NASA's Chicago State University's Saturday Academy for Space Science
CSU SASS Module Descriptions Index Page
Module 2:  Optical Powers
November 16, 23, December 7, 14, 2002

Week 1 Week 2 Week 3 Week 4
Telescopes, Optics and Images Magnification Gathering Starlight Resolving Power
Research and Observing Projects
* Phases * Saturn's Rings and Moons * Sun  * Asteroids * Comets *
* Constellations * Patch of Sky * Variable Stars * Supernova * Big Bang *

In this module you will experiment with telescope components to understand what telescopes do!  You will analyze and plan experiments to test what happens when one  manipulates variables in the telescope and camera systems.  You will investigate images, then collect and analyze data to understand these systems. 

Students will work in teams to conduct research projects.  Part of every project will be observing with a telescope and taking an image to add to a collection of images taken by others.  Understanding the optical powers of the telescope systems you might use for your observations will help you create an observing proposal and understand the images you find, use, or take yourself.

November 16, 2002
Week 1: Telescopes, Optics, and Images

Use a solar filter on the telescope if you observe the Sun. 

Telescopes.  Everyone knows that astronomers use telescopes to study celestial objects. But what makes up a telescope?  How are telescopes different from one another?  How would you choose which telescope to use if you wanted to do an observing project?  We will have some telescopes at CSU this Saturday for you to determine what parts of telescopes are important to make it work.  You can also use this Student Page: Telescopes.  There are links to pictures of the night sky, links to pages about Galileo and historical telescopes, and picture sets of telescopes  we will be using for our observing projects. 


F Box Experimental Components (See more pictures.)
F-Box Optics.  In this session you will use a light box with a cutout of the letter F.  (You can change this to other letters or patterns.)  You will move the light box as far away as possible from a lens holder containing three convex lenses of the same diameter but different thicknesses and curvatures.  You will set up three screens behind the lenses to capture the focused image of the light source.  Then you will measure the distance to the focused image for each lens; this is called the focal length.  You will also measure the size of the image on the screen; this is called image size. There is graph paper on the screens to help you with this measurement or you can use a ruler.  Finally you will analyze your data to find out the relationships between thickness of the convex lenses, focal length and image size. The next experiment you will do is to decrease  the size of the lenses by covering them with a mask.  You will observe the effect of the mask on your images.  The size of a lens or mirror is called its aperture. Astronomers are always trying to build or use telescopes with larger aperture.  Doing this experiment will help you understand why telescopes with large apertures are valuable to astronomers.  Link to Student Page: F-Box Optics.

 


See SASS students in action!

Telescopes are made with either lenses, mirrors or both. Lenses and mirrors which are curved allow astronomers to collect light, magnify, and focus an image. The size of a lens or mirror and the amount of curvature produce similar results on an image.  It is easier for us to set up experiments with lenses. But our conclusions apply to telescopes constructed with mirrors as well. 

Tips 'n Tricks of Image Processing.  If you are just joining the NASA CSU SASS program you will learn to use Hands-On Universe image processing software. Students who have attended SASS Module 1 have already completed this activity and will begin with the Image Quality Lab.  Link to Tips 'n Tricks pages.  There are several pages to this lab; find the next link at the bottom of each page.

Image Quality Lab.  We have collected images of the same object taken with several telescopes and of differing quality.  You will choose a folder of images of a celestial object and compare the quality and attributes of the images. You will invent ways to describe the attributes of the images and then learn the terms usually used by astronomers.  As we learn more about telescopes and camera systems, you will find out how to select a telescope that matches your observing objectives and/or understand how to control the quality of the images you take.  Link to Student Page: Image Quality Lab.

**Note to Teachers:  See Optical Powers, Teacher Pages: 1, 2, and 4, and Tips 'n Tricks for Image Processing.

November 23, 2002
Week 2: Magnification: Size, Distance, and Focal Length

Size in the Sky.  When you are imaging celestial objects, what does the size of the image of that object tell you about it's real size?  Does the distance to the object make a difference in the size of your picture of it?  Our computer lab adds and subtracts images of solar system objects for some interesting 'artistic' effects as well as scientific musings about how distance effects size! Link to Student Page: Size in the Sky.

Dimes Worth of Sky.  Astronomers measure the sky with angles.  To understand how  angular size and distance to an object interplay you will do a lab creating concentric circles each with 360 objects around the circumference.  Each object represents one degree.  What difference does the size of the object make as related to the size of the resulting circle?  If you are able to collect and bring to class 360 objects of the same size, that would be great.  We have some objects ready for this experiment. It is helpful to tape or trace or glue objects on a strip of paper.  Put them in groups of a number that is divisible into 360.  Why 360?  Think about how many degrees there are in a circle! Link to Student Page: Dimes Worth of Sky.

