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UNITS IV, VII AND VIII
THIS GOES WITH UNIT IV
THIS GOES WITH UNIT VII
ES 1010 Unit VIII Assignment Worksheet
Part 1: Finding the Distance to Stars Using the Parallax Angle
Instructions:
Read Chapter 15 and Appendix D (pp. 543-545) in the textbook and the background information below.
Answer the three questions at the bottom directly in this lab worksheet.
This NASA web page provides additional explanation:
http://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_info.html
Background:
Stellar Parallax is the apparent shift in the location of a star due to the orbit of the Earth. In other words, the star will appear to be in a different place depending on the line of sight from the Earth. By knowing the diameter of Earth’s orbit and by measuring the angle of apparent shift (the parallax angle), astronomers can calculate the distance to the nearby stars using trigonometry. This method has been used for centuries. The ancient Greeks were able to measure some of the closest stars this way. Today, sophisticated telescopes have greatly enhanced this method. Figure 1 is a graphic from your textbook showing how this works:
Figure 1. Geometry of stellar parallax, (Lutgens, Tabuck, & Tasa, 2014)
Assignment:
For this assignment, you will determine the distance to a star, “HT Cas”, using the method of stellar parallax. Figure 2 and 3 below are photos of HT Case, taken six months apart:
|
Fig. 3. Image of HT Cas taken 12/96 |
When we super-impose these photos, we get the following image (figure 4):
Fig. 4. Composite image of measurements of HT Cas (shown in red) taken six months apart.
You can see that the position of the star appears to have changed over the six-month time period. However, it is actually the angle from which the photos were taken that has changed. During that 6-month period, the Earth moved from one side of the sun to the other.
Using a stellar astrometric catalog, we find that the two stars closest to HT Cas are a distance of 0.01 arcseconds apart. Based on this information, we can estimate that the angle of shift of HT Cas (the parallax angle) to be approximately 0.015 arcseconds apart.
We also know that the radius of the Earth’s orbit is 1.0 A.U. (astronomical units).
Using these two measurements, we can then determine the approximate distance to HT Cas using the following equation:
d= distance to HT Cas
a=radius of the Earth’s orbit
p=parallax angle
1. (10 points) Given the above equation and information provided, about how far away is HT Cas?
a. 133 parsecs
b. 67 parsecs
c. 33 parsecs
d. 0.015 parsecs
Answer (show work):
2. (10 points) Your answer was calculated in parsecs. Given that 1 parsec = 3.2616
light years
, about what is the distance to HT Cas in light years? (Your answer from above in parsecs X 3.2616 light years = The Distance to HT Cas in light years).
a. 0.025 light years
b. 217 light years
c. 434 light years
d. 219 light years
Answer (show work):
Answer:
3. (30 points) Based on your answer, do you think this is a star that we might be able to send a space probe to? Why or why not? Support your answer.
Answer:
Part 2: Using a Hertzsprung-Russell Diagram
Instructions: After reading the Unit VIII lesson, click
here
to access the NASA web page “Stars” and answer the questions using Figure 5 below. You can also copy and paste the web address into your browser:
http://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve/
Background:
Notice that the stars in Figure 5 are not uniformly distributed. Rather, about 90 percent of all stars fall along a band that runs from the upper-left corner to the lower-right corner of the H-R diagram. These “ordinary” stars are called main-sequence stars. As you can see in Figure 5, the hottest main-sequence stars are intrinsically the brightest, and, conversely, the coolest are the dimmest. The absolute magnitude of main-sequence stars is also related to their mass. The hottest (blue) stars are about 50 times more massive than the Sun, whereas the coolest (red) stars are only 1/ 10 as massive. Therefore, on the H-R diagram, the main-sequence stars appear in decreasing order, from hotter, more massive blue stars to cooler, less massive red stars (Lutgens, Tarbuck, & Tasa, 2014).
Assignment: Use Figure 5 to answer the questions. Once all questions have been answered for both part 1 and part 2, save this worksheet with your last name and student number and upload to Blackboard for grading.
1. (10 points) Main Sequence stars can be classified according to which characteristics? What are the characteristics of our Sun?
Figure 5. Hertzsprung-Russell diagram. (Lutgens, Tarbuck, & Tesa, 2010)
2. (10 points) Which main sequence stars can be found with a surface temperature of between 3000K-4000K? Which stars have a luminosity about 100 times less than that of the Sun?
3. (30 points) Briefly describe the solar evolution time-line of a common star like our own from formation through collapse.
The San Andreas Fault Transcript
The theory of plate tectonics explains so much about the world around us. Mountains, great valleys,
shorelines, sea beds. Yet it’s hard to point to a particular rock or canyon and say “there! That’s plate
tectonics.” Many earth processes operate on time scales that are so long we don’t realize they are
taking place right before our eyes. We’re so small compared to planet earth that it’s hard to get a true
perspective.
