Go
to File, Open Samples and open the image Moon
Stack . Click on = on the keyboard and the stack will be animated.
Click on the image to stop the animation. (Control of the speed of animation
can be found under Image, Stacks in the Menu Bar.)
Density
Slicing
Set the Moon Stack to Waxing Crescent. (Day 4)
Use the Magnifier 
Tool
and click on the Moon Stack. Then grab a corner of the image so you can
enlarge it and see everything at 200%. Then take you Straight Line 
Tool and draw a line across the middle of the moon from left to right.
Choose Analyze/Set Measurements and have only Area, Perimeter
and Limit to threshold checked. (Turn off all other options)
Choose Analyze/Measure and then go to Analyze/Set Scale. You
should get a distance close to 157 pixels. Type in the diameter of the moon
(3476) and put km in the Unit of Measurement.
Under
Image,
Adjust and Threshold. You will see two slide bars. Adjust the top
to 0 (Far to the left) and the bottom slide bar to 216 so that the area
you want to measure is in RED.(What you
have done is to select everything with that pixel density out of 256.)
See the above set of three images.
Select
the Wand 
Tool and click on or next to the red area on Day 4.. You will see a yellow
line surrounding all the red. Now do Analyze, Measure. The Density
of everything that you have selected in RED
has been measured in pixels. Choose Analyze/Measure and you know
have your first area reading for the moon during Day 4.
Continue doing your analysis or all the other phases. When you do it for
the Full Moon then this area will represent 100% visibility. (You will
use this value to calculate the percentage of the Moon visible in the
other phases.
Record your results in Table 1. Round all you results off to the nearest
1,000 sq. km. (for example 8,934,116 rounds to 8,934,000) Calculate the
percentage of area visible compared with the full moon.
Reference
The follow
are WEB reference sites for information on
the Moon's Phases
An explanation
for the appearance of the different phases.
Virtual
Reality Moon Phase Pictures. These "Virtual Reality Moon Phases"
were created by R. Schmidt from ray-traced images of the Moon
Another explanation
- on the Moon's Phases.
Results
Table
1:
|
Phase
|
Day
|
Area
Visible
(km-squared)
|
%
Visible
|
| |
|
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1.
Make a graph of the % Visible vs. Day
2.
Describe how the % Visible changes through a lunar month.
3.
What percent of the moon is visible on day 5? ....on day 17?
Acknowledgments:
Activity developed by LuAnn
Dahlman, Center for Image Processing for
Teaching
Images courtesy of Lick Observatory,
University of California.
The moon goes through a cycle of changing phases as it orbits the earth. The phases have names, but you can also describe them with numbers. Measurements can help you understand the overall pattern of this cycle of nature.
