SUN
(Naato'si)
Image Credit: NASA/SDO
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FORMATION Approximately 4.5 billion years ago, an enormous cloud of Hydrogen and Helium collapsed under its own gravity, forming a nearly perfect ball. The gravity from this immense mass produced enough heat and pressure to initiate nuclear fusion of Hydrogen into Helium. Nuclear fusion produces an enormous amount of energy in the form of heat and light radiating into space. The vast cloud became a star, our Sun. Astronomers believe that nearly all stars are formed in this manner.
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OBSERVING THE SUN: Safety is critically important when observing the Sun. Never attempt to observe the Sun with unprotected eyes, or with equipment that is not designed and rated for solar observation. Also, never use binoculars or telescopes while wearing “Eclipse Glasses”. Glasses like these are intended for direct observation of the Sun and they are not safe to use in combination any other optical aid.
Image Credit: Marshall Space Flight Centre/NASA
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STRUCTURE The Sun’s diameter is about 1.4 million km, equal to about 109 Earths. It contains about 99.9% of the mass in the Solar System. It is composed primarily of Hydrogen (73%) and Helium (25%) with traces of other elements like Oxygen, Carbon and Neon. The sun is often described as a ball of gas, but it is actually a fourth state of matter called plasma - an extremely hot “soup” of positively charged protons and free electrons.
The Sun is comprised of several layers. Nuclear fusion occurs in the core, which produces nearly all of the Sun’s energy and occupies about 25% of its radius. The core temperature is about 15 million degrees C. Energy from fusion (primarily in the form of photons) then passes through the radiative zone, a layer that extends outward to about 70% of the Sun’s radius. Within the remaining 30% lies the convective zone, where energy is transmitted mainly by convection cells (or columns) of plasma to the photosphere, the Sun’s surface. The convection cells give the Sun’s surface a mottled granular appearance, somewhat resembling an orange peel. Temperature at the surface is approximately 5500 degrees C. |
The Sun's coronas, during the 2017 total eclipse.
Image credit: GSFC/NASA/Gopalswamy
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Above the photosphere lies the Sun’s atmosphere. It too has several layers, including the corona which is visible during total solar eclipses. The opportunity to observe the solar corona drives a great deal of scientific interest in solar eclipses. The corona is extremely hot, with average temperatures reaching 2 million degrees C. It is much hotter than the photosphere, and no theory completely accounts for its extreme temperature.
The heliosphere comes next. Though it is nearly a vacuum by human standards, it is technically the outer reaches of the Sun’s atmosphere. It is filled with the solar wind (a stream of charged particles from the sun) and extends well beyond the orbit of Neptune. |
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SURFACE FEATURES: The Sun’s overall surface has a granular appearance caused by convection cells. The Sun’s magnetism varies considerably across its surface, giving rise to local features. Sunspots are areas where high concentrations of magnetism lowers the surface temperature, making these areas appear darker. The number of visible sunspots varies on an 11 year cycle, corresponding to increasing and decreasing magnetic activity. In addition, the Sun’s magnetic poles reverse at each 11 year cycle. The next Solar Maximum is expected in the summer of 2025, when the Sun’s surface will be dotted with dozens of sunspots.
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Image Credit: NASA/SDO
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Solar prominences are enormous looping structures that extend far beyond the photosphere. They are often many times larger than the diameter of the Earth. Like sunspots, they are thought to be caused by the Sun’s magnetic activity. Sometimes, the prominence will completely break away from the Sun- a “Coronal Mass Ejection” or CME. If a CME enters interplanetary space, it can travel all the way to the planet Earth, causing a geomagnetic storm. Such events can be extremely damaging to satellites, telecommunications, power transmission lines and electronic devices. The Carrington Event of 1859 is a well-known geomagnetic storm caused by a CME. It reportedly gave powerful shocks to telegraph operators and set telegraph poles on fire. A major geomagnetic storm in 1989 caused power outages throughout most of Quebec and parts of Ontario and the north eastern USA.
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Parker Solar Probe will orbit through the Sun's corona. Image credit: NASA
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MISSIONS: Solar observations from space began with NASA’s Pioneer 6,7,8 and 9 (1959-1968). Orbiting at similar distances to the Earth, these satellites measured the solar wind and magnetism within the heliosphere. Since then, solar probes have been launched by the USSR/Russia, Japan, the European Space Agency and India. The Parker Solar Probe was launched in 2018, and is the closest orbiting mission to date, with parts of its orbit lying within the solar corona.
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