Chapter 8 MOONS, RINGS, AND PLUTO Small Worlds Among Giants 8.1 THE RINGS AND MOONS OF SATURN Figure 65 shows the rings and moons when Titan is sufficiently close to Saturn to be included in the field. To obtain a better idea of the extremely large orbit for Titan, set a trail for Titan and follow its motion for a month or so. Placing the cursor on each moon and clicking the mouse will reveal the names of the moons. If it is desired to locate Titan, an easy way to find it is to decrease the magnitude setting with key F4 until only one moon remains. Figure 65. The rings and moons of Saturn. 62
8.2 WHAT GALILEO SAW OF SATURN S RINGS Saturn was visible only early evening in January 1612. If Galileo used a 1 diameter telescope with a magnification of 30, he could resolve about 2 arc seconds. See below. Following this for three years shows Saturn mostly edge on. Figure 66. Galileo s view of Saturn s rings. 8.3 HUYGENS VIEW In the four years leading up to 1659, Saturn moves from edge on to slightly tilted one way, back to edge on, to tilted substantially one way. Relying on better telescopes, Huygens surmised the explanation for Saturn s children. 8.4 A CLOCK IN THE SKY VIEW/Center Planet/Jupiter. VIEW/Coordinates/Ecliptic. COMPUTATION/Date & Time, Local Date & Time = 2005/1/1 00:00:00, Time Zone = 0.0. COMPUTATION/Precision, under Planet Position Computations select Correct for Light Time. ANIMATION/1 Minute. 63
Sample Data: Start Time span 2005/01/01 02:43:00 2005/01/02 21:12:00 42:29:00 2005/01/04 15:41:00 42:29:00 2005/01/06 10:09:00 42:28:00 Figure 67. Io will begin eclipsing at 2005/01/01 02:38:00. Note that Io is in the shadow of Jupiter at this time. The time span between eclipses is 42:29:00. 64
8.5 ECLIPSE CHARTS Chart showing data from Project 8.4 and a six-month prediction (some rows hidden). Start Time span 2005/01/01 02:43:00 2005/01/02 21:12:00 42:29:00 2005/01/04 15:41:00 42:29:00 2005/01/06 10:09:00 42:28:00 Predicted Start Time span 5/1/2005 10:29 42:28:00 5/3/2005 4:57 42:28:00 5/4/2005 23:25 42:28:00 5/6/2005 17:53 42:28:00 5/8/2005 12:21 42:28:00 5/10/2005 6:49 42:28:00 5/12/2005 1:17 42:28:00 *Hidden Rows 5/13/2005 19:45 42:28:00 *Hidden Rows 5/15/2005 14:13 42:28:00 5/17/2005 8:41 42:28:00 5/19/2005 3:09 42:28:00 5/20/2005 21:37 42:28:00 5/22/2005 16:05 42:28:00 5/24/2005 10:33 42:28:00 5/26/2005 5:01 42:28:00 5/27/2005 23:29 42:28:00 6 mo. Prediction 5/29/2005 17:57 42:28:00 5/31/2005 12:25 42:28:00 8.6 ACCURACY OF THE PREDICTIONS VIEW/Center Planet/Jupiter. VIEW/Coordinates/Ecliptic. COMPUTATION/Date & Time. Local Date & Time = 2000/05/25 2:48:00, Time Zone = 0.0 COMPUTATION/Precision, under Planet Position Computations select Correct for Light Time 65
Figure 68. The predicted eclipse on 5/31/2005 12:25. Io will actually eclipse at 2005/05/31 11:44:00, a difference of 1 hour and 19 minutes. 8.7 CONJUNCTIONS COMPUTATION/Date & Time, Local Date & Time = 1962/02/05 00:00:00. View/Center Planet/Sun. Deselect Stars, Constellations, and Deep Sky Objects DRAW/Symbols & Grids. Under Draw Planets select Draw As = Stars Conjunction on February 5, 1962 at 06:00:00 (angular span of ~15 ). Note: the conjunctions are ambiguous and the exact positioning and times are location specific. From San Francisco on February 4, 1962 at 18:00:00 the conjunction can be seen along with a partial solar eclipse! 66
Aquarius Capricornus Mercury Moon Sun Jupiter Venus Saturn Mars Viewed from: Mt Wilson 118 03' 36.0" W 34 13' 00.0" N Local time: 06:00:00 1962/02/05 JD 2437701.08 Figure 69. The planets in conjunction. Field of view: 45 00' 00.0" Ecliptic Lon: 315.2254 Ecliptic Lat: -00.0616 Magnitudes: Single star Multiple star Variable star 3.0 2.0 1.0 0.0-1.0-2.0 Deep sky objects: Open Glob Diff Plan Ga 8.8 A CONJUNCTION VIEWED FROM ABOVE COMPUTATION/Date & Time. Local Date & Time = 1962/02/05 00:00:00. COMPUTATION/Location. Select View from Object, Select, enter Sun, Find, Select, Offset. Distance = 60, select AU, Offset R.A. = 00 00 00.00, Offset Dec. = 90 00 00.0. View/Center Planet/Sun. DRAW/Stars, Constellations, Deep Sky Objects and Symbols & Grids Off. Mars Venus Sun Mercury Earth Uranus Viewed from: 60.00000 AU from Sun Local time: Field of view: 06:00:00 22 30' 00.0" 1962/02/06 Ecliptic Lon: 247.8982 JD 2437702.08 Ecliptic Lat: -69.1582 Magnitudes: Single star Multiple star Variable star 10.0 9.0 8.0 7.0 6.0 5.0 Figure 70. Notice Uranus in this alignment. (As opposed to this top-down view, an edge-on view would yield different results.) 67