The photosphere is the visible layer of a star, such as the Sun, made up of hot gases with no solid surface. It is the lowest layer of the Sun’s atmosphere and has a textured appearance due to the convection process. Sunspots are cooler areas with strong magnetic forces. Helium was discovered in the photosphere.
The photosphere is the visible layer of a star, most often brought up in discussions of the Sun. Although the Sun may appear to have a solid outer layer, just like the Earth, it is actually made up of immensely hot gases and has no solid surface . The photosphere marks the boundary where light can penetrate gases, allowing them to become less opaque and, therefore, visible. What a person sees when looking at the Sun is the photosphere.
The density of the atmospheric layer is not constant in all places at all times, but tends to be about 248.5-310.6 miles (400-500 km) thick. The temperature ranges between 5,000 and 6,000 degrees Kelvin, or approximately 8,540-10,340 degrees Fahrenheit. It is the lowest layer of the Sun’s atmosphere, located beneath the much thicker chromosphere and enormous corona. Below the photosphere are the convection and radiation zones of the Sun, and below them, the powerful core.
Looking at the photosphere from afar, it might look like a plain yellow or orange disk with some dark spots, known as sunspots. Up close, however, the photosphere has a textured appearance often referred to as grainy. While not necessarily pretty to look at, the bubbling texture of the photosphere is evidence of exactly how the sun works: the bubbles and bumps are signs of the convection process. Convection on the sun works in essentially the same way as a pot of boiling water; heated photons rise to the surface while cooler ones sink, except instead of a bubbling surface on a pot of boiling water, convection from the sun causes granulation in the photosphere.
Sunspots, the dark spots often seen in images of the sun, are areas of the atmosphere where it is noticeably cooler, sometimes by more than 1,000 Kelvin (1340 F). Sunspots are not constant features and tend to rise and disappear within a few weeks. Despite their relatively cold temperatures, these spots have proven to have exceptionally strong magnetic forces. Though they often look tiny, sunspots in the photosphere are often tens of thousands of miles across.
Interestingly, observing the photosphere has led to the discovery of one of the most abundant elements in the universe: helium. While credit is variously given to the English scientist Norman Lockyer and the French astronomer Pierre Jansen, both observed peculiar yellow spectral lines around the sun that could not be replicated with known elements. Confirmation of helium on Earth did not occur until more than twenty years later, making it the only extraterrestrial element discovered before it was identified on Earth.
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