Explanation:
One of the brightest galaxies in planet Earth's sky and similar in size
to the Milky
Way, big, beautiful spiral M81
lies 11.8 million light-years away in the northern constellation
Ursa Major.
This
deep image of the region reveals
details in the bright yellow core, but at the
same time follows fainter features along the galaxy's gorgeous blue
spiral arms and sweeping dust lanes.
It also follows the expansive, arcing feature, known
as Arp's loop, that seems to rise from the galaxy's disk at the right.
Studied in the 1960s, Arp's loop has been thought to be a
tidal tail,
material pulled out of M81 by gravitational interaction with its large
neighboring galaxy M82.
But a recent investigation
demonstrates that much of Arp's loop likely lies within our own galaxy.
The loop's colors in visible and
infrared light
match the colors of pervasive
clouds of dust, relatively
unexplored
galactic cirrus
only a few hundred light-years above the plane of the Milky Way.
Along with the Milky Way's stars, the dust clouds lie in
the foreground of this remarkable view.
M81's dwarf companion galaxy,
Holmberg IX,
can be seen just above and left of the large spiral.
On the sky, this image spans about 0.5 degrees,
about the size of the Full Moon.
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