The Physics
Factbook
An encyclopedia of scientific essays

Diameter of the Solar System

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Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Abell, George. Encyclopedia of The Universe 2nd ed. 1969: 264, 345. "Distance from Sun(AU): Pluto - 40"
"Vast Cloud of Comets revolving about the sun at distance from 50,000 to 150,000 AU"
80AU
100,000โ€“300,000 AU
Laskar, Jacques. "Solar System." Encyclopedia of Astronomy and Astrophysics. 2001: 1930, 2749. "Mean distance from Sun(AU): Pluto - 39.44"
"Oort Cloud are so distant-typical Aphelion distance are on the order of 30,000 to 60,000 AU from the Sun"
79.88 AU
60,000โ€“120,000 AU
Moore, Patrick The data book of Astronomy 2000: 215, 236. "Distance from Sun(AU): Pluto - 39.5"
"Comets come from a cloud of bodies moving around the Sun at between 30,000 and 50,000 AU from the Sun."
79 AU
60,000โ€“100,000 AU
Simon, Mitton "Solar System." The Cambridge Encyclopedia of Astronomy. 1977: 161. "Mean Distance, Pluto, Astronomical Units: 39.44" 78.88 AU
Saintonge, Amelie. What is the size of the Solar System? Curious About Astronomy? Ask an Astronomer. Nov, 2002. "We took the radius of the solar system to be 39.5 AU, which means it has a diameter of 79 AU. This means you could put the Solar System about 3440 times between the Sun and the nearest star taking this definition." 79 AU
"If you include all the comets like we did in the second part, then the Solar System has a diameter of about 100,000 AU, which means it would fit 2.7 times between the Sun and the nearest star." 100,000 AU

The Solar System is familiar to most of us. A typical educated person can probably name most of the planets in it base on general knowledge of Roman mythology or an unhealthy obsession with horoscopes/astrology. However, the actual measurements of our Solar System, such as the diameter, is a relatively unknown fact.

The debate within measuring the diameter of the Solar System is mainly where the boundary of the Solar System lies. Some consider the orbit of the outermost known planet-Pluto defines the boundary of the Solar System. Other believe that the comets beyond Pluto orbiting the Sun define the boundary of the Solar System. Both opinions are equally valid.

To determine the measurement, we first need a standard unit. For interplanetary level measurements, we use Astronomical Units (AU). One AU is the distance from the Earth to the Sun, or about 150 million km. If we use Pluto's orbit to find the diameter of the Solar System, there is the problem of Pluto's elliptical orbit. To compensate, we use Pluto's mean distance from the Sun. That number is agreed by most sources to be about 39.44 AU. In this case, the diameter of the Solar System is about 78.88 AU.

The second method of measuring the Solar System's diameter involves the population of comets orbiting the Sun outside of Pluto known as the Oort Cloud. This measurement is less accurate since there is not just a single comet in the Oort Cloud. The distance from the Oort Cloud to the Sun has been estimated to an average of 50,000 AU, which makes the diameter of the Solar System to be about 100,000 AU.

Steven Mai -- 2004