Relative Distances of the Planets from the Sun in AUs

Last week, we only explored the relative sizes of the planet in our solar system, including Pluto. The children were very interested in exploring the moon vs. Earth so we started by cutting up the Kinetic Sand into 50 equal parts using several strategies which included first cutting in half, then 5ths and then 5ths again. With one group we cut it into 5ths first, then halves, then 5ths again. One fiftieth of the material represented the moon and 49/50s represented the Earth. Some of the children made the connection that our Moon must be 20 times bigger than Pluto since the Earth is 1000 times bigger than Pluto (50 x 20 = 1000).

Then we opened our discussion to measures of distance. The children explored their knowledge of units of measurement like the centimeter, the inch, the foot, the mile, the kilometer, etc. We then began to speak in astronomical terms like Earth Diameters (roughly 8,000 miles) and Astronomical Units (the distance from the Earth to the Sun is 93,000,000 miles). Then we looked at the relative distance of the Earth and Moon at the scale of 50:1. The Moon is 30 Earth diameters away from Earth. So if you set 30 spheres next to each other that represented Earth, that is the distance from the Earth to the Moon, almost a quarter of a million miles. 

Inevitably, the children asked about the Moon and the Sun. Why do we see the Moon and the Sun appearing the same size? I showed them a linear model of 400:1 based on their relative diameters and then that they are 400:1 far apart. This means that the Sun does not only have a diameter that is 400 times that of the Moon, but the Sun is 400 times further away than the Moon. Therefore, they appear the same distance in the sky. We used a half centimeter wide golf tee (the diameter of the Moon) and a two meter long stick (the diameter of the Sun) to simulate this affect in class. We put the golf tee up to our eye, roughly one centimeter away and then I stood with the 2 meter long stick at four meters from the children. The golf tee (Moon) looked as big as the stick (Sun).

Then we looked at the Relative Distances of the Planets. The following 8 steps will explain what I presented to the children in class. They should spend this week testing others knowledge of the relative distances. See the attached pdf.

1. Ask someone to fold the paper in half the long way and place an "S" on the left to represent the Sun and a "P" on the right edge to represent Pluto.

2. Then, on the top half, ask them to place the planets between the Sun and Pluto in their relative places in our solar system. This is an estimate of what we "think" is the case.

Note: let them know that the way we measure distance in our solar system is in units of measurement from the Sun to Earth (93,000,000 miles = 1 Astronomical Unit or 1AU). For example, 10 AUs is 93 million miles multiplied by 10 or 930 million miles.

3. Then, on the lower half, tell them to fold the paper in half from the Sun to Pluto and draw a light line along the middle crease. Ask them to tell you which planet this is; it is Uranus (write a U). Since Pluto is 40 AUs away from the Sun, have them write the number of AUs that Uranus is from the Sun. This is 20AUs.

4. Then fold from the Sun to Uranus and from Pluto to Uranus. These planets are Saturn (S) and Neptune (N) and are 10AUs and 30AUs, respectively.

5. Then fold from the Sun to Saturn (this is Jupiter at 5 AUs); fold from the Sun to Jupiter (this is the Asteroid Belt [not even a planet] at 2.5 AUs); fold from the Sun to the Asteroid Belt (this is Mars at 1.25 AUs); fold from the Sun to Mars (this is Venus at .7AUs); fold from the Sun to Venus (this is Mercury at .3AUs).

6. Of course, since Earth is 1AU, put an E between Venus and Mars.

7. I gave you a separate piece of paper to find the relative distances from the Sun to Jupiter; fold it in half and follow step 5 above to get a good picture of these distances.

8. Finally, have them open the paper and compare their estimates in the top half to the actual relative distances in the bottom half. It is astonishing how different our imagined picture of the solar system compares to the actual spacing of the planets.

If they want, they can color a solar system of planets on a piece of paper at the relative distances from the Sun.