THE COMPLETE COSMOS Chapter 1: The Sun Birth, life and death of the Sun. Interior dynamics, exterior fireworks. Sunspots, corona, solar wind - latest on our local star. Outline Triggered by the death of a giant star, the birth of the Sun and planets. To the Sun's core, where energy is produced by nuclear fusion. The journey of this energy from the core to the solar surface - and across space to Earth. The Sun as the ultimate source of energy for our planet. Layer by layer, the Sun's structure: first, the yellow photosphere with its sunspots, next the fiery red chromosphere with its prominences, and finally the million-degree corona, the Sun's outer atmosphere. The key influence of the Sun's magnetic field. Much of the information in this section is from the spacecraft SOHO, the Solar Heliospheric Observatory. At the end of the chapter, the death of the Sun. Initially, it becomes a bloated red giant engulfing Mercury, Venus and Earth. Then, the Sun puffs off its outer layers to reveal the white hot core which collapses to a white dwarf, finally cooling to become a dark relic of a star. Sub-chapters A Star Is Born • Our view of the Sun - now and in the past. The Sun as a star. A basic description of its functions. The mechanics of the Sun's birth and the formation of the planets. A brief tour of the Solar System. • How the Sun is the source of most of the Earth's energy resources, particularly fossil fuels. Core to Surface • Internal composition of the Sun. How mass is transformed into energy in the Sun's core and how this energy travels to the Earth. • How the solar spectrum reveals the chemical composition of the Sun. • The temperature and overall physical appearance of the photosphere. The Magnetic Sun • Sunspots and the Sun's magnetic field. The 11-year solar cycle and magnetic reversals. • Differential rotation of the Sun. Solar Eruptions • The chromosphere, prominences and flares. • The overall physical appearance of the chromosphere. • Prominences - arcs of gas looping around magnetic field lines. • Violent flares blasting ripples across the face of the Sun. • Description of the corona, the Sun's outer atmosphere, visible during a total eclipse. • Great ejections from the corona. Reasons for the corona's varying appearance and activity. Observations by the spacecraft SOHO. The solar wind, a stream of electrified particles continuously emitted by the Sun. Secrets of the Sun • The mystery of why the corona is so hot. • Investigations of the Sun by SOHO. SOHO's revelations of the Sun internal behavior. Death of the Sun • Explanation of why the Sun will one day expire. The various stages of its death and the effects on the inner planets. Background Nuclear Fusion The Sun’s energy is generated by nuclear fusion. At very high temperatures, in the hearts of stars like our Sun, the nuclei of small atoms are fused together to make the nuclei of larger ones. Deep inside the Sun’s core, a “fusion reactor” has been in continuous operation since firing up some five billion years ago. But what is nuclear fusion? It works like this: Two hydrogen nuclei combine to release a flash of energy and a positron - a positively-charged electron - and a strange particle called a neutrino. A third hydrogen nucleus joins the combined pair. Instantly, there’s another flash of energy. Like magic the trio has become helium-three. Then, by fusing again with an identical trio, they become - in a flash - helium-four. They emit the two extra hydrogen nuclei - and more energy. The mass of the helium-four nucleus is 0.7 percent less than the combined mass of the four component hydrogen nuclei from which it is assembled. It is this small percentage loss of mass that is converted into energy. Once formed, the helium-four nuclei remain stable because the temperature within the Sun’s core is currently too low for the next stage of thermonuclear fusion, involving carbon nuclei, to take place. In this way, within the core of the Sun, 600-million tons of hydrogen are converted into 596 million tons of helium every second. As a by-product, the “missing” four-million tons of mass is turned into energy every single second. It is this non-stop process that makes our Sun a star - and will keep it blazing for the next five billion years. Albert Einstein first came up with the idea that mass is a form of energy. His celebrated equation E = mc2 describes mathematically this conversion of mass to energy. The amount of energy (E) released by the conversion of a mass (m) is equal to m multiplied by the speed of light (c) squared. Since c is a large number, a very large amount of energy can be released by the conversion of quite small quantities of mass. The Sun as an Energy Source The Sun is the ultimate source of most of the Earth's energy resources. Without the Sun's energy reaching Earth through space, there would be no plant or animal life on our planet. It is the Sun's energy, stored by plants and tiny organisms that lived on the Earth millions of years ago, which is released when we burn fossil fuels such as coal, oil and natural gas. Solar power is an example of a renewable energy source; unlike fossil fuels it will not run out. The Sun's energy, in the form of sunlight, may be harnessed directly to heat water, produce electricity by using solar cells, or by employing mirrors to focus the Sun's rays in a solar furnace. Fossil fuels, however, can only be burnt once and they are not recyclable. The gases produced from burning fossil fuels are responsible, in part, for the pollution of the Earth's atmosphere. The energy of most alternative energy sources, such as wind and wave power, also comes from the Sun. As the Sun warms the Earth, it creates winds. The wind's kinetic energy can be converted into electrical energy by a windmill or wind turbine. Some of the wind's energy disturbs the surface of the sea and creates waves. Wave-power can also be used to generate electricity. The Solar Cycle In 1843, the German astronomer Heinrich Schwabe discovered that the number of sunspots visible on the Sun's face periodically varies. At a maximum in the cycle, over 100 sunspots may be present, but towards solar minimum the number falls considerably. During this period there may be several weeks with no spots visible at all. On average, the sunspot cycle lasts 11 years, but there are considerable variations. Since records began, the length of individual cycles has varied from approximately seven to14 years. In 1893, at the Royal Greenwich Observatory, in England, E.W Maunder concluded from his study of old solar records that between 1645 and 1715 sunspots virtually disappeared – a period known as the "Maunder Minimum." This period coincided with a marked cooling of the Earth's climate. The polar ice sheets and glaciers advanced farther than at any time since the last ice age. In London, winter "Frost Fairs" were celebrated on the frozen River Thames. The period from 1645 to 1715 was called "The Little Ice Age." At the end of each 11-year cycle, when few or no spots are visible, the Sun's magnetic field reverses its polarity. A duration of 22 years, therefore, elapses before the Sun returns to its original magnetic pattern. Roughly midway between magnetic reversals, the Sun is at magnetic maximum: this is when the greatest number of sunspots are evident. Links for Further Information A comprehensive index of site providing images of the Sun. http://sec.noaa.gov/solar_sites.html/ SOHO mission homepage, including picture gallery, resources for teachers, latest images and recent news. http://sohoww.nascom.nasa.gov/ Educational site aimed at school students containing general topics of interest about the Sun. http://solar-center.stanford.edu/ Selection of soft X-ray images of the Sun acquired by the YOHKOH satellite. http://www.lmsal.com/SXT/homepage.html/ General introduction to solar astronomy from a set of lecture notes, including a general description of the Sun and discussion of solar phenomena. http://www-solar.dcs.st-andrews.ac.uk/"alan/sun_course/Introduction/Main_menu/ Very recent full-disc hydrogen alpha images of the Sun - up to three per day – acquired at the Culgoora Solar Observatory in Australia. http://www.ips.oz.au/culgoora/index.html/ Daily solar images - by high resolution and full-disc - and movies of solar phenomena acquired at Big Bear Solar Observatory. http://www.bbso.njit.edu/ Current and archive pictures of full-disc solar images acquired at The National Solar Observatory, Sacramento Peak. http://www.sunspot.noao.edu/ Questions and Activities for the Curious 1. Calculate the Sun's diameter (1,392,000 kilometers), in terms of the Earth's diameter, which is 12,756 kilometers. Find the volume of both the Sun and the Earth, and then give the Sun's volume in terms of Earth's. 2. Investigate at least three ways in which the Sun directly affects Earth. 3. A spectroscope is an instrument used by astronomers to examine the Sun's spectrum. What information can be deduced by using such instrument? 4. The gas helium was identified in the spectrum of the Sun before being found on Earth. Research what other elements have been identified in the Sun's spectrum. 5. What visible features occur on the Sun's surface? 6.