An association is a group of extremely young stars, typically containing 5 to 50 hot, bright stars scattered over a region of space some 100-500 light-years in diameter. As an example, most of the stars in the constellation Orion form one of the nearest stellar associations. Associations also contain hundreds to thousands of low-mass stars, but these are much harder to see. The presence of really hot and bright stars indicates that star formation in the association has occurred in the last million years or so. Since O stars, stars that are over a million times brighter than our own sun, go through their entire lives in only about a million years, they would not still be around unless star formation occurred recently. It is therefore not surprising that associations are found in regions rich in the gas and dust required to form new stars. It’s like a brand new building still surrounded by some of the construction materials used to build it and with the landscape still showing signs of construction.