Overview: In this tutorial, students will learn to use computer
image processing techniques to measure the size of sunspots and analyze
various phenomena visible on in solar system images. These skills can be
used to scale and analyze images of our Sun, the planets, or any other
electronic image found on the Internet.
Learner Outcomes
By completing this activity, the learner will:
find, download and save an image of our Sun from the Internet
convert a GIF or JPG image to TIFF format
use image processing software to view and magnify the image
calibrate and scale the viewed image
use the computer to measure the diameter and area of sunspots
create a surface plot of our Sun
Materials Needed:
NASA scientists use computers to conduct scientific investigations everyday.
One procedure frequently used is called IMAGE PROCESSING. In this activity,
we will learn how to process NASA Yohkoh images of our Sun on the computer.
Be sure you have the following items accessible to your computer before
you begin.
Focus Question: ATTENTION
NASA IMAGING TEAM:HOW BIG ARE SUNSPOTS?
Teacher Lesson Plans
Exploration:
Let's
look at a picture of our Sun.
What do you see in this picture? It is very dangerous to look at the Sun
without special protective lenses. Sunlight will damage your eyes and it
won't even hurt - never look directly at our Sun!!
Ancient peoples used to think that the surface of our Sun was perfectly
smooth and had no spots. Now that we have satellites and telescopes, what
do you think - is the Sun smooth and spotless?
When
the Sun is viewed through a solar telescope dark spots can be observed
on the surface. These spots appear dark to the eye because they are cooler
than the surrounding gas although they are still quite hot! The photosphere
has a temperature of about 5500 degrees Celsius and a typical sunspot has
a temperature about 3900 degrees Celsius.
A sunspot's lifetime can be as short as an hour or two or as long as
several months. The number of sunspots that can be seen on the surface
of the Sun increases and decreases in a regular pattern, known as the solar
cycle, with a maximum number of sunspots occurring every 11 years.
PREDICT:
HOW BIG ARE SUNSPOTS?
ARE THEY AS BIG AS YOUR HOUSE?
ARE THEY AS BIG AS YOUR STATE?
ARE THEY AS BIG AS OUR MOON?
ARE THEY AS BIG AS EARTH?
Concept Introduction:
The concept introduction portion of this lesson is presented as a step-by-step
tutorial. It is divided into two portions, each requiring one session using
the computer. In the first part of the lesson, students learn how to save
images to their computer's hard drive. In the second part of the lesson,
students learn how to scale and calibrate images in order to make measurements.
Part I - Downloading, saving, and converting images from the Internet
Any image that you find on the Internet's World-Wide-Web (WWW) using
Netscape or MS
Internet Explorer can be saved on your hard drive for analysis. Even
better, the process is almost the same on a Macintosh or a PC. All you
have to do is the following:
Start your WWW browser (Netscape or MS Internet Explorer, for example)and
enter in a URL that has lots of images. A great place to start is the Yohkoh
Public Outreach Site (YPOP).
To save an image to your hard drive, position the mouse over the image
and hold down the button for a couple of seconds (use the right button
if you have more than one button on your mouse).
A menu will appear and you can select SAVE THIS IMAGE. This will give
you an option about what to call the image and where to save it. Note where
it goes and what it is called. Choose a different name and location if
you like.
The image is now saved on your hard drive and you can open it with
your WWW browser or with an image conversion program you might have, like
the shareware program PaintshopPro
(more information). With these programs,
you can alter the image's size, color, or even add text to the image as
you wish.
Most images on the Internet are in GIF (pronounced a hard "g"
as in gift but without a "t") or JPG (pronounced
jay-peg) format. Image processing software do not typically use files in
this format so they must be converted to TIFF (rhymes with GIF).
Start your graphics conversion program by double clicking on its icon.
Open your image converter program and
from the file menu, select OPEN. Find the image that you downloaded and
open it using this converter program.
From the file menu, select SAVE AS. In the format box select "save
as TIFF format". Close your graphics converter program and you are
ready to conduct image processing.
Part II - Using Image Processing Software for Scaling and Measurement
If you haven't converted your images to TIFF, you need to go back to
part I and convert your images to TIFF format.
Start your image processsing software (MAC
NIH Image or PC ImagePC or get
more information). Using the FILE pull-down menu,
select OPEN. Select the TIFF image that you converted in Part I (or save
this one).
The first task is to calibrate the image (tell the computer the scale
of the image). If you are looking at an image of Sun you must know the
diameter (you can look this up in a book or on the Internet
as 1.4 million km {or 1.4e6 km). Using the segment tool/select line tool
(fifth from the top on the right), draw a line across the diameter of our
Sun.
Under the ANALYZE menu, select SET SCALE. Note that the computer has
already recorded how many pixels (picture elements) long the line you drew
is. First, change the UNITS to the known diameter units (km).
Second, enter in the known diameter. For large numbers, like
93 000 000, use 93e6. Click OK and your image is now calibrated and you
are ready to measure sunspots!!
Use the magnifying glass in the upper left of the tool bar to focus
in on one of the sunspots by clicking on it. The software will remember
the scale of the image so you can get as close as you need to make a good
measurement. To un-zoom , double click the magnifying icon in the tool
box or hold down Pthe CNTRL or APPLE key on the keyboard while clicking
on the image.
Use the segment tool (select lines) from the middle right of the tool
bar to carefully draw a diameter across the entire sunspot. From the ANALYZE
menu, select MEASURE.
From the ANALYZE menu, select SHOW RESULTS. You might have to grab
the bottom left hand corner of the new window to expand the window to see
your results.
Determine the diameter for several sunspots. How big are they? Are
they bigger than your house? Are they bigger than Earth?
You can use the same Segment Line Tool to Measure Perimeter and Area:
This image processing program has 4 tools for selecting regions for study.
The first tool in the right hand column of the tool window is used
to drag out rectangular areas.
The second tool in the right hand column of the tool window is used
to define oval or circular areas.
Using the third tool in the right hand column of the tool window, you
can connect a sequence of points with line segments, creating a polygon
of your own design. To close the polygon (connect your last point to your
first point), just click the mouse twice in rapid succession.
The fourth selection in the right hand column of the tool window allows
you to freehand any curve you want (this is called the Freehand Tool and
looks like a heart).
Determine the area of a sunspot using the freehand (heart-shaped) tool
to trace the outside. Select MEASURE from the Analyze pull-down menu, then
select SHOW RESULTS from the Analyze pull-down menu to view the measured
value for perimeter and area.
Concept Application:
Sunspots
have two components - a dark inner penumbra and a lighter outer umbra.
Divide up into several NASA imaging teams. Each team needs to analyze a
different set of sunspots and create a written technical report, a multimedia
presentation, and/or an oral presentation that describes:
which images you analyzed
how the images were analyzed
how many sunspots were present, and
how big are sunspots compared
to things in the solar system?
The above process will work on ANY image that you find on the Internet.
Try out the following to demonstrate your skills at image processing.
How far is it from your hometown to the state capital? Find a map
of your state, calibrate the image using the map scale, and measure the
distance by road between the two places.
How big is Jupiter's Red Spot? Use the known diameter of Jupiter
to calibrate your image.
How big are Saturn's rings? Use the known diameter of Saturn to
calibrate your image.
Try the activities, Dynamic Martian Polar Ice Caps from NASA Project CERES,
Investigating Olympus Mons, (the solar system's largest volcano)
or Focus on Hurricane Andrew (an enormous tropical storm) from the
Network Montana Project (NMP).