Tracking Changes in Photoperiod Around the Globe
Mystery Class Update: March 20, 1998
Today's Update Includes:
Celebrating Spring--Happy Vernal Equinox!
In celebration of today's Vernal Equinox, we have gathered a special set of longitude clues from the Mystery Classes which are given below! We'll also be giving you the latest sunrise and sunset times from Mrs. Berger's class, and some responses to last week's challenge question, but first let's get right to our special clues!
**Since this week's Update is chockful of information, you definitely should print it out right away and work from the print out. BE SURE to read through the instructions carefully and completely.
(PLEASE NOTE: For teachers with younger students (under grade 5), please don't be discouraged by this set of challenging clues--the clues will be easier after this, and we want you to know that at the end of the Mystery Class contest, we will group the answers by grade level, so the participants are grouped with others near their same grade level.)
The Longitude Problem
Well, get ready for some help, because here come the clues that we promised for the SPRING EQUINOX. These clues will help you estimate the approximate longitude of the Mystery Classes.
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 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 GMT clues to help you 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:
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.
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, 1998 (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.
The worksheet below will walk you through the calculations, and we have provided two examples to guide you. So let's get started by giving you the GMT sunrise time for the Mystery classes first, and then trying out the two examples.
Now It's Your Turn!!
The following documents will walk you through this activity. Good Luck!
This Week's Sunrise/Sunset Data
In celebration of today's Vernal Equinox, Mrs. Berger and her students, from East Hills School in New York had no "problem" gathering this week's sunrise and sunset data for you.
Remember, this information was recorded on Monday, the same day you collected your sunrise/sunset data.
Data For: Monday, March 16, 1998
Responses To Last Week's Challenge Question # 2
As you will read below, two classes really "hit the mark" and "lined-up"
on their response to this Challenge Question # 2, where we asked "What do you
think your graph will look like on March 20, 1998? Why do you think so?"