How Big is OUR Solar System?

“The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets,  with the remainder being significantly smaller objects, such as dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury.

The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system’s mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth, and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia, and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.”

“The solar system does not really end with Pluto. Besides the planets, there is a thin haze of dust (some of it bunched into comets). Any of this dust that is nearer to the Sun than to any other star may be in the gravitational hold of the Sun and so counts as part of the solar system. So the outermost of such dust may be half way to the nearest star.

On the scale of our model, Pluto is a thousand yards or rather more than a half a mile out. But this true limit of the solar system is two thousand miles out.

A thousand miles, in our model, is the distance called a light-year (in reality, about six million miles).

The distance to the nearest star, Proxima Centauri, is 4.2 such light-years.

The human mind can never conceive this thing called a light-year, which is the currency of our small-talk about the universe. (It is probable that we cannot directly conceive any distances above about 600 yards, which is where we sub- consciously place the horizon). But through the model, we move as far toward conceiving it as we ever can.

I, at least, have seemed to have some respect for the term, light-year; and to have some sense of what I mean when I use it-since I made the sensory approach to it through this model.

The rest of the stars in our galaxy are probably on the order of four to ten light-years apart from each other, as we are from our nearest neighbor.

This is a stunning thought when (having done the Thousand-Yard exercise) you go out at night and look at the Milky Way. It is a haze of light so delicate that it can no longer be seen from inside our light-ridden cities. It consists of the bulk of the stars in our galaxy, piled up in the distance, so numerous and so faint that we cannot see them separately. Yet they are all the same kind of distance from each other as we are from the nearest of them. That is if we could hop to any one of them, cavernous black space would open out around us, and the Sun itself would become part of that same dense far-off wall of stars, the Milky Way!”

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