What is the photosphere of the sun?

The photosphere of the sun is fundamentally understood as the visible surface from which solar radiation is emitted. It is the layer in the sun's atmosphere that we can see, and it emits the light that illuminates our solar system. The temperature in the photosphere is approximately 5,500 degrees Celsius (9,932 degrees Fahrenheit), which is hot enough to produce light in the visible spectrum, making it the source of the sunlight we experience on Earth.

This layer serves as a boundary between the sun's innermost layers and the external atmosphere. The photosphere is often characterized by its features such as sunspots, which are cooler regions on the sun's surface that appear darker. Understanding the photosphere is crucial, as it plays a key role in solar phenomena and impacts space weather that can affect Earth.

By knowing that the photosphere is indeed the source of solar radiation, it becomes clear why the correct choice aligns with this definition. The other options relate to different aspects of the sun’s structure or activity, distinguishing them from the distinct role of the photosphere as the visible light source.