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The Sun

The Sun is the closest star to Earth and is the center of our solar system. A giant, spinning ball of very hot gas, the Sun is fueled by nuclear fusion reactions. The light from the Sun heats our planet and makes life possible. The Sun is also an active star that displays sunspots, solar flares, erupting prominences, and coronal mass ejections. These phenomena, which are all related to the Sun's magnetic field, impact our near-Earth space environment and determine our "space weather". In about five billion years, the Sun will evolve into a Red Giant, and eventually, a White Dwarf star. Many cultures have had interesting myths about the Sun, in recognition of its importance to life on Earth.
The outermost layer of the <a href="/sun/solar_atmosphere.html">Sun's atmosphere</a> is the <a href="/sun/atmosphere/corona.html">corona</a>.  The corona is very, very hot - about 1 million degrees!  Glowing <a href="/sun/Solar_interior/Sun_layers/Core/plasma_state.html">plasma</a>, which is like magnetized gas, sometimes forms loops in the corona. <a href="/sun/atmosphere/sunspot_magnetism.html">Magnetic fields around sunspots</a> make these loops, called coronal loops. The loops are huge - about 30 Earths would fit across them! A satellite named TRACE took this picture in November 1999.<p><small><em>Image courtesy of NASA/Trace Mission</em></small></p>The "surface" of the Sun (the <a href="/sun/atmosphere/photosphere.html">photosphere</a>) is covered with a "granulation pattern" caused by the convective flow of heat rising to the photosphere from the <a href="http://www.windows2universe.org/sun/solar_interior_new.html">Sun's interior</a>. The granulation pattern is similar to what you see when you look at the top of a pot of boiling oatmeal. Note how the hotter centers of granules bulge upward, while the cooler edges are sinking downward.<p><small><em> Image courtesy of Goran Scharmer and Mats G. Löfdahl of the Royal Swedish Academy of Sciences</em></small></p>Astronomers use different wavelengths of light and other <a href="/physical_science/magnetism/em_radiation.html">electromagnetic emissions</a> as <a href="/sun/spectrum/multispectral_sun.html">"windows" into different regions of the Sun</a>. White light with a <a href="/physical_science/basic_tools/wavelength.html">wavelength</a> between 400 and 700 nanometers (nm) shows the <a href="/sun/atmosphere/photosphere.html">photosphere</a>, the visible "surface" of the Sun. Other wavelengths highlight different features of the Sun, such as its <a href="/sun/sun_magnetic_field.html">magnetic field</a>, the <a href="/sun/atmosphere/chromosphere.html">chromosphere</a> and the <a href="http://www.windows2universe.org/sun/atmosphere/corona.html">corona</a>.<p><small><em>Composite image courtesy of Windows to the Universe using images from SOHO (NASA and ESA), NCAR/HAO/MLSO, Big Bear Solar Observatory, and SDO/AIA.</em></small></p>On 21 April, 2010, the Solar Dynamics Observatory captured the launch of a filament from the <a href="/sun/atmosphere/photosphere.html">surface of the Sun</a>.  These are the most detailed images of the Sun ever taken.  The images show light in the <a href="/physical_science/magnetism/em_ultraviolet.html">ultraviolet</a> part of the <a href="/physical_science/magnetism/em_spectrum.html">electromagnetic spectrum</a>.  The Sun is now entering another period of <a href="/sun/solar_activity.html">solar activity</a> after several years of a relatively quiet Sun.  Activity on the Sun varies on an <a href="/sun/activity/sunspot_cycle.html">cycle of about 11 years</a>.<p><small><em>Image courtesy of NASA/Solar Dynamics Observatory and AIA Consortium</em></small></p>Sunspots don't look that big when you see them on the Sun (remember NEVER look directly at the Sun), but in fact they can be enormous!  This composite image shows just how big sunspots can be, to scale with an image of Earth.  Sunspots can be as big, or bigger, than Earth.  The <a href="/sun/activity/sunspot_history.html">earliest written record of a sunspot observation</a> was made by Chinese astronomers around 800 B.C.<p><small><em>Image courtesy of Windows to the Universe using images from the Royal Swedish Academy of Sciences (sunspot image) and NASA (Earth image).</em></small></p>For the Aztecs, who lived in central Mexico, <a href="/mythology/tonatiuh.html">Tonatiuh</a> was a <a href="/sun/sun.html">Sun</a> god. Aztecs believed that four suns had been created in four previous ages, and all of them had died at the end of each cosmic era. Tonatiuh was the fifth sun and the present era is still his. The carvings on this sunstone represent the four cycles of creation and destruction in the Aztec creation story. The skull at the center depicts the god Tonatiuh.<p><small><em>   Image courtesy of Corel Corporation.</em></small></p>

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF