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The motion* of the un are in fact those of the earth, written in the 

 heavriu. If the diurnal motion of the earth wore stopped, tin- MIII 

 would ap|H*r to move slowly among the stars, from went to eaut, at 

 the rU- ( aUmt twice iU own diameter in twenty-four hount by tin- 

 clock. Thin | MOTION] is the conseqm-uo.- of tin- orliital in.ition oi tin- 

 earth, which i* cominuniaiU-d in appearance to the HUH. If the earth's 

 orbital motion were stup|H-d, tin- diumiil motion continuing nit usual, 

 the aun would appear t> move round daily, from cast to west, as at 

 present ; but since there would th.-n be no motion of that body ainoiii,' 



.M, those stars which an at any one time lii.l.len liy the 

 would always be hidden, and the face of the heavens at any given hour 

 of night would be the same at all times of the year. The effect of the 

 orbital motion of the earth combined with the diurnal motion U that 

 the solar day, or the interval between two im ridiaii (.assages of the 

 suu, U a little longer than the sidereal day (about four minutes), or 

 than the actual revolution of the earth ; go that all the stars ha\ 

 turn, and every star in the course of the year conies on tin- im-i idian 

 at every period of tho natural or solar day. [Svtiomr ; TIMK.J 



The great phenomena of day and night are attended with very 

 different circuiiwUnreH in different )rU of the globe. We an- not 

 speaking now of tho high polar regions, north and south, in which tin- 

 sun never sets for days together, but of those part* of the earth iu 

 which there is actual appearance and disappearance of the luminary, or 

 real day and night Lei us take the day of tho vernal equinox as a 

 specimen, when the suu in in the equator (we presume in our reader a 

 knowledge of the terms and notions in SPHERE, DOCTRINK OP THE). 

 If we take one fixed line to represent the horizon of different places, as 

 B A c. the sun will rise to a place on the equator so as to move along 

 the circle DAE, and to come directly up from the horizon ; while at a 

 place near the pole it will move, relatively to the horizon (still B A c), 

 along the circle F A a. Now the first evidence which the sun gives of 



iU approach is this (the diagram, though of very distorted dimensions, 

 may be of use) : before it has risen above the horizon of a place, so as 

 to be visible, it can throw its rays into the atmosphere above the place, 





which atmosphere ^reflect-, something both of light and heat to the 

 place itself. This period U called the twilight, and it U said that there 

 is more or less of twilight as long as the sun is not more than 1 5 

 below the horizon ; though certainly tho twilight which eaves candle- 

 light does not last so long. But be the number of degrees which are 

 allowed to twilight more or less, it is obvious that at the equator, 

 where the whole of the sun's way U made directly to or from the 

 horizon, the intermediate period of twilight must be much shorter 

 than at a place near the poie, where the motion towards the horizon H 

 very oblique, instead of being all ascent, as before rising, or descent, as 

 after setting. The consequence is well known : in the tropics, thu 

 warning is short, and soon after the light begins to break the sun 

 makes its appearance, and it U broad and hot day ; while after the 

 setting the light M soon disappears, and it is dark night. With us, on 

 the contrary, and still more in higher northern latitudes, there is a 

 long warning of the approach of the luminary before the sunrise, and a 

 long remembrance of it after sunset. In all climates the- transition 

 from day to night in broken by the two circumstances mentioned in 

 SEASONS. In the same article it in pointed out that the heat received 

 during the winter and summer halves of the year is the same over the 

 wliol-- earth. 



Immediately after sunrise, the form of the luminary appears some- 

 what elliptic, thu horizontal diameter being longer than the vertical 

 one. This is the effect of KKTHAI i mv whieh \.iricx no rapidly near 

 the horizon that thu upper end of the vertical diameter is lew elevated 

 than the lower end by a sensible quantity, while the two ends of tho 

 horizontal diameter are equally elevated. Tho same phenomenon 

 occurs with the moon, when rising at the full, and woidd also be seen 

 in tho planets, if they were large enough in appearance. It must also 

 be noted that both suu and moon appear larger when near the horizon ; 

 Imt this, as to the sun, is delusion, since when measured with instni 

 tueuts iU apparent diameter is the same at all part* of the day. It is 

 true that both bodies, when in the zenith, are nearer to the spectator 



than when in the horizon, by what may be called without error a seini- 

 liametor of the earth ; the moon is near enough to show the effect of 

 thi- in instrumental measurement* of its diameter, but it in not so 

 v. iih the sun. 



looking at what we know of the physical appearance* 

 sun, ttii distance from the e.u-th must be mentioned, to which we may 

 DOM the other element* of its orbit. Its equatorial horizontal 

 I'AUAI.I.AX, at its mean distance, is 8"-5776, and its apparent 

 diameter 16' 0"'9. Xt U then distent from the earth by 24,000 

 semidiameters of the earth, or about 95,000,000 miles. Its di 

 is 1114 times as great as that of the earth, or upwards of 880,000 

 miles; and its bulk U 1,800,000 times as great as that of the earth. 

