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Astronomy Lab: Planets Phys 102 Astronomy Name ____________________Key POSITIONS OF THE PLANETS PLANETARY POSITIONS WITH RESPECT TO THE SUN: 23 Use appendix 11 in the Field Guide for February 1, 2021 to complete the following table: Object Planetary Longitude Atlas Chart # Constellation Elongation Sol () 313 32 Capricornus ZERO! Planets ☿ in order Mercury ( ) 326 32 Capricornus 13° E of orbit Venus(♀) 300 43 Capricornus 13° W distance from the Mars (♂) 43 22 Aries 90° E Sun. Jupiter (♃) 310 31/43 Capricornus 3° W Saturn (♄) 305 31/43 Capricornus 8° W PLANETARY POSITIONS IN THE SKY The digram below shows an observer looking south at sunset. From the planetary longitude of the sun and planets abovee, show where the planets will be in the observer’s sky (some may be below the horizon). Discuss how these positions correspond to the times the planets will be visible to this observer (eg. after sunset, before sunrise or most of the night). 11 Sun’s PL + 90° _______43° ♂ At E. Quadrature! Observer’s meridian Come look for the planets with me! ☿ Sun’s PL ± 180 Sun’s PL _______133° _______ E observer W ♃ 313° Sun setting on looking ♄ western horizon south ♀ Sun’s PL - 90°: _______223° Phys. 102: Astronomy Spring 2021 PLANETARY POSITIONS IN THE SOLAR SYSTEM A view of the solar system as seen FROM ABOVE THE NORTH ECLIPTIC POLE with the sun in the center is shown below. The line from the Earth ( ) to the Sun ( ) represents the planetary longitude of the sun. For each of the five visible planets, 1) Center a protractor on the Earth, measure the elongation angle from the sun's longitude. 2) Use a ruler to determine where this crosses the orbit of the planet you're plotting, and mark the planet's position on its orbit. 9 Special Note: Can you be certain where Mercury and Venus are in their orbits? How many positions for each planet are possible? What information will help you figure this out? Sol’s Planetary Longitude: __________313° Eastern Elongation Western Elongation Mars, Jupiter & Saturn motion Saturn: seen from Earth 313° - 305° = 8° W Jupiter: 313°- 310° = 3° W Venus & Mercury motion seen Mercury’s elongation on 2/1: from Earth 326 - 313 = 13° E. On 2/15 it will be 327 - 313 = 14° W. Mercury goes from Eastern to Western elongation so it must Mercury: Venus: be on the near side of its orbit 326°- 313° = 13° E 189° - 148° = 41° W about to go through inferior conjunction between February Venus’ elongation on 2/1: 313 - 300 = 13° W. 1 & 15 (8:41 am, 1/8/21) On 2/15 it will be 327 - 317 = 10° W. Since elongation is decreasing, Venus is on the far side of its orbit, approaching superior conjunction (2:20 am EDT, 3/26/21). Mars: (43°+360°) - 313° = 90° E Eastern Quadrature on Febrary 1! CENTER PROTRACTOR ON EARTH! .
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