1. Equatorial coordinate system. https://en.wikipedia.org/wiki/Equatorial-coordinate-system. Equatorial coordinate system. https://en.wikipedia.org/wiki/Equatorial-coordinate-system.
2. Healpix home page. http://healpix.sourceforge.net. Healpix home page. http://healpix.sourceforge.net.
3. Sdss dr12. http://www.sdss.org/dr12/scope/. Sdss dr12. http://www.sdss.org/dr12/scope/.
4. Xmatch: Gpu enhanced astronomic catalog cross-matching;Budavari T.;Astrophysics Source Code Library,2013