# Biggest object in a solar system sky? **URL:** \ **Category:** Factual Questions\ **Created:** [January 12, 2010, 2:45am UTC](https://boards.straightdope.com/t/biggest-object-in-a-solar-system-sky/524608 "2010-01-12T02:45:40Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Jake](https://avatars.discourse-cdn.com/v4/letter/j/f475e1/32.png) [@Jake](https://boards.straightdope.com/u/Jake)\ **Post date:** [January 12, 2010, 8:18pm UTC](https://boards.straightdope.com/t/biggest-object-in-a-solar-system-sky/524608/21 "2010-01-12T20:18:15Z")
Great link, Squink! Thanks ---
**Author:** ![Sapo](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@Sapo](https://boards.straightdope.com/u/Sapo)\ **Post date:** [January 12, 2010, 9:36pm UTC](https://boards.straightdope.com/t/biggest-object-in-a-solar-system-sky/524608/22 "2010-01-12T21:36:34Z")
We are still doing better than Kevin Bacon. All he has is six degrees. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 12, 2010, 10:06pm UTC](https://boards.straightdope.com/t/biggest-object-in-a-solar-system-sky/524608/23 "2010-01-12T22:06:48Z")
> [@](#): > > Wouldn’t there be a practical limit for a natural object of less than 180° – specifically, whatever the visual measurement would be for an object orbiting its primary just outside Roche’s limit? I’d agree that that would be the limit, since the OP specified “standing on the surface”, and you can’t stand on the surface of any object within the Roche limit. But there isn’t actually a single Roche limit: It depends both on the density of the parent object and of the satellite (D = R(2 rho\_p/rho\_m)^(1/3), where R is the radius of the primary, rho\_p is the density of the primary, and rho\_m is the density of the moon). You’d get the biggest view from a very dense satellite orbiting a very low-density primary. Saturn’s the lowest-density object of any significant size in the Solar System, at a mere 0.687 times water, so any moon with a density of at least twice that (quite plausible, if it’s made up of anything other than ice) could get all the way down to the surface before being within the Roche limit. I’d imagine that there are some such objects that come pretty close, but they’re probably not named. ---
**Author:** ![leandroc76](https://avatars.discourse-cdn.com/v4/letter/l/bb73d2/32.png) [@leandroc76](https://boards.straightdope.com/u/leandroc76)\ **Post date:** [January 12, 2010, 10:09pm UTC](https://boards.straightdope.com/t/biggest-object-in-a-solar-system-sky/524608/24 "2010-01-12T22:09:56Z")
> [@billfish678](#): > > I am pretty sure the Roch limit is for fairly big and/or fragile things. > > Small bodies can orbit all the way down the atmosphere/surface. Wouldn’t that mean the two orbs were touching… in a sense, that would be catastrophic! I bet there is a limit before these bodies begin to crash into each other! ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [January 12, 2010, 10:54pm UTC](https://boards.straightdope.com/t/biggest-object-in-a-solar-system-sky/524608/25 "2010-01-12T22:54:15Z")
> [@Squink](#): > > Mars takes up 39 degrees when viewd from Phobos. > Jupiter takes up 19 degrees when viewed from Io. > Saturn takes up 36.5° as viewed from Mimas. > Uranus takes up 22° as seen from Miranda. > Neptune takes up 22° as seen from Nereid. > Pluto takes up 7° as seen from Charon. > The sun takes up 1.6° as seen from Mercury. > > [Solar System Simulator](http://space.jpl.nasa.gov/) > > There might be some minor moon of Jupiter or saturn that puts all these numbers to shame, but the simulator doesn’t cover those. The Earth takes up 179.999º as seen from the Earth. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 12, 2010, 11:03pm UTC](https://boards.straightdope.com/t/biggest-object-in-a-solar-system-sky/524608/26 "2010-01-12T23:03:12Z")
> [@AWB](#): > > The Earth takes up 179.999º as seen from the Earth It does better than that [at some points on the surface.](http://images.google.com/images?q=slot+canyon&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&ei=Vf9MS93JC9KjlAehwPyNDQ&sa=X&oi=image_result_group&ct=title&resnum=1&ved=0CBgQsAQwAA) [Previous page](https://boards.straightdope.com/t/biggest-object-in-a-solar-system-sky/524608.md?page=1)