In Part 1 of “Astrometry for All,” I’ll show you how to easily “solve” just about any reasonably well-exposed astrophotograph in any format (ie jpeg, png, etc.) even if you have no idea from what part of the sky it was taken. You need know nothing about astrometry, nor be an advanced amateur to make use of this process. In the near-future, I will publish additional articles on how you can overlay minor planet information (comets, asteroids, even man-made satellites) onto your images. I’ll also go into more detail about how astrometry is used in almost all aspects of astronomy and astrophysics, as well as how you can contribute to Citizen Science with your astrometrically-solved images.
Astrometry is the process by which one accurately determines exactly to where in the sky a camera was pointed by determining what known celestial bodies are contained in the photographic frame. These known bodies are almost always stars.
The process of applying astrometry to an image is called “solving the plate,” or, simply “solving.” The term “plate” originated from the days where all astrophotography was done using film plates. Today it refers to all images obtained using film or CCD sensors contained within a camera.
Before I get to the cool stuff, you should know that, up until a short time ago, astrometry was something only serious amateurs and professionals made use of. This was due to the somewhat complex requirements (and sometimes high cost) to solve images. That has all changed with the brilliant work of a group of scientists, mathematicians, and programmers at astrometry.net who have created an entirely new approach to astrometry, and they have made it available to everyone!
For those of you who enjoy math and computers, I encourage you to view their fantastic work in a powerpoint presentation or PDF.
In a nutshell, this team has created a new method of solving images and made it available as a website, as well as integrating it into the popular photo repository flickr.com. Their goal is to make entire sources of astrophotography that were previously not astrometrically solved available to the scientific and amateur communities. This includes libraries of plates from old observatories, as well as amateur images that could not be used for scientific study because there was no way to easily solve them.
Now let’s get down to work and solve our first image!
Before we start, you need to join Flickr. You can do this for free, and it is quick and easy. You may wonder, “Huh, why Flickr?” Well, the folks at Flickr’s astrometry group took the astrometry.net software and integrated the two applications! Any image that is placed in the Flickr Astrometry group will automatically be solved by the astrometry.net software.
Note: You can use astrometry.net’s software right from their website, or even install it yourself if you are a *NIX-head. (Be forewarned, installing the software is NOT easy unless you are an experienced UNIX hacker!) I think the Flickr approach is much easier and faster for novices, plus your images become accessible to others and might be of value in the future. You must apply to be part of the beta team to use the astrometry.net site itself. If you are an experienced astrophotographer the beta test might be a better route!
UPDATE! The Astrometry.net team has told me to encourage readers who would like to use their web interface to simply send a short message with their email address to alpha@astrometry.net and they will add you to the website. Please let them know that you heard about them at askyfullofstars.com! Of course you can also use the Flickr.com method described in our article.
Once you have joined Flickr (if you aren’t a member already), select the “Groups” link at the top of your Flickr home page. Locate the “Find a Group” prompt; enter and submit “astrometry“; then follow the simple procedure for joining the Astrometry Group.
OK, now go back to your Flickr home page and . . . well, go get an image! To make it simple, get an image with a large portion of the sky in the frame. An image taken with a digital SLR in your backyard or favorite viewing spot is perfect. I am going to make use of one of my co-blogger Tavi’s marvelous images of the Pleiades and Mercury taken from her backyard:
Go back to Flickr and upload your image. Once you have uploaded it into your account, you need to add it to the Flickr Astrometry group. Just click on the Groups link and select the Astrometry link. You’ll see thumbnails of the most recent images uploaded by other group members. Just above those thumbnails, you’ll see the label “Group Pool.” To the right of that, you’ll see the “Add Photos or Video” link. Click that.
You’ll now be presented with thumbnails of your own image(s). Click on the one you want to submit to the Astrometry group. You can add up to six at-a-time, but just add the one you uploaded earlier.
Now, just sit back and wait a few minutes. Once your image has been solved, you will see the results below the image. You’ll need to refresh to see them. If you don’t see anything when you refresh, then your image hasn’t been solved yet. Depending on how much time it takes to solve, and how busy the Flickr Astrometry group is, it can take up to five minutes; but it is usually less than that. If it fails to solve your image, you’ll see that too.
Once completed, you’ll notice that your image can now be rolled-over, and the objects that were identified will be highlighted. Below the image, is the output of the astrometry.net software, listing all of the objects identified, the right-ascension & declination of the center of your image, and other useful data. But, here is the really cool part. Below the output listing, is a link to view your image in the World Wide Telescope.
Click on the link and follow-the-instructions for accessing the WWT. It is simple and easy. When you arrive at the WWT screen, you’ll notice a little thumbnail of your image in the upper-left. Click on that. The WWT will now show your image superimposed within the WWT screen. Cool? Wait – there’s more.
The WWT allows you to “mix” your image in the foreground with major astronomy catalogs. You’ll see these in a drop-down box at the bottom-left of the screen. You’ll also notice a little slider entitled “Image Crossfade.” You can position this to mix the selected catalog with your image. I thought it extremely interesting to look at the catalogs on non-optical surveys, like the cosmic background radiation, or the Gamma Ray sky. It gives me a grounded perception of the electromagnetic spectra, in perspective with a familiar setting.
OK, there you go – a foundation for experimentation and precisely determining from where in the sky an image is centered, and a simple tool to visualize the image using the WWT!
Our next post in this series will delve into using the astrometry.net images (or images already solved by other means) to overlay comet and asteroid data with your image. Here’s a hint to help you in the next post: You’ll need to know the precise time your image was taken!
If you are a fan of NASA’s Space program, you are probably also well aware of NASA’s budget constraints. Good science does not come cheap and this is especially true of Space-related studies, whether they be Earth-based or beyond.
