Artsnova Digital Art and Space

Trouvelot astronomical illustration: Sonne III

Earlier this evening while doing research for my upcoming presentation on space art at the International Space Development Conference (see Art and the Promotion of Space Exploration), I was looking for information about Étienne Trouvelot, an astronomical artist active during the 1870’s. Quite to my surprise, I found a small gallery of his art at the New York Public Library web site. The 15 images are all from his book The Trouvelot astronomical drawings published in 1881 by Scribner’s Sons.

Of the images contained in the gallery, my two favorites are Mare Humorum, from a lunar study made in 1875, and The planet Mars, drawn based on observations from September 3, 1877. To view these and the rest of the images, visit New York Public Library’s Trouvelot Astronomical Drawings gallery.

P.S. Trouvelot is perhaps more well known as being the individual responsible for the accidental introduction of the gypsy moth to North America.

Ad Astra, Jim

Astronomy Day

Yesterday was Astronomy Day. I had been asked to speak at the Astronomy Day event at Harper College in Palatine IL. My presentation was The Universe According to Monty Python in which I spend an hour explaining the lyrics of the two minute long Galaxy Song which was featured in the movie The Meaning of Life.

I must say that for a bunch of comedians they did a pretty good job of getting their astronomy right but they did have professional help. During the course of my talk lots of big numbers get thrown around. As a rule the best laugh comes with my follow up to the line about the sun being the source of all our power where I segue into an explanation of nucleosynthesis. Whereas Carl Sagan looked at the situation through rose colored glasses when he said that we’re all made of “starstuff”, I level with the audience and tell them the truth: that we’re all nothing more than nuclear waste. Folks really seem to like hearing this.

Also, as a rule, people do not raise questions about the astronomical aspects of my talk but do ask questions when the subject turns to cosmology and relativity. To me this is only natural as those concepts are more alien to our everyday experiences and touch on the very nature of the universe.

For contrast, this Tuesday I’ll be giving a talk to all the third graders at a local grade school. My talk is The Solar System in 3D and the kids get to wear geeky red-blue anaglyph glasses. Believe it or not, third graders are a great audience. They are very curious and not at all afraid to ask questions.

Ad Astra, Jim

Photoshop FITS Liberator screen shot

A new version of the free ESA/ESO/NASA FITS Liberator plugin for Photoshop was released earlier this month. This plugin makes it possible to open FITS files with Photoshop. For you Photoshop users who are not familiar with FITS, the Flexible Image Transport System is the standard file format for astronomical data, like that of the Hubble Space Telescope for example. For more FITS information visit my Making Astronomical Art with your PC Resources page which I created for students in the astronomical art class I taught at the Adler Planetarium.

According to the release notes, the following enhancements are in this new release:

1. Universal Binary for Mac allows native CS3 operation on Intel-based systems
2. Flip image checkbox allows image orientation to be selected on import
3. Stretch Root functions now operate antisymmetrically about x=0
4. Version 1.1 of the Astronomy Visualization Metadata (AVM) standard is fully supported. For more information see http://www.virtualastronomy.org
5. Improvements to importing coordinate metadata from the FITS header

I went to the version 2.2 download page and downloaded this new version. There is also a Photoshop action called Colour_composite.atn that can be downloaded. This action automates the production of color images from the individual RGB grayscale layers. I’ve never used their action preferring to use one I created myself. I installed the plugin without difficulty. On opening a FITS file (M27 for the curious among you) I observed that the main dialog for this new version was essentially the same with the only modifications being to the Stretch Function dialog (item 3 in the list above) and the addition of a Flip Image option (item 2 in the list above).

You can learn more about the plug-in, how to use, and even get some sample FITS files from the ESA/ESO/NASA Photoshop FITS Liberator Home Page.

Ad Astra, Jim

Mars Global Surveyor Image:
Spring Thaw in Northwestern Planum Australe

Saturday I taught the first of a two part four hour class on astronomical image processing at the Adler Planetarium. The class, No Telescope, No Camera? No Problem: Making Astronomical Art with Your PC covers locating and downloading planetary and astronomical image data from the Internet and then using various image processing techniques to create finished pictures.

