one grid piece at a time to transport it from "space" to the Filter student. 

Photo of girl wearing a blindfold feeling 1 of 9 small squares with various tactile stickers representing objects viewed with CCD camera.

Accessible Astronomy Series