binary star system of about third magnitude having one of the longest orbital periods (27 years) among eclipsing binaries (see eclipsing variable star). It is located an estimated 2,000 light-years from Earth in the constellation Auriga. The primary star is a yellow-white star about 200 times the size of the Sun. The secondary star, once thought to be thousands of times the size of the Sun, is now believed to be a hot main-sequence star surrounded by an immense ring or shell of gas that periodically eclipses the primary.