The Sun

24.3 Structure of The Sun

Because the sun is made of gas, no sharp boundaries exist between its various layers.

Keeping this in mind, we can divide the sun into four parts: the solar interior; the visible surface, or photosphere; and two atmospheric layers, the chromosphere and corona.

24.3 The Sun

• Sunspots appear dark because of their temperature, which is about 1500 K less than that of the surrounding solar surface.

• A sunspot is a dark spot on the sun that is cool in contrast to the surrounding photosphere.

• Solar wind is a stream of protons and electrons ejected at high speeds from the solar corona.

Sunspots

24.3 The Sun

• Solar flares release large amounts of energy, much of it in the form of ultraviolet, radio, and X-ray radiation

• Solar flares are brief outbursts that normally last about an hour and appear as a sudden brightening of the region above a sunspot cluster

Aurora Borealis

• Auroras, the result of solar flares, are bright displays of light caused by solar radiation interacting with the upper atmosphere at our poles

24.3 Energy Transfer

• Nuclear fusion is the way that the sun produces energy. • This reaction converts four hydrogen

nuclei into the nucleus of a helium atom.

Heat is the energy transferred from one object to another because of a difference in the objects’ temperature.

17.2 Energy Transfer

Three methods of energy transfer as heat are conduction, convection, and radiation.

Conduction is the transfer of heat through matter by molecular activity.

Convection is the transfer of heat by mass movement or circulation within a substance.

Energy Transfer as Heat

17.2 Heating the Atmosphere

Electromagnetic Waves

• The sun emits light and heat as well as the ultraviolet rays that cause a suntan.

• These forms of energy are only part of a large array of energy emitted by the sun, called the electromagnetic spectrum.

24.1 Electromagnetic Waves

Electromagnetic radiation includes gamma rays, X-rays, ultraviolet light, visible light, infrared radiation, microwaves, and radio waves.

The electromagnetic spectrum is the arrangement of electromagnetic radiation according to wavelength.

Electromagnetic Spectrum

Electromagnetic Spectrum

17.2 Energy Transfer

• Radiation is the transfer of energy (heat) through space by electromagnetic waves that travel out in all directions.

• Unlike conduction and convection, which need material to travel through, radiant energy can travel through the vacuum of space.

• All objects, at any temperature, emit radiant energy.

What Happens to Solar Radiation?

17.2 Solar Radiation

When radiation strikes an object, there usually are three different results.

1. Some energy is absorbed by the object.

2. Substances, such as water and air, are transparent to certain wavelengths of radiation.

3. Some radiation may bounce off the object without being absorbed or transmitted.

Solar Radiation

What Happens to Solar Radiation?

17.2 Solar Radiation

Absorption• About 50% of the solar energy that strikes the

top of the atmosphere reaches Earth’s surface and is absorbed.

• The greenhouse effect is the heating of Earth’s surface and atmosphere from solar radiation being absorbed and emitted by the atmosphere, mainly by water vapor and carbon dioxide.

What Happens to Solar Radiation?

• In the process of photosynthesis, plants convert radiant energy from the sun into chemical energy in the form of glucose (sugar)

Why Temperatures Vary

17.3 Temperature Controls

• Land heats more rapidly and to higher temperatures than water. Land also cools more rapidly and to lower temperatures than water.