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Credit & Copyright: Robert Gendler
Explanation:
How far can you see?
The most distant object easily visible to the unaided eye is
M31,
the great
Andromeda Galaxy
some two million light-years away.
Without a telescope, even this immense spiral galaxy appears
as an unremarkable, faint, nebulous cloud in the
constellation
Andromeda.
But a bright yellow nucleus, dark winding dustlanes, gorgeous blue
spiral arms and star clusters are recorded in this stunning
telescopic digital
mosaic of the nearby island universe.
While even casual
skygazers
are now inspired by the knowledge that there are
many distant galaxies like M31, astronomers
seriously debated
this 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 famous
Shapley-Curtis
debate
of 1920, which was later resolved by
observations of M31
in favor of Andromeda,
island
universe.
Tomorrow's picture: X-ray Moon, X-ray Star
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NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.
Based on Astronomy Picture
Of the Day
Publications with keywords: universe - Andromeda - spiral galaxy - M 31
Publications with words: universe - Andromeda - spiral galaxy - M 31
See also: