Tracking Changes in Photoperiod Around the Globe

Mystery Class Update: March 28, 1997

Please Note: This week's Update is chockful of information, so you should print it out and work from a hard copy. For teachers with younger students (under grade 5), please don't be discouraged by this week's challenging clues. We assure you, the clues will be easier after this. We also want you to know that for the Mystery Class contest we will group students with others near their grade level.

As usual, this week's report includes the latest sunrise and sunset times from Mrs. Berger's class, and some answers to last week's challenge questions, but first some background and then our clues!

The Longitude Problem
In answer to last week's Challenge Question #3, several students said they have been able to draw some conclusions about the LATITUDE of the Mystery Classes, but have not been able to determine anything about their LONGITUDE. Well, get ready for some help. Today's report includes the clues we promised last week. These clues will help you estimate the longitude of the Mystery Classes, using special data collected on the SPRING EQUINOX.

Only on the Equinox (spring or fall) does this clue work. As your graph shows, on the Equinox everyone on earth has the same amount of daylight. At all other times of year, either the Northern Hemisphere or Southern Hemisphere has more daylight. On the Equinox, neither of the poles of the Earth is not tilted toward or away from the sun. Because of this fact, you will be able to estimate LONGITUDE by knowing the time of sunrise at the Mystery Class on the Equinox when you are given that time in Greenwich Mean Time (GMT). Whew, sound confusing? Bear with us, because this is quite amazing!

How Time and Longitude are Related
To use today's clues to find the longitude of a Mystery Class, you must first understand a little about the relationship between time and longitude. Think about this: In order for sunrise to occur everyplace on earth each day, the earth must spin 360 degrees every 24 hours. If you hold your globe with the North Pole on top, you can see that the vertical longitude lines add up to 360 degrees. Using the following equation, you can figure out how many degrees the earth turns in each hour:

Using a division equation again, you can also figure out how many minutes it takes for the earth to spin 1 degree:

Why Greenwich Mean Time is Important
Greenwich Mean Time (GMT) is an international time-keeping standard, based on the local time at the 0 longitude point in Greenwich, England. Using GMT, you have an important clue to the location of your Mystery Classrooms. Each Mystery class has revealed what time it was in Greenwich Mean Time(GMT) when the sun rose at the Mystery Class on March 20, 1997 (the Vernal Equinox.) By knowing this GMT sunrise time for a Mystery Class and also knowing the time the sun rose at Greenwich that day, you can figure out how long the earth spun between the time the sun rose at the Mystery Class location and the time it rose at Greenwich. Once you know this, you can estimate the longitude of each Mystery Class location.

Now It's Your Turn!!
The following documents will walk you through this activity. Good Luck!

• Link to Mystery Class Worksheet

This Week's Sunrise and Sunset Times
(For your regular weekly sunrise/sunset graph.)

Thanks again to Mrs. Berger's students for sending us this week's sunrise and sunset times from the Mystery Classes. Mrs. Berger and her students sent this holiday greeting to you all:

"And to all our participants who are celebrating Easter this Sunday, Mrs. Berger's class has a special message for you: Happy Holiday!"

Here are the sunrise and sunset times:

Journey North Mystery Class
Sunrise/Sunset Data

Data For: Monday, March 24, 1997

Answers to Last Week's Challenge Questions

Thanks to the classrooms who sent in answers to Challenge Question #3, where we asked "From the data so far, what do you know about the longitude of each location? What do you know about their latitude?"

From: CALIFORNIA
Mystery classes. We know somethings about their latitudes: #6 is in the southern hemisphere near the South Pole, #3, 8, and 10 are also in the southern hemisphere. #4 is on the Equator. #s 5, 7, 9, 1, and 2 are in the northern hemisphere. #1 is near the North Pole and #7 is very close to our community, Camino, in latitude. Camino is about 50 miles east of Sacramento in the Sierra Foothills. We can draw a picture that shows the relative latitude of each class. The Harralsons jbharr@telis.org

From: MONTANA
Two weeks ago we used day length from Judith Gap, Mt and compared our day length to the other day lengths. we organized them around Judith Gap and around one another. we think (no promises of correctness) the classes go in this order from north to south- 2, 1, 9, 5, 7,(Same as Judith Gap) 4, 10, 8, 3, 6. Longitude is more difficult to figure out.
Shannon Walden (7swalden@3rivers.net)

In Challenge Question #4 we asked: "Do you notice anything unusual in the times listed for Mystery Classes numbers 3 and 6? What do you notice, and can you explain why this happened?

Mystery Classes numbers 3 and 6 had unusual times because they went off Daylight Saving Time. Here is what one of those Mystery classes had to say:

"Happy St. Patrick's Day to ya. We went off of daylight savings time yesterday. So now our times are an hour earlier. So now it's getting dark an hour earlier. Before long that's not going to matter too much."

Remember, your focus is on the photoperiod, so don't be confused by a Mystery Class' going on or off Daylight Savings Time. The photoperiod remains the same!

The Next Mystery Class Update Will Be Posted on April 4, 1997