Focal Length. Another property of telescopes is the focal length of the mirror or lens that collects the light.  What difference does it make if an optical system results in a long focal length or a short focal length?  When you buy a telescope or make one yourself, you have to make decisions about the focal length of the primary lens or mirror.  When you use telescopes for different observing projects, you will chose which telescope is best.  Knowing about the effect of focal length on resulting images is what this lab is all about. 

In Focus.  First we will see how images look when the camera is not at the focal plane.  Focusing a telescope is very important in the process of getting it ready for imaging.  Link to Student Page: In Focus.

Experimenting with Focal Length.  This computer lab compares images of the same celestial objects taken with telescopes of different focal lengths.  Collecting data and doing some simple mathematical comparisons will reveal to you the difference focal length makes in the images you get from various telescopes. Student Page: Experimenting with Focal Length.

Questions.  We will be asking these kinds of questions when we compare the images taken with telescopes of differing focal lengths. 

Will the size of the image change?  Will the brightness of the image change?  Will the quality of the image change?  Will the field of view of the image change? What do you observe.  Does your analysis of the data lead you to any mathematical relationships about focal length and the resulting images?

What Power Is This Telescope?  This is one of the most common questions asked at any star party.  This is how you figure it out.  Take the focal length of the telescope and divide it by the focal length of the eyepiece. 

** Note to Teachers: See Optical Powers, Teacher Pages: 3a, 3b, 5a, 5b.

December 7,  2002
Week 3: Light Gathering Power

How much light can we collect with our telescopes?  What difference does it make in our images?

We will explore the affect of the size of the telescope's primary lens or mirror (aperture) on images by masking the opening to the telescope and comparing the results.  We will explore how an image changes when we expose for a longer period of time.  We will also compare the light gathering power of our eyes to that of a telescope.  Student Pages:  Gathering Starlight; Dots Project; Exposure Time

**Note to Teachers: See Optical Powers, Teacher Pages. 6a; 6b; 7.

December 14, 2002
Resolution, Pixel Scale and Field of View

Resolution.  How much detail can we see in our images of celestial objects?  What are we missing?   This question has to do with ability of the telescope and camera system to resolve detail.  Resolution depends on the size of the pixel and the aperture of the telescope. But it also depends on the atmosphere and the seeing conditions.  Astronomers are developing ways of compensating for changes in the atmosphere through engineering techniques called Adaptive Optics.  The activities we will do with images will compare the resolution of an image by measuring the diameter of a star, by taking a slice through the star and using a quanitity called FWHM - Full Width Half Maximum.  Then we will compare images of a double double starm, taken with various size apertures to see which aperture allows us to separate a closely spaced double star.  We will also look at a star image with an adaptive optics system turned off and turned on.   Student Page: Resolution. 

Pixel Scale and Field of View. To measure size on an image, you need to know how much sky is covered by each pixel and by the whole array of pixels on the chip.  Our activities will lead us through using formulas to calculate these measures.  We will open various images and find the information we need for the calculations in the Image Info which is also called the Fits Header.  Student Pages: Pixel Scale and Pixel Scale Chart; Field of View and Field of View Chart.

Radians Activity:  We will experiment with dimensions and circles, creating a Radian angle of measure with circle radii.  This project uses pipe cleaners, paper plates and your imagination to give meaning to a geometrical measure useful to astronomical angular measures. 

Your Portfolios and Progress: NASA CSU SASS has met for 8 Saturdays now.  We are setting aside some time for students to share the portfolios of work and projects that they have collected during these Saturdays. We will also share with you some ways to assess your progress.  

Note to Teachers.  Please see Optical Powers, Teacher Pages: 8, 9a, 9b.

Research Projects

Research SS Cygni. We will begin a research project on SS Cygni, a variable Star in Cygnus, the Swan.  Find out the characteristics of this star by calculating its magnitude and plotting the changes over days and months.  Is this star usually bright or dim?  How often does it change?  Is it predictable?  When do you think will be the next big change in its brightness?

Saturn's Rings and Moons.  We have three images of Saturn taken over an interval of 4.5hours.  Would you believe that we can add these images together to see the motions of Saturn's moons!  We can also select sets of images of Saturn, calculate the period and orbital radius of Saturn's moon Titan and use this data to calculate the mass of Saturn. 

This Chicago State University Saturday Academy for Space Science (CSU SASS) is funded by NASA.  The Optical Powers curriculum we are using in Module 2 was developed by a team of teachers working on telescope experiments at The University of Chicago Yerkes Observatory,  funded by the National Science Foundation through the Center for Adaptive Optics. 

Comments, Suggestions, Questions?, Ideas!
Email Vivian Hoette at vhoette@hale.yerkes.uchicago.edu

* NASA CSU SASS *
* Sky Projects * Explorations * Hands-On UniverseTM * Center for Adaptive Optics *
* The University of Chicago Yerkes Observatory * * Northwestern's Collaboratory *