Mystery Class
Jim Gilbert

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Mystery Class

Mystery Class Worksheet
Estimating Longitude using Sunrise Times on the Spring Equinox

Use this worksheet to estimate the longitude of each Mystery Class. For each site, use the sunrise figures provided on today's Equinox Sunrise Table. Follow the step-by-step instructions on this worksheet.

Step # 1
Fill in the GMT sunrise time for the Mystery Class. This is the time it was in Greenwich, England when the sun rose at the Mystery Location.
Put in Box A.
Step # 2
Fill in the time that the sun rose in Greenwich, England on March 20, the spring equinox. This year that sunrise time is 6:03 A.M.
Put in Box B.

6:03 A.M.
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 is not a simple subtraction or addition equation. Remember that hours and minutes are not in decimal form. Be sure to think about your answer!) Put in Box C.
Step # 4
For the next step you'll need to convert hours to minutes. Multiply each hour in Box C by 60. Next add the remaining minutes from Box C. Put the answer in Box D.
Step # 5
Almost done! You now know how many minutes the earth spun between the time the sun rose at Greenwich and the time it rose at the Mystery Class location. Since the earth spins 1 degree longitude every 4 minutes, you must next divide by 4 to get the number of degrees away from Greenwich. Divide the number of minutes given on in Box D by 4. Put the answer in Box E.

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 in Box A is later than the sunrise in Box B, the Mystery Class is west of Greenwich (Western Hemisphere).

  • If the sunrise in Box A is earlier than the sunrise in Box B, the Mystery Class is east of Greenwich (Eastern Hemisphere).