We are gathering archival observations to determine the photometric history of the unique and unexplained eclipses of the pre–main-sequence star KH 15D .
Here we present a light curve from 1967–1982 , based on photographic plates from Asiago Observatory .
During this time , the system alternated periodically between bright and faint states , as observed today .
However , the bright state was 0.9 mag brighter than the modern value , and the fractional variation between bright and faint states ( \Delta I = 0.7 mag ) was smaller than observed today ( 3.5 mag ) .
A possible explanation for these findings is that the system contains a second star that was previously blended with the eclipsing star , but is now completely obscured .