(c) the nautical almanac

8/10/2019 (C) the Nautical Almanac

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The Nautical Almanac

The Nautical Almanac contains the astronomical information

which is needed by the mariner. The information are:

GHA and declination for sun.

GHA and declination for the moon.

GHA and declination for selected stars and planets.

Corrections to reduce the observed values to true.


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The nautical Almanac is devoted to hourly tabulations of

the GHA and declination to the nearest 0.1 arc.

On each page you will find three consecutive days.

The left side of the pagethe GHA of the Aries and the GHA

and the declination of the Venus, Mars, Jupiter and Saturnare placed.

Besides this information you will find the SHA and the

declinationof 57 stars.


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On the right hand pagethe GHA and declinationof the

sun and the moon and the moons horizontal parallax arelisted.

Where applicable in the almanac the vand dare also

given. The vis the difference between the actual change of the

GHA in 1 hourand a constant value used in the

interpolation tables.

The dis the change in declinationin 1 hour. Both of themare listed to the nearest 0.1.


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Also included in the nautical almanac is the LMTof the

sunriseand sunset and the beginning and ending of the

nauticaland civil twilight. The beginning and ending of the twilight is for latitude

72oN to 60oS.

The LMT of moonrise and set is listed at the samelatitude for each of the three days.

Furthermore the Meridian Pass- (UT of transit cross the

celestial meridian of Greenwich) is also listed as well asthe magnitude of each planet at UT 1200 of the middle

day.


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The use of the nautical almanac

The main contents of the nautical almanac consists of data

from which the GHA and the declinationof all celestial

bodies can be obtained and this for any instant UT.

For getting the LHA following formula can be obtained:

LHA = GHA + East longitudeLHA= GHA - west longitude

For the sun, moon and the planets the GHA and the

declination for these bodies are tabulated for eachhour of

GMT.

For the stars the GHA is to be obtained from:

GHA of the star= GHA of the Aries + SHA of the star


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In the nautical almanac the permanent table for the

increments also includes corrections for vand d.

v is positiveunless a negativesign is shown (negative sign

only for Venus).

No sign is given for d. The rule here is:

d is positiveif the declination is increasing and

d is negative if the declination is decreasing.


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Finding the GHA and Declination of the sun

1. Enter the daily page of the nautical almanac for yourdate.

2. Take out the tabulated GHA and the declination for thebody observed for whole hour in GMT.

3. Record also the dvalue at the bottom of the declination

column.

4. Take out the incrementand correction table for theminutes. If there are second take the next earlier wholeminute.

5.Addthe increment to the GHA from the daily page.

6. The sum is the GHAof the sun.

7. Enter now the correction table for the same minute withthe d value.

8. Add the found value to the declination from the dailypage.

9. The sum is the declination of the sun.


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Finding the GHA and declination for the moon.

1. Enter the daily page of the nautical almanac for your date.

2. Take out the tabulated GHA and the declination for the moon for

the whole hour. 3. Take the corresponding vand dvalue tabulated on the same

line (determine the sign for both).

4. Take the increment and correction Table for minutes of GMT.

5. Take the GHA correction from the moon column.

6. Enter the correction table with the same minutes for the v

value.

7.Add both to the GHA from the daily page.

8. The sumis now the GHA of the Moon.

9. Enter the same correction table with the d value and extract thecorrection.

10. Give the correct sign to the d value and apply it to the

declination of the daily page.

11. The result is the declination of the moon.


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Finding the GHA and declination of a Planet

1. Enter the daily page of the nautical almanac for your date.

2. Take out the tabulated GHA and the declination for thebody

observed for whole hour in GMT.

3. Record the vvalue given at the bottom of each of these

columns. 4. Enter the increment and correction table for the minutes

of GMT, and on the line of the seconds of GMT take theGHA correction from the sun - planet column.

5. Now enter the correction table with the v value andextract the correction (give the correct sign for the v value).


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Finding the GHA and declination of a Planet

6. Add now the first correction to the GHA from the daily

page and apply the second correction in accordance with its

sign (+ or -).

7. The result is the GHAof the planet.

8. Take out from the correction table for the same minute

with the d value correction.

9. Extract the correction (with correct sign).

10. Apply the value to the declination from the daily page to

get the declination.


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Finding the GHA and declination of a star

To find the GHA for stars it is similar to sun and moon and

planets.

Instead of the GHA you have to take out the GHA of the

Aries.

Add the increments and as well the SHA of the star.


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Finding the LHA of the Aries Using Nautical Almanac

1. Take the GHA (Aries if for stars) for the month and day

and hour.

2. Take out the increment for the minutes and seconds.

3. Sum = GHA of Aries (if for stars)

4. Subtract (longitude if west) or add (if east)

5. If the sum of GHA and Longitude is bigger than 360o

subtract 360o to get the LHA for the Aries (for stars).


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Finding the LHA of the Aries Using HO table 249

1. Enter table 4a (for month and year).

2. Enter table 4b (for days and hours).

3. And at last enter table 4c (for minutes and seconds).

4. Then summarised to get the GHA for the Aries.5. Subtract (longitude if west) or add (if east)

6. If the sum of GHA and Longitude is bigger than 360o

subtract 360oto get the LHA for the Aries (for stars).


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Problem # 1. On the 30thof April 2000, at position 48oN,

007o50 E, an observer wants to sight the stars at 1900 H

GMT.

Following problems have to be solved with the help of the HO

table 249.

1. What is the LHA of the Aries at 1900 H GMT.

2. What stars are visible?

3. What are the altitude of these stars?

4. What are the azimuth of these stars?


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Solution:

1. Calculating the LHA of the Aries for 1900 GMT.

Table 4a - for April 2000 189o

39Table 4b - for 30th19 H 28o35

Table 4c - for 00m 00 s 00o00

GHA of Aries = 219o14

Assumed longitude = + 7o50 (East)

LHA of Aries = 227o04


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2. Which stars are visible?

Our assumed latitude was 48oN. From the page 65 in the HO

249 (Lat 48o

N) we will take out the LHA of the Aries on theleft side. Under LHA 227o we can take out the following stars

the sight.

Dubhe, Vega, Rasalhague, Antares, Arcturus, Denebola,

and Deneb


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(c) the nautical almanac

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