Yachtmaster Ocean Introduction

Question 1

P’ P,

Answer 1

North and South Poles

Question 2

E,E’

Answer 2

Equator

Question 3

H,H’

Answer 3

Horizon

Question 4

Q

Answer 4

Centre of Earth

Question 5

X

Answer 5

Geographical position of the heavenly body under discussion

Question 6

Z

Answer 6

The Observer, or the azimuth angle of the observer

Question 7

Z’

Answer 7

Observer’s Zenith

Question 8

G

Answer 8

Any point on the Greenwich Meridian

Question 9

Meridian

Answer 9

Line of Longitude

Question 10

Azimuth

Answer 10

Angular Distance

Question 11

Zenith

Answer 11

Point above the centre of the earth

Question 12

Zn

Answer 12

Azimuth

Question 13

LHA

Answer 13

Local Hour Angle

Question 14

Hs

Answer 14

Height Sextant (Sextant altitude)

Question 15

Ho

Answer 15

Height Observed (Corrected sextant altitude or True altitude)

Question 16

Hi

Answer 16

Height Calculated (Tabulated altitude)

Question 17

IE

Answer 17

Index Error

Question 18

GP

Answer 18

Geographical Position

Question 19

GHA

Answer 19

Greenwich Hour Angle

Question 20

Twilight

Answer 20

Civil Twilight - The one we use

During civil twilight, the geometric center of the Sun’s disk is at most 6 degrees below the horizon. In the morning, this twilight phase ends at sunrise; in the evening it begins at sunset. Sunrise and sunset are the moments when the Sun’s upper edge touches the horizon.

Question 21

Nautical Twilight

Answer 21

During nautical twilight, the geometric center of the Sun’s disk is between 6 and 12 degrees below the horizon.

Question 22

Astronomical Twilight

Answer 22

During astronomical twilight, the geometric center of the Sun’s disk is between 12 and 18 degrees below the horizon.

Most stars and other celestial objects can be seen during this phase.

Astronomers may be unable to observe some of the fainter stars and galaxies as long as the Sun is less than 18 degrees below the horizon.