A space to picture the sky, envision the cosmos and lose oneself to the hauntingly endless universe of astronomy—a planetarium is an escape from the earthly tedium into an ambience of childlike wonder. It is a harbour of sheer curiosity, a place no stranger to excited whispers of starstruck children and the relatively restrained gasps of enchanted adults. But how can its structural shell speak of the vastness that lies within? How does an architectural volume invite passersby to step in and travel across the marvel that is the universe?

In the heart of the Université de Strasbourg in France, along Avenue de la Victoire, the new Planétarium du Jardin des sciences has opened its doors in a redesigned garden. Owing to its strategic position, the planetarium has become an important landmark in the French city. The institutional design is moulded into and inspired by the program’s dreamlike dimensions—realised by a team led by frenak+jullien with associate architects Cardin Julien and project architect m+mathieu holdrinet. The singular geometry of the building stands out starkly against the garden’s lush landscape that alludes to cosmic systems such as constellations and planets. “Reaching for the sky, the truncated cone suggests a timeless quest for knowledge of the universe, while the open and radiant lobby points towards the many sites managed by the Jardin des sciences,” reads the project's official release.

France-based architecture firm frenak+jullien has dabbled with public projects since 2007, working closely with the essence of places it transforms. The French architects’ oeuvre includes museum design, library design, art centres and healthcare facilities, largely emphasising bioclimatic solutions and reducing the overall carbon footprint. They are joined by Cardin Julien, a firm founded in Montreal, Canada, in 1992. They work extensively in the design of public buildings and cultural buildings, guided by the tenets of sustainable architecture and harmony with nature. The project architects, m+ mathieu holdrinet, come on board with congruent values of achieving sustainable responses on both urban and architectural scales. With their unique experiences and conforming approaches, the practices come together to conceive the planetarium’s conical envelope, an outcome of a simmering creative cross-pollination.

The curving structure is nestled between the imposing Zoology and Geology institutes, its two striking volumes are in a dialogue with the green backdrop; a truncated cone houses the 138-seat projection room and its entrance gallery while a cylindrical mass accommodates the lobby of the Jardin des sciences and related services. The architecture narrates the university’s dedication to fostering scientific culture, now rendered new visibility. The unconventional geometry is evocative of the 19^th century machine buildings and is reminiscent of astronomical measuring instruments such as the astrolabe. "For passersby, the cone’s metal disc beckons and reacts to the changing colours of the sky; for local residents overlooking the site, the planetarium’s fifth façade evokes an astronomical instrument set in a garden,” the team shares.

The two circular footprints that comprise the planetarium are bridged by shared components yet set apart by how they are planned. The main planetarium is turned inward—empty around its perimeter which acts as the access corridor and full at its core, the auditorium. The reception area, on the contrary, is empty at its centre with a hall circumscribed by rooms, opening outwards to the garden. While one volume allows natural light to flood the interiors and opens to the sky with a glass roof, the other retrieves into intense darkness only to create a sky of its own.

A slightly slanted circular gallery runs between the cone’s hemisphere and its inner face, offering a spatial experience in which the viewers segue from the bright hall to the dim cosmic theatre. The wood panels of the structure stretch up to a height of 17 metres and prepare the visitors for the vastness to come. Spectators walk up a gently sloping ramp towards the top of the auditorium, beneath the projection dome, whose placement enhances the immersive experience. Minimal lighting illuminates the night blue space equipped with precise technology to execute the projection. “The nestled volumes (cone, dome, screen) and the precision required for the suspension of the projection screen led to special constructive solutions and involved an atypical assembly logic during the building phase, such as the mounting of the planetarium’s metal dome prior to that of the cone’s covered enclosure,” the official release states.

The materials employed in the building are simple yet diverse: burnt wood and aluminium on the outside, light-coloured wood and plaster in the interiors. The facade design appears almost volcanic with its deep brown fir slats that become the stage for shimmering reflections in low-angled sunlight. Upon stepping in, the atmosphere turns rather bright owing to the light wood panels. The thoughtfully-placed openings and the compactness of the building limit its heat loss—optimising environmental performance.

The public garden is fundamental to the experience of the planetarium—an external augmentation of the cosmos that unfolds within its walls. The landscape design runs between two streets and is designed as a succession of plant environments, from dense undergrowth in the north to interspersed trees in the south. The existing trees, flowering shrubs and diverse fauna emulate the nearby Botanical Gardens. A long ditch, shrouded by greenery, to the south regulates rainwater and expands the ecosystems’ capacity. Eight circular gardens (the constellations) adorn the site, reflecting the ethos of the institutes of Zoology and Geology and the Botanical Garden, while being landscape manifestations of the solar system’s eight planets. Planétarium du Jardin des sciences—its sweeping mass and the symbolic greens that surround it—emerges as a layered culmination of the imaginations of the collaborators, the spirit of the university and an undying intent to nurture the very act that fuels it: imagination and curiosity.