NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Formulas to Compute LHA
From: Will Ross
Date: 2009 Jun 28, 15:13 +0000
From: Will Ross
Date: 2009 Jun 28, 15:13 +0000
Correct, except its the south pole your looking at. Chempro...Will Ross, PhD
----- Original Message -----
From: glapook@pacbell.net
To: NavList
Sent: Sun, 28 Jun 2009 05:56:13 +0000 (UTC)
Subject: [NavList 8854] Re: Formulas to Compute LHA
The "time diagram" is found in many navigational texts. It consists of
a circle with the north posle as the center. You draw lines across the
circle representing the Greenwich meridian, your meridian, and a line
representing the GHA of the body (or of Aries if using H.O 249 vol.1).
This diagram makes clear the relationship between all of these lines.
gl
On Jun 27, 6:38 pm, Greg Rudzinskiwrote:
> Andrew,
>
> I believe the time diagram refered to is the Weems & Plath celestial
> slide rule. Google search this item for a description then look one on
> eBay.
>
> Greg
>
> On Jun 27, 5:27 pm, Andrew Corlwrote:
>
> > I am interested in this diagram, where can I find it?
>
> > Andrew
>
> > ________________________________
> > From: chempro
> > To: NavList
> > Sent: Saturday, June 27, 2009 11:00:31 AM
> > Subject: [NavList 8849] Re: Formulas to Compute LHA
>
> > Why dont you learn to use a TIME DIAGRAM? It simplfies ALL of the
> > concepts.It can universally used for all reduction methods from Ageton
> > to NASR. Chempro-Dr Will
>
> > On Jun 24, 8:07 am, Gary LaPookwrote:
>
> > > To see that you can use hour angle and LHA equally well, you just have
> > > to look at H.O. 249. Look at the LHA columns at each edge of the page
> > > and you will see that you get the same Hc for two values of LHA. Look at
> > > LHA 10 and LHA 350 on this example page:
>
> > >http://www.fer3.com/arc/img/106576.2007-page%20152.pdf
>
> > > LHA 10 is the same as hour angle 10 west., LHA 350 is the same as hour
> > > angle 10 east.
>
> > > This relationship is not so evident if you just look at H.O 229 due to
> > > the arrangement of the tables.
> > > gl
>
> > > Gary LaPook wrote:
> > > > Remember, LHA is in the range of 0º to 360º and is always measured to
> > > > the west from the assumed longitude (ALon). It is the angle measured
> > > > westward from the meridian of the ALon to the meridian containing the
> > > > body's grographic position (GP). There is no such thing as easterly LHA.
>
> > > > In the past, various computations methods and tables (e.g H.O. 214) used
> > > > "hour angle," (abbreviated "H.A." or "H" or "t"), which is the angle
> > > > measured between the meridian of the ALon and the meridian containing
> > > > the body's GP measured the shortest way, either west or east. Using this
> > > > notation, hour angle ends up in the range of 0º to 180º only and is
> > > > denoted "east" or "west." Because of the the way the trig formulas work,
> > > > using either method computes the same Hc and the same "azimuth angle"
> > > > ("Az" or "Z"). The only thing affected by choice of notation is the
> > > > method used for the final determination of Zn,(azimuth used for plotting
> > > > the LOP.)
>
> > > > The original Bygrave used hour angle, not LHA, and the scales were
> > > > marked from 0º to 90º and then back the other way, 90º to 180º. My
> > > > implementation of the Bygrave eliminated the second set of markings on
> > > > the scale, 90º-180º, to eliminate clutter so I added an extra step to
> > > > bring hour angle into the range of 0º to 90º only and provided the
> > > > necessary rules for the final computation of Zn. This is what is
> > > > happening on the top of the form I provided. If LHA is less than 90º, H
> > > > = LHA; if LHA is greater than 90º but less than 180º, H = 180º - LHA; if
> > > > LHA is greater than 180º but less than 270º then H = LHA - 180º; and if
> > > > LHA is greater than 270º but less than 360º, H = 360 º- LHA.
