With @NoisyAstronomer on a plane and @GeorgiaBracey sick today, we unfortunately have to cancel today's Learning Space. posted about 16 hours ago

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March 27th: A Scale Model Of The Universe


Date: March 27, 2010

Title: A Scale Model Of The Universe


Podcaster: Rob Wolfram

Description: The intro song to the 365 Days of Astronomy podcast contains the words “this stuff is far, far, far away” while referring to astronomical objects. Still, it is very hard to wrap your mind around the actual distances. This podcast aims to visualize the actual sizes and distances of a few of these objects by describing a few scale models of increasing scale factors.

Bio: Rob Wolfram was born and raised in Suriname, South America, but now spends his days as a computer systems engineer in a large academic hospital in Amsterdam, the Netherlands. Although he enjoys his job and living in the Netherlands, he sorely misses the dark skies of his native country.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Keith Brandt – physician, amateur astronomer, and all-around science geek, and is dedicated to his daughter Rachel, who is not a geek, but a hockey star and stellar Rainbow Girl. Happy 15th birthday Rachel!


Hello, my name is Rob Wolfram and I’m an astronomy hobbyist. This is my contribution to the 365 days of astronomy podcast.

I’ve loved astronomy since the age of 10 when I got a children’s book on astronomy and space exploration in which I read about Halley’s comet. I promised myself to see it when it would came back in about 14 years, and I did.

Some 20 years ago I read the description of a scale model of the Solar System and it was a jaw-dropping experience. It was even more so when I calculated a scale model of our galaxy. I would like to share that with you in the hope that you too can appreciate the sizes and distances of objects in our universe.

You sometimes hear that the distance of the star Sirius to us is 8.8 light-years or that the Andromeda Galaxy is at a distance of 18.5Mpc, but what does that actually mean?

We have seen also numerous images of models of the solar system or Earth/Moon models but these are generally woefully out of scale.

By creating a few scale models of both the size and the distance of Astronomical objects, I’ll try to illustrate what our universe looks like. Do try to keep earlier scale models in mind to appreciate the later ones, you can easily lose the perspective.

First, you should get an impression of the size of the earth. If you travel 500km, or slightly over 300mi by car, it would take around 5 hours driving. This distance is approximately from Amsterdam to Paris or from Chicago to Cincinnati. If you would be able to constantly drive around the world with the same speed, it would take 17 days.

With this in mind, we scale the Earth and Moon down to a scale factor of 1 to 50 million. In this scale the Earth has a size of 24cm or 9.5″, approximately the size of a basketball.

The moon would then be a juggle-ball of 6.5cm or 2.5″ and this juggle-ball would orbit the basketball at a distance of 7 meters, that’s one and a half the length of an average car. You can fit 29 Earth diameters between the Earth and the moon.

Now in this scale model, the sun would be too large so let’s bring down the scale to where the sun has a diameter 1.4 m, that’s 4’7″, the height of a 10-year-old kid. This is a scale factor of 1 to a billion and here the earth would be a marble of 1.2 cm or 0.5″. The moon would be a 3.5 mm or 1/8″ bearing ball at a distance of 38 cm or 1’3″ of the earth marble.

Mercury would be slightly larger than the moon at 5 mm, Jupiter would be 14 cm or 5.5″ across. That’s the size of an apple. Neptune would be like a 5 cm or 2″ plum.

Now for the distances. The 5 mm Mercury would rotate the 1.4 m Sun at a distance of 58 m, that’s 63 yd, more than half a football field. The Earth-marble would rotate at a distance of 149 m or 163 yd, the Jupiter apple would be at 780 m or 850 yd of the 1.4 M sun. The Neptune plum would be at a distance of 4.5 km or 2.8 mi.

Such a model with all planets on one side of the Sun wouldn’t even fit in Central Park, New York.

Now, to include other stars, we scale down the model by a factor of 1000 down to a factor of 1 to a trillion. In this scale, the Sun is a grain of sand of only 1.4mm across, that is less than 1/16″.

There are stars in various sizes, ranging from earth-sized white dwarfs, which would be 12 microns in this scale or a fifth of the width of a human hair, to Antares in the constellation Scorpius which would be a 98 cm or 3’3″ ball and a few even larger ones. In this scale, Sirius, the brightest star in the sky, would be a ball of 2.4 mm or 1/11″ at a distance of 81 km or 50 mi! And this is a very close neighbor!

If we would position all 2 to 400 billion grains of sand and salt, marbles, and incidental beach balls that make up the scale model of our galaxy at the correct position, the model would measure close to a million kilometers, that’s 2.5 times the real distance from the earth to the moon.

Galaxies are relatively close to each other, but to include them we have to scale down our model more. A lot more. We scale our existing model down 50 billion times (thats with a B) so that our nearly 1 million kilometer galaxy model scales down to a coin of 19mm in diameter which is approximately a US dime or a 10 Euro-cent coin.

In this model the closest regular galaxy i.e. M31, the Andromeda Galaxy is a disc of 42mm or 1.6″ across, at a distance of 48cm or nearly 1’7″ from our dime. M87, the elliptical galaxy at the heart of the Virgo cluster is a 23mm or nearly 1″ marble at a distance of 11m.

Finally, the current size of the visible universe, or the co-moving size as it’s called, is 92 billion light-years and contains around 100 billion galaxies. This translates in our scale model to a sphere of coins and marbles with a diameter of 17.4km or 10.8 mi.

Remember the song: this stuff is far far far away. Far far far away indeed.

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.

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