The ability to do work or cause change is
Energy
Actually, that does not happen until the protostar becomes a star when nuclear ignition starts and is maintained. It takes awhile for new star to go through its T-Tauri stage and settle down on the main sequence.
<span>A STAR does not reach hydrostatic equilibrium until it on the main sequence. Otherwise, it would remain a brown dwarf with not enough mass to to maintain nuclear fusion for more than 3,000 to 10,00 years. </span>
However, as a result of the Sun's large angular size, solar<span> illumination is only partially blocked in the outer portion of the Earth's </span>shadow<span>, which is given the name penumbra. A penumbral </span>eclipse<span> occurs when the Moon passes through the Earth's penumbra. The penumbra causes a subtle darkening of the Moon's surface.</span>
