How are the planets organized, and how does distance from the Sun affect a planet's orbit?
Describe the structure of the solar system and use the Selected Properties of the Planets table and Kepler's laws to relate a planet's distance from the Sun to its period and orbital velocity.
A Regents answer on the solar system: terrestrial versus Jovian planets, gravity as the controlling force, and Kepler's laws used with the Reference Tables Selected Properties of the Planets so that planets farther from the Sun have longer periods and slower orbital velocities.
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What this topic is asking
The Regents wants you to describe the structure of the solar system, name gravity as the force that holds it together, and use Kepler's laws with the Selected Properties of the Planets table to relate distance from the Sun to period and orbital velocity.
The structure of the solar system
The planets fall into two families:
- Terrestrial (inner) planets: Mercury, Venus, Earth, Mars. They are small, rocky and dense, close to the Sun, with few or no moons.
- Jovian (outer, gas giant) planets: Jupiter, Saturn, Uranus, Neptune. They are large, gaseous and less dense, far from the Sun, with many moons and ring systems.
Gravity holds it together
Gravity is the attractive force between any two masses; it increases with mass and decreases with distance. The Sun's enormous mass produces a gravitational pull that continuously bends each planet's path into a closed orbit, instead of letting it fly off in a straight line. The same force keeps moons orbiting their planets.
Kepler's three laws
The Regents almost always tests Kepler's third law as a data-reading question: read the Selected Properties of the Planets table and notice that mean distance and period both increase together, while orbital velocity falls.
Reading the planetary data
Approximate values from the Reference Tables:
| Planet | Mean distance from Sun (AU) | Period of revolution (years) |
|---|---|---|
| Mercury | 0.39 | 0.24 |
| Earth | 1.0 | 1.0 |
| Jupiter | 5.2 | 11.9 |
| Neptune | 30.1 | 165 |
The pattern is clear: as distance increases, the period increases sharply. Mercury, closest to the Sun, has the shortest period and the greatest orbital velocity; Neptune, farthest, has the longest period and the slowest velocity.
Try this
Q1. State the force that holds the planets in orbit around the Sun. [1 point]
- Cue. The Sun's gravity (gravitational attraction).
Q2. Using Kepler's laws, explain why Neptune takes much longer than Earth to orbit the Sun. [2 points]
- Cue. Neptune is much farther from the Sun, and the period of revolution increases with distance (Kepler's third law).
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (style)1 marksPart B-1. According to the Reference Tables, as the distance of a planet from the Sun increases, its period of revolution (1) decreases (2) increases (3) remains the same (4) increases then decreases. Justify your choice using the data.Show worked answer →
A 1-point Reference Tables question. The answer is (2).
Using the Selected Properties of the Planets table: Mercury (0.39 AU) has a period of about 0.24 years, Earth (1.0 AU) takes 1 year, Jupiter (5.2 AU) takes about 11.9 years, and Neptune (30 AU) takes about 165 years. As distance increases, the period increases (Kepler's third law). The trap is choosing "remains the same"; the data clearly increase with distance.
Regents (style)2 marksPart B-2. (a) Compare the orbital velocity of an inner planet such as Mercury with that of an outer planet such as Neptune. (b) Explain, in terms of gravity, why the planets stay in orbit around the Sun.Show worked answer →
A 2-point constructed-response question.
(a) 1 point: inner planets such as Mercury orbit at a much higher velocity than outer planets such as Neptune; orbital velocity decreases as distance from the Sun increases.
(b) 1 point: the Sun's gravity provides the inward (centripetal) force that continuously pulls each planet toward the Sun, bending its path into a closed orbit instead of moving in a straight line.
Markers reward "Mercury faster, velocity decreases with distance" and "the Sun's gravitational attraction holds the planets in orbit".
Related dot points
- Explain Earth's rotation and revolution, the evidence for each, and how they produce the apparent daily motion of celestial objects at 15 degrees per hour, including the use of Polaris to find latitude.
A Regents answer on Earth's rotation and revolution: the evidence for each, the apparent daily motion of the Sun, Moon and stars at 15 degrees per hour, Foucault's pendulum and the Coriolis effect, and how the altitude of Polaris gives an observer's latitude in the Northern Hemisphere.
- Calculate the eccentricity of an elliptical orbit using the Reference Tables equation (distance between foci divided by length of the major axis) and relate eccentricity to orbital shape and orbital velocity.
A Regents answer on orbital eccentricity: ellipses and foci, the Reference Tables formula (distance between foci over the length of the major axis), worked calculations rounded to the nearest thousandth, and how eccentricity and the Sun's off-center position affect orbital velocity and apparent solar diameter.
- Describe the phases of the Moon, solar and lunar eclipses, and the tides as consequences of the motions and gravitational interactions of the Earth, Moon and Sun.
A Regents answer on the Earth-Moon-Sun system: the cause of the Moon's phases, why solar and lunar eclipses are rare, the roughly two-week phase cycle, and how the Moon's and Sun's gravity produce spring and neap tides.
- Explain how the tilt of Earth's axis and its revolution change the angle and duration of insolation through the year, producing the seasons, the solstices and the equinoxes.
A Regents answer on insolation and the seasons: why the 23.5 degree axial tilt and Earth's revolution change the angle and duration of insolation, the solstices and equinoxes, the Sun's path across the sky at New York latitudes, and why summer is warm even though Earth is near aphelion.
- Use the Luminosity and Temperature of Stars diagram to classify stars, describe the Sun and nuclear fusion, and state the evidence for the Big Bang (red shift and cosmic background radiation).
A Regents answer on stars and cosmology: reading the Luminosity and Temperature of Stars (Hertzsprung-Russell) diagram, the Sun as a main sequence star powered by nuclear fusion, star color and temperature, and the red shift and cosmic background radiation as evidence for the Big Bang.
Sources & how we know this
- Reference Tables for Physical Setting/Earth Science (2011 edition) — New York State Education Department (2011)
- Regents Examination in Physical Setting/Earth Science — New York State Education Department (2026)