That Star, How Far?
Assignments for Class 5
• Before coming to class, watch Episodes 7 and 8 of Cosmic Distance Ladder.
• Watch this animation of a Type Ia supernova.
• Read the poem The Warped Side of Our Universe, written by theoretical physicist Kip Thorne, and illustrated by artist Lia Halloran. This work was included in the email about assignments for this class.
• 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?
Questions to To Think About
• Why do all Type IA supernovae exhibit the same brightness ?
• Why do we need still another rung beyond supernovae?
• What makes the absorption lines of elements in starlight a very precise measure of redshift?
• Why is it more precise to speak of the "distance" to the most distant galaxies as redshift, rather than as a physical distance in light-years or parsecs?
• [ For number lovers only: Use the definition of red-shift (z) to calculate z for a galaxy in which the hydrogen-alpha line of wavelength 660 nm (visible range of EM spectrum) is redshifted to 1980 nm (far infrared range of EM spectrum). ]
This figure shows the red-shifts of objects at increasing distances from the Solar System.
Click to enlarge
(Piquito veloz, CC BY-SA 4.0<https://creativecommons.org/licenses/by-sa/4.0>,
via Wikimedia Commons)
The outer circle is the source of the Cosmic Microwave Background Radiation, whose red shift is 1089. This means that the wavelength of the CMB is shifted from its normal wavelength of 656 nm (red line in visible emission spectrum of hydrogen) to 1063 mm (about one meter wavelength, between microwave and radio wavelengths). Now, that's a big red-shift: from an original wavelength of 0.000000656 m to a currently observed wavelength of 1 whole meter (about 3 feet) !!
Additional Resources
• As a reminder of the historical context of the structure if the universe we are studying, here is a brief history of the whole thing:
• Where does each element come from? Here is a periodic table of the elements, showing the cosmological sources that produced (and are still producing) each element.
Article worth reading !
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