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
 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.
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.