what stages mark the birth of a star?
The birth of a star can typically occur due to the death of another star. There are huge dark clouds made of of gas and dust in space. These are called nebulas. When a nearby star explodes, a shockwave travels through the dark cloud. As the cloud collapses, energy is released, which causes it to heat up.
Planetary Nebula are the outer layers of a star that are lost when the star changes from a red giant to a white dwarf. A star is a luminous globe of gas producing its own heat and light by nuclear reactions (nuclear fusion). They are born from nebulae and consist mostly of hydrogen and helium gas.