4.5 The Sun's Energy
| Site: | Cowichan Valley School District - Moodle |
| Course: | Science 10 with CSS teacher |
| Book: | 4.5 The Sun's Energy |
| Printed by: | Guest user |
| Date: | Tuesday, 11 February 2025, 11:22 PM |
Description
The Sun's Energy
Introduction
Our Sun is a star. It is not a particularly large star, nor is it considered small. In fact, it's rather ordinary, as far as stars go. It is a yellow dwarf star, and is the closest star to Earth.
While the Sun may not be extraordinary in the category of stars, it is of great importance to us on Earth. The Sun controls our climate and weather, and sustains all life on Earth. Without it, we would not exist.
Scientists study the Sun carefully and closely. From it, they have learned many things about stars in general: their structures and the processes that drive them. In this lesson, we will look at the characteristics of the Sun, and the processes that are involved in generating and distributing the heat that sustains us.
Anatomy of the Sun
The vast majority of all matter in the solar system is contained in the Sun. In fact, the Sun contains over 99.8% of the total mass of our solar system!
We can only observe the outer layers of the sun, known as the solar atmosphere. The solar atmosphere is divided into three distinct layers: the photosphere, the chromosphere, and the corona.
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1. The photosphere.
Though the Sun is made up largely of hydrogen and helium, it also contains many of the same elements found on Earth. The extremely high temperatures on the Sun mean that all those elements are in gaseous form. Because of this, there is not really a solid surface on the Sun, but an atmosphere of varying density. As you move from the outer regions of the atmosphere toward the core, the layers of gas get more and more dense. The layer at which we can no longer see through the gases is known as the visible surface. Though the photosphere is not actually a solid boundary, we often think of it as one. When we talk about the size of the sun, we generally refer to the region surrounded by the photosphere. The temperature range on the photosphere is 4200–5800°C. |
| 2. The chromosphere
There are two transparent layers outside the photosphere known as the chromosphere and the corona. The chromosphere is made up of the gases just outside the photosphere. It is about 2500 km thick. As you move away from the photosphere, the density of the chromosphere decreases; but, strangely enough, the temperature increases. The temperature of the chromosphere ranges from 4200°C near the photosphere, to 9700°C at the outer regions. |
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3. The corona
The outer regions of the chromosphere merge into the outermost layer of the Sun, called the corona. The corona extends millions of kilometres into space, and is extremely hot (millions of degrees). Most of the radiation from this region of the sun is in the form of x-rays and ultraviolet rays. The magnetic fields of the Sun play a role in the high temperatures of the corona, but the exact details remain a mystery. The brightness of the photosphere usually blocks our view of the corona. One exception is during a solar eclipse, when the Moon blocks out the photosphere and allows us a peek at the magnificent corona. For viewing at other times, there are special instruments that use a filter to block light from the photosphere so that the corona can be studied. |
The Sun's Energy Source
The energy of the Sun comes from the solar core. In this central region of the Sun, a nuclear reaction takes place. Nuclear fusion converts hydrogen to helium and generates extremely large amounts of energy. This is the energy source of the stars, and of our Sun.
Over millions of years, this energy is transferred from the solar core, to the outer layers of the solar atmosphere. Once it reaches the outer layers, it is radiated out into space in the form of heat, ultraviolet rays, and x-rays.
Cool (or Hot!) Features of the Sun
Click here for more information on solar weather and the features of the Sun.
Sunspots
On the photosphere, some regions are cooler than others. These regions appear darker and are called sunspots. Sunspots vary in size, and often appear in pairs or groups. The life span of a sunspot can range from a few hours to a few months. The frequency with which sunspots appear, that is how many we can see at one time, changes. This change occurs in a cyclical manner, with a period of about 11 years. When the sunspot cycle is at its maximum, more than 100 sunspots are visible. When the cycle is at its minimum, there may be no sunspots at all. This cyclical behaviour is governed by the changing magnetic fields of the Sun.
Solar Flares
Solar flares occur when magnetic energy is discharged from the Sun's corona. Sudden streams of protons and electrons shoot violently out into space, and have the potential to interfere with power and communications here on Earth.
 In 1989, a solar flare caused a blackout across the province of Quebec that left residents without power for more than nine hours! |
Solar Prominences
A solar prominence is an eruption of gas from the chromosphere in the form of columns. These columns of gas can either shoot straight out from the Sun, or they can remain suspended by the Sun's many magnetic fields, looping back towards the Sun.
Solar Wind
The solar wind is made up of charged particles called plasma - mainly electrons and protons - that escape the Sun's powerful gravity and race across the Solar System.
The solar wind is powerful and is believed to have eroded or stripped away the atmospheres of other planets such as Mercury. Earth's relatively strong magnetic and gravitational fields have preserved its atmosphere from the constant onslaught. Observers near the poles sometimes see beautiful lights in the night sky known as auroras, the result of the solar wind interacting with Earth's magnetic field and atmosphere.
Solar Wind BBC Science Accessed January 31, 2012