Archive diving for star clusters

The star clusters Messier 46 (left) and Messier 47 (right)  Credit: Digitized Sky Survey 2  Processing: Chris Casper

This is my take on the star clusters Messier 46 and Messier 47 using data from the Digitized Sky Survey. In my last post I shared an image of the star clusters I took from my balcony and compared it to an image the ESO created using the DSS data. Since that data comes from an archive open to anyone - professional and amateur alike - I decided to see what I could do with the same data.

Nasa's SkyView Virtual Telescope

To get the data I turned to SkyView, a tool Nasa created to make searching the many different astronomical archives easier. You can use it to search for data across the electromagnetic spectrum.

For this project I wanted to reproduce the ESO's image, so I picked the DSS2 data taken with red, blue, and infrared filters. I also entered the name of a star, HD61442, which would lie at the center of the image.

By default SkyView generates images 300 pixels on a side and with a 0.25 degree field of view. Getting the two star clusters into a single image requires a much wider field of view, so after some trial and error I changed that to 3 degrees. I also changed the image size to 1500 pixels to make it large enough for a good full size view.

The results appear as greyscale images for each of the filter options (the example above is red visible light). SkyView has search options that will create a color image for you, but you lose some flexibility. I downloaded the individual greyscale images and brought them into Photoshop to process.

There's a trick to turning individual greyscale images into a color picture. The screen you're reading this on reproduces colors by mixing red, green, and blue light together. The camera in your smartphone records images by recording red, green, and blue light (your eyes work that way too). So the trick is to colorize the individual greyscale images and combine them into a final color image.

After a little tweaking in Photoshop and Lightroom, I reached a point I was happy with. Here's a side by side comparison of the ESO's image on the left and my image on the right. Let me know what you think.