That Star, How Far?
Assignments for Class #2
• Before coming to class, watch Episodes 3 and 4 of Cosmic Distance Ladder.
• Study this animation, which shows the predicted motions of stars in the Milky Way (our galaxy) for the next 350,000 years.
To see motion better, click image to enlarge.
• Watch this video, also from PhysicistMichael.
• Read this poem: "Figures of Thought", by Howard Nemerov.
• Finally, PLEASE: Submit your questions, comments, and/or suggestions on these assignments in the form at the bottom of this (and every) page at That Star, How Far? The content of this course is challenging. Your questions can help me to provide what you need to understand it better. Don't keep me in the dark about what interests you, and about what you are getting and not getting.
Questions to To Think About
• In the animation above, some stars appear to move great distances, especially where the population appears less dense, while in the denser areas, there appears to be hardly any movement. Explain.
• How is parallax involved in the way we see depth in the world around us?
• What does it mean to say that a star has measurable proper motion? Astronomers can learn by parallax measurements both the distance to, and the speed of proper motion of, such a star --- how?
• What does it mean to "measure the color of a star"?
• From all locations on Earth, only about 5000 stars are bright enough to be visible to the average person. Imagine living on a planet whose sun is in a globular cluster of stars. In your night-time sky, there would be thousands of stars as bright as the brightest stars in our sky (see this list).
Additional Resources
• Read more about the Hipparcos and Gaia satellites and their accomplishments in measuring star distances by parallax. Our video series dates from before the launch of Gaia (2013), and the mission is still active and has greatly exceeded its planned mission period of 5 years, and its target of 1 billion stars to characterize, now approaching 2 billion.
• See Viewing Stereo Pairs in 3D, which provides instructions for seeing stereo-pair images in 3D without using a viewer. Can you see any of the images in these instructions in 3D? (Some people can, some just can't seem to do it.)
Do you have any stereo-pair images at home, perhaps with an old stereopticon? Try to look at them in 3D without the stereopticon. Another source of stereo pairs is a Sawyer's View Master.
• Read more about the Hertzsprung-Russell diagram at Wikipedia. Look carefully at the legend of the full diagram at the beginning of the Wikipedia entry.
• Learn more about the The Life Cycles of Stars.
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Unfinished Business from Class #1
• Here's how to use trigonometry to estimate the height of a tree. Walk 120 feet from the base of the tree (about 40 steps). From that point look up to the treetop, and estimate the angle a of your line of sight (about 40 degrees, in the illustration here). Imagine the right triangle shown (in a right triangle, one angle is exactly 90 degrees -- here, that angle is at the base of the tree). By the definition of the term tangent, the tangent of your look-up angle is equal to the ratio of the tree's height (unknown) to your distance from the tree, 120 feet. So,
