Reading before:
There is a truly enormous amount of information that we can access about our current understanding of our solar system. This NASA website for the solar system as a great way to stay caught up on the latest interesting news and pictures as well as general data. Spend a few minutes looking around and see what you find interesting.
In our class discussions a number of topics of interest came up from the overall structure of the solar system to other earthlike planets to killer asteroids and whether Pluto is a planet or not. Given that some scientists spend their entire careers trying to learn about and understand a single planet or aspect of the solar system it's a trifle bold of us to try to explore it all in a week or two.
Solar System: Scale
Surely the first thing we need to do is get a more concrete sense of the scale of the planets and the solar system in general. Remember back to when we did the same thing for the earth and moon and the distance between them? What do you remember from that discussion?
Here is NASA's planetary fact sheet for future reference. Here is a visual reference (thanks NASA!)....
This is great for keeping track of the order of the planets but is potentially so out of scale as to be misleading on many levels. There are two questions of scale that need to be clarified. One is the size of the planets. Consider just the inner planets (Mercury through Mars). What would you say their relative sizes are from the picture? The second scale issues this the distances between the planets. Again, what would you say are the relative distances between the inner planets and then out to Jupiter?
HW: Solar System
Identify what we usually describe as the inner and outer planets. What is one characteristic the inner planets have in common? What is one characteristic the outer planets have in common? These are sometimes referred to as rocky planets and Jovian planets. Which planets do these labels refer to?
HW: Solar System
List the planets (include Pluto if you want) in order of how many moons they have. You will need to dig around on the NASA planetary data information to find what you need. What is the general relationship between the mass of the planet and the number of moons? Which planets seem out of step with this relationship?
Activity: Using the NASA planetary fact sheet linked above to calculate the relative diameters of the different planets compared to earth. Each group will be assigned a subset of the planets.
Scale: Size of planets
To minimize distraction in this part of the breadcrumbs the ratios for diameters and distances are listed on a separate webpage here. We will now go and build a scale physical model for our solar system from these ratios.
Here are some objects we will use for reference:
Large Classroom: 11 m = roughly the Sun
Small Classroom: 6 m
Giant Beach Ball: 400 cm depending
large Exercise ball: 75 cm = Jupiter and Saturn are bigger than this
Beach ball: .4 m = 40 cm = Neptune and Uranus
basketball: 24 cm
volleyball: 21 cm
Softball: 11 cm = Earth and Venus
Hardball: 7 cm
Tennis ball: 6 cm
Golf ball: 4 cm = Mercury and Mars-ish
50 cent: 3 cm
quarter: 2.5 cm = moon
penny: 2 cm
marble: 1 cm
Depending on what I can find in my stockroom I usually have a ball which is roughly 10 cm in diameter to represent the earth. This is just a tad smaller than a standard softball (a quick aside: I had no idea softballs are defined by their circumferences rather than diameter - who knew?) If we take our model earth to be represented by a ball that has a diameter of 10 cm that makes Venus the same size while Mercury and Mars are golf ball sized. Mars is a little bigger it's true. The moon is about the size of a quartermakes Jupiter about 1.1 m in diameter and Saturn 0.9 m in diameter. Both of these are bigger than a large excise ball for sitting. Where is something for reference that is 1 m in diameter? Uranus and Neptune are about 4 times the diameter of earth which makes them the size of a beach ball.
Where does Pluto fit into this? Pluto's ratio is 0.19 which is smaller than our moon and it appears to have elements of a rocky planet and a gaseous planet -- very much like some of the moons of Saturn and Jupiter. Under the circumstances what would you call it?
The ratio for the sun is about 109. That would make the sun about 11 m in diameter -- how does that compare to the size of the classroom?
On some scale could you line all the planets up in the classroom? What about the sun? Do you have an intuition?
The ratio for the sun is about 109. That would make the sun about 11 m in diameter -- how does that compare to the size of the classroom? Are you surprised? By how big it is or how small it is?
Scale: Radius of Orbits
This is where things get really hard to grok.
Activity: Using the NASA planetary fact sheet linked above to calculate the relative distances compared to 1 AU which is the distance from the sun to the earth. Each group will be assigned a subset of the planets.
