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Archive for July, 2007

Can You Classify That Galaxy?

Friday, July 20th, 2007
Spiral Galaxy M101
Spiral Galaxy M101 by Jim Plaxco

Some of you may recall the Mars crater identification project that asked for volunteers to identify martian craters. Named Clickworkers, the project has since been expanded to include review of Mars Reconnaissance Orbiter HiRISE camera images. More about that in an upcoming post.

Now a similar project has been created for the purpose of classifying galaxies. Galaxy Zoo, which opened July 10, is an online project that uses volunteers to visually inspect small deep space pictures in order to identify the type of galaxy seen in the image.

Your job as a classifier of galaxies is to determine whether the image is of a spiral galaxy, elliptical galaxy, merging galaxies, or not a galaxy at all. If it is a spiral galaxy, then one needs to identify whether its rotation is clockwise or anti-clockwise. Figure 1 below shows a sample screen shot, reduced in size for display here.

Galaxy Zoo screen shot
Figure 1. Galaxy Zoo screen shot shown reduced in size.

Unlike Clickworkers, Galaxy Zoo volunteers need to register and pass a test. The test consists of correctly identifying at least 8 of 15 galaxy images. When I took the test I got 13 out of 15 correct. I’m fairly sure of the ones I got wrong. These were objects that were quite fuzzy and I basically just gave it my best shot. Unfortunately there is no feedback given to tell you which ones you did get wrong. That feedback would definitely be useful.

Once you’ve passed the test, you are then free to begin analyzing galaxy pictures. One word of caution: the galaxies that are used in the tutorial section to give you practice at identifying galaxies are, in my opinion, representative of rather clear cut cases. Many of the galaxy images that you are asked to classify are little more than pixellated smudges so be prepared for a challenge.

While classifying, one cool tool at your disposal is the SDSS Skyserver Object Explorer. You access this tool by clicking on the Galaxy Ref. link (see orange text, upper right in Figure 1). There you will find quantitative information about the image you are analyzing. From this tool you can click on the image shown which takes you to a new window for the SDSS DR6 Finding Chart Tool. This tool allows you to zoom in and out on the image you are analyzing. You may find this useful for those hard to classify galaxies.

There are a Sagan’s#1 worth of galaxies awaiting classification so what are you waiting for, get over to Galaxy Zoo because the more of us that help, the quicker the job will be done. Incidentally, M101 (the galaxy shown at the top of this post) is a counter-clockwise rotating spiral galaxy.
Note 1. One Sagan = Billions and billions.

Ad Astra, Jim

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Photoshop, Filters, Speed

Wednesday, July 18th, 2007
Paris in the Spring

A lot of the images that I work on in Photoshop are big. Really big. And no, I’m not digitally manipulating pictures of Paris Hilton, though that is an interesting thought. I can see her sporting a stylish goatee and mustache. Now when I say big, I generally am addressing pictures whose smallest dimension is larger than 3000 pixels.

As it happens I frequently want to experiment with the Photshop filter set to see what impact different filters have on the image. It is especially interesting to see the results of combined filter effects. The problem is that even with a fast PC with loads of memory, Photoshop will take some time to process the complete image and I am just to impatient to wait.

My solution is as follows. First, I identify a section of my original image which is not only representative of the entire image but includes part of the image area for which I am most interested in seeing the filter’s effects. I try to keep the dimensions of this area to that of my screen at 100% resolution – so we’re talking approximately 1400 by 1000 pixels. Using the Rectangular Marquee tool, I then select that area of my image and Ctrl-C to copy it. Then Ctrl-N to open the new document dialog. Just click the OK button and then Ctrl-V to paste the selection into the new document. For the pictures that I work with, on average this new document represents about a 90 percent or more reduction in the number of pixels Photoshop has to work with.

I am now free to speedily experiment with different filters and different combinations of filters. Once I’ve figured out what I want to do, I then go back to the source image and apply the desired filter effects.

So next time you have a really big image and want to test out some filter effects, consider working with a only a portion of your image.

Ad Astra, Jim

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Photoshop for Web Site Design

Monday, July 16th, 2007
Chicago Society for Space Studies web site
Chicago Society for Space Studies web site.

Saturday I completed a total redesign of the Chicago Society for Space Studies web site – which in part explains why I haven’t been posting new entries here lately. And since I was in the process of doing the redesign, I took the opportunity to also write an article outlining the process. That article – A Web Site Redesign – appears on my Astrodigital web site.

