if its noon solar itme at 70 degrees west longitude , what is the solar time

Question

if its noon solar itme at 70 degrees west longitude , what is the solar time at 90 degrees west longitude

Answer 1

Longitude is measured from the Prime Meridian (through Greenwich, England) as though the Earth were cut at the Equator and we were looking at a circle with 360°.  Now, instead of using 0-360°, we use 0-180° E or W of the Prime Meridian (or we could use + and - to indicate this; see later).

 

The problem states that it is noon solar time at 70° W longitude and asks for the solar time at 90° W longitude.  Of course, points further west will have an earlier time (think about the rotation of the earth or visit time.gov).

 

Noon solar time is when the Sun crosses your meridian.  The problem states that this is the situation at 70° W longitude.

 

[Note:  Mean solar time is the time given by a steady clock that on the average matches a traditional sundial.  Sundials run fast or slow by up to 15 minutes relative to a steady clock, an effect called "The Equation of Time".]

 

At 90° W longitude (20° further west), the time equation (given at http://www.polaris.iastate.edu/NorthStar/Unit2/unit2_sub2.htm ) is:

Your longitude is equal to [(your Mean Solar Time) minus (Greenwich Mean Solar Time) ] x 15 degrees

 

So,

           -70 = ( 12.0 - GMST ) * 15       [mean solar time at 70°W longitude is noon (in decimal with fraction); also, use negative for W degrees]

 

            -90 = ( x - GMST ) * 15            [let x = mean solar time at 90°W longitude]

 

        - - - - - - - - - - - - - - - - - - - - -

            +20 = ( 12.0 - x ) * 15             [elimination method; subtract equations]

 

              +20 = 180 - 15x

              15x = 160             [add 15x and subtract 20 from both sides]

                x = 10 2/3

 

The time at 90°W is 1040 hours.     [note: convert fraction back to minutes.]

 

 

 

Answer 2

 

The formula says multiply by 15.

 

(90-70)x15 = 20 x 15 = 300

so 3 pm

 

http://www.polaris.iastate.edu/NorthStar/Unit2/unit2_sub2.htm