Cosmology: The Origin and Evolution of the Universe
Target 2:
I can explain what it means to say that the universe is expanding is.
Key Concepts
1.
The Expansion of the Universe: The Hubble Law describes the continuing expansion of space. The redshifts that we see from distant galaxies are caused by this expansion, not by the motions of galaxies through space.
2.
The redshift of a distant galaxy is a measure of the scale of the universe at the time the galaxy emitted its light.
3.
It is meaningless to speak of an edge or center to the universe or what lies beyond the universe.
4.
The Cosmological Principle: Cosmological theories are based on the idea that on large scales, the universe looks the same at all locations and in every direction.
1.
What does it mean when astronomers say that we live in an expanding universe? What is actually expanding?
2.
How is the analogy activity of the balloon with galaxies drawn on them NOT correctly representing what is actually happening with the expansion of the universe?
3.
Describe how the expansion of the universe explains Hubble’s Law.
4.
Would it be correct to say that due to the expansion of the universe, Earth is larger today that it was 4.56 billion years ago? Why or why not?
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Cosmology: The Origin and Evolution of the Universe
5.
How does modern cosmology preclude the possibility of either a center or an edge to the universe?
6.
Explain the difference between a Doppler shift and a cosmological shift.
7.
Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest – the one that is furthest or closest? Explain
8.
The host galaxy of supernova HST06Sas has a redshift of z = 1.390. The light from this galaxy includes the Lyman-alpha spectral line of hydrogen, with an unshifted wavelength of 121.6 nm.
Calculate the wavelength at which we detect the Lyman alpha photons from this galaxy.
In what part of the electromagnetic spectrum does this wavelength lie?
9.
Below is a graph representing
Hubble’s law. Notice there are two dashed lines and one solid line. The two dashed lines represent two experimental values for Hubble’s constant and the solid line represents the average. a.
What does the slope of the lines tell us about the expansion rate of the
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Cosmology: The Origin and Evolution of the Universe universe? b.
Predict the distance of a galaxy that has a recessional velocity measured at
30,000 km/s.
Below is a graph of Hubble’s original data and Modern Data. a.
What two quantities did Edwin Hubble plot against each other to discover the expansion of the universe? b.
Why do you think the two graphs below are different?
10.
What is the primary practical difficulty that limits the use of Hubble’s law for measuring distances?
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Cosmology: The Origin and Evolution of the Universe
11.
Suppose 𝐻 𝑜
= 65 km/s/Mpc. How fast would a galaxy located 500 Mpc distant be receding from us?
12.
In the image below the top absorption spectrum represents the absorption spectrum from a distant galaxy. The bottom absorption spectrum represents the absorption lines of a light source in a laboratory. Calculate the redshift of this galaxy.
510
530
What is the look back time for this galaxy?
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Cosmology: The Origin and Evolution of the Universe
13.
What is the cosmological principle? Use the boxes below to draw a diagram representing a concept of the cosmological principle correctly and incorrectly.
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