 Having a dark cloud in the solar neighborhood greatly facilitates observation and measurement.If not disrupted by external forces, the stability of dust clouds is a fine balance between outward pressure caused by the heat or pressure of the cloud's contents, and inward gravitational forces generated by the same particles (see Jeans instability and Bonnor-Ebert mass).This causes the cloud to wobble or oscillate in a manner not unlike that of a large soap bubble or a water-filled balloon which is jiggled.