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Astronomy 2021

Closer to Home: The Solar System

“Uncle Bob”

credit: NASA/JPL Edu

The Sun and System Scaling

In our 2021 survey of our Solar System, we’ll begin with the big heavy guy in the middle of the bed that keeps the planets – ever wanting to escape him – rolling somewhat towards him. The Earth, for one, has found a perfect balance between its own considerable tangential momentum and the big guy’s attraction. Stan Laurel manages at times to keep from colliding with Oliver Hardy – well, perhaps they’re not the best example. Earth has managed to keep an ideal distance, near enough but not too near Old Sol.

credit: NASA/JPL
This representation is intentionally fanciful, as the planets are depicted far closer together than they really are.

What is that distance and how can we comprehend it? Like many other physical properties of our Sun, it’s not easy. The Sun is a star, average in size, brightness, and temperature. It is 93 million miles from us. Huh? Allow me to explain. If everyone who voted in the most recent election were a mile tall, we could stand upon one another’s shoulders and reach the Sun – a task that would be greatly assisted after a while by the disappearance of Earth’s pull and the increasing buoyancy provided by the Sun – up to a point anyway. The difficult part would be growing humans a mile in height.

How close are the other stars? The nearest is Proxima Centauri and we won’t give the staggering number of miles away it is. We’ll say this instead: light from our Sun reaches us in 8 minutes. Light from this closest other star reaches us in four years. Imagine trying to make a scale drawing or model of Earth, Sun, and Proxima. By my rough figures, on a sheet of paper one mile wide, we would put the two stars at either end, and Earth would be a speck one quarter inch from our star.

And we haven’t yet accounted for relatives sizes. In the Audubon Guide I found some data which motivated me to write about these measures and the scales involved: the Earth Sun distance is 108 Sun diameters, and the Sun’s diameter is 109 Earth diameters. At first, the closeness of those numbers gave me pause, but combining them made me think of the plight of those communities desiring to display a physical model of the Solar System to scale.
Let’s deal with Sun size first and attempt a typographical representation:

corona (………|………|………|………|………|………) corona

Between coronas are fifty-four periods in six groups. If there were a period in between each period, they would model 108 Earths across the Sun’s three-inch diameter. Clearly our model Sun needs to be bigger than a baseball to make Earth a bit easier to find, but WAIT! Let’s keep it at this scale while we ponder the Earth-Sun distance. One hundred eight of these Suns would put the Earth 27 feet away. Baseball Sun and a speck of Earth would fit in a good sized public parlor. Alas, most of the rest of the Solar System would be left far out in the cold.

I checked the 27-foot estimate at

https://www.exploratorium.edu/ronh/solar_system/

How far? Using the three-inch Sun, the Exploratorium calculator at the site above puts Neptune at about one-fifth of a mile away. Good grief. How is our system model going to attract anyone boasting a speck of an Earth and an 1000-foot walk to a mung bean Neptune? – the size of a small caper, but I liked how "mung bean Neptune" rolled off the tongue of my brain.

In addition to Exploratorium there are more resources to help resolve this dilemma. One of the larger projects “plays in Peoria” and covers 6000 square miles!

https://informal.jpl.nasa.gov/museum/content/community-solar-system-scale-model

I find that many experts recommend the 5-inch Sun model to keep all within walking distance. You can find one at the National Mall (and virtually at the site below).

https://www.jeffreybennett.com/model-solar-systems/voyage-scale-model-solar-system/

Next month: Neptune

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