Urban Astronomy – The Scale of the Solar System

Posted Dec. 29, 2020

I read regularly at AmericanThinker.com (AT) and they have published a few of my articles and blog posts. (that last one is not mine, but from some other author with a similar name)  In a recent AT article What I Learned from the Christmas Star by Mark Deutschle that author wrote:

“…we were looking at Jupiter and Saturn, which are over 700 million miles from Earth.”  That is an oversimplification that implies that those planets are actually near to each other.  They are not.  They only happen to be in the same part of our sky.

Also, in a conversation with my Number-One Son about science fiction, and actual astronomy, he asked me how the batteries were charged on the probe that landed on Titan (the large moon of Saturn).  The answer (They were not charged, they died after a few hours.) surprised him.  Why not solar panels?  Because Saturn is (on average) about ten times as far from the sun as Earth.  (You might have read this in my article called A Nice Place to Visit, But…)*.   That means that the sunlight received at Saturn is only one percent as intense as we get here on Earth.  Add the cloudy atmosphere of Titan and less than 1/10th of one percent (1/1000th) makes it to the surface of Titan. 

You might think that the son of an Astronomy Nerd would know all this.  It might surprise you to learn that my son does not listen in fascination to my every word.  If you, indeed are surprised, I have a premonition that you are, as yet, childless – or at least “teenagerless”.

*I have written another article, along those lines – meant for actual profitable publication.  If you are an editor and have any interest, let me know through the “contact” tab in this website and I can send a link and a password for you to read same.

I wrote all that so I could tell about the Scale of the Solar System.  Since distances of other planets vary due to their orbits and the Earth’s orbit, the way to keep this clear in your mind is summed up with one distance – 93 million miles (close enough) which is called one astronomical unit (AU).

Then remember these numbers:   0.4, 0.7, 1, 1.5, 5, 10, 20, 30 and 40 – which are the distances from the Sun to each of the planets in Astronomical Units.

If you want to know the distance in miles, multiply each of the nine numbers by 93 million.

So:

The Earth is right now on the opposite side of the Sun from both Jupiter and Saturn.  The distance from Earth to Jupiter is 6 AU’s and to Saturn is 11 AUs.  The distances in miles are 465 Million and 1023 Million.  The average of those two is 744 Million.  So, Mr. Deutschle rounded that average down to 700 million and said “Both were farther”.  In fact, Saturn is over twice as far as Jupiter and the maximum distance involved with those three planets is over a billion miles

Below is a Solar System diagram (from JPL Small body dataset browser) of the sun and planets that helps to visualize the Christmas day configuration of these three planets.  In this oblique view, you can see the actual situation

Deutschle’s  point in his article was that the Universe is large and majestic.  So, to appreciate the Solar System even more, we can say (since Neptune is 30 AUs from the sun) that it is 60 AUs in diameter – or Five and a Half Billion Miles. You might think that the popularity of the word “billion” started recently – with the National Debt.  Not so, neighbors!  Astronomy Nerds were in “billions” territory more than a century ago!  In fact, we knew the distances to some stars were in light years early on and the very nearest is Proxima Centauri at 4.24 light years or 1.31 Parsecs or 268,400 AU’s or 25 Trillion miles.  We got to Trillions long before any of those corrupt, big-spending politicians!


Hasta Luego,

Steve

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