How Far are the Planets?

By

Don Porter

OBJECTIVES:

            Content: It is difficult for most individuals to comprehend the vast distance of our solar system and surrounding stars.  It becomes necessary to use alternative measuring systems, such as the Astronomical Unit (AU) and Light Year.

RELATION TO MISSOURI FRAMEWORKS:

5-8: VA1  The universe is so large, distances are expressed in special units.

CONTEXT:

            Grade Level: 5-8

            Group of 15-25 for StarLab presentations.

PREREQUISITE:

            Students should have some knowledge of the planets that comprise our solar system.

MATERIALS:

            StarLab Portable Planetarium

            Solar System and Galaxy Cylinder

            Arrow pointers

            Measuring Tape (50 meters)

            Solar System Distances Worksheet

PROCEDURE:

1. Before entering the planetarium, ask students what unit of measurement they would use to measure the following:

• A piece of paper (centimeter or inches)
• A room (meter of feet)
• City to City (kilometer of miles)
• Planet to Planet (Astronomical Unit – AU)
• Star to Star (light year)

Write the answers on a chalkboard or overhead.

2. Inform the students of the following relationships:
• 1 mile = 1.6 kilometer
• 1 kilometer = 0.62 mile
• 1 AU = 93,000,000 miles (Earth – Sun distance)
• Speed of light = 186,000 miles/sec (300,000 km/sec)
• Light Year = approximately 6 trillion miles
3. Enter planetarium
4. Turn on Solar System and Galaxy cylinder after all students are seated and ready.
5. Ask a student to name the nine planets of the solar system out ward from the sun.
6. Inform the class the mean diameter of the solar system, with reference to planetary orbits is about 12 billion kilometers (7.5 billion miles).  The size of this number is difficult to grasp!
7. Provide the following illustration: Ask students to estimated how long it would take to drive a mile. (one minute) To drive a hundred miles.  (a couple of hours).  A thousand miles. (about two days of sane driving)  To drive seven and a half billion miles. (about 13,172 years driving at 65 miles per hour 24 hours a day and never stopping – not event for a bathroom break!)  In all likelihood, students’ estimates were all reasonable until the final distance; then they had absolutely no idea!
8. Adjust the cylinder and discuss the distances between the sun and each planet.  Within the discussion, indicate the distance between the sun the Earth is equal to 1 AU (93 million miles).
9. Ask students if they know the name of the suns nearest star.  (Alpha Centauri)
10. Ask students if they know the distance between the sun and Alpha Centuri.  (4.5 light years or 26.5 trillion miles)
11. Review the AU distances of the planets in our solar system.
12. Review light year distance.
13. Inform students that the Milky Way galaxy is over 50.000 light years across.
14. Inform students that our star (the sun) is only one of hundreds of billion of stars in the Milky Way galaxy.
15. Inform students that the Milky Way galaxy is one of hundreds of billions of galaxies in the universe.
16. Have students carefully exit the planetarium.
17. Distribute Solar System Distance Activity Worksheet and allow the students to complete them.  (Inform students that on this scale 1 AU = 1 meter)

EXTENSIONS AND/OR ADAPTATIONS:

            After completing the worksheet, extend the tape measure 40 meters.  Place markers (or people) to represent the planets and distances away from the sun. (Remember 1 meter = 1 AU)  Pluto is 39.5 meters away from the sun.  Using this scale, how far would Alpha Centauri be plotted? (7,000 times farther than Pluto or about 172 miles away)

CONTENT BACKGROUND:

            It is difficult to comprehend the immense distances between objects in the solar system.  The Earth-Moon distance of 385,000 km (239,000 miles) seems quite large at first.  However, compared to other solar system distances, it becomes almost insignificant.  The distance between the Sun and Pluto, for example, is a staggering 5,900,000,000 km (3,674,000,000 miles)!

            The Milky Way is but one of hundreds of billions of galaxies and each of those galaxies contains hundreds of billion of stars of its own.  It almost seems impossible to fully realize the true scope and size of the universe.  It has been said that nobody can fully comprehend the immensity of space.  While that may be true, it is hoped that this activity will at least provide students with a tiny insight.

APPENDIX:

            Activity Sheet (Solar System Distances)

RESOURCES:

Earth Science Activities for the Elementary Classroom  Level 4-6

How Big is the Universe Volume 9