Classroom Aid - Hubble's Law
Summary
TLDRIn 1923, Hubble discovered that Andromeda was a galaxy, leading to the understanding that spiral and elliptical nebulae were galaxies too. He mapped their radial velocities against their distances, finding a linear relationship between a galaxy's velocity and distance, known as Hubble's Law. This law, with its Hubble constant, allows us to measure cosmic distances and infer the universe's age, currently estimated at 13.4 billion years.
Takeaways
- 🌌 In 1923, Hubble discovered that Andromeda was a galaxy, not just a nebula, and was over 2 million light years away from the Milky Way.
- 🔭 Hubble's subsequent studies revealed that other spiral and elliptical nebulae were also galaxies.
- 📊 Hubble mapped the radial velocity of galaxies against their distance from Earth, observing a correlation between the two.
- 🌀 He found that galaxies were moving away from us, with the velocity of recession increasing with distance.
- 📉 The spectra of galaxies were predominantly redshifted, indicating their motion away from us.
- ⚖️ Hubble's Law was established, showing a linear relationship between a galaxy's recession velocity and its distance from us.
- 🔑 The Hubble constant was introduced, a key value in determining the distance of galaxies based on their redshift.
- 🔍 The accuracy of distance measurements in astronomy and cosmology hinges on the precise value of the Hubble constant.
- 📈 Over time, the Hubble constant has been refined, with the current best value being 22.4 kilometers per second per million light years.
- 🌠 The Hubble flow describes the steady movement of galaxies away from each other, implying an expanding universe.
- 🕰 By using the Hubble constant, the age of the universe can be estimated to be around 13.4 billion years.
- 🔮 Modern cosmology recognizes that the Hubble constant is not truly constant and refers to it as the Hubble parameter, which provides a slightly older universe age of about 13.8 billion years.
Q & A
What significant discovery did Hubble make about Andromeda in 1923?
-Hubble discovered that Andromeda was not just a nebula but an entire galaxy, over 2 million light years away from our own Milky Way.
What did Hubble observe about other spiral and elliptical nebulae after his study of Andromeda?
-Hubble found that other spiral and elliptical nebulae were also galaxies, not just part of the Milky Way.
What method did Hubble use to determine the radial velocity of galaxies?
-Hubble used the shift in spectral lines to map the radial velocity of galaxies.
What is the relationship between a galaxy's distance and its receding velocity according to Hubble's observations?
-Hubble found a linear relationship where the further away a galaxy is, the faster it is moving away from us.
What is Hubble's Law and how is it used to determine the distance of a galaxy?
-Hubble's Law states that the receding velocity of a galaxy is equal to the Hubble constant times the distance of the galaxy from us. It allows us to calculate the distance of a galaxy if we know its redshift.
What is the Hubble constant and what does it represent?
-The Hubble constant is a value that describes the rate at which galaxies are receding from us. It is used in Hubble's Law to calculate distances in the universe.
What is the current best value for the Hubble constant as mentioned in the script?
-The current best value for the Hubble constant is 22.4 kilometers per second per million light years, with an uncertainty of plus or minus 3.2.
What is the Hubble flow and what does it imply about the universe's past?
-The Hubble flow refers to the steady movement of galaxies away from each other. It implies that in the past, galaxies were closer together, suggesting an expanding universe.
How can the Hubble constant be used to estimate the age of the universe?
-By using the Hubble constant, one can estimate the age of the universe by calculating the time it would take for a galaxy to reach its current distance from us at its current velocity, which is the inverse of the Hubble constant.
What is the estimated age of the universe based on the Hubble constant?
-Using the Hubble constant, the estimated age of the universe is approximately 13.4 billion years.
How has the understanding of the Hubble constant evolved in modern cosmology?
-In modern cosmology, the Hubble constant has been refined and is now referred to as the Hubble parameter. It gives a slightly larger age for the universe, around 13.8 billion years.
Outlines
🔭 Hubble's Discoveries and the Expanding Universe
In 1923, Edwin Hubble identified the v1 c feed variable in the Andromeda galaxy, determining it was an entire galaxy over 2 million light years away. Hubble then studied other spiral and elliptical nebulae, confirming they were also galaxies. By mapping their radial velocities using spectral line shifts against their distances, he discovered that all galaxies, except some nearby ones, were moving away from us. This led to the revelation that the further a galaxy is, the faster it recedes, establishing a linear relationship known as Hubble's Law. The receding velocity of a galaxy equals the Hubble constant times its distance from us. This law provided a new method to measure cosmic distances using redshift. The current best value for the Hubble constant is 22.4 kilometers per second per million light years. This steady movement of galaxies away from us, known as the Hubble flow, suggests that galaxies were closer together in the past, indicating an age for the universe of approximately 13.4 billion years.
