# What is the average density of the solar system? The galaxy? **URL:** \ **Category:** Factual Questions\ **Created:** [April 16, 2008, 10:48am UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576 "2008-04-16T10:48:40Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 16, 2008, 10:48am UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/1 "2008-04-16T10:48:40Z")
If all the matter in our solar system were distributed evenly throughout a cylindrical section of space, the thickness of the sun and the diameter of, say, the orbit of Neptune, how dense would it be? Same question for the Milky Way galaxy - how dense would it be if the matter were evenly dispersed throughout the a cylinder the height of the thickest region, and the diameter of the widest span? ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [April 16, 2008, 10:59am UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/2 "2008-04-16T10:59:19Z")
Just to help others: > **[List of Solar System objects by size](https://en.wikipedia.org/wiki/List_of_solar_system_objects_by_mass)** > > This article includes a list of the most massive known objects of the Solar System and partial lists of smaller objects by observed mean radius. These lists can be sorted according to an object's radius and mass and, for the most massive objects, volume, density, and surface gravity, if these values are available. > These lists contain the Sun, the planets, dwarf planets, many of the larger small Solar System bodies (which includes the asteroids), all named natural satellites, and a number of smal... And: “the Sun […] contains 99.86% of the system’s known mass” ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 16, 2008, 11:02am UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/3 "2008-04-16T11:02:04Z")
Just to clarify - define the solar system as the objects within the described cylinder - no need to deal with the Kuiper belt and Oort cloud (although feel free to do this as a separate exercise, if you like). ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [April 16, 2008, 1:45pm UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/4 "2008-04-16T13:45:09Z")
Sun: Mean diameter 1.392×109 m Neptune: Average distance: 4.55 x 1012 m Mass of sun: 1.9891 × 1030 kg Volume = pi r^2 h = pi \* ( 4.55 x 1012 m / 2 )^2 \* 1.392_10^9 = 7.204_10^33 Density = 1.9891_10^30 kg / 7.204_10^33 =\*\* 276\*10^-6 kg/m^3 \*\* ---
**Author:** ![puppygod](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@puppygod](https://boards.straightdope.com/u/puppygod)\ **Post date:** [April 16, 2008, 2:00pm UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/5 "2008-04-16T14:00:13Z")
Wow. Solar system is much denser than I thought. It’s more than gram per four cubic meters. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 16, 2008, 2:02pm UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/6 "2008-04-16T14:02:42Z")
Thanks. So one kilogram of matter is going to occupy about 3,600 cubic metres? ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [April 16, 2008, 3:33pm UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/7 "2008-04-16T15:33:23Z")
Milky Way Diameter = 100,000 light years Thickness: 1,000 light years Volume = 2.5_10^12 light years = 6.65_10^60 m^3 Mass = 5.8_10^11 Suns = 5.8_10^11 \* 1.9891_10^30 kg/Sun = 1.15_10^42 Density = 1.15_10^42 kg / 6.65_10^60 m^3 = \*\*173 \* 10^-21 kg/m^3 \*\* Divide that by 12 if you want to use a thickness of 12,000 for the Milky Way to include gas instead of just stars. [QUOTE=puppygod] Wow. Solar system is much denser than I thought. It’s more than gram per four cubic meters. [/QUOTE] If I hadn’t forgotten to multiply by pi. :smack: It’s closer to 11.4 Updated numbers: Volume = pi r^2 h = pi \* ( 4.55 x 1012 m / 2 )^2 \* 1.392_10^9 = 22.63_10^33 Density = 1.9891_10^30 kg / 22.63_10^33 = 87.9\*10^-6 kg/m^3 [QUOTE=Mangetout] Thanks. So one kilogram of matter is going to occupy about 3,600 cubic metres? [/QUOTE] So, it’s actually closer to one gram every 11,400 m^3, once you take into account the whole forgetting to multiply by pi thing. Something like that. I used 1.99 instead of 1.9891 for the mass. I figure with the precision we’re using, it’s as good of an estimation as any. ---
**Author:** ![The\_Them](https://avatars.discourse-cdn.com/v4/letter/t/898d66/32.png) [@The\_Them](https://boards.straightdope.com/u/The_Them)\ **Post date:** [April 16, 2008, 11:06pm UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/8 "2008-04-16T23:06:00Z")
Heck, you want amusement? How dense is the Sun? Mass of Sol=1.9891x10^30kg Radius of Sol=6.96x10^8m So rho(Ithink that’s the one)={1.9891x10^30kg}/{4/3π[(6.96x10^8m)^3]}={1.9891x10^33g}/{1.412x10^33(cm^3)}=1.408 g/cm^3 That is, the Sun is not that much denser than water. And since it’s REALLY dense toward the core, the part we see is more like brightly glowing _fog._ It gets even more fun when you consider the Sun as a red giant in ~5 billion years, with a radius of about 100 times what is now, and considerably less mass. _Should any arithmetic be in error, this office will deny all knowledge._ ---
**Author:** ![alterego](https://avatars.discourse-cdn.com/v4/letter/a/6bbea6/32.png) [@alterego](https://boards.straightdope.com/u/alterego)\ **Post date:** [April 17, 2008, 5:29am UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/9 "2008-04-17T05:29:10Z")
[QUOTE=The Them] Heck, you want amusement? How dense is the Sun? =1.408 g/cm^3 [/QUOTE] The sun is 50% more dense than my brain. Surprising 🙂 ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 17, 2008, 8:20am UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/10 "2008-04-17T08:20:17Z")
**Santo** , you were also dividing the orbital radius by 2 for some unaccountable reason. OK, maybe you thought it was the orbital diameter. Using the semimajor axis of Neptune (Santo actually used the aphelion distance, which is somewhat larger) and adding in the masses of the gas giants (they change the answer in the 4th significant digit), I get Volume: 3.14159 \* 1.392e9 \* (4.503e12)^2 = 8.867e34 m^3 Mass: 1.9891e30 + 1.8986e27 + 5.6846e26 + 8.6810e25 + 1.0243e26 = 1.9918e30 Kg Density: 2.246e-5 Kg/m^3 So your Kg of matter will occupy about 44,500 cubic meters. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 17, 2008, 8:29am UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/11 "2008-04-17T08:29:17Z")
[QUOTE=alterego] The sun is 50% more dense than my brain. Surprising 🙂 [/QUOTE] Compared to the solar system though, you are incredibly dense. _Thick_, one might even say. ---
**Author:** ![The\_Them](https://avatars.discourse-cdn.com/v4/letter/t/898d66/32.png) [@The\_Them](https://boards.straightdope.com/u/The_Them)\ **Post date:** [April 17, 2008, 10:40am UTC](https://boards.straightdope.com/t/what-is-the-average-density-of-the-solar-system-the-galaxy/445576/12 "2008-04-17T10:40:08Z")
This MUST be from my previous self-subjection to chemicals that are not supposed to be used for human consumption… CAN YOU, given the information contained ONLY within the movie itself, work out a decent guesstimate of the specific gravity of the material used to construct the mothership in **Independence Day**? Don’t worry, the result is silly. We all have our slow days… Boulder, eh? I remember that place…a hotbed of subversion, perversion, and HORROR!