YOU CAN WEIGH JUPITER

AST 1022L

RELATIVE SIZES OF THE PLANETS

DISTANCE SCALES OF THE SOLAR SYSTEM

If the Earth were ~1 cm across:• The Sun would be ~1.5 m across and ~150 m away• The Moon would orbit Earth ~30 cm away• Jupiter would be ~15 cm across and orbit the Sun at a

distance of ~5 city blocks (750-800 m away)

PORTRAIT OF JUPITER

• More massive than other 7 planets combined

• Comprised mostly of H & He

• >60 moons

• Great Red Spot alone is nearly 3x Earth’s diameter & has existed at least as long as Jupiter has beenobserved

GALILEAN MOONS

• 4 major moons of Jupiter are:

• Io (Jupiter-I),

• Europa (Jupiter-II),

• Ganymede (Jupiter-III), &

• Callisto (Jupiter-IV)

• First 3 orbit in a 1-2-4 resonance (for every 4 orbits Io completes, Europa completes 2 and Ganymede completes 1)

THE GALILEAN MOONSFirst objects ever observed that clearly did not orbit Earth one of the first arguments against the geocentric (Earth-centered) model of the universe

SO HOW DO YOU WEIGH A PLANET?

KEPLER'S LAWS OF PLANETARY MOTION

• 1st Law: A planet orbits in an ellipse with the Sun at one focus.

• 2nd Law: A line from the planet to the Sun will “sweep out” equal areas in equal times

KEPLER'S 3RD LAW (ALSO APPLIES TO PLANET-MOON SYSTEMS!)

*

* With T in years, a in AU and M in Solar Masses (M⨀)

Remember: T = Period, which is sometimes given as P (like on your data sheet)

Original form:Original Form

Newton’s Correction:

Simplification for M>>m:

SINE FUNCTION REVIEW

SINE FUNCTION REVIEW CONT.When viewing the orbital plane edge on, plotting the positions of one body orbiting another as a function of time produces a sine wave (as you will see in your own plots)

LAB PROCEDURES

1. You & a partner will observe 1 of Jupiter's Moons in a simulation.

2. Set your observation intervals to times appropriate for your Moon: 3 hours for Io, 5 hours for Europa, 10 hours for Ganymede, or 22 hours for Callisto. These times were chosen so the given Moon completes at least 1 orbit within about 20 data points.

• Your starting date can be arbitrary, but the hour must be set to 0

3. Record date, time, & position in Jupiter Diameters. The computer will give you position in terms of East & West, which you should record as Negative (-) and Positive (+) respectively. E.g.:

• X = 3.12W should be recorded as +3.12

• X = 1.41E should be recorded as -1.41

Note: You will see the same number without the E/W distinction output elsewhere as R. Ignore that one.

LAB PROCEDURES CONT.:

• Plot distance (in Jovian diameters or JD) vs. decimal days on provided graph paper

• Scale your axes appropriately – don’t squeeze everything to one side or you’ll have a hard time measuring amplitude & period!

• Note that X=0 in the middle, not at the bottom

• Answer questions on pages 8.9 through 8.11

• Distance & time conversion factors are given on your worksheets

FOR NEXT WEEK:

• Read “Measuring the Hubble Constant” (#10 in the manual)

• Dual Moon/Deep Sky Night-Lab Makeup on Tuesday Nov. 8th – starting at 7:30 PM sharp!