system
Given the following post, respond as if you're commenting on Reddit:
human
If the photons take around 10,000 years to reach the outer surface from the core of the sun , was the sun dark for the first 10,000 years after nuclear fusion started to occur?

Did the sun start out much darker than now and reach its peak and then start decreasing its brightness?
gpt
No. When the Sun started fusing, it was still glowing from the energy release of slow gravitational contraction. The Sun was actually similar in luminosity before it started fusing, but slightly brighter and cooler because it was larger. When fusion began, the contraction stopped, but the Sun's outer properties didn't change much.