Emission nebula NGC 281, optical image. This is a starbirth region, a huge cloud of gas and dust in which stars form by gravitational coalescence. Radiation from the hot young stars formed here ionises gases in the nebula, causing them to emit light. Emission is colour-coded here, sulphur in red, hydrogen in green and oxygen in blue. Several dark Bok globules are seen silhouetted against the bright nebula, for instance at upper centre. These are very dense regions of dust and gas in which star formation is taking place. Several gas pillars are also seen, pointing inwards towards the star cluster (IC 1590) at the nebula's centre. The nebula lies some 10,000 light years from Earth in the constellation Cassiopeia.