Getting to know the neighborhood – our solar system

Modern science shows us a world that is frustratingly difficult to comprehend and appreciate. In quantum mechanics we deal with a world that is tiny beyond anything we experience. And in astronomy we deal with a world that is huge beyond anything we experience.

Our experiential knowledge is confined to the middle.  That’s where we live. And the middle appears to be the only place where intelligent life can take place. A life form much larger than us – say the size of our galaxy – would take thousands of years to have a thought. And a life form much smaller than us – say the size of a flea – just can’t be complex enough to create the emergent property of awareness.  So here we are int he middle of things, trying to comprehend the two extremes and having nothing in our experience that helps much.

Still, I think we should make an effort to move from our experiential knowledge – something we know, not simply in our minds, but in our whole bodies because we have experienced it – and try to apply that to the huge numbers we deal with in astronomy so we can at least begin to appreciate the reality they represent. That’s the purpose of this little exercise. Not to test your math knowledge. Not to try your patience. But to help you move a little closer to the wonder that is our solar system.

We will deal with one simple thing – the distances involved – and we’ll start with a basic distance that will serve as a key to all the others, the distance between the Earth and Sun. In good round numbers that distance is 93 million miles.  But, of course, no human being has taken a trip of a million miles, let alone 93 million, so we have no experience that can relate to this number. So let’s first pick a starting point – one your comfortable with – and see how that relates to this number. Choose one of the following travel means, or make up one of your own that is something you have experienced.

  • Brisk walk – 4 miles an hour
  • Automobile – 65 miles an hour
  • Indy race car – 200 miles an hour
  • Maglev train – 300 miles an hour
  • Commercial Jet – 500 miles an hour
  • F-15 fighter – 1900 miles an hour
  • Space Shuttle – 18,000 miles an hour
  • Apollo Moon rocket – 25,000 miles an hour

I’m not sure anyone can really relate to the last three – unless you happen to be a fighter pilot or astronaut – but if they are in your experience, feel free to use them. For me, I relate to the speed of a commercial jet. I have some idea of  how fast that is and how long it takes me to cover the distance between Rhode Island and Florida. That fits my experience.

The question you want to answer is, at your chosen speed, how long will it take you to travel from here to the Sun?

That is,what is 93,000,000 divided by the chosen speed?

Do your answer first in miles an hour, but to get it down to a manageable number, calculate it in years – and round off. we’re not trying for precision here – just trying to get a feel for the distance involved. So when you get your final answer, sit back and try to imagine making such a trip.

Your travel means: __________________________

Your travel time from Earth to the Sun:_______________________________

OK – now let’s apply this to the rest of the Solar System. That’s really a lot easier than it may sound. See, the distance from the Earth to the Sun – 93,000,000 miles –  is known as an “astronomical unit.”  Many other distances can then be stated in terms of that unit. And you’ve just created an astronomical unit of travel time.

Here is the average distance – in astronomical units – between Earth and the other planets in astronomical units. To calculate travel time to each simply multiply the average distance in astronomical units by the number you arrived at above and create your own Solar System Travel Guide.

Average distance in Astronomical Units                Calculated Travel Time

Mercury    .61                    ______________________________

Venus        .28                    ______________________________

Mars        .5                    ______________________________

Jupiter    4.2                    ______________________________

Saturn        8.5                    ______________________________

Uranus    18.2                    ______________________________

Neptune    29.1                    ______________________________

Pluto        38.5                    ______________________________

Bonus Section: Want to try a few more?

How long would it take to carry on a radio conversation with someone on Neptune? Radio waves – and light waves – travel at 186,200 miles a second.  You can calculate an astronomical unit of time by dividing that into 93,000,000 – round your answer off in minutes to get a good approximation, then use the numbers in your table.  (By the way – when you see a TV anchorperson talking to a correspondent half way around the world  and you notice a delay in the conversation, that is NOT due to the speed of radio waves. Radio waves travel around the world  seven times in a second. The delay is due to other issues with the technology used.)

Radio waves to Neptune: ______________________

Use 238,000 miles as the distance to the Moon. How long would it take to get there by your chosen travel speed?

Travel time to the Moon: _________________________

How long would it take you to travel around the Sun – what Earth does every year? Fudge it a bit by considering our orbit circular. You can calculate the distance involved by finding the circumference of that circle – the formula is 2 pi R. In this case “R” is the astronomical unit and since you have already calculated the time of a single astronomical unit at your chosen speed, you can just substitute that for “R.”

Your new “year”: _______________________________

How long would it take to go to the next nearest star, Alpha Centauri, which is 4.3 light years away? (A light year is equal to  63,239.6717 astronomical units – you can round that off to 63,240 astronomical units. So use your “astronomical unit” and multiply it by 63,240 – then remember to multiply that answer by 4.3.

Travel time to the next nearest star: _________________________________

I hope this  begins to help you develop a feel for astronomical numbers. We will return to them another time. Living in the “middle” is nice – but not always easy ;-)

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