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of those West will be behind. When
doing calculations, revert everything
to UTC first, and don't forget the
date! The International Date Line is
where a change of date is officially
made, being mainly the 180°
meridian which bends to
accommodate certain islands in the
South Sea and parts of Siberia.
314 Canadian Professional Pilot Studies
Canadian time zones are:
Zone Convert (UTC-)
Newfoundland 3.5
Atlantic 4
Eastern 5
Central 6
Mountain 7
Pacific 8
They don't necessarily coincide with
the correct longitude lines, but align
with province boundaries, for
convenience (some places in BC, like
Fort Nelson, use Alberta time).
Since we take 24 hours to go round
the Sun, in one hour, we move
through 15°, or we take 4 minutes to
go through 1°. Similarly, in 1 minute
we transit 15 minutes, or take 4
seconds to go through 1 minute.
Just to remind you, a degree is split up
into minutes, which in turn are split
into seconds. Also, meridians diverge
in the Southern Hemisphere.
Astro Navigation
This is the process of finding your
way by looking at the stars, and used
in this context to set your DGI in
the Frozen North. For this you need
and astro compass, and a clear sky. The
compass is pointed towards a
heavenly body and a bearing taken,
which is set on your DGI when the
aircraft is lined up with it. You need
to know your latitude, declination and
local hour angle (LHA).
The latter is the angle between the
Sun and the present longitude (that
between the prime meridian and the
Sun is the Greenwich Hour Angle, or
GHA). Since the difference between
the GHA and LHA is the present
longitude, you can find LHA with:
LHA=GHA +E or –W Long
You need to know this, because only
the GHA is given in the tables
mentioned below. The declination is
the vertical angle of a planet from
the ecliptic (the path of the Sun's
disc), measured North or South (the
ecliptic is in the middle of the zodiac,
which is a narrow band in which the
Sun, Moon and planets move).
Now you need to look in the Air
Almanac, on the page containing the
tables for the current date, which has
details of the positioning of various
heavenly bodies to get the GHA and
declination. Standard times are listed
in three tables, for places fast on
UTC, keeping UTC and slow on
UTC. When using it read the
footnotes at the bottom of each
page, as they may be relevant. Also
get used to interpolation.
Set the latitude, declination and
LHA on the compass, line up on the
Sun and set the True North bearing
on the plate.
If you wish to use fixed stars, as
opposed to the planets, Sun or
Moon, which all move, you also
need to find the sidereal time, which is
just "star time" measured from the
first point of Aries. The difference is
that a sidereal day is nearly 4 minutes
shorter than a normal one.
GHA(Star)=GHA(Aries)+SHA(Star)
In other words, clock time (or Sun
time) is slower than star time. You
need to find the SHA (Sidereal Hour
Angle) before you can find the GHA
of a star, using the above formula.
Deviation
We saw above that the magnetism
from the Earth will vary the
Navigation 315
direction displayed by a compass.
The aircraft's magnetism, created
from large amounts of metal mixed
with electric currents, will do the
same thing, called deviation, which is
applied to the magnetic heading to
get Compass North.
The phrase here is Deviation West,
Compass Best, Deviation East, Compass
Least. This means that if the
deviation is to the left of the
magnetic North, the difference
should be added to the course to get
the correct magnetic heading.
Deviations will be displayed on a
small correction card next to the
compass, and are obtained after a
compass swing, a complex procedure
normally done by an engineer. There
will be an area on every aerodrome
well away from buildings, etc. set
aside for this purpose. Allowing for
deviation is called compensation.
Maps & Charts
The words map and chart are
nowadays used interchangeably but,
officially, a chart will show parallels
and meridians with minimum
topographical features, and be used
for plotting. A map will show greater
detail of the Earth's surface.
The point about them both is that
their representation of the Earth's
surface is only accurate within a
　
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