M31, the great Andromeda Galaxy some two and a half million light-years away. But without a telescope, even this immense spiral galaxy – spanning over 200,000 light years – appears as a faint, nebulous cloud in the constellation Andromeda.

In contrast, details of a bright yellow nucleus and dark winding dust lanes, are revealed in this digital telescopic image. Narrow band image data recording emission from hydrogen atoms, shows off the reddish star-forming regions dotting gorgeous blue spiral arms and young star clusters. While even casual skygazers are now inspired by the knowledge that there are many distant galaxies like M31, astronomers seriously debated this fundamental concept in the 20th century.

via apod