Table of Observations for Calculating Latitude and Longitude

  1. Longitude
    1. Set up vertical post (at least one meter high) and use a magnetic compass or GPS device to layout "north". With a straight-edge, use the chalk to draw a one meter "ray" due north from the verticle post.
    2. At each time interval, mark with chalk the end of the shadow cast by the post, measure the distance and then record the entry.
    3. You will know it is solar noon when the shadow crosses the meridian; that should also be the mark with the shortest measurement.
    4. At true /solar “noon” record the time on your watches.  The time difference to GMT “noon” is 8 hours plus. Convert the minutes into the decimal system, so 6 min = 0.1 of an hour, etc.  Take the difference between GMT noon and local noon (about 8.1 or .2 hours, multiply the number x 360◦ and then divide by 24 (hours).  Note this is a ratio (time lag between GMT noon and local noon is to 360◦ and 8.2 hours is to 24hours.  The answer is the number of degrees west of Greenwich.  This should yield a value of about 123◦ W.  Note that one degree is about 35 miles at our latitude.

Time

Length of shadow

Angle off “true” north

Angle of shadow

12:40

      

12:50

      

13:00

      

13:05

      

13:10

      

13:15

      

13:20

      

13:25

      

13:30

      

2. Latitude:       = (90◦- measured altitude) + declination (derived from table above "angle of shadow") or from the Altitude entry in the handbook provided below)

                        = (90 – 62) = 28 + 16

                        =44◦ N

                        Marine astrolabe = http://www.astrolabes.org/mariner.htm

                        Declination table for Eugene:

                        http://www.weatherunderground.com/cgi-bin/findweather/getForecast?query=Eugene+Oregon

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May 3, 2004

Sun
Rise

Solar
Noon

Sun
Set

Actual Time

6:00 AM PDT

1:09 PM PDT

8:18 PM PDT

Civil Twilight

5:28 AM PDT

  

8:50 PM PDT

Nautical
Twilight

4:48 AM PDT

  

9:30 PM PDT

Astronomical
Twilight

4:04 AM PDT

  

10:15 PM PDT

Altitude

-0.8°

61.9°

-0.8°

Azimuth

66.7°

180.2°

293.5°

Hour Angle
of the Sun

-107.2°

0.1°

107.4°

Mean Anomaly
of the Sun

-241.23°

-240.94°

-240.64°

Obliquity

23.44°

23.44°

23.44°

Right Ascension
of the Sun

40.98°

41.26°

41.55°

Sun Declination

15.87°

15.96°

16.04°

Moon

7:18 PM PDT
(5/3)

  

5:26 AM PDT
(5/3