How big is the solar system?

By "big", I guess I mean "wide", i.e. how far away from the Sun is the farthest object that is considered part of the Solar System?

I've checked Wikipedia's pages on the Solar System, as well as Pluto, the Kuiper belt, and Trans-Neptunian Objects, but couldn't see the answer.

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    $\begingroup$ en.wikipedia.org/wiki/Solar_system $\endgroup$ – Keith Thompson Feb 7 '12 at 2:03
  • $\begingroup$ Hi Keith, yes, I looked at that page, but couldn't see the answer, despite clicking through to Pluto, Kuiper Belt, and Trans-Neptunian Object. $\endgroup$ – gkrogers Feb 7 '12 at 3:33
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    $\begingroup$ @gkrogers We strongly encourage providing your reference routes and previous efforts in research as part of your question, otherwise we're A) left to assume you didn't research and/or B) provide answers that cover from a baseline. These points coupled can often make answering a much more laborious process when information is 'missing'. And, well, with it we then know you're learning to fish, not just begging. $\endgroup$ – Grant Thomas Feb 7 '12 at 14:17
  • $\begingroup$ @Mr.Disappointment OK, I've included references to where I looked before I asked here. $\endgroup$ – gkrogers Feb 7 '12 at 22:32
  • $\begingroup$ @gkrogers Thank you for taking the time to do so. (: $\endgroup$ – Grant Thomas Feb 7 '12 at 23:06

There are a variety of definitions, most of which can be put into the graphic below, grabbed from Wikipedia. Note that the scale is a log scale, so don't think the solar system is quite like is shown.

enter image description here

The most commonly accepted is based off of what is known as the Heliosphere. Simply put, the Heliosphere is where the force from the solar wind equals the force from the galactic pressure. It is about 200 AU, perhaps a bit further, where 1 AU= the mean distance of the Earth from the sun.

Alternative definitions might include the distance of Neptune from the sun, 40 AU, the edge of the gravitational influence of the sun, which would be almost 1 light year (There are bodies orbiting at 1 light year away from the Sun), the distance of the Kuiper Belt, at around 200 AU, or a fair other number of methods.

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    $\begingroup$ Hint: the above diagram uses a log scale :-) $\endgroup$ – Nic Feb 7 '12 at 14:53

If Oort's hypothesis is correct, the Oort cloud should be considered part of the solar system, as it is the ultimate origin of comets. It's a spherical cloud of (trillions of) bodies orbiting the sun at distances out to about 50,000 AU, more than 1000 times further out than Neptune. One lightyear is 63,250 AU, so the outer edge of the cloud is almost a quarter of the way to the nearest star. Due to it's distance from Earth, no bodies have yet been observed in the Oort cloud, so it remains hypothetical - but it does explain a lot of things about comets.


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