august 19, 1999

Reading: article from Sky and Telescope: Sky on a Chip: the Fabulous CCD

To start HOU on the NT network,

To start HOU in the back Physics lab, click on Start, then Programs, then Hands On Universe

To start HOU in the EFC lab,

• Under File, select Open, and then double click on unit, then on browsers_guide_to_the_universe, then on browser5
  
• To maximize the image space, first click the rectangle in the upper right corner (this maximizes the window on the screen); then drag the browser 5 image’s blue bar up as high as it will go in the dark gray area; then click on the square in the upper right corner of the browser 5 frame
• The screen should display a black-and-white image of an astronomical object. Investigate the options under the View menu (i.e., Tool Bar, StatusBar, Color Palette Bar, and Display Controls Bar; click these on and off to see what each name refers to. After experimentation, you will want to have the ToolBar, StatusBAR, Color Palette Bar, Display Control Bar "on" and the others "off."

By this time you know something about CCDs and understand the concepts of pixels and digital imaging. Each pixel is "colored" the appropriate shade of gray according to the "Counts" measured for that pixel; the translation table from "Counts" to "color" is the palette at the right of the screen. Experiment with the zoom by increasing the zoom factor to 2, 4, 8, 16, all the while looking at the object’s center. [To keep track of where the object’s center is, note that it continues to have the same x-y pixel coordinates at the bottom right of the screen (as long as the Status Bar Option has been selected). Have you also noticed that the x-y coordinates and the "Counts" number change as you move the mouse cursor around the screen?] At what zoom factor can you first begin to see the actual pixels?

• Return to Zoom 1, and center and maximize the object in your window. The black-and-white image is not very interesting because of the lack of detail. Can you tell what type of object it is? How much of the image box does it occupy?
  Astronomers use the idea of "false coloring" to bring out contrast and detail.
• Under the File Menu Bar, click on Load Color Palette.... select rain.pal
  it’s the best; you can experiment with other palettes later if you want
• Under the View Menu Bar, click on Color Palette Bar so that it is displayed on the right hand part of the screen... move the mouse/cursor around on the screen over different color areas of the image.... does the color match what the "Counts" number (in the lower right of the screen) and Color Palette Bar predict?

At some point , I will ask you to describe in a quantitative manner how false color digital imaging works; i.e., what does the computer actually do (given the minimum and maximum counts recorded on the image) in order to display the false-colored image…

• Your goal is to fiddle with the false coloring so that the object’s detail is brought out; you do this by changing the max and the min in the color palette (upon opening the image, the min was probably set to 215 and the max to 459) . some hints follow:

a) To find a good min,

move the mouse around and notice the Counts reading; select a min value that is not the

absolute minimum, but is a little bit (10 or so?) above most of the very smallest values of

the Counts (which are the Counts values in the black areas)

Record your chosen min in the lab journal, and adjust the min to your selected value. There

are three ways to adjust the min:

(1) click in the box next to the word Min and then type in the desired value,

(2) drag the red bar left or right to decrease or increase the min,

(3) click on the left-pointing arrow box....

after you make a change in the min, the HOU software should immediately refresh the

image to your new standards

b) To find a good max,

start with the max given; what happens to the image as you decrease the max?

what are trade are you making as you decrease the max?

c) The image will probably still not look very good. Now click on the box for Log Scaling. The

result should be impressive. You want to do some additional fine tuning with min and max.

At some later point, I will ask you to describe how log scaling works. For the moment,

notice (and record) what has happened to the Color Palette bar during the switch from linear

to log scaling.

how much of the image box does the galaxy occupy? did you give the same answer as

one the previous page?

4. Now open each of the other browser images, and identify (or at least try to) each of the other astronomical objects… in many cases, something interesting will be hidden unless you process for the most detail….

Additional questions for the browser images

(Browser 1)

how big do you think the crater is across? (what additional information would you need in order to determine the diameter?)

how deep do you think it is?

how tall is the central peak inside the crater? Have any idea where it came from?

Bonus question: the crater’s name?

Bonus bonus question: what famous astronomer-mathematician is it named for, and what is this person’s claim to fame?

(Browser 2)

can you separate the two close moons and simultaneously see the detail on the surface of Jupiter?

(Browser 3)

what do we call the bright spots over the limb of the sun?

a number of rows on the left side of the image have been saturated: the maximum number of electrons holdable on one or more pixels was reached and electrons spilled over onto adjacent rows of pixels… this is called blooming

browser images 4, 6, and 7 can all be found somewhere in the text; so I want you to find the corresponding figure in the text that goes with each of these, in addition to finding out a little about that object and where it fits in the syllabus; to narrow down your search somewhat, the pictures come from one of the following chapters: 20, 22, 23, 26

for the image that has the pulsar, I want you to image process it so that it looks like the picture in the text, and to draw a diagram of the HOU image in your notes with the pulsar labeled;

what do you have to do to the original HOU image to make it look exactly like the text image?

(flip it? or rotate it? which way? or by how many degrees? or a combination of flip and rotate?

the software, by the way, can do all these things; look under Manipulation)

(browser 5)

this image is important in the history of the Hubble Space Telescope? Do you know why?

Random questions:

Which image(s) cannot be duplicated fairly accurately at any time during the next year? Why not?

Which image has a July 4^th connection? Why?

If we could travel 6 billion years into the future and then take an image of the sun, which image would it look like?

In which image could you (had the image had better resolution) see active volcanoes?

In which image (had the image had better resolution) could we see a liquid water ocean?

In which image(s) is the bulk of what you see solid or liquid (as opposed to gas)?