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30 { By sun time: it is therefore noon only on the 90th meridian. It is much past noon, by sun time, at Cleveland, but it is just noon at Cleveland, by Cen- tral standard time. At every place on © the lakes, from Duluth as far east as Conneaut, it is noon, by Central stand- ard time, at exactly the same time. So in order to turn our standard time into sun time we have to make "Cor- rection for longitude," which really means "Correction for standard time." When our watch shows noon at Cleveland by Central: standard. time, we must. find out. how far the sun has gone past Cleveland. We have shown before that the sun is on the 90th. meridian. But Cleveland is be- tween the 81st and 82d meridian. 'As the "sun travels, "westward at the rate of one degree in four minutes she therefore passed the meridian at Cleveland 33 minutes before. So when it is noon at Cleveland by stand- td time it is 12:33 by mean sun time. But at Duluth the sun time slower than standard time because 'Duluth is west of the 90th meridian and the sun has not yet arrived there. A list is prepared showing just how much should be added or subtracted from Standard: time to turn it.cinto mean time. This list is found under the head of "Pelorus Cards." Now when we have figured our standard time into mean sun time we still have another correction to make to get Apparent sun time. Apparent time is the exact time shown by the sun, Mean sun time is the time shown by a sun-time clock or watch, If the sun made its trip around the earth every day in exactly the same time we have no need for any more corrections, but she is very unsteady with her trips. Sometimes it. takes her longer than 24 hours and some- times she gets around in less than 24 hours. _Now a clock can't be made to run in this unsteady fashion. A good timepiece will show noon at the same time every day, but where would the sun be this day--she might be a few minutes late or a little ahead of time. , But no matter what the clock might "show the sun must be exactly on the 'meridian in order to have true sun time. Fortunately, astronomers can tell usy just how much late or early the: sun will be for-each day and they supply us with a list called Equation of Time. The time shown by. .the clock is called. meanesun time. We can change is this into trae (or. apparent) sun time | by adding-or- subtracting -the-. number of minutes shown Equation of Time. in the "table of All calculations of THe Marine REVIEW the sun are figured by True Sun time. A table of Equation of time is here shown and is also ge under the head of "Pelorus cards." same manner that the earth is, These lines are made to correspond with the lines on the earth. The equator ip the heavens is directly over the earth- EQUATION OF TIME. This table is computed to the nearest minute and is sufficiently correct for use in taking Azimuths from the Red Book. Jan. -. Feb... Mar. Apr. May June sy ne Sept, Oct. Ney. fae b- . Sub- Sub-. Sub- Su ub- oe tracted tracted tracted tracted oo ae a from from from from Add to Addto from from to to Addto Add to Mean Mean Mean Mean Mean Mean Mean Mean Mean Date of Mean Mean Mean ath Time Time Time Time Time Time Time 'Time, Time: Time -.Time. Time. mt 3 14 13 4 3 3 3 6 0 10 1652 4 2 4 14 13 4 3 2 4 6 0 10 16 11 3 4 14 12 4 3 2 4 6 0 11 16 10 4 5 14 12 3 3 oA 6 1 11 16 10 5 5 14 12 3 3 2 4 6 1 11 16 10 6 6 14 12 3 3 2 4 6 1 12 16 9 7 6 14 11 2a 2 4 6 2 12 16 9 8 6 14 11 2 4 1 5 6 B 12 16 8 9 7 14 11 2 4 1 5 5 2 13 16 8 10 Z 14 11 2 4 1 5 5 3 13 16 7 11 8 14 10 1 4 1 5 5 3 13 16 7 12 8 14 10 4 4 1 5 5 4 13 16 7 13 9 14 10 1 Ae 0 5 5 - 4 14 16 6 14 9 14 10 1 4 0 5 5 4 14 16 6 15 9 14 9 0 4 Sub. 6 5 5 14 15 5 16 10 14 9 Add 4 0 6 4 5 14 15 5 17 10 14 9 0 4 0 6 4 5 14 15 4 18 10 14 8 1 4 1 6 4 6 15 15 4 19 11 14 8 1 4 1 6 4 6 15 15 3 20 11 14 8 1 4 1 6 3 6 15 14 3 21 11 14 8 1 4 1 6 3 7 15 14 2 22 12 14 7 1 4 2 6 3 Z 15 14 2 23 12 14 7 2 4 2 6 3 Z 15 14 1 24 12 14 Z 2 3 2 6 3 8 16 13 1 25 12 13 6 2 3 2 6 Z 8 16 13 0 26 13 13 6 2 3 2 6 2 8 16 13: Sub. a7 13 13 6222 as 6 2 9 16 13 1 28 13 13 5 2 3 3 6 1 9 16 12 1 29 13 13 5 3 3 3 6 1 9 16 12 2 30 13 13 5 3 3 3 6 1 10 16 12 2 31 13 13 5 3 3 3 6 1 10 16 12 3 When you are told that the sun's ly equator. And declination starts at rays do not make perfect trips around this equator and figures north or the earth you might think the earth does not turn steadily--like a poorly balanced wheel. But she does turn in perfect time. The trouble is caused principally by the fact that the earth does not travel in a perfect circle in - h.r yearly revolution around the sun. At certain times she is two million miles closer to the sun than at other times. You can easily understand that the farther away an object is the slower it changes its bearing. There- fore, on account of the varying dis- tance, the sun can not be a perfect mark to time the earth's daily whirl. You remember that we required to know three things in order to be able to find the correct azimuth in the book. These were--the. correct sun time, the latitude of the ship, and the declination of the sun. We still have to find out what Declination is, Declination. We locate places on the earth by latitude and longitude. We locate heavenly bodies by declination and right ascension. We would have un- derstood better had they called it heavenly latitude and heavenly longi- tude. If the sun is in declination 20 she is directly over latitude 20 on the earth. For thé purpose of location of heavenly bodies the heavens must be divided up with imaginary lines in the south in the same manner you figure latitude. The sun comes north of this equator in the summer and goes south of it in the winter. It crosses the equator about March 21st and comes north until it gets to about declination 23 when it starts back again, crosses the equator about Sept. 2lst and goes to about 23 south dec- lination, when it wheels around and starts back again: The sun: nevef gets far enough north to shine direct- ly down on us. The great lakes are all between latitude 40 and 50, while the sun comes only to latitude 23. N POLE