Feedback on Mars Exploration booklet

From: Chris Rowan <>
Subject: Feedback on Mars Exploration booklet
Date: Wed, 23 Oct 1996 17:55:17 -0700 (PDT)

Hello Dr. Diarra,

I was in Washington D.C. during the "Live From Mars" conference.  We met,
but I was only one of a hundred or so and doubt you remember me.  

In any event, I wanted to provide some feedback on the _Mars Exploration_

On page 8, there is a chart showing Mars' rise time.  My students wondered
which time zone the chart was made for.  Is the chart made for Pacific
Standard Time?  Pacific Daylight Time?  GMT?  UTC?

On page 10, the chart showing the planets and their relative sizes shows
Mercury as being larger than Earth and Mars.

The activity, "How Do the Planets Compare in Size," could be simplified.
For starters,  we really need the RADIUS of the circle to draw with the
compass, not the diameter.  

The radii for Mercury, Venus, Earth, and Mars (derived from the diameters
given in the booklet) were too small to draw circles with our cheap
compasses.  We need radii with a minimum of 2 cm.

Couldn't the radii of the planets be derived by making each some fraction or
mixed number of Earth?  We need radii that measure in whole numbers at best,
or halves.  Let me explain . . .

Let Earth's radius equal 2 cm.  Drawing a circle with a radius of 2 cm is
pretty easy, even for 5th graders.

According to the chart on p. 11, the actual diameter of Mercury is 4,880 km
and the actual diameter of Earth is 12,800 km.  That means Mercury's radius
is 2,440 km and Earth's radius is 6,400 km.  Taken a step further, Mercury's
radius is about 38 percent of Earth's radius. So, what is 38% of the scale
radius of Earth (2 cm)?  It's 0.76, which can be rounded off to 0.75, or 3/4
of 1 cm.  Difficult, but not entirely impossible to draw with a compass.

Short version
Diameter: 4,880 km
radius:  2,440 km
percent Earth's radius:  38%
scale radius:  0.75 cm

Diameter: 12,100 km
radius:  6050 km
percent Earth's radius:  95%
scale radius:  1.9 cm

Diameter: 6,800 km
radius:  3,400 km
percent Earth's radius:  53%
scale radius:  1.1 cm

Diameter: 142,000 km
radius:  71,000 km
percent Earth's radius:  1109 %
scale radius:  22.2 cm  (difficult to draw with a compass, but it can be
done with a 23 cm length of string and a pencil)

. . . and so on.  

On step 4 of page 11, the instructions for making a scale model of the sun
are not very specific.  "Cut out a circle that is 139 centimeters and label
it "sun."  Which is it - 139 cm in diameter?  Radius?  Circumference?  And
just how are we supposed to draw a circle with a diameter of 139 cm witih
our puny 79 cent compasses?  (I used a length of string and a pencil)

Oh, and the word "label" is misspelled on page 11 in Step 2.

The activity, "How far are the planets from the Sun" could be simplified, too.  
We have done something similar to this in the past.  We used the
distance between Earth and Sun as our unit of measurement (actually, 1
AU or "astronomical unit").  I had tied this to a discussion of how in
olden times, the unit of measurement had been based on the length of the
king's foot.  A yard was 3 times that, and a mile was 5,280 times that,
and so on.  We reasoned that we'd need something else to measure very
large distances, so we decided to compare everything to the distance
between Earth and Sun.

We were VERY sophisticated with our measurements.  Four giant steps was
equal to 1 AU.  So, one student (Earth) took four giant steps away from
another student (Sun) to begin our human model of the solar system. 
That was easy enough.  But how do we represent the distances between
Mercury and the Sun?  Between Venus and the Sun?

We found out that we needed to find the AU for Mercury, which happens to
be .387 AU

This means Mercury is about 39% of the distance between Earth and the
Sun.  What is 39% of four steps??  Using a calculator, we found that 39%
of 4 is 1.56, which is about 1 1/2 steps.

We could do that.  So we did it.

We then found the AU's for all the other planets, and it wasn't long
before we realized that we were going to have to take our human model of
the solar system outside.  For Pluto, we had to take 158 giant steps
away from the Sun!!

This makes a BIG impression on the kids, and they really enjoy it.

I'd like to suggest inserting a list of vocabulary words at the beginning of
each activity with a corrsponding Glossary at the end of the booklet.

Overall, we are having a lot of fun with the activities in the booklet.  We
have created our Mars Exploration journals and created sections, such as
Glossary, Research Ideas, and Mars Art.  We'll add more sections as needed.

We did two more activities today (relative sizes and relative distances).
The activities took a lot longer than I thought they would, mainly because I
tried to use the numbers given in the booklet.  If radii had been given
instead of diameter, it owuld have gone a lot smoother.  But we finished,
and now I know what to do next time.

Best regards,

Chris Rowan
Teacher, Morningside Elementary
Brownsville, TX
Chris Rowan                   
"I'm not much for sports.  I get a headache
putting my socks on."        Michael Caine