SS Cygni is a variable star in the northern constellation Cygnus (the Swan).

It was discovered in 1896 by Louisa D. Wells, a computer working under Edward Pickering at Harvard College Observatory.

The northerly declination of SS Cygni (about 44° N) makes the star almost circumpolar from European and North American latitudes, allowing a large proportion of the world's amateur astronomers to monitor its behavior.

In 2007 Hubble Space Telescope data indicated a distance of about 540 light years, though this value caused difficulties with the theory of dwarf novae;[10] this was checked during 2010–2012 using radio astrometry with VLBI, which yielded a smaller distance of 114 ± 2 parsecs (371.8 ± 6.5 ly).

[6] This value is much more in accord with the old (≈400 light-year) value, and it removes completely the difficulties the larger HST distance made for the theory of dwarf novae.