An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

ANALYSIS. X
Art. Art.
Earth never seen on the opposite side Successive degrees of accuracy atof the moon.................... 220 tained... 2482
Appearances of the earth to a specta- Periodic and secular irregularities distor on the moon.......... 220 tinguished.................. 243
Why the earth Would appear to remain Acceleration of the moon's mean mofixed............220 tion explained................... 243
Path of the mloon in space.......... 221 Its consequences............... 243
How nluch more is the moon attracted Lunar inequalities of latitude and
toward the sun than toward the parallax.......................... 244
earth?.............. 222I
earth.222. Chapter VII.-ECLIPSEs.
When does the sun act as a disturbinog
force upon the moon?............. 222 Eclipse of the moon, when it happens. 245
Why does not the moon abandon the Eclipse of the sun, when it happens. 245
eairth at the conjunction........... 222 When only can each occur.......... 245
The moon's orbit concave toward the Why an eclipse does not occur at
sun............................ 223 every new and full moon.......... 245
Why eclipses happen at two opposite
Chapter VI.-LuNAR IRREGULARITIES. onths.......................... 245
Specify their general cause......... 225 Circumstances which affect the length
Unequlal action of the sun upon the of the eartl's shadow.246
earth and tnoon................... 225 Semi-angle of the cone of the earth's
Obliqiue action of earth and sun..... 225 shadow, to what equal............ 247
Gravity of the moon toward the earth Length of the earth's shadow....... 248
at the s:izyges.................... 226 Its breadth where it eclipses the moon. 249
Gravity at the quadratures....... 226 Lunar ecliptic limit defined......... 250
Expb, in the disturbances in the Solr do..... 250
mnoonl's motions fronl figure 48.... 228 Amount of the lunar ecliptic limit... 251
Figure of. the mooln's orbit......... 2:0 Appulse defined. 251
How its firgure is ascerta'ined....... 230 Partial, total, central eclipse, each deMIoomll' greattest and least apparent fined................. 251
diameters..... 230 Penumt bra defined 252
Her greatest and least distances from Senli-angle of tile moon's penumbra,
the earth........................ 230 to what equal.253
the ewrtl.... 28() to whiat equlal.................. 253
Perigee and Apooee defined......... 230 Senli-langle of a section of the penulEc-cenltricities ot the solar andt lunar bra whlere the nioon crosses it. 254: orbits colllpa ed.................. 230 Moon's horizontal parallax increased
MooR's nodes, their chiangre of place.. 231 J, why2 55
Rate of tllis change per annuml....... 281 Wily the moon is visible in a total
Period of their revolution........... 231 eclipse.............. 256
lrreullar curve described by the Calculation of eclipses, general mode
0oon0........................... 232 of proceeding.......... 257
Cause of the retrograde- motion of To find thle exact time of the beginnodes. 232 ning, end, di ration, and magnitude
Explain froml firllre 50.............. 232 ofa lunar eclipse, by figures 53, 54.. 258
Sylnodical revolution of the node de- Elements of an eclipse defined 259
fined.............. 283 Digits defined..................... 260
Its period........................ H H3.ow the shadow of the mnoon travels
Thie Sarms explained.............. 233 over the earth in a solar eclipse.... 262
The Metonic Cycle................. 234 Wlly the calculation of a solar eclipse~
Golden Number..................... 234 is more coiuplicated than a lunar.. 262
Revolution of the line of apsides.... 23.5 Velocity of the moon's shadow...... 2683
Its period.......................... 235 Different ways in which the shadow
How tile places of the perigee may be traverses the earth, according as
found............................ 235 the conjunction is near the node or
Moon's anomaly defined., 2.. 3....2 285 near the limnit.................... 263
Cause of tlic revolutioll of the apsides. 2:6 W hen do the greatest eclipses happen? 264
Anllollnt of the equation of the center. 237 Case in which the moont's shadow
Evection, defined.................... 238 nearly reaches the earth.. 265
Its calse explained.......... 239 How far may the shadow reach beyond
Vaviation defined............ 240 the cente.r of the earth?.... 265
Its cause.... 240 Greatest diameter of the imoon's shadAnnall Equation explained.......... 241 ow where it traverses the earth.... 266
How tihese irregularities were first dis- Greatest portion of the earth's surface
covered........ 242 ever covered by the toon's penti nHow nlany equations are applied to bra..................... 267
the oo's otiois?............... 242 Moo's apparent diameter compared
Method of proceedinlg in finding the with the sun's................. 268
-mooRns place........ 242 Annular eclipse, its cause........... 268