Page:Practical astronomy (1902, John Wiley & Sons).djvu/17

CONTENTS. ix OTHER METHODS OF DETERMINING LONGITUDE. PAGE 1. By Signals 153 2. By Eclipses and Occultations 153 3. By Jupiter's Satellites 153 a. From their Eclipses 153 b. From their Occultations 153 c. From their Transits over Jupiter's Disc 154 d. From the Transit of their Shadows 154 Application to Explorations and Surveys 154 TIME OF OPPOSITION OR CONJUNCTION. 156 TIME OF MERIDIAN PASSAGE. 157 AZIMUTH. Definitions 158 The Astronomical Theodolite or Altazimuth 159 Classification of Azimuths 160 Selection of Stars 160 Measurement of Angles with Altazimuth 162 Observations and Preliminary Computations 164 REDUCTION OF OBSERVATIONS. 165 J* 1. Diurnal Aberration in Azimuth 166 2. To Reduce an Azimuth observed shortly before or after the Time of Elongation, to its Value at Elongation 167 DECLINATION OF THE MAGNETIC NEEDLE. 168 SUN-DIALS. 168 Values of Equation of Time to be added to Sun-Dial Time 173 SOLAR ECLIPSE. Solar Ecliptic Limits 174 PROJECTION OF A SOLAR ECLIPSE. 1. To find the Radius of the Shadow on any Plane Perpendicular to the Axis of the Shadow 176 2. To find the Distance of the Observer at a given time from the Axis of the Shadow 178 3. To find the Time of Beginning or Ending of the Eclipse at the Place of Observation 180 4. The Position Angle of the Point of. Contact 182 5. The necessary Equations for Computation arranged in order for the Solution of the Problem 182 TABLES. 185 FORMS. 203