"Where there is an observatory and a telescope, we expect that any eyes will see new worlds at once."
--Henry David Thoreau, "Friday: The Poet's Delay," A Week On The Concord And
Merrimack Rivers, 1849
Equipment (per group)
Cuesta ThinkPad laptops (wireless networking, internet browser)
(Print this worksheet out instead; no online activities for laboratory this week)
Galileoscope (*.html)
Project STAR telescope (*.html)
tripod
1-m meter stick
rulers
Telescopes.com catalog
Current Events Quiz
(First 10 minutes of laboratory.)
Briefing
Telescopes & Powers (*.blog)
Big Idea
Telescopes are constructed to improve upon the light-gathering, resolving, and magnification powers of the naked eye. Simple measurements and published parameters can be used to compare the relative powers of historical and modern commercially available telescopes.
Goal
Students will conduct a series of inquiries in analyzing the relative telescope powers of simple refractors, and other commercially available telescopes.
Tasks
(Record your lab partners' names on your worksheet.)
1. Exploration
- Focus the Galileoscope (black plastic telescope) on a nearby object inside the classroom. Then take it outside and focus on a distant object. Describe whether the sliding tubes should be almost fully extended/collapsed to focus on a distant object, compared to being focused on a nearby object (inside the classroom).
Distant object configuration vs. nearby object configuration: ___________.
- Describe/draw a diagram, indicating whether the view through the telescope is upside-down, reversed left-to-right, or rotated 180° (which is upside-down and reversed left-to-right).
Description of view through telescope: ___________.
- Measure the (usable) diameter of the primary lens, in cm. Calculate the light gathering power LGP (in cm2) = (π)⋅(radius, in cm)2; and the resolving power RP (in arcseconds) = 14/(diameter, in cm). (The RP value is the smallest detail, measured in arcseconds, that can be seen through a telescope. Details that have angular sizes smaller than the RP value will not be visible.)
Primary lens diameter (aperture) = __________ cm.
Primary lens radius = __________ cm.
LGP = __________ cm2.
RP = __________ arcseconds.
- Measure the primary focal length fprimary (in cm), which is approximately the length of the telescope (while focused on a distant object--was that with the sliding tubes almost fully extended or almost fully collapsed?).
fprimary (distant object telescope length) = _________ cm.
- Take the eyepiece assembly out of the back end of the tube, and hold it right up against your eye, using it to focus on and magnify a (very) close-up object such as a pencil tip, or your fingerprints, which may be close enough to be almost touching the eyepiece lens (*.gif). Measure the eyepiece focal length feyepiece (in cm), which is the object-to-lens distance when the object is magnified and in sharp focus.
feyepiece (close-up focusing distance) = __________ cm.
- Calculate the magnifying power MP = fprimary ÷ feyepiece (this is a unitless factor, e.g. "10×" or "100×").
MP = fprimary ÷ feyepiece = __________×.
- Repeat (c)-(f), for the Project STAR telescope (brown cardboard tube telescope). (Note that the primary lens diameter (aperture) is set by the inside of an embedded white cardboard ring.) Make a table compiling the LGP, RP, and MP for both telescopes(*).
2. Does Evidence Match a Given Conclusion?
Galileo Galilei observed the rings of Saturn, which has an angular size of approximately 10 arcseconds. Discuss whether the Galileoscope, Project STAR telescope, or both modern reproduction telescopes are capable of reenacting this historic observation. Explain your reasoning and provide specific evidence from data, with sketches if necessary, to support your reasoning(*).
3. What Conclusions Can You Draw From This Evidence?
The Museo Galileo Institute and Museum of the History of Science has several of Galileo's telescopes in its collection:"...Telescope [inventory no. 2427, late 1609-early 1610] made by Galileo consisting of a main tube with separate housings at either end for the objective and the eyepiece. The tube is formed by strips of wood joined together. It is covered with red leather (which has become brown with the passage of time) with gold tooling. The [primary lens has an] aperture of 15 mm, a focal length of 980 mm. The original eyepiece was lost and was replaced in the nineteenth century by a biconcave eyepiece with...a focal length of [47.5 mm]."
--brunelleschi.imss.fi.it/museum/esim.asp?c=405002 What conclusions and generalizations can you make from the information given above, where 10 mm = 1 cm, in terms of "Which modern reproduction telescope (Galileoscope or Project STAR) best matches the powers of this museum telescope?" Explain your reasoning and provide specific evidence, with sketches if necessary, to support your reasoning(*).
4. What Evidence Do You Need to Pursue?
Imagine your team has been assigned the task of writing a purchase order for a set of new eyepieces to be used for one of Cuesta College's telescopes, to obtain a given magnifying power.
Look through a commercial telescope catalog and note that it typically does not specify the magnifying powers of eyepieces. Thus given a magnifying power requirement (e.g., MP = 20× or 50×, etc.), describe how to calculate the eyepiece focal length to be purchased for a telescope with a given primary focal length--not just "divide the MP," but exactly how, step-by-step, to accomplish this for any telescope and magnifying power requirement in general. You might include a table and sketches--the goal is to be precise and detailed enough that someone else could follow your procedure(*).
5. Formulate a Question, Pursue Evidence, and Justify Your Conclusion
Design an answerable research question (*.html), propose a plan to pursue evidence, collect data using a commercial telescope catalog, and create an evidence-based conclusion about an aspect that you have not completed before. (Have your instructor approve your whiteboard research question before proceeding further.)
Research report summary on whiteboards(*), to be worked on and presented as a group, should include:- Specific research question.
- Step-by-step procedure to collect evidence.
- Data table and/or results.
- Evidence-based conclusion statement.
Be sure to specifically cite telescope brands and models, as well as other relevant details (cost, measurements, etc.).
Preparation/Reflection Points
1.0 = Pre-lab reading assignment
1.0 = Current events quiz
1.0 = Post-lab reflection assignment
Group Work Points(*)
Documentation (Tasks 1-4, graded from randomly selected group member)
2.0 = exploration complete and reasoning correct
1.5 = minor problem with exploration or reasoning
1.0 = minor problems with both exploration and reasoning
0.5 = problematic exploration and reasoning
Poster/presentation (task 5)
2.0 = research report complete and competent presentation
1.5 = minor problem with research report or presentation
1.0 = minor problems with both research report and presentation
0.5 = problematic research report and presentation
(Backwards Folded Scaffolding framework adapted from: Tim Slater, Stephanie Slater, Daniel J. Lyons, Engaging in Astronomical Inquiry, W.H. Freeman & Company, New York (2010).)
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