> > > > Conceptually, this is the smallest angle measured from either the upper
> > > > branch or from the lower branch of the observer's meridian to the
> > > > meridian containing the body's GP.
>
> > > > See the revised form at:
>
> > > >http://www.fer3.com/arc/img/108719.revised%20form%206-18-09.pdf
>
> > > > The formulas for calculating LHA are:
>
> > > > If your AP is in west longitude: LHA = GHA - ALon. (If necessary, add
> > > > 360 ºto GHA prior to subtracting ALon.)
>
> > > > If your AP is in east longitude: LHA = GHA + ALan. (if LHA then exceeds
> > > > 360º, subtract 360º from the result.)
>
> > > > Using the first formula for your first two examples, GHA (55º + 360º) -
> > > > 77º = LHA = 338º.
>
> > > > GHA 95º - 77º = LHA = 18º
>
> > > > The third example you bring up makes no sense since GHA is never
> > > > measured to the east, it is always measured west from Greenwich.
>
> > > > gl
>
> > > > Andrew Corl wrote:
>
> > > >> All,
>
> > > >> I need some help. I am attempting to work the problem in Ocean
> > > >> Navigator using the Lapook-Bygrave Slide Rule. I am uncertain how to
> > > >> compute the Local Hour Angle (LHA).
>
> > > >> In the following cases I am assuming my longitude to be 77 degrees
> > > >> west of Greenwich.
>
> > > >> 1. The GHA of the Sun is 55 degrees west of Greenwich
> > > >> 2. The GHA of the Sun is 95 degrees west of Greenwich
>
> > > >> In the following cases I am assuming my longitude to be 120 degrees
> > > >> west of Greenwich
>
> > > >> 1. The GHA of the sun is 170 degrees east of Greenwich.
>
> > > >> Also what is the formula if my position is east of Greenwich and the
> > > >> sun has a GHA of more than 180 degrees?
>
> > > >> Thanks
> > > >> Andrew- Hide quoted text -
>
> > > - Show quoted text -
>
>
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Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
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----- Original Message -----
From: glapook@pacbell.net
To: NavList
Sent: Sun, 28 Jun 2009 05:56:13 +0000 (UTC)
Subject: [NavList 8854] Re: Formulas to Compute LHA
The "time diagram" is found in many navigational texts. It consists of
a circle with the north posle as the center. You draw lines across the
circle representing the Greenwich meridian, your meridian, and a line
representing the GHA of the body (or of Aries if using H.O 249 vol.1).
This diagram makes clear the relationship between all of these lines.
gl
On Jun 27, 6:38 pm, Greg Rudzinski
> Andrew,
>
> I believe the time diagram refered to is the Weems & Plath celestial
> slide rule. Google search this item for a description then look one on
> eBay.
>
> Greg
>
> On Jun 27, 5:27 pm, Andrew Corl
>
> > I am interested in this diagram, where can I find it?
>
> > Andrew
>
> > ________________________________
> > From: chempro
> > To: NavList
> > Sent: Saturday, June 27, 2009 11:00:31 AM
> > Subject: [NavList 8849] Re: Formulas to Compute LHA
>
> > Why dont you learn to use a TIME DIAGRAM? It simplfies ALL of the
> > concepts.It can universally used for all reduction methods from Ageton
> > to NASR. Chempro-Dr Will
>
> > On Jun 24, 8:07 am, Gary LaPook
>
> > > To see that you can use hour angle and LHA equally well, you just have
> > > to look at H.O. 249. Look at the LHA columns at each edge of the page
> > > and you will see that you get the same Hc for two values of LHA. Look at
> > > LHA 10 and LHA 350 on this example page:
>
> > >http://www.fer3.com/arc/img/106576.2007-page%20152.pdf
>
> > > LHA 10 is the same as hour angle 10 west., LHA 350 is the same as hour
> > > angle 10 east.
