The Sun is the star closest to us. Sunspots and patterns of convection can be seen on its surface, revealing its state of activity.
Basic Knowledge
Structure of the Sun:
① Core: The center. Nuclear fusion (hydrogen→helium) occurs here. The temperature is approximately 1500万K.
② Radiative Zone・Convective Zone: Carry energy from the interior to the surface.
③ Photosphere: The surface that we see. The temperature is approximately 6000K.
④ Chromosphere: A thin atmosphere outside the photosphere.
⑤ Corona: A tenuous gas in the outermost layer. Its temperature is over 100万K, and it can be observed during a total solar eclipse.
Sunspots: Dark spots on the photosphere that are darker than their surroundings. Their temperature is approximately 4000K (2000K lower than the surroundings). They have strong magnetic fields and increase and decrease in an approximately 11-year cycle.
Prominences (Solar prominences): Flame-like structures erupting from the chromosphere. Flares: Explosive phenomena on the solar surface in which magnetic-field energy is released.
Photosphere（The surface of the Sun. Temperature approximately 6000K. The part we see）
Sunspots（Dark spots on the photosphere. Lower temperature and stronger magnetic fields than the surroundings. Approximately an 11-year cycle）
Chromosphere（A thin atmospheric layer outside the photosphere. Red）
Corona（A tenuous, high-temperature atmospheric layer outside the chromosphere (over 100万K)）
Prominences（Flame-shaped gas structures erupting from the chromosphere）
Flares（Explosive phenomena on the Sun. Emit electromagnetic waves and charged particles）
Further Exploration (Background・Significance)
The Sun was born approximately 46億 years ago and is thought to continue shining steadily for about 50億 more years. After that, it will become a red giant and eventually end its life as a white dwarf.
When sunspots are observed by projecting them onto a projection screen with an astronomical telescope, they can be seen moving from east to west. This is because the Sun itself rotates. The Sun’s rotation period is approximately 25 days at the equator and approximately 35 days at the poles, so it differs according to latitude (differential rotation). This is because the Sun is made of gas rather than a solid.
Large-scale flares can cause magnetic storms, which may lead to satellite failures, power-grid disruptions, and reduced GPS accuracy. In 1989, a major blackout occurred in Quebec. Space weather forecasting is forecasting intended to prepare for these risks.
An aurora is a phenomenon in which charged particles (solar wind) from the Sun are trapped by Earth’s magnetic field, collide with the atmosphere in polar regions, and emit light.
- Photosphere temperature = approximately 6000K (surface)
- Sunspots = lower temperature (approximately 4000K) and strong magnetic fields than the surroundings
- Sunspot cycle = approximately 11 years
- Corona temperature = over 100万K
- The Sun rotates in approximately 25 days at the equator and approximately 35 days at the poles (differential rotation)
- Flares→magnetic storms→space weather
- Auroras = solar wind colliding with the polar atmosphere
Points to Note (Easily Confused)
① Remember the order: photosphere (surface), chromosphere (outer atmosphere), and corona (outermost layer). ② Prominences (structures) and flares (explosions) are different. ③ Sunspots are not black (they are only darker than their surroundings). In reality, they are glowing red at 4000K. ④ The corona is unrelated to coronavirus (corona means “crown” in Latin, and both have crown-like shapes).
Practice
- Approximately how many K is the temperature of the Sun’s surface?
- Approximately how many years is the activity cycle of sunspots?
- What is the name of the atmosphere in the Sun’s outermost layer that can be observed during a total solar eclipse?