Epsilon Aurigae was first suspected to be a variable star when German astronomer Johann Heinrich Fritsch observed it in 1821.

Later observations by Eduard Heis and Friedrich Wilhelm Argelander reinforced Fritsch's initial suspicions and attracted attention to the star.

Richard Hinckley Allen reported that Oxford scholar Thomas Hyde recorded the traditional name Almaaz in his 1665 translation of the catalogue of Ulugh Beg, which he identified with the Arabic Al Maʽaz "the billy goat", corresponding to the name of the star Capella (Latin for "nanny goat").

[22] Although the star is easily visible to the naked eye, Johann Fritsch's 1821 observations suggest he was the first to notice that the system was a variable.

Eventually, from 1842 to 1848, German mathematician Eduard Heis and Prussian astronomer Friedrich Wilhelm Argelander began observing it once every few years.

Both Heis' and Argelander's data revealed that the star had become significantly dimmer by 1847, attracting the full attention of both men at that point.

The observational data revealed that Epsilon Aurigae did not just vary over a long period, but also experienced short-term variations in brightness as well.

[26] Astronomer Su-Shu Huang published a paper in 1965 that outlined the defects of the Kuiper-Struve-Strömgren model, and proposed that the companion is a large disk system, edge-on from the perspective of Earth.

Robert Wilson, in 1971, proposed that a "central opening" lay in the disk, a possible reason for the system's sudden brightening midway through the eclipse.

[23][27] Another hypothesis by astronomers Alastair G. W. Cameron and Richard Stothers states that the companion of Epsilon Aurigae A is a black hole, consuming solid particles from the dusk cloud that bypass its event horizon which sends out the infrared light detected from Earth.

Early explanations with exceptionally large diffuse stars, black holes, and odd doughnut-shaped discs are no longer accepted.

[11] The Gaia Data Release 2 parallax is somewhat more precise, leading to a distance of 1,350±350 ly, towards the low end of estimates by other methods.

[3] The low mass model, popularized by the Citizen Sky project, proposes that the primary is an evolved asymptotic giant branch star of 2–4 M☉.

To match the observed eclipse and orbital data, the secondary is a fairly normal B main sequence star of about 6 M☉ embedded in a thick disc seen nearly edge on.

[3] The visible component, Epsilon Aurigae A, is a semiregular pulsating post-asymptotic giant branch star belonging to the spectral class F0.

The observed orbit, assuming a fairly normal F-type supergiant for the primary star, requires a secondary with a mass over 13 M☉.

Repeating the observation on different nights allows a light curve to be produced showing the variation in brightness of the star.

[37][38][39] The project, called Citizen Sky,[40] organized and trained participants to observe the eclipse and report their data to a central database.

In addition, participants helped validate and analyze the data while testing their own theories and publishing original research articles in a peer-reviewed astronomical journal.