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

ANALYSIS. iX
Art. Art.
Describe it........... 128 Theory of the spots................. 151
Sextant described................... 129 ZODIACAL LIGHT.-Where seen...... 152
How to measure the angular distance Its form............................ 152
of the moon from a star........... 129 Aspects at different seasons......... 152
How to take the altitude of a heavenly Its motions................. 152
body............................ 129 Its nature.......................,.. 152
Use of the artificial horizon......... 130
Chapter II.-APPARENT AN NUAL MOTION
In what consists the peculiar value of Chapter II.-APPARENT ANNUAL MOTION
the sextant.,,,, 130 OF THE SUN-SEASONS-FIoURE OF THE
ASTRONOMICAL PnOBLEMS.-Given the EARTHS ORBIT.
sun's right ascension and declina- Apparent motion of the sun........ 153
tion, to find his longitude and the How both the sun and earth are said
obliquity of the ecliptic.......... 132 to move from west to east......... 154
Napier's rule of circular parts.......132 Nature and position of the sun's orbit,
Given the sun's declination to find his how determined.. 155
rising and setting at any place whose Changes in declination, how found.. 155
latitude is known............. 133 Ditto, in right ascension............ 156
Given the latitude of a place and the Inferences from a table of the sun's
declination of a heavenly body, to declinations........ 156
determine its altitude and azimuth Ditto, of right ascensions...... 156
when on the six o'clock hour circle. 134 Path of the sun, how proved to be a
The latitudes and longitudes of two great circle....................... 156
celestial objects being given, to find Obliquity of the ecliptic, how found.. 157
their distance apart............. 135 How it varies....................... 157
FIGURE AND DENSITY OF THE EARTH- Great dimensions of the earth's orbit. 158
reason for ascertaining it with great Earth's daily motion in miles. 158
precision.............. 136 Ditto, hourly, ditto................. 158
How found from the centrifegal force. 137 Diurnal motion at the equator per hour 158
From measurillg an arc of the meridian 138 SEAsoNS.-Causes of the change of
From observations with thependulum 189 seasons................... 159
From the motions of the moon...... 140 How each cause operates............ 159
Fronl precession..................... 141 Illustrated by a diagram............. 160
Density of the earth..............' 141 Change of seasons had the equator
Howascertained by Dr. Maskelyne.. 141 been perpendicular to the ecliptic.. 161
Why an important element.......... 141 FIGURE OF THE EARTH'S ORBIT.-Proof
that the earth's orbit is not circular. 161.......- Radius vector defined............... 162
Figure of the earth's orbit, how obPart II.-OF THE SOLAR SYSTEM. tained........................... 162
Relative distances of the earth from
Chapter I.-THE SUN-SOLAR SPOTS-ZO- the sun, how found................ 63
DIACAL LIGHT. Perihelion and Aphelion defined..... 164
Figure of the sunl................. 143 Variations in the sun's apparent diamAngle subtenlded by a line of 400 miles 143 eter................... 164
Distance frolm tile earth............. 144 Angular velocities of the sun at the
Illustrated by motion on a railway car. 144 perihelion and aphelion. 165
Apparent diameter of the sun-how Ratio of these velocities to the disfound. 145 tanrces.......... 165
hIow to find the linear diameter..... 145 How to calculate the relative distances
How rmuch larger is the sun than the of the earth from the sun's daily moearth............................ 145 tions........................... 165
Its density and mass compared with Product of the angle described in any
the earth's....................... 146 given time by the square of the disWeight at the surface of the sun.... 146 tance......................... 167
Velocity of falling bodies at the sun. 146 Space described by the radius vector
SOLAR SPoTs.-Tlleir number........147 of the solar orbit in equal times... 168
Size............................... 147 How to represent the sun's orbit by a
Description..................... 147 diagram.......................... 168
What region of the sun do they occupy 147
Proof that they are on the sun...... 148 Chapter III.-CENTRALFORCES-GRAVITAHow we learn the revolution of the TION.
sun on his axis.................. 148 Two forces in curved motion........ 170
Time of the revolution............. 148 Centripetal and centrifugal............ 170
Apparent paths of the spots.......... 149 Kepler's laws....................... 171
Inclination of the solar axis......... 149 First law-second-third........... 171
Sun's Nodes-when does the sun pass First principles in mechanics and astheml.......................... 150 trononmy Identical.............. 171
Faculae........................... 151 Kepler's first law proved............ 172