COSMIC QUIZ: Where’s the Closest Star?

Seth Jarvis

This week’s KUTV Cosmic Quiz winner is Cameron Porcaro. Cameron’s question was, “How far away is the nearest star to our solar system?”

Fun question!

The closest star to our solar system is, of course, our Sun.  Earth orbits the Sun at an average distance of 93 million miles.

Our Sun is one of about three hundred billion stars in the Milky Way Galaxy.  Of those hundreds of billions of stars in our galaxy, the next closest star to our Sun is a little red dwarf star called Proxima Centauri, at a distance of 4.2 light-years, which works out to be roughly 25 trillion miles (40 trillion kilometers).

Proxima Centauri is a "Red Dwarf" star - small and fairly cool.

Proxima Centauri is a "Red Dwarf" star - small, dim and fairly cool.

What is the practical difference between 93 million miles to the Sun and 25 trillion miles to Proxima Centauri?  Numbers that large are generally impossible to grasp.  You could just as well say that it’s “a Gajillion Bazillion” miles to Proxima Centauri and most people would just shrug and say, “If you say so.”


Even though Proxima Centauri (the red star in the center of this image) is only 4.2 light-years from us, viewing it requires a telescope.

Getting your head around interstellar distances is a challenge astronomy educators are always grappling with.  One of the best ways devised to communicate the vastness of space is to mathematically shrink the universe to a much smaller scale size so that sizes and distances can be appreciated in terms that are more intuitive to us.

If aircraft designers, architects and city planners can construct cool little models of their projects so that they can get a better idea of what they’re dealing with, why can’t astronomers make little models of solar systems and galaxies?

Let’s scrunch the universe down to a manageable scale.

If Earth were shrunk down to the size of a grain of sand, then:

  • One inch represents over 200,000 miles.
  • The Sun is the size of a grapefruit and is 38 feet away.
  • Jupiter is the size of a pea 200 feet from the grapefruit-sized Sun.
  • Neptune, the most distant “classical” planet from the Sun, is the size of a BB and orbits the grapefruit-Sun at a distance of 400 yards.  That’s right – with Earth shrunk to the size of a single grain of sand this scale model solar system would still be so large that it would cover more than four square blocks of downtown Salt Lake City.
If our grapefruit-sized Sun were in the center of downtown Salt Lake City, Neptune's orbit would encompas multiple city blocks.
If our grapefruit-sized Sun were in the center of downtown Salt Lake City, Neptune’s orbit would encompass multiple city blocks.
  • And Proxima Centauri, our Sun’s closest stellar neighbor, is the size of a cherry, and is 2,000 miles away. That’s the distance from Salt Lake City to Orlando, Florida.
A scale model of the distance between the Sun and Proxima Centauri
A scale model of the distance between the Sun and Proxima Centauri

And in between?


Seriously… nothing.

Interstellar space contains roughly one hydrogen atom per cubic centimeter (about the volume of a sugar cube).  Do you have any idea how empty that is?  No?

Imagine that you have attached a bucket on the outside of your spaceship so it can scoop-up interstellar hydrogen as you travel to Proxima Centauri.

During your 25 trillion mile Sun-to-Proxima Centauri trip, the bucket on your spaceship would collect one tenth the number of atoms that are normally in the bucket when it’s just sitting empty on a shelf here on Earth.

Now you know why they call it “space.”

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One thought on “COSMIC QUIZ: Where’s the Closest Star?

  1. I am not generally pleased as I live in West Jordan and am an avid Trax rider when I need to get downtown. The transfering part is ok but why did they have to discontinue the service? In the winter walking would not be so easy.

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