Lunar Imaging: Moon Mosaic

“The Moon puts on an elegant show, different every time in shape, color, and nuance.”

-Arthur Smith

Final edited version of Moon mosaic, taken by PROMPT 5 in Cerro Tololo Inter-American Observatory, Chile

As a human living on the planet Earth, you probably see the moon nearly every day. However, most people don’t get to see the moon up close and personal and thus miss out on all the various craters and colorations of the moon. Luckily, I got the opportunity to dive into the world of astrophotography and get a glimpse at all the unique complexities that make up our closest neighbor in space. How? Let’s dive in and see!

Skynet Observations

To begin our journey, we must start with the observation of the Moon itself in Skynet. Unfortunately, the telescope I chose, PROMPT 5, does not have a large enough FOV (field of view) to capture the Moon in just one image. This meant that in order to achieve this singular image of the Moon, a mosaic composed of multiple images stitched together was needed. The first step in order to do this was to enable the “dithering” feature with a 5′ x 5′ grid for PROMPT 5 (triple 5’s). The next step was choosing the best filters for the Moon. Instead of using the standard blue, red, green filters, I used U, Halpha, and OIII filters, respectively. This was done in order to lengthen exposure time and minimize a problem called the iris effect, which is when your image is brighter in the center and darker on the edges. I then requested 25 exposures for each filter with an exposure duration of 0.2 seconds and submitted the observation into the void of Skynet.

Image Processing

Once all 75 images came back in, it was time for the real work. Most of the images came back with no problems, but the ones that were either duplicated or too dark were easily fixed by the patches provided by Professor Reichart. I then hopped over to Afterglow to begin the two most important tasks, aligning and stacking my images. First, I selected all of the images, then I enabled Mosaic Mode, disabled Rotation, Scale, and Skew all under the Aligner tab and submitted the aligning job. Once I checked to make sure there weren’t any alignment errors, I moved on to stacking. Stacking required 3 individual stacks, one for each filter. I did this by enabling Multiplicative, Additive, and Global Equalization (Equalization Order set to 0), and then submitting the stacking job and repeating the process twice more.

Coloring and Post Processing

After all of the Moon images were aligned and stacked, I got to get started on the most fun parts of the mosaic, coloring and messing around with image settings. I first selected my 3 stacks and grouped them together. I then right clicked on each individual layer and colored them, U being colored blue, Halpha being red, and OIII being green (as visible in the images A-C below). It was amazing to see these individual layers come together to form a color image! Even though the unedited image isn’t as impressive as its final version, I was so excited to see the Moon and knew that I had put it together myself. Once my initial excitement wore off, I knew I wanted to hurry and start editing the image. I started the editing in Afterglow by changing the stretch mode to Midtone and pressing the default brightness preset. I altered the Background Level to about 40 and the Midtone Level to about 98 and felt content with how the image looked. Then I moved on to editing the image on my computers default image settings, which allowed me to play with the saturation, brightness, exposure, etc. until I felt good with my final Moon mosaic product!

But what do the colors mean?

So, I’ve walked you through the process of how I made my Moon mosaic, but what does it mean? Why are some parts of the moon tinted yellow, blue, or red/brown? Well, blue areas of the moon indicate titanium basalts, yellow areas, which are often found around craters, can indicate glassy deposits, and red or brownish areas indicate iron-rich lava flows found on top of the basalts. Even though these colors are virtually invisible when simply gazing at the Moon, they exist, and getting the chance to image the Moon and extract and enhance its subtle colors was a very unique/cool experience.

Labeled Important Features of the Moon

Above I have labeled Aristarchus, Tycho, Copernicus, Mare Serenitatis, and Mare Tranquillitatis. The first three are all well-known craters caused by impactors colliding on the Moon. The last two are two of the “seas” of the Moon, let’s examine these a little closer shall we.

Zoomed in Area of the Moon

Mare Serenitatis, commonly known as “The Sea of Serenity,” is an example of one of the lunar maria. It is brownish red, which indicates that it is there are iron rich lava flows present. Mare Tranquillitatis, commonly known as “The Sea of Tranquility,” is southeast of Mare Serenitatis and is blue-ish in color, which indicates titanium basalts.