Click Here to
Order this information in Print

Click Here to
Order this information on CD-ROM

Click Here to
Download this information in PDF Format

 

Click here to make tpub.com your Home Page

Page Title: The Relationship between Time and Longitude
Back | Up | Next

Click here for a printable version

Google


Web
www.tpub.com

Home

   
Information Categories
.... Administration
Advancement
Aerographer
Automotive
Aviation
Combat
Construction
Diving
Draftsman
Engineering
Electronics
Food and Cooking
Math
Medical
Music
Nuclear Fundamentals
Photography
Religion
USMC
   
Products
  Educational CD-ROM's
Printed Manuals
Downloadable Books

   


 

Share on Google+Share on FacebookShare on LinkedInShare on TwitterShare on DiggShare on Stumble Upon
Back
Standard Time Zones - 14220_152
Up
Quartermaster 1 & C - Military manual for the Quartermaster rate
Next
The Relationship Between Time and Longitude, Continued - 14220_154
The Relationship between Time and Longitude Background Information Ordinarily,  we  use  mean  solar  time,  which  is  measured  by  the  motion  of the  mean  Sun  around  the  Earth.  Let’s  suppose  your  ship  is  on  longitude 60°W.  When  the  Sun  is  on  your  longitude  or  meridian,  it  is  noon.  As  the Sun  continues  to  move  west  and  crosses  over  longitude  61°W,  it  is  noon there  and  the  time  on  your  meridian  is  later.  In  fact  it  is  the  time equivalent  of  1°  later.  But  you  can’t  measure  1°  on  your  watch;  you  must convert this 1° of arc to units of time. To  have  a  standard  reference  point,  every  celestial  observation  is  timed according  to  the  time  at  the  Greenwich  meridian.  Usually  this  is determined  by  means  of  the  chronometer  which  is  set  to  GMT.  To  clarify the relationship between time and arc, let’s consider a situation in which you know your longitude exactly at noon, and you want to find out the time  in  Greenwich. Arc to Time When  the  Sun  is  on  a  particular  meridian,  it  is  noon  at  that  meridian.  In other words, when the Sun is on the Greenwich meridian (0°), it is noon by  Greenwich  time.  To  make  the  problem  easier,  let’s  say  you’re  in  90°W longitude.  It’s  noon  where  you  are,  so  the  Sun  must  also  be  in  90°W longitude.  So,  since  leaving  Greenwich,  the  Sun  has  traveled  through  90° of  arc.  Because  it  was  1200  (noon)  Greenwich  time  when  the  Sun  was  at 0°, the time at Greenwich now must be 1200 plus the time required for the Sun to travel through 90° of arc. The  following  information  provides  all  the  elements  of  a  problem  for converting  arc  to  time.  If  you  know  that  it  takes  24  hours  for  the  Sun  to travel 360° or one complete revolution, it should be easy to find how long it  takes  it  to  go  90°.  If  the  Sun  goes  360°  in  24  hours,  it  must  go  15°  in 1  hour.  If  it  goes  15°  in  1  hour,  it  must  go  1°  in  4  minutes.  Then,  to  go 90°, it takes 90 x 4 minutes, or 360 minutes, which is the same as 6 hours.  Six  hours  ago  it  was  1200  Greenwich  time;  therefore,  the  time  at Greenwich  now  must  be  1800.  You  actually  have  converted  90°  of  arc  to 6  hours  of  time.  In  doing  so,  you  discovered  the  basic  relationship between  arc  and  time.  This  relationship  is  stated  as  15°  of  longitude  (arc) equals 1 hour of time. Your  problem  could  be  converting  time  to  arc--the  reverse  of  the  one  we worked  out.  Tables  for  converting  either  way  are  in  The  Nautical Almanac  and in  Bowditch,  but if you acquire the following easy methods of  converting,  you  won’t  have  to  refer  to  publications.  First,  you  must memorize the values for arc and time. 5-7

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing

comments powered by Disqus

Integrated Publishing, Inc.
9438 US Hwy 19N #311 Port Richey, FL 34668

Phone For Parts Inquiries: (727) 755-3260
Google +