Again, using our 10 cm ball to illustrate the earth, we can ask how far away the sun is. The sun is 1.5 1011 m away, also known as 1 AU (astronomical unit) from the earth which is about 12000 times the earth's diameter (check the numbers) which would put the earth 1.2 km (about 3/4 mi) away from the COCC campus on the same scale. What would an 11 m sun look like at that distance? In very rough terms Mercury and Venus are divide that distance into 3rds. Mars is roughly 50% further away. Try to imagine those inner planets spread over 1.8 km (just over 1 mi) to get a sense for the space between the planets relative to their size. Where is the moon on this scale (3 m)?
Sun at Center:
| size | distance | Bend (20W) | Redmond (26W) | Prinevville (26E) | Madras (B St) | |
| Sun | small bldg | 0 | Trader Joes | Airport | Courthouse | Hwy 97 |
| Mercury | golf ball | .5 km | Robal Ln | Hwy 97 | > Tastee Treat | creek |
| Venus | softball | .85 km | < Cooley Rd | Lowes | Middle School | Bean Park |
| Earth | softball | 1.2 km | Cooley Rd | < Dutch Bros | Best Western | < top of hill |
| Mars | golfball | 1.8 km | < Old Bend/Red | RHS | Forest Service | COCC Campus |
| Jupyter | > exercise ball | 6.2 km | +Tumalo | > Cline Falls | Reserv' grade | Deer Ridge |
| Saturn | > exercise ball | 11.5 km | Tweed Rd | Dry Canyon | Och Res inlet | < Hereford |
| Uranus | beach ball | 23.6 km | Sisters | > Sisters | Rocky Butte Rd | Little Willow |
| Neptune | beach ball | 36 km | Camp Sherman | Camp Sherman | Marks Lake | 3/4 Mitchell |
The outer planets take this to a whole new level. Jupiter is pretty much 4x the distance from the earth that the earth is from the sun - 6.2 km (4 mi). Saturn is that far on the other side of Jupiter. Uranus and Neptune are each separated by the distance between the earth and Saturn (10 km - 6 mi) from each other and from Saturn.
To summarize, when we envision the earth as a 10 cm diameter green ball, the 4 inner planets are within 1.8 km (1 mi) of the sun. Jupiter and Saturn are 6 km (4 mi) and 12 km (8 mi) from earth. Neptune is 36 km (19 mi) from the sun and could be thought of as the edge of the planetary solar system. I trust you find this difficult to grasp. There is a really remarkable amount of empty space in the solar system!
If you want to explore this at a slightly smaller scale where Saturn is at the other end of a football field. Here's a doc with the data in case you ever want to recreate this.
What is your take away about the scale of the solar system? Here's a lovely video of a scale solar system smaller than the one we discussed here (the sun is a 1 m ball). It does a lovely job of clarifying the scale of the emptiness in the solar system and it's beautiful to boot.
In this age when information propagates rapidly in many different directions it feels like students in my classes have heard of events or objects that haven't crossed my path. As a result I feel I need to track some of these and offer some background for the science associated with them. This link will take you to a separate page where I collect such things.
HW: Solar System
The nearest stars to us are about 4.3 ly (light years) from us. 1 ly = 9.46 1015 m. How many meters is it to the nearest stars? Look up the radius of Neptune's orbit which is a rough measure of the size of the solar system. What is the ratio of the distance to nearby stars to the size of the solar system (remember that when we do ratios we use the same units top and bottom)? In our scale model of the solar system (green ball (10 cm) for earth) Neptune is about 36 km (22 miles) from the sun. How far away would the nearest stars be in this same scale? The moon is 380,000 km (240,000 miles) from the earth -- what does this tell you about the distance to the nearest stars?
Assignment: HW: Solar System
Complete and assemble your solutions to all the HW problems listed here. Scan to a pdf and turn in on LMS. Please review HW format expectations for guidance about your homework solutions.
Reading Ahead:
Next time we will continue our explorations of the solar system on the Solar System II breadcrumb. This will support our discussion about the formation and evolution of our solar system.
