From the January 2013 issue

Galaxy rising

March 2013: Sometimes, your astroimaging goal may be more than meets the eye.
By | Published: January 28, 2013 | Last updated on May 18, 2023
Imagination is a powerful tool. It allows you to create something that doesn’t exist. It is also the foundation for what I call the creative force — the ability to invent a new reality. In this column and the one next month, I’ll show you how some simple techniques will help bring your mental images to life. True, some people are more imaginative than others, but we all can be on the lookout for appropriate base images from which our “hybrids” can spring forth.

In this case, my base image is an arch in Arches National Park near Moab, Utah. I photographed it many different ways. In one of the shots, I positioned the Sun at the bottom right corner of the arch to create a “starburst” effect. Months went by. Then one day I looked at the image, and the idea occurred to me to fill the sky with something. But what?

The image at bottom left shows the arch as I shot it. Note that most of the background is blue sky. Blue sky can act like the green screen that television and movie studios use to drop out a background and replace it with something else. After trying out various backgrounds to substitute for the sky, I came upon my image of the Andromeda Galaxy (M31). Immediately, I imagined the possibility of creating an out-of-this-world image.

Image 1
The author traveled to Arches National Park in Utah, where he captured a tiny bit of the Sun’s disk within this arch. // All images: Tony Hallas
In this example, I want to replace the blue sky with the Andromeda Galaxy. Using layers, I will show you two ways to accomplish this. The first is to make the arch image a layer sitting on top of M31 and then clear away the blue sky, leaving the galaxy showing through.

The other is to put the arch on top as before but turn a selection into a mask that blocks the open sky, letting the glorious galaxy show through.

The first step is to use Photoshop to open both images on your desktop and scale them to approximately the same size. Make them the same width (in pixels) and the same resolution. Be sure to check the “Constrain Proportions” box.

Next, make the arch image a layer on top of M31 by pressing F7, and with the arch image active, drag the icon of the arch on top of the galaxy image. This automatically turns the arch into the layer you want. Close the single image of the arch. It now has duplicated itself, so you don’t need it anymore.

By using Photoshop, he cleared out the blue sky in his original image so that a second image of the Andromeda Galaxy would show through.
Take the “Magic Wand” tool, set the strength at about 20, and click in the middle of the blue sky. The “marching ants” will show you what you have selected. Most likely, there are areas where you will need to extend the selection. To do that, hold down the “Shift” key to make the “Magic Wand” additive, and continue clicking throughout the sky until you have selected all of it.

Now, go to “Select,” then “Modify,” and then “Expand.” Enter “2” to expand by two pixels, and click “OK.” Usually when you select an area, a tiny bit remains along the edge. By expanding (by two pixels), we make sure the edge is into rock.

With the arch layer still active, go to “Edit” and then “Clear,” and Photoshop will clear the sky you have carefully selected, revealing the galaxy underneath (the right image).

Next month, I’ll show you how to do this with a mask and continue to the final image. Our goal will be to make the arch seem like it’s giving us a view of M31 from an alien world.