Recreating the Earth's Atmosphere In a Computer

The Earth as sunset approaches
(computer generated, my own work)

There is a common expression that says something is more of an art than a science. This usually means that there is no precise formula or set up steps (what we call in computer science an "algorithm") to produce the desired result. To get results you must use a large amount of intuition and previous experience. Scientific approaches are repeatable if the same steps are followed; that is part of the definition of "scientific." 

Computer generated art is very much a mix of science and art. We take the scientific principles of computer science and make something that must be interpreted from an intuitive or emotional approach. Taking the quantitative ones and zeros and making something that is described as pretty.

In creating a model of the Earth I have used a lot of scientific data. The relative diameters of the Earth and Moon for example. The altitude of clouds above the surface of the earth. Images taken of the Earth from satellites in orbit.

Mountains majestically fading out to purple
(actual photo, not my work)

The atmosphere of our planet appears transparent on the short distances we usually pay attention to, about under a mile. Fog and smoke can change this, but usually it is pretty clear. But look at the mountains in the distance and you will notice that they are not their natural color. This effect is immortalized in the song "America the Beautiful" in the line describing the beauty of the United States referring to "purple mountain majesty." This effect is caused by the atmosphere scattering and absorbing different colors of light by different amounts, referred to as Rayleigh Scattering after the man who discovered the scientific principles behind it. This is the same effect that causes the sky to be blue.

When creating a model of the Earth as viewed from space the atmosphere is the most important part. While the surface and clouds are important, most of the blue coloring of the Earth comes not from the water but from the atmosphere. In reality you are seeing the sky from the backside.

To recreate the effect properly the science is very important. For a more technical explanation of the science you can read about Rayleigh Scattering. In a nutshell the atmosphere scatters blue light in random directions more than other colors. This means that the sky looks blue during the day because that is the color most redirected to our eyes. During sunrise or sunset most of the blue has been scattered out, leaving reds and yellows. This is why sunsets and sunrises are reddish, especially near the horizon.

While I was creating my model of the Earth, I used actual scientific data on how the atmosphere scatters light to get the colors right. I simulated in the computer the scattering effect of the air. Below is a view of the atmosphere at sunset, seen from about 90 miles above the surface of the Earth, created using my model of the Earth. You can see the red color of the lower atmosphere which fades to blue at higher and thinner altitudes, finally fading to black at the extremely thin portions. The effect of scattering is dependent on the density of the air, and the density is dependent on the altitude.

Atmosphere at sunset as seen about 150 km (about 90 miles) above the surface of the earth.
(computer generated, my own work)

This image was created using a mathematical model. All of those ones and zeros being converted into something that looks like something real, something this artist thinks is beautiful. By applying the math in just the right way I am able to create an image that both looks true to nature and is pleasing to the eye

Gifts

I paint gifts for other people. Thanks to Mother's Day, my mom's birthday, and Father's Day happening so close together, I was back to painting.

For my mom's birthday, I did a small painting of her favorite perfume. Now she always has a full bottle of Cristalle!

I forgot to take a picture of the final painting.

For Mother's Day, I experimented with bleeding a second color before the first one was dry. I loved how it took on a life of its own. For Father's Day, I was inspired by an artist I follow on Instagram. Jessica was doing so many gorgeous starry night scenes that I knew would be perfect for my dad.

Sooner or later, I will paint for myself too!

BJ's Story

Growing up, I didn't realize that I was crafty or creative. I could brain storm with my mom, but I didn't feel like I could actually make what ever it was. I still remember when I was about 11 or 12, one of my favorite church leaders was trying to teach us girls how to sew a button. I was such a punk that night to her! I kept making excuses and complaining. I feel badly for making a simple lesson so difficult on her! That's how I felt about anything crafty like that. I just couldn't do it! At some point in high school, I started changing my tune. I still stayed away from anything that involve needles and thread, but I was helping my mom with some of her projects around the house. After taking Honors Physics, I helped my mom switch the order of the switches in the kitchen because the order that the builder put it in made no sense. Then we installed a new ceiling fan in my bedroom. Slowly but surely, my confidence was growing. After getting married, I have been busy with a wide variety of projects: painting furniture, assembling Ikea furniture, patching my husband's jeans, recovering an office chair, and making homemade presents.

