Hubble's Law and Age of Universe - Guided Notes
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Jan 9, 2024
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Guided Notes – Hubble’s Law and Age of the Universe
Name:
Leah Walker
These notes cover slides 23 – 36 of
Video Lecture – Galaxies
.
For slides 23 – 36 please type or handwrite notes as you watch the video lecture
and answer the included questions.
Types of Galaxies:
Spiral galaxies
: consists of a flat, rotating disk with spiral arms. It contains young stars, dust, and
gas in a central bulge. The Milky Way is an example of a spiral galaxy..
Barred spiral galaxies
: Galaxies with a bar-like structure connecting the central bulge to spiral
arms are common in the universe.
Elliptical galaxies
: Spherical or oval, old stars dominate. Little dust and gas. Largest, most
massive galaxies.
Lenticular galaxies
: are disk-shaped with a central bulge and halo of old stars. Unlike spiral
galaxies, they lack spiral arms and have little dust and gas.
irregular galaxies:
have no specific shape, with no central bulge or spiral arm structure. They are
believed to have originated from galaxy collisions or gravitational interactions with other
galaxies.
Hubble expansion:
Hubble's Law states that galaxies move away from us at a speed proportional to their distance. This is
known as the Hubble flow, and the proportionality constant is the Hubble constant, usually measured in
km/s/Mpc. The current value is around 70 km/s/Mpc.
Doppler Shift:
The Doppler effect is a change in the frequency of a wave perceived by an observer when a wave source
and the observer are in motion relative to each other. This effect is used to measure the radial velocity of
celestial objects such as stars and galaxies, which refers to the velocity of an object along the observer's
line of sight. The wavelength of light emitted by the object is shifted due to the Doppler effect, which can
be used to calculate the radial velocity.
Test Yourself: Doppler Shift
A star is emitting light with a wavelength of 547 nm. When you observe it you find the light has a
wavelength of 542 nm. Is the star moving towards or away from you?
a) towards
b) away
c) cannot be determined
Your answer:
a) towards
Your Turn: Redshift and Velocity
A spectral line in a galaxy is measured to be 670.493 nm. We know that this line is emitted at 656.285
nm.
a)
What is the galaxy’s redshift?
Your answer: 0.0216
z=λ-λ0/λ0
z=670.493nm−656.286nm/656.286nm
Z=
0.0216
b)
How fast is it going?
Your answer: 6475.68 km/s
v=cz
v=(2.998×10^5 km/s)(0.0216)
V=
6475.68 km/s
Hubble’s Law:
Hubble's law, introduced by Edwin Hubble in 1929, states that the farther a galaxy is from us, the faster it
moves away from us in proportion to its distance. The constant of proportionality is known as Hubble's
constant, currently estimated to be between 67 and 73 km/s per megaparsec.
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Your Turn: Hubble’s Law
For the galaxy in the “Your Turn - Redshift and Velocity”, calculate the distance using Hubble’s Law. Is this
galaxy in the local group or not?
Your answer:
Click or tap here to enter text.
Age of the Universe: