Epsilon Aurigae was first observed to be a variable star by German astronomer Johann Fritsch observed it in 1821, and it's been confounding scientists ever since. Wikipedia describes it this way:
Epsilon Aurigae is an unusual eclipsing binary system comprising an Fo supergiant and a companion which is generally accepted to be a huge dark disk orbiting an unknown object, possibly a binary system of 2 small B-type stars. About every 27 years, Epsilon Aurigae's brightness drops from an apparent visual magnitude of +2.92 to +3.83. This dimming lasts 640–730 days. In addition to this eclipse, the system also has a low amplitude pulsation with a non-consistent period of around 66 days. The distance to the system is still a subject of debate, but modern estimates place it approximately 2,000 light years from Earth.
Citizen Sky is currently running a project encouraging armchair astronomy enthusiasts to help observe the Epsilon Aurigae eclipse, which is currently still ongoing. They provide you with a finder chart and tutorials so you can collect and contribute scientific data to help solve the mystery. No equipment is necessary, nor is any prior experience in amateur astronomy. Epsilon Aurigae is very bright in fall, winter and spring - sufficiently so that it can be observed by anyone with decent eyesight.