How to read The Night Watch in 90 seconds 

The painting delivered in 1642 shows the militia company of District II of Amsterdam under Captain Frans Banninck Cocq and his lieutenant Willem van Ruytenburch. Its real subject is a company stepping forward. The title The Night Watch is a later nickname, attached when centuries of darkened varnish and grime had made the picture look nocturnal. Cleaning revealed daylight.

Here is how to read it standing in front of it. Start with the two men in the middle. Cocq is in black with a red sash, his lieutenant beside him in pale yellow that catches most of the available light. Cocq's left hand is extended in the gesture of an officer giving a command, and his outstretched arm casts a small clear shadow on the lieutenant's coat. That shadow is the picture's clock. It tells you the two men occupy real space, at a real moment, and that the moment is now.

Second, follow the diagonals. A pike leans one way, a banner another, a musket is being loaded, a drum is being struck at the right edge. Nothing is parallel to the frame. A traditional militia portrait was a static row. This one is a group that has been interrupted and is beginning to move, which is why your eye cannot settle.

Third, find the girl. A small brightly lit figure in gold appears behind the officers, carrying a dead fowl whose claws hang at her waist. The claws are the emblem of the company's guild of arquebusiers, so she functions as a walking coat of arms rather than a portrait of a specific child. She is the second brightest thing in the composition, which is a deliberate provocation in a painting that men paid to appear in.

Fourth, count what you cannot see. In 1715 the canvas was moved to the Amsterdam town hall and trimmed to fit a wall, losing a substantial strip from the left side and slices from the other edges. A small copy made in the seventeenth century shows what was there: more space, more figures at the left, and a bridge and railing that made the company look as though it were emerging from an arch rather than crowding the frame. The version in the Rijksmuseum today is a cropped composition, which is part of why it feels so densely packed.

So the modern viewer stands in front of a mistitled, trimmed, once filthy painting and still cannot look away. That is worth noticing, because the reason has nothing to do with the story of the militia and everything to do with where the light falls.

Light was the tool he had spent twenty years sharpening, and it is the one thing you can learn to see in any gallery.