A combination of factors caused this beautiful solar prominence, an eruption of hydrogen gas, that NASA recorded in ultraviolet light
The sun has a strong but uneven magnetic field. The stronger magnetic areas are visible as sunspots, which are surrounded by closely spaced magnetic field lines. Strung along these field lines is a cloud of gas cooler than the surface of the sun. That gas appears darker than what's in the background, as loops on the sun's surface.
When observed on the sun's edge, against the darker background of space, these loops are called solar prominences, visible in the mesmerizing video below. Read more...
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