The Stars Like Dust

(Wikimedia Commons)

(Wikimedia Commons)

By The Metric Maven

Arthur C. Clarke, when discussing the solar system in his pre-Apollo book The Promise of Space stated: “(Dr. Isaac Asimov once remarked that the Solar System Consists of Jupiter plus debris.)” (pg 262). Clarke knew and conversed with Isaac Asimov and so it is possible he said it. What one finds in print is a lot of misquotes of this assertion. One university website discussing Jupiter also uses parenthesis: “(Isaac Asimov once said, accurately, that the solar system consists of the Sun and Jupiter and a little debris.)” What Isaac actually said is in his book View From a Height is “4 planets plus debris” When expressed in terms of planetary volume, one can see Dr. Asimov’s point:

Planetary_VolumeThe Earth has 58 times less volume than Neptune, the smallest of the outer gas giants. Mercury, Venus, Earth, and Mars combined are but 2239 Zettaliters and so possess 28 times less volume than Neptune. Neptune is the runt of the outer planets as the table makes clear. When the four outer planets are added together, the total of the inner planets have about 1000 times less volume, a full metric triad. Asimov’s assertion is on solid ground in my view.

When I saw the original The Outer Limits Series as a boy, the ending credits showed black and white photographs of galaxies. It made me feel like this tiny vulnerable insignificant speck of nothing floating out in interstellar space viewing the image. People of the 19th century might have called it sublime. It was exhilarating and terrifying at the same time. Many years later, thanks to Astronomy Picture of The Day, I learned to recognize some of those galaxies when watching reruns of The Outer Limits. I very much like the look of the Sombrero Galaxy. It was in those same years that a grade school teacher of mine pondered out loud “I sometimes wonder if we are not just a speck of dust floating around in someone’s living room.” The notion seemed absurd, but it made me wonder, just how small we really are when cosmic dimensions are involved. A spec of cosmic dust is about 100 nanometers in extent. This is essentially an invisible item from our standpoint. We are three metric prefixes larger (three triads) or 1 000 000 000 times as large as a particle of cosmic dust.

The Earth has a diameter of about 12.8 Megameters and is two metric prefixes larger than ourselves. We are not quite dust, but are compatible to dust when one more triad is breached. Gigameters are useful for describing the size of the solar system, so we become dust sized when compared with the dimensions of our solar system. The Earth is in the Megameter range and so becomes a dust sized particle when compared with Petameter distances. The distance to our nearest star is about 41 Petameters from Earth.

The Milky Way Galaxy is about 1 Zettameter in extent. The observable Universe is about 880 Yottameters and so we are only about one triad down from this figure. If the universe is thought of as meters, our galactic dimensions are millimeters. When do stars become dust? The diameter of our sun is about 1.39 Gigameters, so when we reach the distances that describe “far away” stars within our galaxy, or Exameters, our star becomes a dust mote.

The metric system allows one to tame the dimensions of the Universe. When a single measurement “unit” called a light-year is used, no context may immediately be obtained. A light year is shorter than the distance to our nearest star. Isaac Asimov knew this, and used it to promote the idea of using the metric system in Astronomy. Unfortunately, So many years after his death, Dr. Asimov’s thoughts on this subject have themselves been reduced to dust.

Isaac Asimov’s birthday was on January 2nd.

Related essays:

Long Distance Voyager

The “Best Possible Unit Bar None”


The Metric Maven has published a new book titled The Dimensions of The Cosmos. It examines the basic quantities of the world from yocto to Yotta with a mixture of scientific anecdotes and may be purchased here.


4 thoughts on “The Stars Like Dust

  1. I can’t visualize zettaliters very well. The liter (and prefixes less than one) is handy for smaller volumes but we should note that it is NOT an official SI unit, only a non-SI unit accepted for use with the SI. Once we open the can of worms we get AUs and parsecs because they are exactly defined in metric units too (technically, not lightyears, because there are too many year flavors).

    If the goal is proper SI usage in astronomy, I would recommend 1.08 x 10^21 m³ or 1080 Mm³ in lieu of zettaliters for earth (for the others 1 Mm³ = 1 ZL)

    In another paragraph the (equatorial) radius of the earth is about 6.4 Mm, the diameter about 12.8 Mm

  2. I just discovered what’s pissing me off.

    It’s my years of tolerating the acceptance of non-SI units within the SI!

    Bless you, John Steele, for using the SI properly in your comments above! For, after all, isn’t a megameter meant to be a megameter? And, ban the tonnage once and for all! Let bygones be bygones, and let megagrams be megagrams! Not even in a WORLD devoted to the SI have we yet to see the routine use of this soft-spoken but quite correct SI multiple. Call me a fanatic for being ordinary.

  3. Another correction:
    “The diameter of our sun is about 1.39 Gigameters”

    Not until it super-novas and we are FUBAR (debatable then, but no debaters left). Units s/b megameters (Mm). Note that AU (our average distance from sun) is about 149.6 Mm.

    • Scrub that. I slipped a factor of 1000, converting to kilometers instead of meters.

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