Thursday, June 28, 2018

The Sun in Various Wavelengths

My physics curriculum has shifted in response to our new state frameworks, and one shift has been a greater emphasis on electromagnetic radiation. I've been having fun concocting new examples and demonstrations (including an "in-house" field trip to our metal fabrication shop to experience welding).

This spring my class was having a discussion about the Sun's radiation, and how so much of what it radiates is invisible to us. They wondered what it would look like if we could see the different kinds of radiation. I explained that we can create devices or sensors that detect different wavelengths of radiation, and then construct false-color images from the information gathered. Immediately I went online and hunted for something to show them. A great resource, which I have used before, is the wonderful and painstakingly-built website called Windows to the Universe. This site is a project of the National Earth Science Teachers Association.

In particular, I went to the page entitled The Multispectral Sun, and found this animated GIF:

I liked this concept a lot, and looked around for other examples. I found What's the Sun doing lately? and Compare Multispectral Sun Images, and lots of imagery, including this NASA composite image from the Solar Dynamics Observatory:

I decided to try making something of my own. My project would be a video replication of the animated GIF above, but using many more images. And I would start with the images in the NASA image above.

Here is what I wanted: a video file so playback can be controlled, a broad and representative spectrum of images, and captions with either a specific or representative wavelength indicated. I shamelessly borrowed some aspects of the animated GIF (images scaled to the same size, captions colored to match the image, images taken on the same day). Because I started with the NASA SDO chart, I needed to know what date those images were taken. A little hunting revealed July 11, 2012.

So I was off and running. I decided to stick with spectroheliograms, rather than dopplergrams or magnetograms. I searched for quite a while for solar images in various wavelengths that were taken on 7/11/12. Depending on what time and from where the image was taken, 7/10/12 images sometimes worked as well or better.

As I accumulated my images, I had to decide on wavelength units. My students didn't know about Angstroms, so I used nanometers instead. I came to realize that I could use just three units; nanometers, millimeters, and meters. Then came the laborious Photoshop work, including colorizing a couple of the images. The video was constructed and edited with Filmora. I posted the final video on YouTube.

An interesting issue is the color of the Sun as we see it. Ask anyone, what color is the Sun? Almost everyone will say "yellow," but of course it isn't, it's white, at least to our eyes. (Please don't go out now and look at the Sun - it's bad for your eyes. But if you have a chance to look at it when it's obscured by fog or clouds, you'll see.) I found many images of yellow suns with the caption "visible light." These images were either taken through a yellow filter or they were colorized yellow because of a belief people will think it should be yellow (white light, of course, does not have a specific wavelength).

When I showed the final video to my students, they loved it. But many suggested it should have music. I was telling this to one of my fellow science teachers, and she said, "I have exactly what you need!" She owns a small, portable planetarium called Star Theater Pro, and it comes with a music CD having 15 minutes of suitably cosmic-sounding music composed by Donovan Reimer. She was right, it was perfect.

Here's the final video product:

And here's a shorter animated GIF:

Here are links for downloading the most recent versions:
MP4 Video: 4 seconds per image, with audio
MP4 Video: 4 seconds per image, no audio
MP4 Video: 3 seconds per image, no audio
Animated GIF: 2 seconds per image, continuous loop


Radio: 0.9 m, 2.0 m - BASS2000/Nançay Radioheliograph
Microwave: 17.6 mm - Siberian Solar Radio Telescope
Microwave: 52.6 mm - Nobeyama Radioheliograph
Infrared: 1083 nm - HAO/Mauna Loa Observatory CHIP
Visible: 656 nm (Hα) - Big Bear Solar Observatory
Visible: white - NASA/SDO AIA
Visible: 393 nm (CaIIK) - Langkawi National Observatory
Ultraviolet: 170 nm through X-Ray: 9.4 nm - NASA/SDO AIA
X-Ray: 5 nm, 1.9 nm - NOAA/GOES Solar X-Ray Imager

Music - Star Theater Pro/Donovan Reimer

Cross-posted to Teaching Is . . .

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