APOD: 2005 December 22 - Andromeda Island Universe (original) (raw)

Astronomy Picture of the Day

Discover the cosmos!Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2005 December 22

Andromeda Island Universe
Credit & Copyright: Robert Gendler

Explanation: The most distant object easily visible to the unaided eye isM31, the greatAndromeda Galaxysome two 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 theconstellation Andromeda. In contrast, a bright yellow nucleus, dark winding dust lanes, gorgeous blue spiral arms and star clusters are recorded in this stunningtelescopic digital mosaic with a cumulative exposure of over 90 hours. While even casualskygazersare now inspired by the knowledge that there aremany distant galaxies like M31, astronomersseriously debatedthis fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famousShapley-Curtis debateof 1920, which was later resolved byobservations of M31 in favor of Andromeda,island universe.

Tomorrow's picture: dusty red rose

Authors & editors: Robert Nemiroff(MTU) &Jerry Bonnell(USRA)
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& Michigan Tech. U.