A glassy addition to Mount Auburn Cemetery’s Bigelow Chapel is opened Saturday. (Photo: Tom Meek)

Renovations to the Bigelow Chapel at Mount Auburn Cemetery were completed last month, with the official public opening taking place Saturday. The result, conceived and executed by William Rawn Associates and Halvorson Design, is a mix of past and present, a union of styles that will dazzle most and perhaps put off traditionalists.

“It looks like a space shuttle,” one passerby observed of the austere glass sleeve wrapped around the side of the stoic medieval structure, though she added she never much liked the original facade to begin with. Other observers said that they appreciated the mix of old and new, which reminded them of blends found on the Harvard and Lesley University campuses.

The addition, by William Rawn Associates and Halvorson Design, blends old and new. (Photo: Tom Meek)

The addition around the original 1840 structure can accommodate 80 guests, said officials hosting the ceremony. Before the buildout, if there were more people than could fit in the nave, use of the front lawn for larger parties could mean a dicey dance with Mother Nature under tents.

It took some 15 months to complete the $15 million construction, which includes an updated crematorium. Because of the cemetery’s distinction as a historic landmark, renovation plans got great scrutiny by the Watertown Historical Commission and other agencies. (The cemetery with such luminaries as Cabot, Lodge, Longfellow and Booth buried in its grassy knolls has a Cambridge mailing address, but 90 percent of the property is in the part of old Newtowne now known as Watertown.)

The addition overlooking the 170-acre cemetery can accommodate 80 guests. (Photo: Tom Meek)