Why is it difficult to see stars in the sky when in a big city?

Question

Of the two, which factor more significantly impacts the inability to see stars clearly in a big city sky:

Is it more:

1) Air Pollution (smog, smoke, dirty air, etc.)
2) The presence of so many lights within the city

Answer 1

It's a combination of both.
While the light pollution is a major factor, the atmosphere is the other, and both are factors for the reason we build optical observatories on mountaintops. Less atmosphere in the way, means better viewing conditions.

Imagine you are looking at a penny on the bottom of a swimming pool. The water represents the atmosphere. And since the atmosphere is not stationary, but has constant shifts and movement, it's now like someone os making small waves on the surface of the pool, distorting the view. It gives the penny (star) a twinkling effect. Now someone throws in a handful of dirt. The water gets cloudy. Harder to see the penny right? And when the pool light(city light) gets switched on, this dirt reflects it right back at you, making it harder to see the penny(star).

Answer 2

Many lights in the city. This is called light pollution. Most lights are poorly designed and allow light to go other places (scatter) besides where you need to see. Actually, city lights don't contribute much to safety. They ruin night vision and cause deep shadows where crime and criminals will lurke. I have been under a "Magnitude 7" sky and before long, my eyes are adapted to the dark and I can see reliable outlines of my telescope, other people, my car and other features that a non-dark adapted person can't see at all.

Answer 3

The bigger of the two culprits is number 2. Even with 'less-polluted' air, the excess light makes the atmosphere 'visible' (photons of light are being refracted back to the observer) and reduce the contrast between the faint sources and the background. It is particularly bad for low contrast sources (like nebulae).

Of course, if the air is also polluted, then it is much worst.

Answer 4

It's both. Some cities are affected more by the pollution, but there are cities with less pollution where it is difficult to see the stars because of the lights.

Answer 5

It's not either/or, it's both. The many lights in the city would have little effect on the night sky if they had nothing to reflect off. But instead they have a canopy of particulates to act as a screen to bounce back their light.

Answer 6

You have given two answers yourself for your question. There are so many reasons.
To see stars we need a place where no buildings are in the view. Tall buildings block the view of the sky.
Another reason is that you need a flat land when looking at the sky.
It is good that if no trees are visible.

Answer 7

I agree with the above. Light pollution makes it difficult to see stars in the city. Try driving to the country and have a look, you'll be amazed.

Answer 8

Light pollution

Answer 9

Hi. The lights. A star has to be brighter than the background to be visible.

Answer 10

it is the presence of so many lights. the eye cannot focus on the light in the sky.