Mystery Class Update: March 11, 2005

Today's Report Includes:

• Spring Begins March 20--Happy Vernal Equinox!
• The Longitude Clues Are Here!
• Note to Teachers with Younger Students
• The Longitude Problem
• How Time and Longitude are Related
• Why Greenwich Mean Time is Important
• Let's Get Started! Instructions to Approximate Longitude
• This Week's Sunrise/Sunset Times
• Coming Together or Growing Apart? Discussion of CQ #3 and #4
• Important: Plan Ahead and Mark your Calendars

• Bookmark the Mystery Class Glossary

IMPORTANT: Be sure that you read and follow ALL the instructions in this report very carefully. We suggest you print this report and work from the printed copies. The special Longitude Clues can help you estimate the APPROXIMATE Longitude for the 10 secret Mystery Classes. But remember, it's only an ESTIMATE, and you'll certainly need to use all the clues that you'll receive in the coming weeks too.

Everything you need to get started is available in today's report. NOW, let's get to our special Longitude Clues!

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The Longitude Problem (IMPORTANT: Please Read Carefully)
The changing photoperiods that you've tracked have provided some clues about the LATITUDE of the Mystery Classes. But that photoperiod information doesn't help you much when you try to determine the LONGITUDE of the Mystery Classes.

Credit: Illinois State University

Well, get ready for some help, because here are the clues that we promised for the SPRING EQUINOX. These clues will help you estimate the approximate longitude for the 10 Mystery Classes. (Remember, they're estimates--they may not provide a location's exact longitude.)

Only on the Equinox (spring or fall) do these clues work. As your graph will show, on the Equinox everyone on earth has about the same amount of daylight. At all other times of year, either the Northern Hemisphere or Southern Hemisphere has more daylight due to the tilt of the Earth's axis. But on the Equinox, neither of the poles of the Earth is tilted toward or away from the sun. Because of this fact, you will be able to estimate approximate LONGITUDE by knowing the time of sunrise at the Mystery Class on the Equinox when you are given that sunrise time in Greenwich Mean Time (GMT). Whew, sound confusing? Hang in there, because this is quite amazing!

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How Time and Longitude are Related
In order to use the GMT/Longitude clues to help you ESTIMATE the approximate longitude of a Mystery Class, you must first understand a little background about the relationship between time and longitude. A sphere such as the Earth is divided by longitude lines into 360 degrees. If you hold your globe with the North Pole on top, you can see that the vertical longitude "meridians" add up to 360 degrees.

Think about this: In order for sunrise to occur everyplace on earth each day, the earth must spin or rotate 360 degrees on its axis every 24 hours.

Using the following equation, you can figure out how many degrees the earth turns in each hour: 360 degrees divided by 24 hours = 15 degrees per hour. Using a division equation again, you can also figure out how many minutes it takes for the earth to spin 1 degree: 60 minutes divided by 15 degrees = 4 minutes per degree.

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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--called the Prime Meridian--in Greenwich, England. Longitude values to the east of the Prime Meridian are designated as 0 to 180 degrees East longitude; while those values to the west of the Prime Meridian are designated as negative numbers of 0 to -180 degrees West longitude. Using GMT, you have an important clue to the approximate longitude location of your Mystery Classrooms.

All Mystery Classes have revealed what time it will be using Greenwich Mean Time (GMT) when the sun rises at their Mystery site on March 20, 2005 (the Vernal Equinox.) By knowing this GMT sunrise time for a Mystery Class and also knowing the time the sun rises at Greenwich that day, you can figure out how long the earth spins between the time the sun rises at the Mystery Class location and the time it rises at Greenwich. Once you know this, you can estimate the approximate longitude of a Mystery Class location.

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Let's Get Started! Instructions to Approximate Longitude

Instructions to Approximate Longitude

1) Print 10 copies of the GMT Worksheet (one for each secret Mystery site) and follow the step-by-step instructions on the Worksheet to estimate the approximate Longitude of each Mystery Class: Mystery Class GMT Worksheet

2) In order to use the GMT Worksheet, you will also need to print out the: Equinox Sunrise Table

3) To help get you started, we've already calculated the approximate Longitude for two of this year's Mystery Class sites, using the GMT Worksheet (two freebies!). Be sure to review the two examples below: GMT Worksheet Example One GMT Worksheet Example Two

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This Week's Sunrise/Sunset Times
Remember, the secret Mystery sites recorded their times last Monday, the same day you collected your own local sunrise/sunset data.

• Link to This Week's Sunrise/Sunset Data

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Coming Together or Growing Apart? Discussion of CQ # 3 and #4
In Challenge Question #3 we asked you to study your graph and explain "What type of weather changes do you think Mystery Class #2 might be experiencing right now? How does that compare to your hometown weather?"

Grade Six students Olivia, Muriel and Natalie from St. John Greek Orthodox Day School in Tampa, FL correctly compared their own location to MC #2 and drew these conclusions:

"MC #2 is getting less sunlight, shorter days, and colder weather. In contrast, Tampa, our home city, is getting more sunlight, longer days, and warmer weather. The differences at the two locations are happening because MC#2 is in the southern hemisphere and heading into fall, while we are in the northern hemisphere and heading into spring."

Mrs. Anderson's 6th Graders from Plymouth, MN made a similar comparison: "In our hometown the days are getting longer and the sun's rays are getting stronger and more direct. We are looking forward to warmer weather. In MC #2 they are experiencing shorter days and looking for their weather to get cooler."

"all Mystery Classes will be at about the same point on the graph because March 20 is the equinox, when the days will be the same length as the nights" Alex and Reid from St. John Greek added that "all the lines on the graph will have the same photoperiod on March 20, 2005, and all places on earth will have about the same amount of sunlight on that day."

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