The HR diagram is a powerful tool to analyze evolution and characteristics of stars. The HR diagram is used to plot the temperature/luminosity evolution of stars from the interstellar medium to the main sequence. As a star evolves along this path it crosses what is referred to as the "birth line". The birth line defines the point at which a star: A) a dense core contracts and heats up to over 1000K B) the star emits enough radiation to disperse its surrounding cocoon C) The stars interior heats up to the point that nuclear reations ignite in its core D) The newly forming star exhibits strong stellar winds and becomes a T-Tauri star