Paint By Numbers
An activity from NASA's Space-Based Astronomy Activity Guide
related to the song:
'Come and Visit Mars'
A pencil and paper activity demonstrates how astronomical spacecraft and
computers create images of objects in space.
To simulate how light collected from a space object converts into binary
data and reconverts into an image of the object.
Discuss with the students how we can't use conventional film on space
missions (how would we get it back?). Image data is stored on the
satellite and transmitted to Earth as a series of numbers and computers
are used to reconstruct the numerical data into the pictures we see.
This activity touches on the following standards:
- Patterns, function, and algebra
- Data analysis, statistics, and probability
- Evidence, models, and explanation
- Change, constancy, and measurement
- Abilities of technological design
Materials (per group of two students)
Picture of house
- Divide students into pairs.
- Give one student (A) in each pair a paper copy of the blank grid
below. Give the other student (B) in each pair the picture of the house
(also below). Instruct student B not to reveal the picture to student
A. Also give student B a copy of the grid on transparency film.
- Explain that the picture is an object being observed at a great
distance. It will be scanned by an optical device like those found on some
astronomical satellites and an image will be created on the paper. The
students with the transparent grid represents the spacecraft and the
student with the paper grid represents the radio receiver on the ground
and the image-processing computer that will assemble the image of the
- Have Student B place the grid over the picture. Student B should look
at the brightness of each square defined by the grid lines and assign it a
number according to the chart above the picture. Student B will then call
out the number to Student A. If a particular square covers an area of the
picture that is both light and dark, student B should estimate its average
brightness and assign an intermediate value to the square.
- After receiving a number from student B, Student A will shade the
corresponding square on the grid. If the number is 0, the square should be
shaded black. If it is 3, the square should be left as it is.
- Compare the original picture with the image sketched on the paper.
The image created with this activity is a crude representation of the
original picture. The reason for this is that the initial grid contains
only 100 squares (10x10). If there were more squares, each square would be
smaller and the image would show finer detail. You may wish to repeat this
activity with a grid consisting of 256 squares (16 x 16) or 400 squares
(20 x 20, provided in this lesson plan). Increasing the number of squares
will require more class time.
Space-based observatories, like HST, have more than 2.5 million pixels and
they are shaded in 256 steps from black to white instead of the 4 shades
used in this activity. Color images of an object are created with color
filters. The spacecraft observes the object through a red filter, a blue
filter, and then a green filter. Each filter creates a separate image,
containing different information. These images are then colored and
combined in a process similar to color separations used for printing
colored magazine pictures.
Optional 200-Pixel Grid
This activity comes directly from NASA's Space-Based Astronomy Activity
Guide for Science, Mathematics, and Technology Education. We thank NASA
for the use of this activity.