Astrometry.net is easy to use on Linux, macOS, and Windows. Windows uses Windows Subsytem for Linux for Astrometry.net. To get star index files, use downloadIndex.py.

Download/install the pre-compiled binary code:

• Linux / Windows Subsystem for Linux: apt install astrometry.net
• macOS Homebrew

The major steps in achieving a useful WCS starfield polynomial fit are:

1. source extraction (identifying star position in image frame)

2. quad asterism hashing, including tolerance for star position wiggling due to noise.

3. Match hash to star catalog, at least 3 choices are available:

   • USNO-B
   • Tycho-2
   • 2MASS (infrared)

4. Bayesian decision process, find extremely high probability solution or reject.

Astrometry.new tips and techniques

Optional compile: normally not necessary.

Prereqs:

apt install libcairo2-dev libnetpbm10-dev netpbm libpng12-dev libjpeg-dev zlib1g-dev swig libcfitsio-dev

curl -O https://astrometry.net/downloads/astrometry.net-latest.tar.gz

tar xf astrometry.net-*.gz

cd astrometry.net-*

make
make py
make extra

make install INSTALL_DIR=~/astrometry.net

Add to ~/.profile

export PATH="$PATH:$HOME/astrometry.net/bin"

do not use ~ to avoid error:

cannot find executable astrometry-engine

Uncomment inparallel in ~/astrometry.net/etc/astrometry.cfg (or /etc/astrometry.cfg)

Copy the star index files with downloadIndex.py

python downloadIndex.py

If it can’t find the index file, be sure ~/astrometry.net/etc/astrometry.cfg contains:

add_path /home/username/astrometry/data

~ or $HOME will NOT work!

Reference paper

Program giving azimuth/elevation for each pixel of sky image

Alternative: online astrometry.net image scaling