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A close cropping of spiral galaxy M101 shows an array of stunning details have never been seen before in this galaxy. Due to the high sensitivity and fine resolution of Hubble's Advanced Camera for Surveys (ACS), individual dust lanes in the spiral arms are as clearly visible as  rivers flowing through a mountain range here on Earth taken from an aerial photo. Bright, hot regions that are areas of active star formation also dot the spiral arms, akin to ground photos of the bright lights of major cities when photographed at night.

Several bright stars appear in this small section of M101 (also known as the Pinwheel Galaxy).  They are in our own galaxy, superimposed in the line of sight and appear much brighter than the stars within M101 because they are so much closer.  So too, a background spiral galaxy, millions of light-years behind M101, appears between two spiral arms.

The bright nucleus of M101 just off to the upper left appears brighter and redder than the rest of the galaxy seen in the image. Stars near the halo that surround the nucleus are older and redder compared to the blue, young, hot stars that delineate the spiral arms and populate the metropolitan-style star-forming regions.

M101 lies in the direction of the constellation Ursa Major, at a distance of 25 million light-years from Earth.  This image is a portion of the of a much larger mosaic of M101, created by combining Hubble data with ground-based images of the galaxy where Hubble data is not available. This cropping contains only Hubble ACS data from blue, green and infrared filters taken in November 2002.

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: K.D. Kuntz (GSFC/JHU)