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The Scale of Things: The Sun and the Planets


This week, let’s continue discussing the size and scale of things in astronomy.  Our Solar System has one Sun, 8 planets, 5 dwarf planets, hundreds of natural satellites, thousands of comets, and hundreds of thousands of minor planets.  It has a basic shape of disc and the Sun at the center.  For this discussion, we are just going to focus on the Sun and the planets.

To compare the size of the Sun and the planets, we’ll use the Earth’s diameter as our scale. Mercury has about one-third the diameter of the Earth, Venus has about the same diameter, Mars has about one-half the diameter, Jupiter has about eleven times the diameter, Saturn has about nine times the diameter, and Uranus and Neptune have both about four times the diameter. The Sun has about one hundred times the diameter of the Earth, which means in terms of volume you could fit a million Earths inside the Sun! The compare the distances between the Sun and the planets, we’ll use the average distance between the Earth and the Sun. In miles, this distance is 93,000,000, but astronomers have defined this distance to also be equal to 1 astronomical unit (AU).  With this scale and unit, the distances become much easier to compare.

Mercury is about one-third of an AU from the Sun, Venus is about seven-tenths of an AU, the Earth is 1 AU (of course), Mars is one and a half AU, Jupiter is about 5 AU, Saturn is about 10 AU, Uranus is about 20 AU, and Neptune is 30 AU.  In an attempt to connect the size of the Sun and the size of the Solar System out to Neptune, we can imagine the Sun being a dime and the location of Neptune 60 yards away!

Next week we’ll try to imagine our place in the Milky Way galaxy!


Follow your curiosity to the Fred G. Dale Planetarium at Wayne State College.

Dr. Todd Young hails from Minnesota and received his undergraduate degree in Physics & English from the University of Minnesota – Morris, his Master’s degree in Physics from Purdue University, and his Ph.D. from the University of Nebraska – Lincoln in Astrophysics. He has worked at Wayne State College since receiving his doctorate in 1998 and is currently a full professor of physics and astronomy. He teaches a variety of courses at Wayne State College, including university physics, astronomy, general education science, and astrophysics.
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