I’ve been taking some astronomy pictures with a pro-sumer level DSLR with no tracking mount. This results in very grainy images. So I thought I’d see how much of an improvement I would get with taking a small number of images in a row and stacking them.
First step, since I don’t have a tracking mount, is to align the images. The sky moves a little bit between each exposure (and during exposures, which is why I have to keep them short at high ISO to avoid star trails). I could probably use the alignment tools that Hugin uses for panoramas, but I would also like to have a good record of what section of the sky the image is of and what sort of objects are there. The right answer for this is Astrometry.net.
I am using OSX. I already have XCode and the command line tools installed. My package manager is fink. I already had cairo installed (probably from some other image processing library), and the other libraries that Astrometry.net needs, and just had to have fink install cfitsio. After a few failed attempts at getting Astrometry.net working (compile completed and so did install, but all attempts to use the code failed), I realized that I did not have the fink CFLAGS and LDFLAG variable set up in my login scripts (see the Astrometry.net documentation or fink’s documentation for details). Once I added those variables to the shell I was compiling in, things worked fine.
Neither the configure nor the make install step recognise the –prefix flag. Instead, you specify your install directory during the make install step like this:
make install INSTALL_DIR=/Users/<me>/Code/astrometry/
Since I am using standard DSLR lenses, I only downloaded the wide field data files. I used a bash for loop to wget them:
for i in $(seq -f "%02g" 7 19); do wget http://broiler.astrometry.net/~dstn/4100/index-41${i}.fits ; done
When using the solve-field command, I did need to have the bin directory in my path since this command will call other commands located there.
I have successfully installed the code and run it on one of the included example files (apod4.jpg, the suggested test file for wide fields). Next step is to save one of my own images as a jpg and run the code on it. Then I will try converting my RAW files into FITS files to preserve all the data and run Astrometry.net to get wcs, so that I can open them all in ds9 or IRAF and make a stack. Hopefully that will improve the noise levels to give me some cleaner images of the Magellanic Clouds.
Documenting Making 