Assuming they were all about the same distance
from us,
Leavitt discovered that brigher ones had longer periods;
in fact, she found that the logarithms of their periods
is directly related to their brightnesses.
Leavitt’s discovery let Harlow Shapley use
the periods
and brightnesses of cepheids to measure the size of our
galaxy, the Milky Way,
and to locate our solar system in the galaxy.
The big debate was whether spiral nebulae were
inside the Milky Way
or were similar in size as the Milky Way but very far away.
This debate was settled when Edwin Hubble
discovered cepheids
in the Andromeda Galaxy, since their periods and
brightnesses
let him determine how far away they were.
Walter Baade was the first to recognize
different types of cepheids,
some younger and brighter, and some older and less bright,
which helped him double Hubble’s estimate for the
size of the universe.
Cepheids
The cepheid stars are named after the star Delta
Cephei
in the constellation Cepheus
identified by John Goodricke in 1784.
Delta Cephei is in the Milky Way
about thirteen hundred light-years from us,
the Milky Way being a hundred thousand light-years in
diameter.
The Milky Way has under four hundred billion
stars.
The observable universe has over ten sextillion stars.
Obviously we don’t have names for them all.
Standard candles
The mind is a candle
that burns over many years, determining
the size, the distance, and the importance
of everything in its narrow scope.
But it’s often wrong.
Unacceptable events disturb it;
contrary evidence confuses it;
self-calibration is difficult.
When a window opens
it flickers in the wind.
Useless in the sunlight;
better than nothing in the dark.
The span between us and the oldest and most distant
observable objects in the universe might be only a fraction of
what lies beyond, unless you assume that no space exists beyond
our cosmic horizon. But even comparing ourselves to the observable
universe, whose edge is perhaps under 47 billion light years from
us, makes us very very small.
The span between us and the oldest and most distant observable objects in the universe might be only a fraction of what lies beyond, unless you assume that no space exists beyond our cosmic horizon. But even comparing ourselves to the observable universe, whose edge is perhaps under 47 billion light years from us, makes us very very small.
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