A few years ago, I asked my husband to give me watercolor supplies for my birthday. I stumbled across Alisa Burke's blog about a year before and finally wanted to start being more artistic. I didn't do much with the supplies for a long time, but I had them. After getting an Instagram account, I started following many talented artists. After seeing their work for a few months, I thought to myself, "I can do that!" And so I did! I got out my watercolors again and went all out for my first painting.

Thanks to doing a lot of ambitious projects for my lack of experience, I was confident enough to do a watercolor of the Los Angeles Temple. Though, I still took my sweet time doing it. I started the sketch of it in August and finished painting it just a few days before Christmas. I took a hiatus and didn't paint until the following December. This time I painted the Oakland Temple in about a week and the Idaho Falls Temple in one day.

I started a painting using acrylics, but I like the first layer so much that I haven't touched it in months.

I go through sporadic periods of creativity and I hope that they will continue to get closer together.

Jonathan's Story

When I was in high school I took the entire four year course of drafting and computer aided design (CAD) courses offered by my my school. I loved the classes. They gave me the chance to see how computers are used in creating images that had been popular for a while at that time. This was in the late 90's, and computer generated imagery (CGI) had been in movies since the previous decade but was before the explosion in CGI based movies seen after Toy Story.

One of my favorite parts of the class was the chance to play with the tools made available to me. I created several Star Trek style space ships and made them fly around on my computer screen. It was amazing. I thought I might want to do something related to this field as a career. This gradually shifted to programming computers, but I never lost interest in making images with computers. There was just one problem; it was expensive. In addition to needing a pretty powerful computer to handle the processing, the software I used in high school (called 3D Studio Max) was on the order of several thousand dollars per copy. There was no way I could afford that for a hobby.

Flying temple, printed onto an iron on transfer

Fast forward about ten years. My wife was working on a project for the young women's program at church. For their theme they needed a picture of a temple flying with balloons like the house in Up. She asked me if I was able to find anything like that premade on the Internet. After a quick unsuccessful search I realized that it should be possible to do in a 3D animation program. I had been playing with SketchUp, a 3D modeling program from Google. I found a model of the Salt Lake City Temple that I could import into SketchUp and was able to create an image of the temple from below as if it were flying.

Image of the Earth created in Blender

This reminded me how much fun I had had doing 3D animation when I was in high school. I started looking around for a free animation software since SketchUp was really only designed for light modeling to create buildings for Google Maps. In searching I found Blender, a free 3D animation suite that includes many features only available as add-ons in expensive suites. I started following some tutorials on YouTube (there are tons of them; this is what YouTube was invented for). After animating a cup, a ball, and some different cloth animations I followed a tutorial on making a realistic Earth model. I enjoyed making planets a lot. I adapted and updated a few of the techniques used in the tutorial. I am still learning how to use Blender, and using these planets to understand how the different pieces of the software interact. 

Blue Marble recreation

For Earth Day this year I decided to something to celebrate. Since I had the computer model of the Earth already I recreated the famous Blue Marble photo taken by the crew of Apollo 17 on their way to the Moon. You can see my version to the right. 

I have learned a lot about the Earth in doing these images. Often times I will find something that looks like a mistake. As I find reference images to figure out how to correct the error I actually find that my model was correct all along. It is really exciting to find that the techniques I am using are accurate enough to predict features of the Earth without me specifically putting them in there.

Image of Saturn created in Blender

I have branched out into other planets as well. I have created a model of both Mars and Saturn and some preliminary work on Jupiter and Uranus. Saturn has proved particularly difficult. The rings of Saturn are very complex and require a lot of attention to get right. In addition there are a lot fewer quality reference photos of Saturn compared to the Earth. 

I have enjoyed making these images. I have always enjoyed making art, but never spent enough time to get beyond an amateur level. Since I am a computer scientist by training making art with the computer makes sense. While it is a very complicated field (just as any art is) I am very pleased with the work I have been able to do.