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Credit & Copyright: Courtesy
Carnegie Institution for Science
Explanation:
How big is our universe?
This very question,
among others,
was debated by two leading astronomers 100 years ago today in what has become known
as
astronomy's Great
Debate.
Many astronomers then believed that our
Milky Way Galaxy was the entire universe.
Many others, though, believed that our galaxy was just
one of many.
In the
Great Debate,
each argument was detailed, but no consensus was reached.
The answer came over three years later with the detected variation
of single spot in the
Andromeda Nebula, as shown on the
original glass discovery plate digitally reproduced here.
When Edwin Hubble
compared images, he noticed that this
spot varied, and so wrote "VAR!" on the plate.
The best explanation, Hubble knew, was that this spot was the
image of a variable star that was very far away.
So M31 was really the
Andromeda Galaxy --
a galaxy possibly similar to our own.
The
featured image
may not be pretty, but the variable spot on it
opened a door
through which humanity gazed knowingly, for the first time, into a
surprisingly vast cosmos.
Centennial Celebration:
Astronomy's Great Debate
was
100 Years Ago Today
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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