29.1 The Sun

Properties of the Sun

· The Sun is the largest object in the solar system in both diameter and mass.

· It would take 109 Earth’s or almost 10 Jupiter’s lined up edge to edge to fit across the sun.

· It is about 330,000 more times as massive as the Earth.

· In fact, the sun contains more that 99% of all the mass in the solar system. Therefore, the Sun’s mass controls the motions of the planets and other objects.

· The Sun’s interior is gaseous throughout because of the high temperature, which is about 10,000,000°K or 17,999,540°F at the center.

· All of this temperature and mass means that the interior of the Sun is composed only of atomic nuclei and electrons. This state of matter is called plasma. The outer layers of the Sun are not hot enough to be plasma.

· The sun produces enough light each second equal to that of 4 trillion 100-W light bulbs.

The Sun’s Atmosphere

Photosphere

· This is the visible surface of the Sun.

· It is approximately 400km (249mi) thick

· It has an average temp of 5,800°K (9,980°F).

· It is the innermost layer of the sun’s atmosphere. Even though this is the innermost layer, we can see it because this is where the visible light emitted by the sun comes from and the two outermost layers are transparent.

Chromosphere

· This layer is outside the photosphere.

· It is approximately 2,500km (1,553mi) thick

· It has a temperature of nearly 30,000°K (53,540°F).

· The chromosphere is usually only visible during a solar eclipse when the photosphere is blocked. However, astronomers can use special filters to observe the chromosphere when the Sun is not eclipsed.

· The chromosphere appears red because its strongest emissions are in a single band in the red wavelength.

Corona

· This is the outermost layer of the Sun’s atmosphere.

· It extends several million km (about 1.2 million miles) from the edge of the chromosphere.

· It has a temp range of 1 million to 2 million °K (1,799,540°F to 3,599,540°F).

· Because the gas in the corona has such a low-density causes it to be very dim, and therefore it can only be seen when the photosphere is blocked by special instruments or when the Moon blocks it during an eclipse.

Solar wind

· Hot gas flows outward from the corona at high speeds and forms solar wind.

· This solar wind carries charged particles, or ions, that when deflected by Earth’s magnetic field becomes trapped into two huge rings called the Van Allen belts. The highly charged particles in these belts collide with gases in Earth’s atmosphere and cause the gases to give off light. This light is called the aurora. We call them The Northern Lights or Aurora Borealis.

Solar Activity Features of the Sun that change over time. Solar activity can cause electrical power outages, damage communication satellites, and interrupt radio communications.

Sunspots

· Dark spots on the surface of the photosphere.

· They are bright but appear darker because they are cooler than the surrounding area.

· These sunspots are caused by the Sun’s magnetic field.

Solar activity cycle

· The number of sunspots changes on a regular schedule, which is about every 11 years. This is when the Sun’s magnetic field reverses.

Solar Flares

· These are associated with sunspots

· They are violent eruptions of particles of radiation from the surface of the Sun.

Prominence

· These are sometimes associated with flares. Also associated with sunspots and the magnetic field.

· This is an arc of gas that is ejected from the chromosphere, or gas that condenses in the inner core and rains back to the surface.

· They can reach temperatures of 50,000°K (89,540°F)

· They can last for a few hours or a few months.

Solar Interior

Energy Production

· Fusion occurs in the core of the Sun where pressure and temperature are very high.

· Lightweight hydrogen nuclei fuse into heavyweight helium nuclei.

· The mass lost when hydrogen fuses to helium is converted to energy, which powers the Sun.

· The Sun is about half way through its fusion process, which means it’s only halfway through its lifetime.

· It still has about 5 billion years left before it reaches then end of its life cycle.

Energy Transport

· Energy is produced in the core and travels outward through 2 zones.

· Radiation zone

· This is the inner portion of the Sun extending to about 86% of its radius.

· Energy is transferred here by radiation. (Sun’s energy is carried from particle to particle.)

· Convection zone

· This is above the radiation zone.

· Here, convection currents transfer energy the rest of the way to the Sun’s surface.