Discussion - OpenStax Chapter 24 and 26.5, 28.4 and 29.1 Topics
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Discussion - OpenStax Chapter 24 and
26.5, 28.4 and 29.1 Topics
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22 replies.
For this Discussion, please address
three
things that you found most
interesting in Chapter 24 and Chapter Sections 26.5, 28.4 and 29.1 of our
OpenStax Astronomy textbook. You should frame your discussion of the
topics you choose as if you are explaining them to someone that has not
read the chapter and may not have much background knowledge on either
topic.
Discussion Board Post DUE by Wednesday, November 29th, before
11:59pm. (6 points)
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the due date above.
Discussion Board Comments DUE by Friday, December 1st, before
11:59pm. (2 points)
A few important things:
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Chapter 24
Gravitational redshift
Gravitational redshift is a phenomenon that happens when light waves or photons travel out of a
region with strong gravity. This causes the waves to lose energy, resulting in a decrease in wave
frequency and an increase in wavelength. It's called a redshift. We can observe this phenomenon
in the solar system, the sun, white dwarfs, and GPS satellites. Scientists have a few different
explanations for gravitational redshift, including the equivalence principle, mass-energy
equivalence, and gravitational time dilation. When light emerges from a region with strong
gravity where time slows down, it changes frequency and wavelength. To understand this
phenomenon, we need to know that a light wave is like a little clock. Each crest follows the other
at a regular pace. If stronger gravity slows down time, the rate at which crests follow each other
slows down too. This means the frequency of light waves decreases.
Sections 26.5
Hubble's Law
Hubble's Law is an observation in physical cosmology that suggests that galaxies are moving
away from Earth with a speed that is directly proportional to their distance. In simpler terms, the
farther a galaxy is, the faster it's moving away from Earth. The Hubble flow is the motion of
astronomical objects due to this expansion. This law is considered the first observational basis
for the expansion of the universe, and it supports the Big Bang model. The law is described by
the equation D = H0 × v, where D is the proper distance to a galaxy, v is its velocity, and H0 is
the Hubble constant. The Hubble constant is the constant of proportionality between the proper
distance to a galaxy and its speed of separation. The velocity of the galaxies has been determined
by their redshift, which is the shift of the light they emit toward the red end of the visible
spectrum. The Hubble constant is most frequently quoted in km/s/Mpc, giving the speed in km/s
of a galaxy 1 megaparsec (3.09 km) away, and its value is about 70 (km/s)/Mpc. Sections 28.4
Sections 29.1
Universal Acceleration
In 1998, two independent projects discovered that the universe is expanding at an increasing rate.
They used type Ia supernovae, which are nearly identical in brightness, to measure the
acceleration. The farther away an object is, the faster it is receding, according to the Hubble law.
Astronomers showed that type Ia supernovae are standard bulbs that can be used to measure
distance and motion independently. These supernovae occur when a white dwarf accretes enough
material from a companion star to exceed the Chandrasekhar limit and then collapses and
explodes. At maximum brightness, they can briefly outshine the galaxies that host them, and
hence, they can be observed at very large distances. The researchers found that these type Ia
supernovae in distant galaxies were fainter than expected from Hubble's law, given the measured
redshifts of their host galaxies. This discovery received the 2011 Nobel Prize in Physics.
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