>
> > > This relationship is not so evident if you just look at H.O 229 due to
> > > the arrangement of the tables.
> > > gl
>
> > > Gary LaPook wrote:
> > > > Remember, LHA is in the range of 0º to 360º and is always measured to
> > > > the west from the assumed longitude (ALon). It is the angle measured
> > > > westward from the meridian of the ALon to the meridian containing the
> > > > body's grographic position (GP). There is no such thing as easterly LHA.
>
> > > > In the past, various computations methods and tables (e.g H.O. 214) used
> > > > "hour angle," (abbreviated "H.A." or "H" or "t"), which is the angle
> > > > measured between the meridian of the ALon and the meridian containing
> > > > the body's GP measured the shortest way, either west or east. Using this
> > > > notation, hour angle ends up in the range of 0º to 180º only and is
> > > > denoted "east" or "west." Because of the the way the trig formulas work,
> > > > using either method computes the same Hc and the same "azimuth angle"
> > > > ("Az" or "Z"). The only thing affected by choice of notation is the
> > > > method used for the final determination of Zn,(azimuth used for plotting
> > > > the LOP.)
>
> > > > The original Bygrave used hour angle, not LHA, and the scales were
> > > > marked from 0º to 90º and then back the other way, 90º to 180º. My
> > > > implementation of the Bygrave eliminated the second set of markings on
> > > > the scale, 90º-180º, to eliminate clutter so I added an extra step to
> > > > bring hour angle into the range of 0º to 90º only and provided the
> > > > necessary rules for the final computation of Zn. This is what is
> > > > happening on the top of the form I provided. If LHA is less than 90º, H
> > > > = LHA; if LHA is greater than 90º but less than 180º, H = 180º - LHA; if
> > > > LHA is greater than 180º but less than 270º then H = LHA - 180º; and if
> > > > LHA is greater than 270º but less than 360º, H = 360 º- LHA.
> > > > Conceptually, this is the smallest angle measured from either the upper
> > > > branch or from the lower branch of the observer's meridian to the
> > > > meridian containing the body's GP.
>
> > > > See the revised form at:
>
> > > >http://www.fer3.com/arc/img/108719.revised%20form%206-18-09.pdf
>
> > > > The formulas for calculating LHA are:
>
> > > > If your AP is in west longitude: LHA = GHA - ALon. (If necessary, add
> > > > 360 ºto GHA prior to subtracting ALon.)
>
> > > > If your AP is in east longitude: LHA = GHA + ALan. (if LHA then exceeds
> > > > 360º, subtract 360º from the result.)
>
> > > > Using the first formula for your first two examples, GHA (55º + 360º) -
> > > > 77º = LHA = 338º.
>
> > > > GHA 95º - 77º = LHA = 18º
>
> > > > The third example you bring up makes no sense since GHA is never
> > > > measured to the east, it is always measured west from Greenwich.
>
> > > > gl
>
> > > > Andrew Corl wrote:
>
> > > >> All,
>
> > > >> I need some help. I am attempting to work the problem in Ocean
> > > >> Navigator using the Lapook-Bygrave Slide Rule. I am uncertain how to
> > > >> compute the Local Hour Angle (LHA).
>
> > > >> In the following cases I am assuming my longitude to be 77 degrees
> > > >> west of Greenwich.
>
> > > >> 1. The GHA of the Sun is 55 degrees west of Greenwich
> > > >> 2. The GHA of the Sun is 95 degrees west of Greenwich
>
> > > >> In the following cases I am assuming my longitude to be 120 degrees
> > > >> west of Greenwich
>
> > > >> 1. The GHA of the sun is 170 degrees east of Greenwich.
>
> > > >> Also what is the formula if my position is east of Greenwich and the
> > > >> sun has a GHA of more than 180 degrees?
>
> > > >> Thanks
> > > >> Andrew- Hide quoted text -
>
> > > - Show quoted text -
>
>
--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
