Nav time diagram

A time diagram is a diagram on the plane of

the celestial equator or equinoctial in which

the celestial equator appears as a circle, and

celestial meridians and hour circles as radial

lines. It is used to facilitate solution of time

problems and other problems involving arcs

of the celestial equator or angles at the pole,

by indicating relations between various

quantities involved. Conventionally, the

relationships are given as viewed from a point

over the south pole ( Ps ) westward direction

being counterclockwise.

TIME DIAGRAM

A DIAGRAM ON A PLANE OF CELESTIAL

EQUATOR AS SEEN FROM THE SOUTH

POLE.

Time diagram

HOW ARE HOUR ANGLES( HA ) AND UNITS OF TIME

MEASURED?

Longitude – ( measured from going G going E or W, 000⁰- 180⁰

As view from the south pole, if the Greenwich G is on top, to theright are east longitudes and to the left, are west longitudes. Byconventions, the diagram is oriented so that M is at the top.Therefore G will move either left or right of M depending on thegiven longitude. Ex.

G

g

EastWest

M

G G

m

g g

E W

GHA – measured from G counterclockwise to the

body.

G

g

• M –UPPER BRANCH OF LOCAL MERIDIAN.

• m –LOWER “ “ “ “

• G –UPPER “ “ GREENWICH “

• g –LOWER “ “ “ “

• G – M –LONGITUDE OF OBSERVER (E/W)

• MERIDIAN ANGLE (t) – ANGULAR

DISTANCE MEASURED FROM FIXED

MERIDIAN UP TO THE BODY, EASTWARD

OR WESTWARD FROM 0° - 180°, NAMED

E/W DEPENDING IF IT IS RISING OR

SETTING.

• IF LHA < 180° / LHA = t NAMED “W”

• IF LHA > 180°/360° - LHA = t NAMED “E”

• GHA) – ANGULAR DISTANCE MEASURED

FROM GREENWICH MERIDIAN “G” UP TO

THE BODY FROM 0° - 360° COUNTER

CLOCKWISE. (WESTWARD)

• LHA – ANGULAR DISTANCE MEASURED

FROM LOCAL MERIDIAN “M” UP TO THE

BODY FROM 0° - 360° COUNTER

CLOCKWISE. (WESTWARD)

• SHA – ANGULAR DISTANCE MEASURED FROM

THE 1ST. POINT OF ARIES UP TO THE

BODY,FROM 0° - 360° COUNTER CLOCKWISE.

(WESTWARD)

• RA – ANGULAR DISTANCE MEASURED FROM

THE 1ST. POINTOF ARIES UP TO THE BODY,FROM

0° - 360° CLOCKWISE.

(EASTWARD)

SHA + RA = 360°

360° - SHA = RA

360° - RA = SHA

Example computation

Video show