A Nebula is a interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a name for any diffuse astronomical object, including galaxies beyond the Milky Way.


A protostar is a large mass that forms by contraction out of the gas of a Giant molecular cloud in the Instellar medium. The protostellar phase is an early stage in the process of star formation.

Main Sequence

The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell.