Written and compiled by Fred Jaicks.
The Sun: Introduction
The sun is a star at the center of the solar system around which all local planets orbit. It is made mainly of the gasses hydrogen and helium, with hydrogen taking up about 70% of its mass and helium 28%. A sphere about 864,000 miles in diameter, the sun has a total mass equivalent to just fewer than 333,000 Earths. It is approximately 4.5 billion years old. Although certainly no infant, the sun is still fairly young compared to the age of the universe, which is estimated at 13 billion years. The sun maintains an average distance of 92 million miles from the Earth, and burns at a temperature of about 11,000 degrees Fahrenheit. At the core, temperatures are far hotter.
The Sun, a Most Familiar Star
The sun is classified by scientists as a yellow dwarf star. Such stars burn at 9,080 – 10,340 degrees Fahrenheit, produce energy through nuclear fusion reactions between helium and hydrogen in their cores, and last an average of ten billion years before their gaseous “fuel” runs out. The Earth’s sun has entered a period called the “main sequence,” indicating that it is about “middle-aged.” Near the end of its lifecycle, it will balloon into a vast red giant star before collapsing into a super-dense white dwarf. The sun has four distinct layers, each with unique properties. At the center is the core, a dense, superheated region that takes up about a quarter of the sun’s interior radius. The photosphere is the visible surface of the sun, the source of most of the sun’s infrared, ultraviolet, and visible light. These are all forms of electromagnetic radiation, some rendered visible and others invisible by their wavelengths. Above the photosphere are the chromosphere and the corona, the latter visible only during a solar eclipse.
The Sun’s “Weather”: Sunspots and Eclipses
Sunspots are regions on the surface of the sun that burn thousands of degrees cooler than their surroundings. Because of the difference in temperature, they appear dark and can often be seen with the unassisted eye. They are formed by complex “magnetic storms” on the sun, and can be as large as 50,000 miles in diameter or more. Sunspots were known to ancient astronomers, but their nature still holds many mysteries. By contrast, eclipses are well understood. The most famous kind of eclipse is the total solar eclipse, which takes place when the moon’s inner shadow passes between Earth and the sun, obscuring the entire sun. An eclipse is only “total” from the perspective of onlookers on a small portion of the Earth when it happens, determined by the orbits of the bodies involved. Eclipses can also be “partial.” This is when the moon only partially obscures the view of the sun. In either case, eclipses last only a short time. The time between total eclipses that are visible as such from any one spot on Earth can be many hundreds of years.
Dangers of the Sun and Precautions
Unprotected exposure to the sun can lead to burns, premature aging of skin, and other complications. The sun’s ultraviolet radiation is considered a major factor in many kinds of cancer, especially skin cancer. Viewing the sun with the naked eye, even under eclipse conditions, can cause serious eye damage. When prolonged exposure to the sun is expected, use protective clothing, including hats. Waterproof sunscreen should be applied to reduce exposure to harmful radiation. Whenever possible, wear sunglasses in daylight to reduce eye strain. When viewing the sun through a telescope or during an eclipse, proper equipment should be used to shield the eyes from directly viewing any part of the surface. Special filters can be attached to telescopes for viewing the sun at various times.
The sun is the star at the center of our solar system. A massive ball of helium and hydrogen, it is a nuclear fusion furnace over 4.5 billion years old and with at least as long to go. Though fairly “typical” of yellow dwarf stars, it offers amazing phenomena like sunspots and eclipses, and provides the Earth with an incredible amount of light and energy. Without it, we wouldn’t be able to survive. Though the sun has its dangers, it is better understood now than any time before. See the links that follow for more information on the sun.
Earth Science Links: Some great pages on the sun, plate tectonics and other topics.
The Sun: Information and statistics on the sun and its satellites, the planets.
Sunspots: History of and information on sunspots.
Sun Safety: Tips, risk assessment, and info on dangerous solar radiation.
Stanford Solar Center: Great information on the sun and solar phenomena.
The Sun: Visible Light: Illustrated guide to the sun’s visible and invisible radiation.
TRACE Online: Imagery and information from NASA’s Transition Region and Corona Explorer satellite mission.
Solar Background: Information on the sunspot cycle and galactic magnetism.
Solar Eclipse: How to View: Information on safe eclipse-watching.
Helioseismology: An introduction to the science of studying the sun by its vibrations and “sounds.”