🌌 The Hubble Parameter and the Age of the Universe
In modern cosmology, the Hubble constant is referred to as the Hubble parameter. This parameter provides a slightly larger estimate for the age of the universe, around 13.8 billion years. The adjustment accounts for variations in the Hubble constant over large timescales and distances, refining our understanding of the universe's history and expansion.
Mindmap
Keywords
💡Andromeda
💡Galaxy
💡Radial Velocity
💡Spectral Lines
💡Virgo Supercluster
💡Redshift
💡Hubble Constant
💡Hubble's Law
💡Type 1a Supernova
💡Cosmic Distance Ladder
💡Hubble Flow
💡Age of the Universe
Highlights
In 1923, Hubble discovered that Andromeda was a separate galaxy, over 2 million light years away from the Milky Way.
Hubble's studies revealed that other spiral and elliptical nebulae were also galaxies.
Hubble mapped the radial velocity of galaxies, determined by the shift in spectral lines, against their distance from us.
Galaxies were found to be moving away from us, with velocity proportional to their distance - Hubble's Law.
The Hubble constant, representing the proportionality between a galaxy's velocity and distance, was introduced.
The Hubble constant is a key number in astronomy and cosmology, crucial for measuring cosmic distances.
The current best value for the Hubble constant is 22.4 kilometers per second per million light years.
Hubble's Law allows us to determine a galaxy's distance by measuring its redshift.
The Hubble flow describes the steady movement of galaxies away from each other over time.
The Hubble constant can be used to estimate the age of the universe at 13.4 billion years.
In modern cosmology, the Hubble constant is referred to as the Hubble parameter, providing a slightly larger universe age of 13.8 billion years.
NGC 1068, a galaxy 35 million light years away, is receding at 784 kilometers per second.
NGC 3949, located 50 million light years away, is receding at 1,120 kilometers per second.
NGC 4414, studied by the Key Project, is 62 million light years away and receding at 136 kilometers per second.
NGC 4319, with both Cepheid variables and Type Ia supernova, is 80 million light years away and receding at 1,792 kilometers per second.
NGC 1309, another galaxy with Cepheid variables and Type Ia supernova, is 100 million light years away and receding at 2,244 kilometers per second.
Transcripts
in 1923
after finding the v1 c feed variable in
andromeda
and determining that andromeda was an
entire galaxy
over 2 million light years from our own
hubble turned his sights
on other spiral and elliptical nebula
and found
that they were galaxies as well
in his studies of these galaxies he
mapped
their radial velocity as determined by
the shift in spectral lines
against their distance from us he found
what we see here in the virgo
supercluster
ngc 1068 is 35 million light years away
and receding at 784 kilometers per
second
ngc 3949 is 50 million light years away
and receding at 1 120
kilometers per second
ngc 4414 a galaxy studied by the key
project on
extragalactic distance scales is 62
million light years away
and receding at 1 36 kilometers per
second
ngc 4319 a galaxy with both
seafield variables and type 1a supernova
is 80 million light years away and
receding
at 1 792
kilometers per second
and ngc 1309 also a galaxy with both c
field variables and type 1a supernova is
100 million light years away
and receding at 2 244 kilometers per
second
hubble found that except for a few
nearby local group galaxies
all the spectra shifts were to the red
all the galaxies were moving away from
us
and more than that he found that the
further away from us they are
the faster they are moving away from us
and even more than that he found that
the relationship between velocity
and distance is linear the graph is a
straight line
the equation is simple the receding
velocity of a galaxy
is equal to the slope of the line a
constant
times the distance the galaxy is away
from us
today that constant is known as the
hubble constant
and the equation is known as hubble's
law
if we measure the redshift of a galaxy
we can determine its receding velocity
and knowing its receding velocity this
equation tells us how far away it is
this gives us a new rung on our cosmic
distance ladder
called redshift the accuracy of this
rung
depends entirely on the value of the
hubble constant
that's why it's one of the most studied
numbers in astronomy
and cosmology
this constant has been refined over time
and the distance is used to see how far
it holds
has increased by orders of magnitude
with our modern ability to determine
distances
with space telescopes like hubble
analyzing type 1a supernova
out to billions of light years the box
at the lower left shows the region
that hubble probed
the current best value for the hubble
constant using this approach
is 22.4 kilometers per second
per million light years plus or minus
3.2
that's around 13 miles per second per
million light years
that is a receding velocity of a galaxy
goes up
by 22.4 kilometers per second
for each additional million light years
away from us
it is this slow and steady movement of
galaxies away from us
is called the hubble flow
this hubble flow where galaxies are
getting further away with time
also implies that in the past they were
closer together
it follows that we can ask how long
would it take a galaxy to reach its
current distance from us
given its current velocity that's simply
the distance divided by the velocity
or one over the hubble constant
13.4 billion years
that's the age of the universe
we'll see later in our chapter on the
cosmos
that the hubble constant turned out to
not be constant over large enough times
and distances
in modern cosmology it is called the
hubble parameter
and it gives us a slightly larger age
for the universe
around 13.8 billion years
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