When plans were drawn up for a major expansion of the adjacent Royal Ontario Museum in the mid-1970s, it was initially assumed that the planetarium, then still a comparatively new facility, would be left untouched. As the scope of the expansion increased, it was realized that its north annex would need to be demolished in order to make way for the museum's need for a wing devoted to curatorial facilities. As a result, a theatre entrance, sound studio, workshop, passenger elevator and a third of the existing gallery area of the planetarium had to go. The remaining gallery area was removed in March 1978 to make space for temporary space to replace the workshop and studio.