The redesign I performed would not have been possible without the use of 2D graphics software. Of course my software of choice is Adobe Photoshop. While I have used Photoshop before to create buttons, logos, banner images, and web page elements, I had never used it to create a total graphic page design. That design, shown above, was actually quite easy to create.

For the banner image, I felt that a night view of the Chicago skyline would be most appropriate since it combines the elements of Chicago and space via the presence of the night sky. The Chicago skyline is a composite of two photographs taken at night from the site of Chicago’s Adler Planetarium. To capture the two images, I set my camera up on one of my tripod’s and shot in manual mode, which allowed me to control ISO, speed, and aperture. I also created a new version of the CSSS logo that fit in better with the banner image color wise.

The most time consuming part of the design process was not the actual creation of the design, but rather coming up with the mental image of the type of design I wanted to create. I was guided in this process by looking through free web site template sites. There is more on that in the A Web Site Redesign article.

Realization of the site graphic/design was accomplished by creating a multi-layered Photoshop document. I started by creating a solid background, the color for which I was sure to note as I would use this color to define the web page’s background color in the CSS (Cascading Style Sheet) file. This was layer one. On layer two I made a rectangular selection of an area of the same size as the page area, feathered the selection, and filled it with a dark gray: this would serve as the shadow area around the page content area. Back to the rectangular marquee, on layer three I selected a rectangle and filled it with white: this would serve as the content area background. On layer four I added the Chicago skyline image. I placed the CSSS logo on layer five. By putting the logo on its own layer, I was free to experiment with positioning the logo and while keeping my options open for any future changes. Next up the layer ladder, on layer six I created a rectangular selection and filled it with gray: this would be the area used to hold the horizontal navigation bar. Layer seven was used to create the frame that serves as the page border. The frame around the page was made by simply creating a rectangular selection, feathering the selection, converting the selection to a border selection, and then stroking the path. I then used a layer style to give the border a 3D effect.

It was all pretty simple actually. The final step was to switch to ImageReady and slice up the image into the appropriate components. It was then necessary to create the CSS that would reassemble the individual graphic components while allowing for content control within each of those individual areas.

Once I had my CSS and XHTML template created, it was just a matter of replacing the old page layout code with the new code. Not mentally challenging but tedious. The worst part of the whole process was validating all the HTML associated with the content as I had decided to change from coding using an HTML doctype to an XHTML doctype.

If you want to take a closer look at the design, and learn a little bit about space in the process, I encourage you to visit the Chicago Society for Space Studies web site.

Ad Astra, Jim

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The European Southern Observatory Messenger

Tuesday, July 3rd, 2007
ESO photo of Spiral galaxy NGC 1232
ESO photo of Spiral galaxy NGC 1232

The European Southern Observatory (ESO) publishes a periodic e-newsletter about ESO’s activities and astronomy. The June 2007 issue of ESO Messenger is now available. Articles in this issue include:

  • Astronomy in the Czech Republic
  • Progress of the ALMA Project
  • Exploring the Near-infrared at High Spatial and Spectral Resolution:
  • First Results from CRIRES Science Verification
  • Towards Precision Photometry with FORS: A Status Report
  • Using the h-index to explore the scientific impact of the VLT

The 80 page PDF can be downloaded from Back issues of the ESO Messenger are also available from the same page.

You can receive email notification of the release of new issues by sending an email to with the following line as the message body:
subscribe eso-enews your_email_address

The ESO web site also hosts an excellent Public Image Archive featuring a wide variety of astronomical pictures. In addition to having a variety of resolutions available for download, the text descriptions provide good background information on the associated image.

As an example, see the image above used to illustrate this article. The description on the ESO web page for this photograph of Spiral galaxy NGC 1232 is: “This spectacular image of the large spiral galaxy NGC 1232 was obtained on September 21, 1998, during a period of good observing conditions. It is based on three exposures in ultra-violet, blue and red light, respectively. The colours of the different regions are well visible: the central areas contain older stars of reddish colour, while the spiral arms are populated by young, blue stars and many star-forming regions. Note the distorted companion galaxy on the left side, shaped like the greek letter ‘theta’. NGC 1232 is located 20_ south of the celestial equator, in the constellation Eridanus (The River). The distance is about 100 million light-years, but the excellent optical quality of the VLT and FORS allows us to see an incredible wealth of details. At the indicated distance, the edge of the field shown corresponds to about 200,000 lightyears, or about twice the size of the Milky Way galaxy.”

So feed your eyes and feed your brain by taking a tour of the Public Image Archive.

Ad Astra, Jim

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