§ 24 – 28

Where appropriate, use the ANC N.A. pamphlet extracts, Sight Reduction Tables for Marine Navigation N.P.401 (H.O. 229) and Brown’s Nautical Star Chart. Sights should be worked on the ANC Sight Forms and Astro Plotting Sheets.

93. Explain the phenomenon in the night sky commonly known as the Milky Way.

94. Explain the apparent stellar magnitude scale.

95. What is absolute stellar magnitude and what purpose does it serve?

96. Briefly explain each of the following: –

a. a main-sequence star

b. an asterism

c. aphelion

d. a planisphere

e. Astronomical twilight

f. the ‘Summer Triangle’

g. Spica’s Spanker

h. the Midnight Sun

97. What is the Bayer system of reference for the stars, which comprise a particular constellation?

98. What are the particular names and magnitudes of the following navigational stars: –

a. Giminorum

b. Bootis

c. Aquilae

d. Orionis

99. Draw a rough diagram of stars to show how you would locate the navigational stars Sirius and Aldebaran. naming the constellations and stars involved.

100. Draw a rough diagram of stars to show how you would locate the navigational star Spica naming the constellations and stars involved.

101. At Zone Time 17:44 (-1) on Jan 20th 199X in D.R. Lat. 35º 00.0’ N., Long.  20º 07.0’ E., identify (using Brown’s Nautical Star Chart): Show all your calculations and explain the reasons for your conclusions.

a. a bright body bearing 120º at altitude 52º

b. a bright body bearing 225º at altitude 33º

102. For a vessel steering 220º T. in Lat 14º 05.0 N., Long. 63º 35.0’ W. on 04th Jul 199X find the time at which evening star sights should be taken, and, draw a rough diagram showing the approximate bearings and altitudes of the available celestial bodies (including any planets) relative to the vessel’s head.

103. Explain. the use of: –

a. a Star Globe

b. Planisphere, for star identification.

104. At 17:45 (Zone+3) Jan 29th 199X, the navigator of a slow moving vessel in D.R. Lat. 49º20.0’ N., Long. 39º 43.0’ W. made the following stellar observations: –

✴︎ Capella         DWT        20h.      43m.      01s.      Sext. Alt.        58º 21.5’

✴︎ Aldebaran   DWT        20h.      44m.      07s.     Sext. Alt.        45º 32.2’

✴︎ Hamal          DWT        20h.      44m.      55s.     Sext. Alt.         64º 06.0’

The D.W.E. was lm. 03s. slow on G.M.T.., I.E. of the sextant + 1.3 and Ht. of eye. of the navigator 12ft.

Reduce, plot and state the observed Position at 17:45 (Zone + 3) hours.

105. During morning twilight on Jan 03rd 199X in D.R. Lat 44º 58.0’ S., Long. 164º 50.0’ E. an

observation of Sirius at 03:44 (Zone – 10) gave a Sext. Alt. 24º 21.5’ at DWT 17h. 43m. 15s. Further observations were impossible until 04:10 in D.R. Lat 45º 02.0’ S., Long. 164º 57.0’ E. when the following observations were obtained: –

✴︎ Spica             D.W.T.       18h.     08m.      32s.    Sext. Alt.          51º 43.7’

✴︎ Regulus         D.W.T.       18h.     09m.      03s.    Sext. Alt.          27º 55.2’

Reduce, plot and state the vessel’s position at 04:10 (Zone – 10) if the I.E. was 0.5’ on the arc, the D.W.E. was 0m. 50s. slow on G.M.T.. the H of E. of the observer was 11 ft. and the vessel was making good a Course of 121º T. at 10 knots.