The Sun is our nearest star and the main source of energy for Earth. It is a huge sphere of hot plasma held together by gravity, about 150 million kilometers away. Its light warms the planet, drives weather, powers photosynthesis, and makes life possible.
Studying the Sun up close helps scientists understand stars, space weather, and the conditions that shape our solar system.
Inside the Sun, energy is produced in the core by nuclear fusion, where hydrogen nuclei combine to form helium. That energy slowly moves outward through the radiative zone and convective zone before reaching the visible surface called the photosphere. Above the surface are the chromosphere and corona, where magnetic fields can launch flares and coronal mass ejections into space.
These events can affect satellites, radio signals, power grids, and auroras on Earth.
Key Facts
- Average Sun to Earth distance = 1 AU = 1.496 x 10^8 km
- Solar luminosity = 3.83 x 10^26 W
- Photosphere temperature is about 5,800 K
- Core temperature is about 15 million K
- Energy from fusion follows 4 H nuclei -> 1 He nucleus + energy
- Light travel time from Sun to Earth = distance / speed of light = about 8.3 minutes
Vocabulary
- Plasma
- Plasma is a hot ionized gas made of charged particles that respond strongly to electric and magnetic fields.
- Nuclear fusion
- Nuclear fusion is the process in which light atomic nuclei combine to form heavier nuclei and release energy.
- Photosphere
- The photosphere is the visible surface layer of the Sun that emits most of the sunlight we see.
- Corona
- The corona is the Sun's outer atmosphere, a very hot and thin layer that extends far into space.
- Solar flare
- A solar flare is a sudden burst of radiation from the Sun caused by the rapid release of magnetic energy.
Common Mistakes to Avoid
- Calling the Sun a ball of fire is wrong because fire needs chemical combustion, while the Sun shines because of nuclear fusion in plasma.
- Thinking the corona is cooler because it is farther from the core is wrong because magnetic processes heat the corona to millions of kelvin.
- Using 150 million meters instead of 150 million kilometers for the Sun to Earth distance is wrong because it makes travel time and scale calculations off by a factor of 1,000.
- Assuming sunlight reaches Earth instantly is wrong because light has a finite speed and takes about 8.3 minutes to travel from the Sun to Earth.
Practice Questions
- 1 The average distance from the Sun to Earth is 1.496 x 10^8 km and light travels at 3.00 x 10^5 km/s. Calculate the time in minutes for sunlight to reach Earth.
- 2 The Sun's radius is about 696,000 km and Earth's radius is about 6,371 km. About how many Earth radii fit across one solar radius?
- 3 Explain why solar flares and coronal mass ejections can affect technology on Earth even though the Sun is about 150 million kilometers away.