The first session covered both the basics of image processing and manipulation with Adobe Photoshop and how to use these techniques to transform raw PDS (Planetary Data System) image files into attractive colorized pictures. An added bonus was that these techniques are also applicable to the processing of images produced by digital cameras. The class consisted of both a lecture component and a demonstration component. Images used during the class were all downloaded from NASA JPL PDS Missions site.

For the demonstration component of the class, I demonstrated the following techniques:

• contrast enhancement and colorization of a single Viking Lander image of the Martian surface
• combining separate red, green, and blue Viking Lander images in order to produce a color picture while employing the contrast manipulation techniques previously illustrated
• combining red and blue filter images from the Mars Global Surveyor Wide Angle Camera and synthesizing a green channel to create a color picture
• using a Galileo image of asteroid Gaspra to explain enlarging and sharpening.

For some of the techniques, I showed that there was more than one way to get the job done and that the choice of methods really depended on the picture that was being worked. There was a lot of ground to cover and the class ran longer than its scheduled two hours. In addition to using Photoshop, I used both GIMP (with the PDS plug-in) and NASAView software to demonstrate how to open PDS image files and save them in standard graphics formats.

One of the exercises was to create a color picture of Mars by combining the image data from two Mars Global Surveyor Wide Angle Camera images: one taken using the blue filter, the other using the red filter. A small section of that picture is shown above. For purposes of comparison, you can compare this image with the Spring Thaw in Northwestern Planum Australe version posted on the Malin Space Science Systems web site.

Part two of the class will be held this Saturday and will cover the processing of astronomical images stored in the FITS (Flexible Image Transport System) format. For a list of this and other classes currently available from the Adler Planetarium, visit their classes page.

Star Map: Mars at 2:23am CST 11/06/2007

Tomorrow night (Tuesday Nov. 6) I’ll be giving a presentation to the Naperville Astronomical Association. Titled Imaging Mars, the lecture will focus on the processing of raw PDS (Planetary Data System) IMG files in order to create attractive pictures of Mars. For the most part I’ll be using images from the Viking orbiters and Mars Global Surveyor. The work flow for transforming these IMG raw data files into finished images is rather straight forward. Things are a little trickier with the Mars Exploration Rover and Mars Odyssey images. As this is an introductory level presentation, I strive to keep it simple.

This is actually a good time to be talking about Mars as an opposition of Mars is fast approaching. On December 18, Mars will make it’s closest approach to Earth this opposition. At that time, Mars will appear 15.9″ arcseconds in diameter as seen from Earth. Not nearly as good as the opposition of 2003 when its diameter was 25.1″ arcseconds but the best we’ll be treated to until 2016. Thus this is an excellent opportunity to check out your local observatory or astronomy club for the opportunity to get a good look at the red planet.

As to my presentation: the Naperville Astronomical Association meeting begins at 7:00pm and is held in downstairs rooms A-B-C of the Naperville Municipal Center at Aurora Ave. and Eagle St. in downtown Naperville IL.

Ad Astra, Jim

Are the Stars Out Tonight?

I just got an e-mail in my JPL Solar System Ambassador Inbox about a new survey that is underway for amateur astronomers. Note that the survey must be done by Monday October 8. What is the survey about? To quote from the e-mail:

“Through funding from the National Science Foundation, the Astronomical Society of the Pacific (ASP) and the Institute for Learning Innovation (ILI) are conducting a national study to better understand the amateur astronomy community and the activities and mechanisms that promote astronomy education to the public… By completing this survey, you are eligible to enter into a drawing for one of five $50 gift certificates to Sky and Telescope’s online store.”

The survey is a part of a program titled “Sharing the Universe”. I just completed the survey myself. It is straight forward and there were no questions that anyone could consider an invasion of privacy. If before taking the survey you would like to know more, then visit the Astronomical Society of the Pacific’s Sharing the Universe page.

Again, the deadline is Monday October 8. The survey only takes a few minutes so why not take the survey right now. Take me to the Survey.

About the Picture

The picture used to illustrate this post, titled Are the Stars Out Tonight? is a small section of a starfield that I am working on in Photoshop. The starfield will serve as a background for an as yet to be determined foreground scene.

