HELP for Teachers

MYSTERY CLASS:  HELP FOR TEACHERS

For Use With March 20th Data:

We're all learning, aren't we?  This step of the Mystery
Class project may present a challenge to your students.  I
hope the discussion and activities below will help them
understand the concepts which make it possible for you to
use today's clues to estimate the longitude of our Mystery
Classes. The ANSWERS are also included at the end of this
report.

Please reassure your students that the clues will get easier
as time goes on.  It may encourage them to know that
they're learning something many adults don't quite
understand!

The Big Picture

It's helpful to start by explaining the significance of the
equinox.  Using a globe and flashlight, review these things
with your students. During the discussion, walk the globe
around the "sun" a few times to simulate the yearly cycle.

1)  It takes a year for the earth to rotate around the sun.

2)  The earth is tilted on its axis.  Notice that the
northern hemisphere is tilted AWAY from the sun during half
of the year and TOWARD the sun during the other half.  Put
the earth in the position when it's summer in the northern
hemisphere. Ask your students where the days would be the
longest when the earth is in this position. Where would they
be the shortest?  Have them notice how the latitude lines
are oriented in relation to the sun.  Ask them how latitude
and daylength might be related.

3)  The dividing lines are the spring (vernal) equinox and
fall (autumnal) equinox.  As you walk the earth around the
sun, stop when you're at the spring and fall equinox.
Notice how the latitude lines are now oriented in relation
to the sun.  Point out that the "north/south" tilt of the
earth doesn't matter when the earth is "sideways" to the sun
as it is on the equinox. Refer to your Mystery Class graphs.
Show them that all places on earth have (almost!) equal day
length at the equinox.  Spin the globe a few times so
students can see that the amount of time the sun shines on
all parts of the earth is the same during the equinox.

How Time and Longitude are Related

In order for sunrise to occur everyplace on earth each day,
the earth must spin 360 degrees. Hold your globe so students
can see it with the North Pole on top.  Point out that the
longitude lines add up to 360 degrees.  Have students figure
out how many degrees the earth turns in 24 hours   You may
need to give them this equation:

360 degrees divided by 24 hours =   (15)  degrees per hour.

This also means that:
60 minutes divided by 15 degrees = ( 4 ) minutes per degree.
We'll use this figure in Step #5 below.

Why Greenwich Mean Time is Important

You have an important clue to the location of your Mystery
Classrooms this week.  Each has revealed what time it was
(GMT) when the sun rose.  This will tell you how long it
took the Earth to spin so the sun would appear (rise) at
their location.

Since Greenwich is at 0 degrees longitude, it's easiest to
count from this point.  All we need to know is the time the
sun rose in Greenwich and we can estimate the longitude of
each place. The worksheet below will walk you through the
calculations.  We have provided an explanation for each step
in hopes that your students will understand the rationale.

(This worksheet is also being sent in a seperate message so
you can print it out for your students.)

MYSTERY CLASS WORKSHEET #2   ESTIMATING LONGITUDE

Here's a worksheet that will help you estimate the longitude
of each Mystery Class.  Just follow these steps for each
Mystery location.

1) Fill in the GMT sunrise figure from the Mystery Class.
This is the time it was in Greenwich, England when
the sun rose at the Mystery Location. Put on Line a).

    a)  ______

2)  Fill in 6:05
This is the time of sunrise in Greenwich, England on
the spring equinox. Put on Line b).

    b) ______

3)  Subtract b) from a) and put answer on line c).

    c) _____

This is the difference in time between sunrise at Greenwich
and sunrise at the Mystery Location. CAUTION!!!  This is not
a simple subtraction equation. Remember that hours and
minutes are not in decimal form. For example:  Mystery Class
#7's sunrise at 5:24 am is 41 minutes earlier than 6:05.  Be
sure to think about  your answer!  Note also, if the sunrise
is earlier than sunrise in Greenwich, the location is east
of Greenwich.

For the next step you'll need to use minutes, so this
step converts hours to minutes.

4) Multiply each hour by 60, add the remaining minutes
and put the answer on line d).

    d) _____

Now you've almost got the Mystery Class' longitude!
You now know how many minutes it took for the earth to
spin enough for the sun to rise at the Mystery Class.

5)  Divide d) by 4 and put the answer on line e)

   e) ______

Since the earth spins 1 degree longitude every 4 minutes,
when you divide by 4 you get the degrees longitude.

Note:
If the number is larger than 180 the location is more than
halfway around the world from Greenwich and is in the
eastern hemisphere.  This means the longitude will be in
degrees East. Just subtract the number on line e) from 360.

****************************************************************

Here are the answers your students should get.  These are
ESTIMATES of longitude.

Mystery Site       Estimated Longitude
#1                         19 E

#2                        147 W

#3                        170  E  (see note below)

#4                        106 W

#5                        155 W

#6                         38 E

#7                         10 E

#8                         95 W

#9                         35 E

#10                    No Data

#11                       147 E

Note concerning Mystery Class #3:

As described in step #5 above, since the initial answer
(190) is greater than 180 degrees, the location is in the
eastern hemisphere.  Therefore, you must subtract 190 from
360.  This gives you the 170 degrees E answer.