The Equation of Time

posted by .

The reason for this post is I think I understand it and am seeking reassurance.

I am just starting to study celestial navigation and am trying to get to grips with some of the fundamentals. I need to use the Equation of Time of the Sun to establish Longitude.

Longitude is time and if it were not for the equation of time noon would occur at noon at the Prime Meridian (Greenwich) throughout the year every day. Longitude is established by judging when noon occurs at your location. This is when the Sun reaches its highest point in the sky from your location and is called Local Apparent Noon LAN. When this occurs you consider it is 1200 hrs at your location irrespective of what your watch says. This time (1200) is compared to GMT (UTC) and your longitude can be calculated from the difference, 4 minutes of time for every 1 degree of longitude. Just work out if you are East or West of the Prime Meridian.

Back to the Equation of Time.

When I first read about the Equation of Time I printed a couple of tables off the internet and read how it should be applied. I initially understood the figures given in the tables if stated as + or F (FAST) should be added to UTC. (Today the Equation of Time is + 16 minutes 18 seconds). My new understanding is that the + or F indicates that the Sun is FAST therefore noon (highest point of the sun from your location LAN) will occur before the clock time. This means if you wish to synchronise UTC and Sun time any figures given as + or F should be subtracted from UTC.

So at Greenwich today noon (LAN) will have occured at 16 minutes and 18 seconds to 12.

Conclusion. If Equation of Time is given as + subtract it from UTC. If given as - add it!

Anyone agree/disagree with my conclusion?

Mike.

I suggest you grab a Navigation text, a current one (the EOT changed in the last twenty years). Dutton's if you can find one (it is the one I used as a basic reference for years).
The EOT has to be applied to an observation at Greenwich also. I am uncertain of your meaning on that sentence.
If the Sun is running Fast, LAN then is before local noon.
The use of this is really simple in practice: Grab a text and run through the examples. I could not find any exercises on the internet.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Substitution Method-Plz help

    Use the Substitution method to solve the system of equations. x + y = -4 x - y = 2 solve for x in the second equation. x= y+2 Put that in for x in the first equation: x+y=-4 (y+2) + y = -4 solve for y. Then, x= y+2 i don't get it.How …
  2. Nautical

    I am just taking my first steps in learning Celestial Navigation. Some elements are becomong clear to me and with practice I will soon be able to take sights and establish the GP of a star. However I am having difficulty with sight …
  3. Nautical Studies

    I am just beginning to study celestial navigation and initially wish to concentrate my limited powers on the intercept method. I understand this involves the creation of a spherical triangle PZX which must be solved. I also understand …
  4. Navigation

    Solution to yesterdays problem I think! I am just beginning to study navigation & on top of that do not have a clue about how things should be expressed mathematically and on top of that have difficulty typing formulas on the computer …
  5. Just a message(please read)

    First of all I would like to thank everyone for helping me. The reason that I post my questions like I do is b/c they are multiple choice and all I'm looking for is to know if my answer is correct or not. If its not right then I would …
  6. Physics-repost, sorry, I still don't understand :(

    A forearm with a mass of 1.2kg supports a ball with a mass of 5.44 kg. The forearm is 0.050m long; it's perpendicular to the arm is 0.35m long, the center of gravity is at 0.15m from the elbow. Find the force exerted by rhe biceps …
  7. social studies

    I just needed some general help.................can you give me some tips on how to study for a socials final exam (PLEASE!). I am just not able to study, every single day I think that I will study and make my notes, but I keep postponing …
  8. English help

    From the words below, supply the words needed to complete the sentences. Chronic, clairvoyance, inadvertent, pretentious, celestial, vanguard. A. John had a CHRONIC back pain that left him bedridden. He refused, however, to visit the …
  9. Calculus

    At a certain point on the beach, a post sticks out of the sand, its top being 76 cm above the beach. The depth of the water at the post varies sinusoidally with time due to the motion of the tides. The depth d is modeled by the equation …
  10. Math-calculus

    At a certain point on the beach, a post sticks out of the sand, it's top being 76 cm above the beach. The depth of the water at the post varies sinusoidally with time due to the motion of the tides. The depth d is modeled by the equation …

More Similar Questions