## Sunday, March 16, 2014

### How Big is the Solar System?

 The image of the Solar System was made using real images of the planets. It is not to scale; the Solar System is so large with respect to the size of the planets, that to fit it on the screen, the planets would have to be small dots. Thus, some artistic license is involved. However, the planets are in the correct order. Also shown is comet Hale-Bopp, photographed by the author.
One way to help visualize the relative distances in the solar system is to imagine a model in which the solar system is reduced in size by a factor of a billion (109). The Earth is then about 1.3 cm in diameter (the size of a grape). The Moon orbits about a foot away. The Sun is 1.5 meters in diameter (about the height of a man) and 150 meters (about a city block) from the Earth. Jupiter is 15 cm in diameter (the size of a large grapefruit) and 5 blocks away from the Sun. Saturn (the size of an orange) is 10 blocks away; Uranus and Neptune (lemons) are 20 and 30 blocks away. A human on this scale is the size of an atom; the nearest star would be over 40,000 km away!

While you are talking and introducing the idea of the model, it may be helpful (depending on the age of the audience) to build up on a blackboard something like this:
```
real   in model
Earth's width   8,000 miles  8/100 inch
Sun's width   800,000 miles  8 inches
therefore scale is  100,000 miles  1 inch
therefore   3,600,000 miles  36 inches or 1 yard
and Sun-Earth distance  93,000,000 miles 26 yards```
`Read more: http://www.noao.edu/education/peppercorn/pcmain.html`
```

Mercury is only 0.39 astronomical units from the Sun, while Jupiter orbits at a distance of 5.5 astronomical units. And Pluto is way out there at 39.2 astronomical units.

That’s the equivalent of 5.9 billion kilometers.

If you could drive your car at highway speeds, from the Sun all the way out to Pluto, it would take you more than 6,000 years to complete the trip.