A blog named for the muse of Astronomy containing musings by an astronomer

Ripley’s Believe it or Not Understatement

Posted on March 30, 2011 by Juan

Astronomically Offensive Panel from March 30, 2011 Ripley's Believe It or Not comicToday’s Ripley’s Believe It or Not comic contained an understatement of extraordinary proportions.  I include a copy of the panel of particular interest to me.  It states the “unbelievable” fact that

By driving at 100 miles per hour in a car, if it were possible, it would take more than 28 years to reach the nearest star – Proxima Centauri.

This implies that you would get there in a little more than 28 years.  Unfortunately, this is horrifically off the mark!

Let’s see, at 100 miles per hour, you go 876,600 miles per year (assuming 365.25 days per year and 24 hours per day).  In 28 years you have gone about 24.5 million miles.  That doesn’t even get you to Venus, the closest planet, which at closest approach is about 25.5 million miles away!

This is a problem a lot of my incoming students have, they don’t realize just how “astronomical” astronomical distances tend to be.  Let’s use a few examples with this 100 mile per hour space car.

  • Driving to the Moon: The closest heavenly body is the moon, at an average distance of about 240,000 miles.  At 100 miles per hour, it will take this space car 2400 hours or approximately 100 days to reach the Moon. The Apollo astronauts took just over 3 days to get there!   I guess the Saturn V rocket moved them a bit faster than 100 miles per hour!
  • Driving to the Sun: The distance to the nearest star, the Sun, (yeah, Ripley’s got this one wrong too!) is approximately 93 million miles.  This distance is so huge, astronomers often replace miles with “astronomical units” where one “AU” is the average distance to the Sun.  It would take this space car 930,000 hours or just over 106 years to travel 1 AU to reach the Sun. So remember that, about 106 years to drive 1 AU (NOTE: Actually, that is the time to reach the center of the Sun, shave off half a year if you just want to reach the surface of the Sun.  Yes, the Sun is that big! It’s a star baby!)
  • Driving to the Neptune: The minimum distance to Neptune, the furthest planet out is approximately 28.8 AU.  So you are looking at a travel time in this space car of about 3050 years.
  • Driving to the Edge of the Solar System: The farthest large object in the solar system that I am aware of is Eris, the dwarf planet.  It’s average distance from us is about 67.7 AU or a drive time of about 7175 years.
  • Driving to Proxima Centauri: But all these distances pale in comparison to the distance to nearest star other than the Sun, Proxima Centauri.  Proxima Centrauri is 4.2 light years away.  1 Light year is the distance light travels in one year and light is the fastest thing in the universe.  Light travels about 186, 282 miles per second or 5,878,625,372,000 miles per year.  This works out to about  63240 AU per light year, so the distance to Proxima Centauri is about 265,600 AU!  This is enormous!  It would take Ripley’s space car traveling 100 miles per hour over 28 million years to get to Proxima Centauri.  “More than 28 years” indeed!

In all honestly, I suspect a typo on behalf of Ripley’s Believe It or Not (after all, that word “millions” is hard to fit in the space provided, might as well drop it), but this is illuminating to say the least!!!

I’ll close with an analogy I use in my intro astronomy classes.  If we shrunk the Sun to be the size of a tennis ball, the Earth would be a small dot (roughly the size of a printed ‘period’ at the end of a sentence) about 38 feet away.  The entire solar system lies within 2000 feet of the tennis ball.  Proxima Centauri would be 1185 miles away.  Its a long distance between star systems compared to the distances between planets.

[Edit: Fixed a stupid error because I used kilometers like a good scientist, but normal Americans use miles.]

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