Up to 32 students

Two 45-60 minute sessions


Each planet has its own gravity and special set of circumstances; this lesson plan covers some general ideas about the planets, their diameters and locations in space.

The inner planets are smaller than the outer planets in diameter. Inner planets are denser than the outer planets. As one travels from the sun outward the distance between the planets increases. The distance between the sun and Earth is called an astronomical unit (AU), this is an average distance of about 93 million miles or 150 million kilometers. Hence Venus and Mercury are less than 1 AU and planets beyond Earth are more than 1 AU from the sun.

Pluto is no longer considered a planet for numerous reasons: According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.

Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

In addition, bodies that dominate their neighborhoods, clear asteroids, comets, and other debris along their orbits. By contrast, Pluto's orbit is untidy.

Learning Objectives:

  1. Generally the inner planets are smaller in diameter than the outer planets.
  2. An astronomical unit is 93 million miles and it is based on Earth’s distance from the sun. The distance between planets increases the further from the sun they are located.


Guiding Questions:

Is the diameter of Earth smaller or larger than Neptune? Why might it be different? Is the distance between Earth and Mars the same as the distance between Jupiter and Saturn? Why might it be different?







(For Class Demonstration)

Giant Pumpkin or Super Big Beach Ball/Workout Ball (sun)

Coffee Bean (Mercury)

Large Grape (Venus)

Cherry (Earth)

Pea (Mars)

Grapefruit or Cantaloupe (Jupiter)

Large Orange (Saturn)

Kiwi or Plum (Uranus)

Nectarine or apricot (Neptune)

(Optional: Pluto – grain of rice)


Glue or tape



Register Tape or Long Sheet of Paper

Activity 1: Scaled to Size

Place the fruits and such in order (do not have to distance to scale yet) in the front of the class and ask the students what they think the items may represent. Why are the outer planets so much bigger? Why are the inner ones so much smaller? Write on board or supply students with a worksheet with the following data on the planets and ask them to draw the planets in order to the correct scale given.

Mercury 4.9mm

Venus 12.1mm

Earth 12.7mm

Mars 6.7mm

Jupiter 142.8mm

Saturn 120.6mm

Uranus 51.3 mm

Neptune 49.1mm

(Pluto) (2.3mm)

Activity 2: Drawn to Scale in Place

Depending on the ability of students either have them calculate AU by length of the register tape or supply them with a scale AU to base their scale model of the solar system on. If you feel that your students are up for the math, measure the tape being used assume that it covers the distance from the sun to Neptune, so if your tape is 1 meter it spans 30 AU. Therefore each centimeter is about equivalent to 0.3 AU. Please note that the AU and cm scale distances are measured always from the sun and not from the prior planet.

Tell students to cut out their “planets” they constructed in the last activity and place them in the correct order on their solar system scale.

Planet Distance in AU Scale Distance

Mercury 0.4 AU 0.4 cm

Venus 0.7 AU 0.7 cm

Earth 1.0 AU 1cm

Mars 1.5 AU 1.5 cm

Asteroid Belt 2.8 AU 2.8 cm

Jupiter 5.2 AU 5.2 cm

Saturn 9.5 AU 9.5 cm

Uranus 19.2 AU 19.2 cm

Neptune 30.1 AU 30.1 cm

(Pluto) (39.5 AU) (39.5 cm)


Conclusion and Wrap Up:

Have students reflect in their notes about the activities of the day and any additional questions they may have in class or for homework.

Vocabulary to note:

Astronomical Unit

Have students add new concepts to their LINK.

New York State Scope and Sequence

Intermediate and High School Science Standards

Physical Setting:

Key Idea 1.1a - 1.1c, 1.1e, 1.2 a - 1.2d

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