Weekend Amateur: Using Nasa's SkyView virtual observatory to create stellar images

The Messier 3 globular star cluster in the visible and ultraviolet spectrum. Credit: Chris Casper Data Source: Sloan Digital Sky Survey Data Release 7 using Nasa Goddard Space Flight Center's SkyView facility

The Messier 3 globular star cluster in the visible and ultraviolet spectrum. Credit: Chris Casper

Data Source: Sloan Digital Sky Survey Data Release 7 using Nasa Goddard Space Flight Center's SkyView facility

Nasa puts terabytes of professional astronomy data at your fingertips through the SkyView virtual observatory. A quick search, some downloads, and then tweaking for cosmetic effects let me create this image of the globular star cluster Messier 3.

SkyView and other virtual observatory archives don’t exist so amateurs like me can make pretty pictures. They exist because the data collected by the world’s telescopes don’t spoil. Unlike a piece of fruit, an observation collected a year ago, a decade ago, a century ago is just as “fresh” as an observation collected last night. 

That lets modern astronomers produce new research using “old” data. They can study the way things in the Universe changes over time or they can take a new approach to studying objects. Between the growing volume of data in astronomical archives and the increasing difficulty reserving time on professional telescopes, more astronomers turn to these archives to conduct part or even all of their research. The scientists who run the Hubble Space Telescope track the number of research papers that use Hubble data. More than half of those papers use archived data.

Having your cake and eating it too

Of course there’s a catch. As the digital revolution swept professional astronomy in the 1980s, searching for data became a huge effort. As Nasa astronomer Tom McGlynn, in an interview with the Blueshift podcast, recalled:

…there were all these all-sky surveys that were coming on-line, and they were being placed in lots of different archives, and they all had very difficult, customized mechanisms for getting access to them. 

Dr. McGlynn decided to fix the problem by creating SkyView in 1994 as a one-stop-shop for data collected by astronomical surveys. From the original three surveys, SkyView now serves up data from more than 100 surveys that cover the entire electromagnetic spectrum from radio through gamma wavelengths. Both professional and amateur astronomers download millions of images every year from SkyView’s service.

The Weekend Amateur’s SkyView of M3

To demonstrate how easy it is to use SkyView, I chose the globular star cluster Messier 3. M3 is one of brightest clusters orbiting the Milky Way in the galactic halo. It formed about 8 billion years ago, not too long after the Milky Way. Most of its 500,000 stars are now so old that they burn red. But it's the variable stars that make M3 a popular target for amateur and professional astronomers. Princeton University astronomer Joel Hartmann demonstrates M3's variability in this timelapse movie from a single night's observations. Here's an image of M3 from the National Optical Astronomy Observatory taken in blue and near-infrared wavelengths.

An image created by astronomers studying M3's variable stars. Credit: S.Kafka and K.Honeycutt, Indiana University/WIYN/NOAO/NSF

An image created by astronomers studying M3's variable stars. Credit: S.Kafka and K.Honeycutt, Indiana University/WIYN/NOAO/NSF

SkyView doesn’t dumb things down for the public. Everyone uses the same search interface. The pros - or advanced amateurs - use more of the advanced features, but the SkyView team designed the interface so novices. The tutorial for non-astronomers will walk you through the basics. Even then, you may need to go through some trial and error before finding the right combination of target and data sources.

Both professionals and amateurs use the same form to search for images with SkyView.

Both professionals and amateurs use the same form to search for images with SkyView.

In my case, I typed M3 into the search box. I decided to use data from from the Sloan Digital Sky Survey - the highest resolution data source in SkyView. The SDSS uses a 2.5-meter telescope to capture data in several bands of light from the infrared to the ultraviolet. Since the SDSS data doesn't have a blue waveband, I chose the ultraviolet u-filter to represent the blue channel. I then adjusted the output size from the default 300 pixels to 1500 pixels.

The SkyView query produced, from left to right, a greyscale image in the red, green, and ultraviolet wavebands. Data Source: Sloan Digital Sky Survey Data Release 7 using Nasa Goddard Space Flight Center's SkyView facility

The SkyView query produced, from left to right, a greyscale image in the red, green, and ultraviolet wavebands.

Data Source: Sloan Digital Sky Survey Data Release 7 using Nasa Goddard Space Flight Center's SkyView facility

The query's results page gives you two options. You can simply save the jpeg images shown on the page. The downside to this approach is that you lose some flexibility when processing the images. Amateur photographers avoid using jpegs for the same reason, preferring to use their camera's "raw" format. The equivalent for astrophotographers is the fits format created by scientists to standardize the sharing of data. Since SkyView's main purpose is to make science easier, it also gives you the option to download the data as a fits file.

Unfortunately, consumer photo-editing software can't read fits files. I converted each file into a Photoshop-friendly tiff using Fits Liberator. Then it's a matter of combining each file to create a full-color image. I copied the red and green files into the red and green channels of the new image. I copied the ultraviolet SDSS data into the new image's blue channel. I used Photoshop's levels and curves as well as Lightroom to tweak the final image.

The final image of the Messier 3 globular star cluster in the visible and ultraviolet spectrum. Credit: Chris Casper Data Source: Sloan Digital Sky Survey Data Release 7 using Nasa Goddard Space Flight Center's SkyView facility

The final image of the Messier 3 globular star cluster in the visible and ultraviolet spectrum. Credit: Chris Casper

Data Source: Sloan Digital Sky Survey Data Release 7 using Nasa Goddard Space Flight Center's SkyView facility

That was it - easy with a little practice. It took me longer to write this blog post than to find and process the image. SkyView is just one of the virtual observatory tools that puts the data from professional astronomy in the hands of amateur space explorers.

Try it yourself and let me know how you do.