A strong double bill starts Modern Art Oxford’s programme for the year. A solo show by Swiss sculptor Hans Josephsohn runs in MAO’s Pembroke Street galleries, while off-site at the Radcliffe Observatory, Green Templeton College, Oxford, is a fascinating film about one of the rarest of celestial events, the transit of Venus, by Turner Prize-winning British artist Simon Starling.

This is the first solo exhibition in a UK public gallery of the late Swiss sculptor’s massive bronze ‘semi-figures’ and reliefs. Josephsohn, who died last year aged 92, though not well known in this country had in the later stages of his career begun to be recognised as a sculptor of note. Born in East Prussia, Josephson fled Nazi Germany aged 18, and after a spell in Florence arrived as an émigré in Zurich where in his words, he “spent 60 years, day after day working away calmly in my studio”. My first glimpse of the work was from the street through the glass door to the Yard: a monumental tomb-like form lying on its side, seeming at first like a stone sculpture of a knight in some side chapel, until you get up close and see the indeterminate lumpy physicality of a much less refined shape. Clinging to the wall further on, a monstrous entity catches you unawares as you see a face watching you over its shoulder. Over at the Pembroke Street entrance another figure reclines, this one lying jauntily on its side, head in crooked arm, feet crossed, striking a more definite pose. Downstairs at MAO, in a film showing the elderly sculptor at work, cigar in mouth, slapping on dollops of plaster, hacking into it once dry, developing a form, he says: “Sometimes I think the main feature of this job is uncertainty.” And uncertainty is the mood here. These hefty bronze sculptures suggest all sorts to the viewer. It’s amazing what the imagination does given the right material. Moving round a line of five thickly powerful sculptures upstairs – faces, torsos, primitive forms? – I’m reminded of Easter Island Moai figures and of Michelangelo’s ‘slave’ torsos where humanity seems to emerge from stone. Tuning in, I begin to see features, a nose, an eye, giving each identity. Imagination powered up, I seek out facial expressions, rather like those universal emotions in psychological research, except in the pinch-faced head in the next room, I see aloofness or scepticism – or do I? Sculptural inspiration came to Josephsohn from mediaeval art in the churches in Italy, Ulrich Meinherz from the Kesselhaus Josephsohn, St Gallen, Switzerland, co-curating the show, told me: “It was the most important thing. “It was so strong that from that time he realised sculpture was for him.” He spent the rest of his life making sculpture, driven to work out his ideas. Fellow Swiss artist Alberto Giacometti was an influence, but not at the start of his career when he was making more abstract works, developing into figurative sculpture later. MAO’s show, focusing on his productive final 25 years of life, Josephsohn’s mighty figures responding well to the gallery’s vast spaces, is on until April 14.

Simon Starling often makes pilgrimages. He won the Turner Prize in 2005 with Shedboatshed, a shed he found on the banks of the Rhine and took apart, making it into a boat and floating it downriver to reassemble as a shed in a museum in Switzerland. Now, at the Radcliffe Observatory until this Sunday, Starling debuts his film Black Drop, the result of a journey to Hawaii and Tahiti to capture on 35mm film the 2012 transit of Venus, which was visible in its entirety only from the mid-Pacific. The film has the perfect setting. Specially commissioned by MAO in association with the University of Oxford, Starling’s recording of last June’s transit is shown within the historic space built on the suggestion of the astronomer Dr Thomas Hornsby following his own observation of the 1769 transit of Venus. Starling’s multi-layered film responds not only to the history of observing Venus transits – the tiny black drop crossing the sun’s key for astronomy to unlock the scale of the universe – but also to the backstories stories of people such as astronomer Pierre Jules César Janssen and Captain James Cook, and the early stages of moving image.

Actor Peter Capaldi narrates the film. Sadly the sound quality wasn’t great (doubtless due to challenges posed by the octagonal space), but this was more than made up for by seeing it inside that unique and lovely 18th-century tower.