In 1967 when she produced Syncopated Rhythm (main picture), Sonia Delaunay was 82; far from any decline in energy or ambition, the abstract painting shows her in a relaxed and playful mood. Known as The Black Snake for the sinuous black and white curves dominating the left hand side, this huge, two and a half metre wide canvas is deliciously varied.

The Iranian-born New York resident painter YZ Kami, now in his mid-fifties, continually plays with our hunger to look at “reality” while being seduced by abstraction and repetition. In 17 canvases, painted over the past two years, Kami explores two distinct and recognisable styles or idioms that however much in common they have with contemporary concerns he has made his own. The results are both powerful and pleasurable. 

At 86, Jo Baer is still painting vigorously. In the mid 1960s, she was an established New York Minimalist along with artists like Carl Andre and Sol Lewitt; but while they continued to explore abstraction, she changed tack – dramatically, or so it seemed. In the mid 1970s, she turned toward figuration declaring that the “naivety” of Minimalism (its refusal to engage with events in the real world) no longer made it relevant. Yet she still thinks of herself as an abstract painter and this survey, which spans 55 years, allows us to guage what she means by the claim.

MK Gallery has a knack for showcasing mid-career artists before any other public space and this is Ellen Altfest’s first survey in the UK. There are 22 paintings here which, given their demands on her time, represent a significant proportion of the 44-year old’s output to date. Most of the pieces come from private collections, representing her commercial success with White Cube.

Look at me, and think of England. This marvellous array of quirky, idiosyncratic watercolours by Eric Ravilious (1903-1942) from the 1930s until his premature death during wartime when his plane, on an air sea rescue mission for which he had volunteered, crashed in Iceland. It is full of memorable and haunting pictures.

On a snowy day in early spring in New York, the On Kawara – Silence show at the Guggenheim is unlikely to warm you up. His date paintings, postcards, telegrams and other coldly ur-conceptual accountings spiral up those famous white Frank Lloyd Wright stairs, seemingly ad infinitum. But it’s a powerful, hypnotic experience, one that seeps into your subconscious and becomes a meditation on time and space.

This is work that wears its heart on its sleeve. That’s what gets you in the end in this big retrospective of the work of Niki de Saint Phalle.

The young, rather homely yet grand gentleman is lounging under a tree, behind him a formal knot garden. His costume is extravagant and rich, and his hat is charming. This exquisite 1590s miniature by Isaac Oliver, watercolour on vellum, titled indeed A Young Man Seated Under a Tree, is the first depiction in art of a knot garden; flowers and plants by the tree are meticulously detailed, and in the background is the classic Renaissance knot garden. 

We think we know it when we see it. But how, pray, do we define beauty? The ancient Greeks thought they had the measure of it. In the 4^th century BC, the “chief forms of beauty,” according to Aristotle, were “order, symmetry and clear delineation.” A century earlier, during the golden age of Athens, Polykleitos, one of the ancient world’s greatest sculptors, set out the precise ratios for the ideal male form in a treatise he called The Canon.

One masterpiece and two superb portraits both dominate and sum up in vivid fashion the complex personality, long life and astonishing trajectory of the first Duke of Wellington