EXPLANATION OF NAUTICAL ALMANAC Flashcards
meridian passage of Aries at the Prime Meridian- Greenwich- 0°. Time
figure is GMT/UT.
Mer. pass
Date and Time based on ____________.
GMT/UT
“The change in hour angle arising from v of the body at the time of the sight observation is
accounted for with the v correction.” Source- Bowditch 2017, Chapter 19- Sight Reduction p. 313. The planet’s v is positive unless proceeded by a minus sign which is sometimes the case with Venus. The sign of the Moon’s v is positive.
v
“The change in declination of the body at the time of the sight observation is accounted for
with the d correction.” Source- Bowditch 2017, Chapter 19- Sight Reduction p. 313. The sign of the Moon or planet’s d correction is determined by the declination trend- positive if successive declination values increase and negative if they decrease.
d
_____ is the magnitude or brightness of the planet.
m
A bright planet will have a ________ beside the figure. A fainter planet will have no sign
beside its magnitude figure.
minus sign
planet meridian passage time at the Prime Meridian- Greenwich- 0°. Time figure is GMT/UT.
Mer. pass
planet SHA.
SHA
_______ is calculated by subtracting Aries GHA from planet GHA.
Planet SHA
for Venus and Mars.
Horizontal parallax
_________ is the angle subtended by half the Earth’s diameter as viewed from the
planet in minutes of arc.
Horizontal parallax
Semi-diameter of the Sun in minutes of arc. One half of the angular width of the Sun as observed on earth.
SD
the daily average change, per hour, in the Sun’s declination in minutes of arc.
d
Semi-diameter of the Moon in minutes of arc.
SD
________ is one half of the angular width of the Moon, as observed on earth.
Semi-diameter
the angle between two lines, one from the center of the Moon to the center of the
Earth, the other from the center of the Moon to the edge of the Earth. This angle is about 56’, but it changes slightly from day to day as the distance to the Moon changes along its elliptical path around the Earth.
HP
_______ is the approximate GMT/UT when the Moon crosses The Prime Meridian (at Greenwich) or the 180° line of longitude.
Moon- Mer. Pass
_____ means the GMT/UT when the Moon crosses The Prime Meridian (Greenwich).
Upper
______ means the GMT/UT when the Moon crosses the 180° line of longitude.
Lower
this is the number of days past a new Moon
Moon- Age
Typically, there are ____ days in a lunar month.
29 days
the amount of the Moon’s illumination
Moon- %
_____% would be a full moon.
100%
____% would be about 1⁄2 of the Moon is illuminated
49%
A _________ range percentage is provided but only one graphic for the phase.
3 day range percentage
the approximate GMT/UT when morning Nautical Twilight begins.
(Morning) Twilight- Naut.
___________ is the time when the center of the sun is 12° below the horizon and the horizon is visible enough to be used for marine sextant observations.
Nautical twilight
the approximate GMT/UT of morning civil twilight starts when the geometric center of the sun is 6° below the horizon.
(Morning) Twilight- Civil
the approximate GMT/UT when the Sun is 0° 50’ (semi-diameter plus refraction) below the horizon.
Sunrise
the approximate GMT/UT when the Sun is 0° 50’ (semi-diameter plus refraction) below the horizon.
Sunset
the approximate GMT/UT of evening civil twilight that ends when the geometric center of the sun is 6° below the horizon.
(Evening) Twilight- Civil
the approximate GMT/UT of when evening Nautical Twilight ends. Nautical twilight is the time when the center of the sun is 12° below the horizon and the horizon is no longer visible enough to be used for sextant observations.
(Evening) Twilight- Naut.
the approximate GMT/UT when the Moon is about 0° 05’ to 0° 10’ below the horizon.
Moonrise
the approximate GMT/UT when the Moon is about 0° 05’ to 0° 10’ below the horizon.
Moonset
______ means the Sun or Moon remains continuously above the horizon on that day.
▭
______ can also mean twilight lasts all night
‒:‒
______ means the Sun or Moon remains continuously below the horizon on that day.
▬
______ means Moon does not rise or set on that day but may have risen or set the previous day or following day.
‒:‒
TRUE OR FALSE
Time of Sunrise, Sunset, Moonrise, Moonset and twilight is based on GMT/UT of the event at 0° (Greenwich) and can be considered as approximate LMT (Local Mean Time)
with a tolerance of +/- 30 minutes depending on where you are within a time zone.
TRUE
TRUE OR FALSE
Basically the Equation of Time (EoT) is the difference between clock time and time seen on a sundial. This is comparing “clock time”, as a mechanical measurement of time, and the sundial being time determined by the position of the Sun at any given moment. The figures listed are for 00h and 12h
TRUE
TRUE OR FALSE
Using the EoT you can get fairly accurate determination of when Meridian Passage (Local Apparent Noon) occurs at your position. Unshaded EoT values are subtracted from 12:00 to get Meridian Passage.
TRUE
TRUE OR FALSE
Shaded EoT values are added to 12:00 to get Meridian Passage. An Equation of Time chart (as a curve) is provided in each almanac on The Nautical Almanac.com
TRUE
_____ just to the right of the Eqn. of Time is the approximate GMT/UT when the Sun crosses The Prime Meridian (at Greenwich) for that specific date.
Sun- Mer. Pass
TRUE OR FALSE
To find the correction for either v or d enter the Increments and Corrections pages for the minutes in time of the observation and find the value in the v or d corr. Columns. Find the
v, or d, value in the left side of one of the three columns. To the right of that value is the v, or d, correction. Be sure to add or subtract the values depending upon the sign of the value as mentioned above.
TRUE
TRUE OR FALSE
Typically, only 59 stars are used for navigational purposes in both Northern and Southern
Hemispheres.
FALSE
57 STARS
SHA, Sidereal Hour Angle, and Declination.
Stars
TRUE OR FALSE
Stars- SHA, Sidereal Hour Angle, and Declination. 59 stars are listed.
TRUE
SHA
Sidereal Hour Angle