 But its mass, u determined from its action on the planets, i 

 355,000 times as great as that of the . .nth ; win -n. e 

 is only oue-quarter of that of the earth. But this last result takes into 

 tho body of the sun all that is seen of it : if the surmise presently t 

 be mentioned, of its having a luminiferous atmosphere of en 

 extent, be well founded, the real body of the nun may have a nun h 

 density as the earth, or more. It revolves on its axis in 25J of our 

 mean solar days ; according to Delambre, in 23-01154 days : tie 

 being inclined to the ecliptic at on angle of 824. 



The ecliptic is the circle in which the sun appears to move, in 

 common language. In strictness, however, the earth does not move 

 round the sun in a true plane, though it does go very nearly . The 

 centre of gravity of the earth and moon (a point near the earth) does 

 much more nearly describe a plane; that is, a spectator situated at that 

 point would more nearly see the sun move in a great circle than \\e 

 do. But to us, the sun is sometimes on one side and sometimes on tho 

 other of this mean ecliptic, and therefore generally has some hi 

 though a very small one : the column entitled " the Sun's latitude " in 

 ' The Nautical Almanac ' is a puzzle to those readers whose astronomy 

 is drawn from the usual elementary writings : in truth, it is only a 

 fraction of a second, and the sun crosses the mean ecliptic twiee in 

 every lunation. Tho obliquity of the mean ecliptic, for January 1 , 

 1860, is 23 27' 27"'38, and it is diminishing yearly by 0"-l, r >7 : thus 

 this same obliquity for January 1, 1842, is 23 -IT 35"-6. If this 

 diminution could go sufficiently far, it would in time bring the ecliptic 

 and equator to coincidence, or equalise days and nights all over the 

 world ; and if it could be held to have continued long enough, 

 entitle us to presume that the poles were once in the plane of the 

 ecliptic, or that every part of the earth went through all gradati 

 a year from equal days and nights to a polar day and a polar night. 

 But the cause of this diminution of the ecliptic is known from tin- 

 theory of gravitation ; and it is also known that, under existing causes, 

 it cannot be permanent, but must diminish in quantity and finally 

 turn into an increase before its effect has amounted to many degrees. 

 Persons acquainted with the phenomena of the heavens, but not with 

 the results of the theory of gravitation, remembering the fact of 

 tropical productions being found buried in high latitudes, SOUK 

 imagine that they can look back to the time when the poles v. 

 near the ecliptic, that these same high latitudes were within tho 

 tropics. Tills, however, is a pure fancy, and they had better ii 

 another cause ; the one they think of will not do. 



The mean longitude of the sun, at Greenwich mean noon on the 1st 

 of January of the year 1800 + 1, may be determined from 



280 53' 32 > '-75 + 27"'605844+ 0001221805 2 -14' 47'-083/, 



where/ is the remainder of t divided by 4, or 4 if the remainder be ; 

 that is, the number of years after the Julian leap-year, or after tho 

 'i-ii/'ii'iun leap-year for all years after 1804. The mean motion in 

 longitude in a mean solar day is 59' 8"'33. 



The excentricity of the sun's orbit is '016783568 (according to 

 Laplace, '01685318), or the greatest and least distances of the sun from 

 the earth are in the proportion of 1-017 to '983, or as 30 to J:>. or ni,.n- 

 nearly as 91 to 88. The greatest equation of the centre [TiMKJ in 

 1 55' 27"'S. The excentricity diminishes by -00004163 iu a century. 



The mean longitude of the perigee, at noon, January 1, 18(11, via* 

 279 30' 5"-0. It has a real yearly increase of ll"-8, which, with tin- 

 precession of the equinoxes, makes an increase of longitude of <>l''".i. 



The appearance of the sun is simply that of a ball of intense light, 

 such as the human eye cannot bear, unless a hazy atmosphere or a dark 

 glass be used as a screen. This light is so strong, that the brightest 

 flames which human art can produce, when held before the suu, 

 disappear, ami ignited solids become dark spots. " The ball of ignited 

 quicklime," says Sir J. Herschel, " in Lieut. Drummond's oxy-hydrogcn 

 lamp, gives the nearest imitation of the solar splendour which has yet 

 been produced. The appearance of this against the sun was howc\oi , 

 as described," merely a dark spot, " in an imperfect trial at which I 

 was present. The experiment ought to be repeated under favourable 

 circumstances." A very small portion of the rays collected int.. . me 

 spot I liriiNiNO-GLASSEs] is sufficient to melt metals. On examining 

 the face of the sun with a telescope (of course with a dark glass before 

 the eye), two circumstances are observed. The disc is not nniii-rmly 

 bright. " The ground is finely mottled," to use the words of tliu 

 observer just quoted, " with an appearance of minute dork dots, or 

 .\ lu'ch, when attentively watched, are found to be in a constant 

 state of change. There is nothing which represents so faithfully this 

 appearance as the slow subsidence of gome flocculeut chemical pre- 



