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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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