the
shortest length of time.

Put in your Note-Book:

North Declination is expressed +.
South Declination is expressed ---.

Now turn to page 6 of the Nautical Almanac. You will see opposite Jan.
1st 0h, a declination of --23 deg. 4.2'. Every calculation in this Almanac is
based on time at Greenwich, i.e., G.M.T. So at 0h Jan. 1st at
Greenwich--that is at noon--the Sun's declination is S 23 deg. 4.2'.

You learned in the lecture the other day on solar time, that the
difference between mean time and apparent time was called the equation
of time. This equation of time, with the sign showing in which way it is
to be applied, is given for any minute of any day in the column marked
"Equation of Time." You will also notice that there is an H.D. for
equations of time just as there is for each declination, and this H.D.
should be used when finding the equation of time for an odd hour.

Put in your Note-Book:

1. The equation of time is to be applied as given in the Nautical
Almanac when changing Mean Time into Apparent Time.

2. When changing Apparent Time into Mean Time, reverse the sign as given
in the Nautical Almanac.

That is all there is to finding sun time, either mean or apparent, for
any instant of any day in the year 1919. Do not forget, however, that
all this data is based upon Greenwich Mean Time. To find Local Mean Time
you must apply the Longitude you are in. To find Local Apparent Time you
must first secure G.A.T. from G.M.T. and then apply the Longitude.

(Note to Instructor: Make the class work out conversions here if you
have time to do so and can finish the rest of the lecture by the end of
the period.)

So much for time by the sun. Now let us examine time by the
stars--sidereal time. Turn to pages 2-3. There you find the Right
Ascension of the Mean Sun at Greenwich Mean Noon for every day in the
year. You remember that, roughly speaking, the Sun's Right Ascension was
the distance in time the sun was from the First Point of Aries. So these
tables give that distance (expressed in time) for noon at Greenwich of
every day. For the correction to be applied for all time after noon at
Greenwich (i.e., (+).C.P.), use the table at the bottom of the page. For
instance, the (.).R.A. at Greenwich 9h 24m on Jan. 1st would be

(.).R.A. 18h--40m--21s
(+).C.P. 1 33
--------------
18h--41m--54s

Now we must go back to some of the formulas we learned when discussin