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To get an idea of the tremendous size of our solar system, imagine for a moment that our Earth is just one inch across. At this scale, the distance from the Earth to the Moon would be 30 inches, and the Moon itself, just a quarter of an inch across.

The size of the Sun at this scale is enormous, a sphere 9.1 feet across!

The Sun could hold 1.3 million Earths!!


The distance from the Sun to the Earth would be 977 feet. As amazing as it sounds, even at this shrunken scale, the distance from the Sun to the outermost planet, Pluto, would be 7.3 miles!!

The astronomical distances are hard to grasp, yet astronomers deal with these values daily. To simplify their work, they created a unit of measurement called the Astronomical Unit (AU). One AU is defined as the distance from the Earth to the Sun (92,957,130 miles). While this makes the numbers more manageable when dealing with our Solar System, the distance between the stars dwarf even this measurement.

The nearest star to Earth is the Sun. When we see the other stars at night, they seem dim only because of the vast distances to them.  In order to simplify interstellar distances, astronomers use another unit of distance called the Light Year (ly). This is defined as the distance that light travels in one year! How far is one Light Year? 63,240 Astronomical Units which is 5,878,500,000,000 miles. To put it another way, if our Sun was the size of a ping pong ball and was located in New York City, the nearest star would be another ping pong ball located in Chicago! This represents a fairly standard distribution of stars in the spiral arms our Milky Way Galaxy, and there are about a hundred billion stars in our galaxy. Astronomers estimate the Milky Way to be about 100,000 ly across. The closest star to our Sun is called Alpha Centauri at 4.3 ly away. Itís 8.6 ly to the star Sirius, the brightest star in our sky.

Astronomical distances may seem at the same time both awe-inspiring and unimportant as we turn our gaze upward in the evenings. Your eye can sweep across the breadth of the Milky Way in a moment, or linger while you contemplate the vastness of the space between the stars.


Determining Distances to Astronomical Objects

Determining distances to celestial objects is fundamental to understanding our universe.  For a discussion of the various methods used, see http://www.talkorigins.org/faqs/astronomy/distance.html and http://www.astro.ucla.edu/~wright/distance.htm


A listing of the distances to the nearest stars may be found here.