Mystery Class GMT Worksheet 2007
Estimating Approximate Longitude using GMT Sunrise Times on the Vernal Equinox

Step # 1
Fill in the GMT sunrise time and date for the Mystery Class. This is the time it is at Greenwich, England when the sun rises at the Mystery Location.

Put answer in Box A.

BOX A

_______time______date
Step # 2
Fill in the time that the sun rises at Greenwich, England on March 21, the spring equinox. This year that sunrise time is 06:02 A.M.

Put answer in Box B.
BOX B

06:02 A.M. (3/21)

Step # 3
Figure out how many hours and minutes there are between the time in Box A and the time in Box B. Put answer in Box C. This is the difference in time between sunrise at Greenwich and sunrise at the mystery location. (CAUTION!!! This may not be a simple subtraction or addition equation. Remember that hours and minutes are not in decimal form. Be sure to think about your answer!) Put answer in Box C.
BOX C

_______hours______minutes
Step # 4
For the next step you'll need to convert hours to minutes. Multiply each hour in Box C by 60, then add the remaining minutes from
Box C.

Put answer in Box D.
BOX D

________minutes
Step # 5
Almost done! You now know how many minutes the earth spins between the time the sun rises at the Mystery Class location and the time it rises at Greenwich. Since the earth spins 1 degree longitude every 4 minutes, you must next divide by 4 to get the number of approximate longitude degrees away from Greenwich. Divide the number of minutes given in Box D by 4.

Put answer in Box E.
BOX E

________degrees

Step # 6: Eastern or Western Hemisphere?
To determine the site's longitude you need to know if it is in the Eastern or Western Hemisphere (i.e east or west of Greenwich, which is 0 degrees).

  • If the sunrise time in Box A is later than the sunrise time in Box B, the Mystery Class is west of Greenwich (Western Hemisphere).
  • If the sunrise time in Box A is earlier than the sunrise time in Box B, the Mystery Class is east of Greenwich (Eastern Hemisphere).
BOX F


East or West?