Loop I in the Northern Sky.

One of the largest coherent structures on the sky is known simply as Loop I and can best be seen in radio and X-ray maps. Spanning over 100 degrees, part of Loop I appears so prominent in northern sky maps that it is known as the North Polar Spur (NPS). Loop I, shown above in X-ray light , is a thin bubble of gas about 700 light-years across with a center located only about 400 light-years away. Surprisingly, the cause of this immense structure is still debated, but is possibly related to expanding gas from a million-year old supernova . Loop I gas is impacting the nearby Aquila Rift molecular cloud , and may create relatively dense fragments of the local interstellar medium . Were our Sun to pass through one of these fragments in the next few million years, it might affect Earth's climate .