There’s not really one instant where a new star goes from not shining to shining where a human looking up at night would see a star “turn on.” The process of turning on takes between 10,000 - 1,000,000 years, depending on the size of the star and how many stages you include in the process.
There’s not really one instant where a new star goes from not shining to shining where a human looking up at night would see a star “turn on.” The process of turning on takes between 10,000 - 1,000,000 years, depending on the size of the star and how many stages you include in the process.