How bright would an object need to be in order to block out stars at night?

Question

I am wondering just how bright a star or other object would have to be before it starts blocking out the night sky. I'm looking for an answer in apparent magnitude.

I'll note the Full Moon gets to magnitude -12.74 but doesn't come close to causing a blue sky like you see right before dawn.

The Sun has magnitude -26.74.

I also tried to gather info from other planets. Wikipedia has an article on extraterrestrial skies. There is an article on the martian sky too and I noticed the martian day has an illuminated sky with no stars, but unfortunately this is not relevant to me because I'm only considering the Earth's atmosphere. Mars' atmosphere is too different.

I also noticed this question and answer. It's really great info, but still missing a few key numbers needed to use the equations. For example, what is the sky's luminance (in mag/arcmin^2) when the sun is directly overhead, when the sun is at x angle, and ideally for any magnitude object at any angle.

Answer 1

About magnitude -17, or about 100 times brighter than the moon now.

I've found reference to the sky brightness at full moon as being about magnitude 18 per square arcsecond (and equivalent to light pollution in the suburbs)

I've also found reference to the sky brightness twenty minutes after sunset as about 13 magnitude per arcsec², and this is roughly the point at which magnitude 0 stars appear.

Magnitude is a logarithmic scale and a difference of five magnitudes (from 18 to 13) corresponds to a hundred-fold difference in brightness. Hence if the moon were five magnitudes brighter it could hide most stars. The moon is magnitude -12 when full, so a magnitude -17 body would scatter enough light to hide most stars. Very bright stars (Sirius, Canopus etc) would still be visible, as would the bright planets.

The actual ability to see stars is against a bright sky is quite individual. And so to be reasonably sure to hide all stars from all observers you would need a moon that was much brighter than this.

Sources:

• The moonlit sky is 18 mag per arcsec²
• The twilight sky is 13 mag per arcsec²

Answer 2

Here is a link to a question about the visibility of stars in the moon light of a fictional planet. It might be of some use to you.

https://worldbuilding.stackexchange.com/questions/250524/how-to-find-visibility-of-stars-given-a-certain-moon-brightness