At night, I can look up and see the Milky Way across the sky. My question is, supposing our Solar System was, instead of way out on an 'arm' of the galaxy, near the galactic center, would the night sky be much brighter? If so, how close would we have to be to never have darkness of night?

  • $\begingroup$ I just got through an episode of science.discovery.com/convergence/cosmos/cosmos.html were one of the scientists talked about if you were on a planet closer to the middle it would basically be daylight all the time from all the stars. If you are actually close to the galactic center you would get sucked into a black hole! $\endgroup$
    – polynomial
    Oct 5 '11 at 0:19

The Wikipedia article on "Stellar density" says the stellar density near the Sun is only 0.14 stars per cubic parsec. It suggests that the density in the central core and in globular clusters is about 500 times as great.

According to the List of nearest stars and brown dwarfs in Wikipedia , there are 61 stars within 15 light years of the Earth. Dividing 61 by the volume of sphere of this radius, we obtain 4.3e-3 stars per cubic light-year, or 0.15 stars per cubic parsec. Thanks to user31264 for providing this information, which is consistent with the information from the previous link.

According to the Wikipedia article on "apparent magnitude", the total integrated magnitude of the night sky as seen from Earth is -6.5. Making that 500 times as bright produces a total magnitude of about -13.2 (5 magnitudes is a factor of 100 in brightness). The maximum brightness of the full Moon is -12.92.

So even with 500 times as many stars in the sky, the total brightness would be only slightly greater than that of a full moon.

(This assumes that the average brightness of the core stars is similar to the average brightness out here in the Galactic suburbs.)

Parts of the core might be even denser than that.

(I've updated this with new information and deleted and old link whose numbers appear to have been incorrect.)

  • $\begingroup$ Thanks so much! Unfortunately, your first link is currently broken. Is there a paper somewhere that would help me generate a 3D plot of the density of stars in the Milky Way? $\endgroup$ Feb 26 '13 at 6:58
  • $\begingroup$ @theJollySin: Not really. I've updated my answer with a link to a Wikipedia article that gives different figures. $\endgroup$ Feb 26 '13 at 15:53
  • $\begingroup$ According to the en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs , there are 61 stars within 15 light years of the Earth. Dividing 61 by the volume of sphere of this radius, we obtain 4.3e-3 starts per cubic ly, or 0.15 stars per cubic parsec. $\endgroup$
    – user31264
    Mar 15 '18 at 19:47
  • $\begingroup$ @user31264: Thanks for the update. I've updated the answer (on top of your edit) and removed the reference to the dead link; the numbers there seem to have been wrong anyway. $\endgroup$ Mar 15 '18 at 20:42

Okay the notion that the sky would be 100 times brighter because there are 100 more stars within a cubic parsec is ludicrous. First it would discount the 100x 100 more stars that would lie within the next parsecs distance from us. More importantly it discounts the far closer proximity of the stars within our Parsec. With 100 stars within our particular cubic parsec odds are one would be just outside of our solar envelope... heck one very possibly would be closer than Planet 9!

Could you imagine if Betelgeuse was a solar month away! The answer is in the galactic bulge you would never need a flashlight but bring SPF1,000,000 !

  • $\begingroup$ On the one hand, picking two points at random in a cube of 1 pc puts them on average at 0.66 pc (c.f. Cube line picking](mathworld.wolfram.com/HypercubeLinePicking.html)). On the other hand, the distance from the Sun to Planet 9 is of the order of $10^{-3}$ pc. Even with 100 stars to place, you are not even close: the probabilities of the occurrence you entertain is minuscule, I reckon. However your point about the next shells of stars outside that parsec cube stands indeed. $\endgroup$
    – user154997
    Jul 6 '17 at 15:58
  • 1
    $\begingroup$ The nearest star would be at a distance $\sim 100^{-1/3}=0.2$pc. It would be overwhelmingly likely to be a less luminous star than the Sun, with very little chance $(<0.01\%)$ of it being a supergiant. If the distribution of stellar luminosities is the same near the Galactic centre, then the number of visible stars and the power incident on Earth from them does just scale from Earth values as the stellar density. $\endgroup$
    – ProfRob
    Jul 6 '17 at 19:36

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