Let’s gain a little elevation above one of North America’s greatest examples of tectonic movement. And
see what comes into focus. Over California’s San Andreas Fault we’ll be asking questions like ‘can I really
see evidence of plate tectonics?’ , ‘how does this Fault actually move?’ and ‘Am I likely to be directly
affected by the San Andreas?’. While we’re climbing let’s review some basics. Earth’s rigid outer layer
called the lithosphere is divided into 7 dominate plates. When plates move around the surface of the
earth, they can interact in only one of three ways. They can converge, diverge or they can slide past one
another. During convergence, an oceanic plate usually slides under a continental plate. At divergent
boundaries, plates are being pulled apart. The third interaction where plates slide past one another
produces what’s called a transform Fault. Finally it’s tempting to think of plates as either thick
continental or thin oceanic. But that’s not always correct. The pacific plate is mostly oceanic but has
some continental lithosphere on it’s edges. Conversely, a lot of the North American plate is continental.
But it also contains a large amount of oceanic lithosphere over on it’s Eastern edge.
You gotta understand, California is mess. During past collisions, exotic terrains arrived here from all
corners of the globe. Great volumes of magnum beneath California rose toward the surface to become
the Sierra Nevada. Volcanoes belched the salt that now covers many parts of the state. And then,
beginning 28 millions years ago, along comes the San Andreas Fault slicing cleanly through the
smorgasbord, 750 miles south to north from the salt sea to shelter cove. The San Andreas offers a world
class illustration of two plates, North America and the Pacific, sliding past one another along a transform
Fault.
*See text on video screen*
The first stop on our search for tectonic motion is Pinnacles National Park. The parks volcanic rocks have
been eroded into elegant canyons and spires. These same rocks are also found in Antelope Valley, 195
miles to the southeast. Same age, same chemistry, same rocks. They were created as a single body 23
million years ago. But the two halves are now separated almost 200 miles by the San Andreas Fault.
Pinnacles is riding aboard the Pacific plate, moving steadily away toward the North-West. The Calaveras
Fault, a splendor of the San Andreas lies directly beneath the town of Hollister where sidewalks buckle a
little more every year. You can sit and stare, hoping to see movement on the Fault but if you blink,
you’ll miss it. Homeowners though, know that their fences and foundations are being twisted maybe a
quarter inch every year.
In places, the presence of water can mark the trace of the San Andreas. Unlike Northern parts of the
state, central California tends to be dry, so any lake automatically stands out. So called sag ponds are
found where the Fault is shoved up scarfs to form small enclosed basins. These otherwise unlikely lakes
are found along the Fault near the Coalinga and the San Bonito valley.
Now, lets’ head for the Carrizo Plane. Not much grows here, some grass and an occasional scrub tree.
The geology is stark, undeniable.
This is Wallace Creek. Not surprisingly, it is dry today. When water does fall it flows west out of the
Temblor Range. But something funny happens right there. The creek bed suddenly jogs to the North
West before resuming it’s Westerly downhill course. The jog marks the exact trace of the San Andreas
Fault where lower Wallace Creek has been carried to the North West. There is an even older, lower part
of the creek that has been carried so far that is has been cut off entirely from the upper section. In fact,
creek beds all along the face of the Temblor Range show this offset. Each in the same direction. If you
stand on either side of the Fault, the other side always moves to the right during an earthquake. So the
San Andreas is called a right lateral strike-slip Fault.
The San Andreas accommodates most movement of the Pacific plate as it slides past North America.
Most, but not all. Did you notice the little jog in the San Andreas, north of Los Angeles? The jog ,called
the Big Bend, acts locally to bind up movement between the two plates. Here, instead of just slipping
occasionally, the two plates are squeezed together. As a result, the transverse ranges have been shoved
thousands of feet above sea level in the last 2-4 million years.
How does offset occur along the San Andreas? In Hollister, we saw that a Fault can slowly and inexorably
creep. This is true because the Fault isn’t locked and the two edges glide past one another.
But along most other portions of the San Andreas, movement is much more likely to be abrupt. Here,
the Fault is usually locked. The respective plates continue to move and stress builds up at the boundary.
When the boundary eventually snaps, energy is instantly released as an earthquake. The Creza Plane
experienced it’s last big earthquake in 1857 when the Fault edges jumped 30 feet. 30 feet. Do
earthquakes matter? Of course they do. 30 million people live within a stone’s throw of the San Andreas
Fault. When the Loma Prieta earthquake struck San Francisco in 1989, 63 people died. But this occurred
when just a small branch of the San Andreas slipped near Santa Cruz. Historically, major earthquakes
have occurred along the main San Andreas Fault about every 150 years. The last time the San Andreas
itself slipped beneath San Francisco was 1906 when thousands of lives were lost. A century has passed
and now millions more live in harms way. The two plates are still moving relative to one another, almost
an inch a year. Having studied the San Andreas, geologists know that the plates continue to move and
that earthquakes will happen again.
*See text on video screen*
This volcano was a single intact cinder cone. Does it offer any clues about what sort of Fault runs under
this part of California’s Death Valley National Park. Less than 300,000 years ago, magma rose along the
southern Death Valley Fault zone where the lithosphere has already been fractured. Since then,
movement along the Fault split the cone and has carried the two halves apart. So this is likely to be a
strike slip Fault.
