Photosphere

Sun diagram

Highest resolution photo of Sun (NSF) as of January 20, 2020

Sun Atmosphere Temperature and Density SkyLab

Photosphere is the sun's or another star's outer shell from which light is emitted. It extends from the star's surface visible during a solar eclipse to the region where the star becomes completely opaque. The photosphere is not a solid surface but a layer of gas that is about 500 km thick for the Sun, although this thickness is much less than the Sun's radius. The temperature of the photosphere of the Sun is approximately 5,500 degrees Celsius (9,932 degrees Fahrenheit).

Composition

The photosphere is primarily composed of hydrogen and helium, which make up about 74% and 24% of its mass, respectively. The remaining 2% consists of heavier elements, such as oxygen, carbon, neon, and iron. Despite its relatively low density, the photosphere is opaque due to the absorption of light by hydrogen atoms and negative hydrogen ions, which results in the visible light that reaches Earth.

Structure

The photosphere is characterized by a granular structure, with each granule representing the top of a convection cell within the Sun's convective zone. These granules are about 1,000 km in diameter and have a lifespan of about 8 to 20 minutes before dissipating. The darker regions, known as sunspots, are areas of intense magnetic activity where the temperature is lower than the surrounding areas.

Observation and Study

The study of the photosphere is crucial for understanding the Sun's atmosphere and its influence on space weather. Observations are typically conducted using telescopes equipped with spectroscopic instruments to analyze the light emitted by the photosphere. This allows scientists to determine its composition, temperature, and other properties.

Importance

The photosphere is significant because it is the region of a star that emits the light we see. It plays a crucial role in the star's energy production and distribution. Understanding the photosphere's dynamics helps astronomers learn more about stellar atmospheres, stellar evolution, and the processes that govern them.