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Click a term on the left, then click its matching meaning on the right. 1 point per correct match · 10 total
For thousands of years, people watched Jupiter wander among the stars without knowing how far away it really was. Jupiter looked like a slow, bright point of light, but its true distance and the shape of its orbit were a mystery. Astronomers needed a way to measure something they could never reach.
In the late 1500s, the Danish astronomer Tycho Brahe collected the most accurate naked-eye observations of the planets ever recorded. His assistant, Johannes Kepler, used those careful measurements to figure out the shapes of the orbits. Kepler discovered that every planet, including Jupiter, travels in an ellipse, not a perfect circle. The Sun sits at one of the two foci of each ellipse. The point in the orbit closest to the Sun is called the perihelion, and the point farthest from the Sun is called the aphelion.
To find where Jupiter is in space at any moment, astronomers use a technique called triangulation. They record two things: where Earth is on its own orbit (the heliocentric longitude of Earth) and the direction we see Jupiter from Earth (the geocentric longitude of Jupiter). Because Jupiter takes about 11.86 Earth years to circle the Sun once, astronomers wait for Jupiter to return to the same spot in its orbit, then take a second observation from a different Earth position. Two sight-lines drawn from those two Earth positions cross at Jupiter's true location.
Repeating this process for six different points lets you plot the whole orbit. Then, by measuring the longest line through the ellipse (the major axis) and the offset between its center and the Sun, you can calculate Jupiter's eccentricity — a number that tells you how stretched-out the orbit is. The accepted value for Jupiter's eccentricity is about 0.048, which means Jupiter's orbit is almost (but not quite) a perfect circle.
Jupiter orbits the Sun.
Eccentricity describes orbit shape.
In this simulation you will plot four Jupiter positions using a virtual protractor. Two positions (J1 and J2) are already plotted for you as examples.
Filled in automatically as you plot each Jupiter position. All six rows must be plotted for full credit.
| Position | Earth Helio (Date 1) | Jupiter Geo (Date 1) | Earth Helio (Date 2) | Jupiter Geo (Date 2) | Status |
|---|
Once all six Jupiter positions (J1–J6) appear in the data table above, tap Connect Points → Draw Ellipse in the simulation. A dashed line will appear from J3 to J6, passing through the Sun. This line is the Major Axis of Jupiter's orbit. Continue with the steps below — you will use the on-screen measuring tool in Part 4 to find each length. All measurements are in model units (the digital equivalent of a ruler on paper).
eccentricity = distance between foci ÷ major axis
📍 The measuring tool and answer boxes for all of these steps are waiting for you in Part 3.
Now that you have plotted Jupiter's six positions, drawn its orbit, and calculated its eccentricity, step back and look at what the shape and your numbers reveal about Jupiter's path around the Sun.
The chart below shows how far each plotted Jupiter position is from the Sun in your model. A perfect circle would show six equal distances. An ellipse shows variation between aphelion (farthest) and perihelion (closest).
Tip: If your chart is empty, return to Part 2 and finish plotting all six Jupiter positions.
Base your answers to Questions 14 through 18 on the passage, diagrams, data table, and graph below. Each question is worth 1 point.
For thousands of years, astronomers believed every object in the solar system traveled along a perfect circle, with Earth fixed at the center. That picture began to fall apart in the late 1500s when the Danish astronomer Tycho Brahe spent more than twenty years recording the positions of the planets — most carefully, Mars. His measurements were the most precise of his era, accurate to within four arc-minutes (one fifteenth of a degree).
After Brahe's death in 1601, his German assistant, Johannes Kepler, inherited the data. Kepler spent eight years trying to fit Mars's path to a circle around the Sun. No matter what radius or center he chose, the model could not match Brahe's observations. In 1609 Kepler finally abandoned circles and tested another shape: the ellipse. With the Sun placed not at the center but at one of the two foci, Mars's position fell into place at every recorded date.
From that breakthrough Kepler eventually published three rules — now called the Laws of Planetary Motion — that describe how every planet orbits the Sun:
Kepler's three laws still describe the motion of every planet, moon, comet, and artificial satellite in our solar system, more than four centuries after they were first written down.
| Planet | Mean Distance from Sun (×10⁶ km) | Period of Revolution (Earth years) | Eccentricity of Orbit |
|---|---|---|---|
| Venus | 108.2 | 0.62 | 0.007 |
| Earth | 149.6 | 1.00 | 0.017 |
| Mars | 228.0 | 1.88 | 0.094 |
| Saturn | 1432.0 | 29.5 | 0.054 |
| Neptune | 4515.0 | 163.7 | 0.009 |
Part A: Describe how a planet's orbital speed changes as it travels from aphelion to perihelion.
Part B: Explain how this change in speed produces equal areas swept out in equal intervals of time (Kepler's Second Law).
Compared to Earth, the planet Mars has a mean distance from the Sun that is . According to Kepler's Third Law, the period of revolution of Mars is therefore than the period of Earth. The average orbital speed of Mars is than the average orbital speed of Earth, because planets farther from the Sun travel more slowly along their orbits.
Key: P = perihelion (closest to Sun) · A = aphelion (farthest from Sun)
Use the tools below to measure distances on your plotted orbit, then calculate Jupiter's eccentricity. The accepted eccentricity of Jupiter's orbit is 0.048.
Your six Jupiter positions and the orbit ellipse from Part 2 appear automatically below. Click Start Measuring, then click two points on the diagram. The line will snap to the Sun or a Jupiter dot if you click near it, so each measurement is precise.
Follow the steps from Part 2. Use the measuring tool above for each measurement.
distance between foci = aphelion distance − perihelion distance
eccentricity = distance between foci ÷ major axis
% deviation = |your value − 0.048| ÷ 0.048 × 100
Five questions drawn at random from a 20-question bank, modeled on the January 2026 and June 2025 NYS Earth & Space Sciences Regents exams. You need 60% (3 out of 5) to pass. You may retake the quiz as many times as you need — a fresh set of questions will be drawn each time.
Tap the button below to print this lab. The print includes your data table, plotted orbit, calculations, quiz results, and final grade. Save it as a PDF and submit to Mr. Brown.