Scribd
Upload
378 views2 pages

The Nautical Almanac

The nautical almanac provides Greenwich hour angle and declination for celestial bodies. It gives the sun's GHA hourly and its declination can be found between hours using the hourly change. For planets, it provides hourly GHA and declination, with the GHA change varying between planets and corrected using hourly values. For stars, it lists their position relative to the first point of Aires instead of individual GHA, whose change is found using increments tables, and provides each star's constant declination.

Uploaded by

GNS
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
378 views2 pages

The Nautical Almanac

The nautical almanac provides Greenwich hour angle and declination for celestial bodies. It gives the sun's GHA hourly and its declination can be found between hours using the hourly change. For planets, it provides hourly GHA and declination, with the GHA change varying between planets and corrected using hourly values. For stars, it lists their position relative to the first point of Aires instead of individual GHA, whose change is found using increments tables, and provides each star's constant declination.

Uploaded by

GNS
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 2

Nautical Almanac:

GREENWICH HOUR ANGLE & DECLINATION


The Nautical Almanac is a publication that gives relevant details of celestial
bodies.
The position of celestial bodies is given in the form of Greenwich Hour Angle
(similar to Longitude) and "Declination" (similar to Latitude).
UT (GMT) times must be used when extracting information from the Almanac.

Sun:
The GHA is tabulated for every hour. The increment for the minutes and seconds is
obtained from the "Increments and Corrections" tables. (Buff coloured pages.)
The declination is also tabulated for every hour. To find the declination of the sun
at a time between the tabulated hours the hourly change of declination, "d", given
at the foot of the table, is used. How much of this hourly change is required is
found by use of the "Increments and Corrections" tables. (Note, only the minutes
are considered, the seconds are neglected.) The declination at an intermediate
time must lie between the given declinations at the adjacent hours.

Planets:
GHA and declination information for the 4 navigational planets; Venus, Mars,
Jupiter & Saturn, are tabulated for every hour. The increment for the minutes and
seconds is obtained from the "Increments and Corrections" tables. (Buff coloured
pages.)

Celestial Navigation HR09 35


V1.1 (Nov 18) BAF
However, the GHA of the 4 planets does not change at exactly 15° per hour, nor is
the hourly change constant. Hourly change of GHA varies between:

Venus: 14° 59.0' 15° 05.0'


Mars 15° 00.0' 15° 04.0'
Jupiter 15° 02.0' 15° 03.4'
Saturn 15° 02.0' 15° 03.4'

This discrepancy is given in the form of a "v" correction, the hourly "v" for each
planet being given at the foot of their respective column. How much of this hourly
correction is required is found by use of the "Increments and Corrections" tables.
(Note, only the minutes are considered, the seconds are neglected.) NOTE The
correction for Venus may be negative, all other planets are always positive.
The declination for the planets is tabulated hourly, with the hourly "d" given at the
column foot. The declination at intermediate times is found by the same process
as the sun.

Stars:
Instead of tabulating the GHA of each star separately the Almanac shows the GHA
of the "First Point of Aires" () and gives the position of each star relative to this
point, called the Sidereal Hour Angle. (SHA). The SHA is always added to the
GHA. The GHA at intermediate times is found by the use of the "Increments and
Corrections" tables, Aries having its own column.
The declination of stars hardly change, consequently the declination of each star is
listed.

Celestial Navigation HR09 35


V1.1 (Nov 18) BAF

You might also like