12 Our Solar System

Formative Assessment: The Moon & Stars 


Planets in the Solar System “A representative image of the solar system with sizes, but not distances, to scale” by WP is licensed under CC BY-SA 3.0

There are 8 planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. To remember the order of the planets (closest to farthest from the sun), use the acronym “My Very Educated Mother Just Served Us Nutella.”

The four inner planets–Mercury, Venus, Earth, and Mars–are rocky planets because they have a solid surface. The four outer planets–Jupiter, Saturn, Uranus, and Neptune–are gaseous planets because they are composed of gases, mainly hydrogen and helium. Notice that the rocky planets are much smaller in size and the gaseous planets are larger. One theory for this is that when the Sun turned on and became a star, it caused the gas clouds of the four inner planets to blow away. The rocky planets were left with a smaller, solid planet. The gaseous planets are farther from the sun, so they retained their composition. As they increased in mass, their gravity increased which allowed them to attract more and more material from space and grow larger in size.

Sizes and Distances of Planets

The image below shows the huge variance in size between planets in our solar system. Notice the differences in size between the inner, rocky planets and the outer, gaseous planets.

Size planets comparison” by Lsmpascal-Own work is licensed under CC BY-SA 3.0/labels added from original

Measurements of Our Solar System

Element Diameter (km) Distance from the Sun (x106) (km)
Sun 1,392,000 ————————–
Mercury 4,897 57.9
Venus 12,104 108.2
Earth 12,756 149.6
Mars 6,794 227.9
Jupiter 142,980 778.6
Saturn 120,540 1433.5
Uranus 51,120 2872.5
Neptune 49,530 4495.1

Watch the following video to see a size comparison of the planets across Iowa’s campus.

Size comparison of the planets

To understand the scale of the Hubble eXtreme Deep Field, watch the video below:

Video credit: “How Small are We in the Scale of the Universe?” by Alex Hofeldt/TED-Ed  is licensed under CC BY-NC-ND 4.0

Why is Pluto Not a Planet?

Pluto was the ninth planet in our solar system until a controversial 2006 decision when it was reclassified as a dwarf planet. Pluto meets two requirements to be a planet: it orbits around the sun and its gravity formed the planet into a round shape. However, it does not meet the third requirement of “clearing the neighborhood.” Planets must have gravitational dominance and clear the neighborhood around their orbit; this means that large planets (more mass=more gravity) either attract or eject other, smaller bodies from that region of space. Several other dwarf planets and similarly-sized space objects were discovered in the solar system near Pluto’s orbit in the Kuiper Belt. Therefore, Pluto has not cleared the neighborhood and so it cannot be considered a planet.


K-6 Standards

5-ESS1-1. Support an argument that differences in the apparent brightness of the sun
compared to other stars is due to their relative distances from Earth.


1-ESS1-1. Use observations of the sun, moon, and stars to describe patterns that can be predicted. [Clarification Statement: Examples of patterns could include that the sun and moon appear to rise in one part of the sky, move across the sky, and set; and stars other than our sun are visible at night but not during the day.] [Assessment Boundary: Assessment of star patterns is limited to stars being seen at night and not during the day.]
MS-ESS1-1. Develop and use a model of the Earth-sun-moon system to describe the cyclic patterns of lunar phases, eclipses of the sun and moon, and seasons.  [Clarification Statement: Examples of models can be physical, graphical, or conceptual.]

ESS1.A: The Universe and its Stars


Fifth Grade

ESS1.B: Earth and the Solar System

Middle School

ESS1.A: The Universe and Its Stars

ESS1.B: Earth and the Solar System


Crosscutting Concepts


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            Connections to Nature of Science


Scientific Knowledge Assumes an Order and Consistency in Natural Systems

  • Science assumes natural events happen today as they happened in the past. (1-ESS1-1)
  • Many events are repeated. (1-ESS1-1)

Lesson ideas:

Take children outside to see the Moon in the daytime. Show them how to observe the Moon, and keep a Moon journal, and encoruage them to look for the Moon day and night. Look at your Moon journal to see what the patterns are.

Try to recreate what they see outside with the Earth Sun Moon system.


Performance Expectations

5-ESS1-1. Support an argument that differences in the apparent brightness of the sun compared to other stars is due to their relative distances from the Earth. [Assessment Boundary: Assessment is limited to relative distances, not sizes, of stars. Assessment does not include other factors that affect apparent brightness (such as stellar masses, age, stage).]
5-PS2-1. Support an argument that the gravitational force exerted by Earth on objects is directed down. [Clarification Statement: “Down” is a local description of the direction that points toward the center of the spherical Earth.] [Assessment Boundary: Assessment does not include mathematical representation of gravitational force.]
MS-ESS1-2. Develop and use a model to describe the role of gravity in the motions within galaxies and the solar system. [Clarification Statement: Emphasis for the model is on gravity as the force that holds together the solar system and Milky Way galaxy and controls orbital motions within them. Examples of models can be physical (such as the analogy of distance along a football field or computer visualizations of elliptical orbits) or conceptual (such as mathematical proportions relative to the size of familiar objects such as students’ school or state).] [Assessment Boundary: Assessment does not include Kepler’s Laws of orbital motion or the apparent retrograde motion of the planets as viewed from Earth.]
MS-ESS1-3. Analyze and interpret data to determine scale properties of objects in the solar system. [Clarification Statement: Emphasis is on the analysis of data from Earth-based instruments, space-based telescopes, and spacecraft to determine similarities and differences among solar system objects. Examples of scale properties include the sizes of an object’s layers (such as crust and atmosphere), surface features (such as volcanoes), and orbital radius. Examples of data include statistical information, drawings and photographs, and models.]  [Assessment Boundary: Assessment does not include recalling facts about properties of the planets and other solar system bodies.]


5th Grade


PS2.B: Types of Interactions

ESS1.A: The Universe and its Stars

middle School


ESS1.B: Earth and the Solar System


Crosscutting Concepts



Cause and Effect

Scale, Proportion, and Quantity



Scale, Proportion, and Quantity

Systems and System Models



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