Ad Astra, Jim

NASAView JPEG vs GIF of a Mars Reconnaissance Orbiter HiRISE image

For those wanting to work with the raw data files returned by various NASA planetary missions the first order of business is to convert the data from its native PDS (Planetary Data System) IMG format into something usable by standard image processing software, like Adobe Photoshop. The NASA PDS Software Download site provides a variety of software packages for use in processing various NASA data products. For Windows users the only program available there for converting IMG files is NASAView. The most recent version of NASAView is 2.14 and was released in June 2007. Earlier versions of NASAView supported saving IMG files only as GIFs. Recent versions have included the option to save to JPEGs.

By design, GIF files are limited to 8 bits of color information per pixel. In the case of PDS IMG files, this means that each image is limited to a palette of 256 gray levels with 0 representing black and 255 representing white. Because the PDS IMG files from earlier missions contained only 8 bits of information per pixel, there was no data lost in the translation from IMG to GIF.

But what about when saving the IMG file as a JPEG. I do not know what the rationale was for adding the ability to save JPEGs. Perhaps so people could easily have an image that was more web friendly in terms of the file’s size. I strongly advise against ever saving an IMG file as a JPEG in NASAView. The reason is because of the JPEG compression. Unfortunately NASAView does not give the user any control over the level of compression. From what testing I have done, it appears that NASAView defaults to a quality setting of 75%. While this may be fine for dumping an image on the web, it fails when it comes to producing quality print images, especially if you want to enlarge the image.

To illustrate the impact of JPEG compression in NASAView take a look at the image at the top of this article. This is a 300% magnified view of a segment of a Mars Reconnaissance Orbiter HiRISE image. On the left is the JPEG version and on the right is the GIF version of the same area, only mirrored. The JPEG artifacts are obvious and take the form of square blocks. Of course there is a significant difference in file size. Whereas the GIF version is just about 7 megabytes, the JPEG version is just over 1 megabyte. Another differences between the JPEG and GIF versions are that the JPEG version is brighter than the GIF version.

In closing, my advice is that if you are using NASAView to convert IMG files to a standard graphic format file, never ever use the “Save JPEG” or “Save JPEG AS” options. If you need a JPEG version, then save your file as a GIF and use another pieces of software to do the conversion to JPEG so that you can control the amount of image compression used. Hopefully in the future a more robust version of NASAView will be released which offers Window’s users greater control on output file format and quality.
Ad Astra, Jim

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.

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

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 http://www.eso.org/sci/publications/messenger/. 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 majordomo@eso.org 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

For some time now I have been using a particular technique to search the web for pictures of astronomical and planetary objects. That technique relies on the ability to limit searches to specific domains. I also make use of the ability to specify the size of the images I am searching for because I don’t want to see every thumbnail, banner ad, and site logo out there - I am only interested in full size images.

As an example, let’s say that I want to search for any picture that Google associates with the search term “Mars”. Here’s what to do.

1. Go to the Google Advanced Image Search page.
2. In the Find results section, for the option related to all of the words box, enter the word “Mars” without the quotes
3. For Size, click the drop-down arrow for the box and select “large”
4. For Domain, let’s limit the search to the Mars Art Gallery so enter the domain name “marsartgallery.com” without the quotes.
5. Click the Google Search button to execute the search and see the results.

That’s all there is to it. Some of my favorite search terms are nebula, galaxy, planet, exoplanet, messier, and supernova.

Taking a look at the Google Search Box you will see that the search term is:
mars site:marsartgallery.com.

It should be apparent that to switch to a different site, all you need to do is replace the domain name component so if you want to you can skip using the Advanced Image Search by entering the search term directly. Some of my favorite domains to site search on are (including the site keyword):
site:esa.int
site:hubblesite.org
site:apod.nasa.gov
site:observe.arc.nasa.gov
site:ipac.caltech.edu

And don’t forget to make sure that you have the large image option selected.

For a final suggestion, if you want to see all the images available on a site, you can do each of the following searches in sequence:
jpg site:marsartgallery.com
jpeg site:marsartgallery.com
gif site:marsartgallery.com
png site:marsartgallery.com
Note that you can search on only one image file extension at a time, otherwise it does not work.

Happy Searching.