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Observatory III - Jupiter and Saturn PDF version of this lab Printable Lab Report INTRODUCTION: You will make observations of the two largest planets in our Solar System, the gas giants Jupiter and Saturn. While some bands and belts in the atmospheres of the planets should be visible and are fun to look at, your quantitative work will focus on one of the satellites of Jupiter Ganymede and on the ring system of Saturn. You will use a Meade astrometric eyepiece on a Meade LX-200 computer-controlled telescope. The red illuminated "RULER" in the center of the eyepiece will allow you to measure the separation between Jupiter and Ganymede and between the outer edges of Saturn's ring system. PREDICTIONS: (1) The Earth's mass is only 3x10-6 of the Sun's mass; Jupiter's diameter is about 10 times the Earth's diameter. Estimate the mass of Jupiter, as a fraction of the Sun's mass, and enter this number on your Report Sheet. (2) Saturn has numerous satellites like Jupiter, whose orbital periods are typically several days. Do you think Saturn's rings are stationary, or do they also orbit the planet? If they are in orbit, what would you guess their orbital period to be? Answer these questions on your Report Sheet. THEORY: Kepler's Third Law can be applied to orbits around any central, dominant mass to calculate the mass of the central object. Jupiter presents an interesting case: since the plane of its satellites' orbits is pretty much in the same plane as the Earth's orbit, we view the orbits edge-on, which gives the appearance of a system undergoing one-dimensional (back-and-forth) Simple Harmonic Motion. A sinusoidal plot of a satellite's separation from Jupiter can therefore be used to determine the period and amplitude of the periodic motion, which will correspond to the orbital period P and the radius a of the (assumed) circular orbit. Kepler's Third Law, M = a3/P2, can then be used to find the mass M of Jupiter (in solar mass units) if a is in Astronomical Units (AU) and P is in years. Turning the problem around, if the central mass and radius of the orbit are known, the orbital period can be determined. For Saturn, you will use its known mass and your own measurement of the radius of the ring system to calculate the orbital period (if any) of the rings. OBSERVATIONS: Make sure your eyepiece is turned on so that you can see the red illuminated scale. You can focus the red scale by rotating the top of the eyepiece (NOT the whole eyepiece assembly). Enter the object you want to observe on the telescope keypad (FOR JUPITER: "STAR 905"; FOR SATURN: "STAR 906"). Press "ENTER". If the correct planet comes up on the display, press "GO TO". DON'T TOUCH THE TELESCOPE AS IT SLEWS TO ACQUIRE THE PLANET. Once it beeps, use the LEFT, RIGHT, UP, and DOWN buttons to CENTER the planet, and the silver focus knob on the end of the telescope tube to bring it into sharp focus. ROTATE the entire eyepiece by loosening the set screw A LITTLE BIT, turning it to ALIGN the "system" parallel to the RULER, and then tightening the set screw (FOR JUPITER: the "system" is Jupiter and its westernmost satellite Ganymede; FOR SATURN: the "system" is the major (widest) diameter of Saturn's rings). READ OFF the DIAMETER OF THE PLANET (D) and the SEPARATION (S) in TICK MARKS along the illuminated ruler scale (FOR JUPITER: the "separation" is between the center of Jupiter and Ganymede; FOR SATURN: the "separation" is between the eastern and western outer edges of Saturn's rings). Record D and S on your Report Sheet. Record the TIME OF OBSERVATIONS on your Report Sheet. CALCULATIONS: Finally, follow the steps on your Report Sheet to calculate the radius a of the orbits of Ganymede and Saturn's rings, and to determine the mass M of Jupiter and the orbital period P (if any) of Saturn's rings. |