Solar prominences are large, glowing clouds of gas suspended in the magnetic field loops above the Sun's photosphere. Prominences are typically huge- several times larger than Earth. Graceful prominences like this one last for several days; more violent eruptive prominences only last a few hours.
Prominences are part of the solar activity cycle. The hot gas that comprises the Sun is magnetized. As the Sun rotates the heat of its interior churns its subsurface layer in great bubbles. The magnetic field becomes increasingly tangled and large magnetic loops burst through the Sun's photosphere and into its atmosphere. The hottest areas appear almost white, while the darker red areas are cooler by comparison (still very, very hot- over 100,000 degrees Fahrenheit!)
This next picture is an animation of the sun's activity taken over six days, starting June 27, 2005. You can see how the prominences erupt and subside as part of the solar cycle.
Just how big is our sun?
It would take over 1 million earth-sized marbles to fill up a fish bowl as large as the sun : ) This still leaves empty space between the 'marbles'. If we crushed up the earth-sized marbles so there were no empty spaces between, it would take 1.3 million of them to match the volume of the sun.
A sun spot- notice the grandular surface of the sun. The surface of the sun is anything but flat. The height of the structures has been estimated to be between 200 and 450 km (approx. 150 - 300 miles high)
Detailed closeup of magnetic structures on the Sun's surface, seen in the H-alpha wavelength on August 22, 2003.
Cooling down a bit... the planet Venus is seen by NASA's TRACE satellite, at the start of its transit across the sun on June 8, 2004.
The total solar eclipse of February 16, 1980 was photographed from Palem, India, by a research team from the High Altitude Observatory of the National Center for Atmospheric Research.
A transit of the Moon across the face of the Sun on February 25, 2007 - but not seen from Earth. This sight was visible only from the STEREO-B spacecraft in its orbit about the sun, trailing behind the Earth. NASA's STEREO mission consists of two spacecraft launched in October, 2006 to study solar storms. STEREO-B is currently about 1 million miles from the Earth, 4.4 times farther away from the Moon than we are on Earth. As the result, the Moon appears 4.4 times smaller than what we are used to.
Our sun at rest... the Sun is now in the quietest phase of its 11-year activity cycle, the solar minimum - in fact, it has been unusually quiet this year - with over 200 days so far with no observed sunspots. The solar wind has also dropped to its lowest levels in 50 years.