Visibility of stars

[PeterB]

I happened to catch a plane last night. The plane left Sydney at about 7.30 and arrived in Canberra about 8.15. Both boarding and disembarking meant walking out on the tarmac.

Both in Sydney and Canberra I looked up at the sky, which was largely cloud-free in both cities. In both cases, I could see Venus and one star. At both airports, the apron lights were bright and my eyes adjusted accordingly.

I dare say people attending a night game at a stadium will experience the same effect.

Therefore, there should be little surprise that astronauts on the Moon with the Sun in the sky aren't going to see many other stars in the sky.

[Count Zero]

peterb said:

I dare say people attending a night game at a stadium will experience the same effect.

I used a similar argument with a guy at work. To prove my point, I googled "high school football photographs". I came up with many, many photos of night games with a nice black sky in the background.

[skinbath]

This is "light pollution" and in any built up area on Earth the effect is noticeable.In the software "Starry night backyard" there are several settings that equate to large/small city light pollution etc,the effects vary drastically.....I`m told,but never seen for myself in order to verify,that if you look up through one of the old industrial chimneys that you can see stars in the line of sight in the daytime.One of the concerns of astronomers is that due to light pollution,children will never experience the view of sights such as the "milky way".

[PhantomWolf]

It's not Light Pollution. Light Pollution is when light reflects off of air molecules and reflects back down thus making the sky brighter and blocking stars. What PeterB is talking about is being in a brightly lit area that would be the equivilent of daytime, but having a night sky, that the eyes cannot see the bright area you are in and the dim stars at the same time. The difference would be in trying to view the stars above a city and not being able to see through the orange glow compared to having all the patio lights on about the yard and trying to see the stars.

[skinbath]

phantomwolf said:

It's not Light Pollution. Light Pollution is when light reflects off of air molecules and reflects back down thus making the sky brighter and blocking stars. What PeterB is talking about is being in a brightly lit area that would be the equivilent of daytime, but having a night sky, that the eyes cannot see the bright area you are in and the dim stars at the same time. The difference would be in trying to view the stars above a city and not being able to see through the orange glow compared to having all the patio lights on about the yard and trying to see the stars.

I guess I misread/misunderstood/misinterpreted peterb`s post.

I sometimes take my kids out to show them constellations.On a night of a bright full moon you can`t see many stars due to what I would have called the "pollutant" effect of the moon.I don`t know if this post is what`s being talked about but if so is perhaps the easiest to equate with in terms of star visibility on the moon,(I imagine)...and thanks for the differentiation.

[gwiz]

Again, there are two effects: the scattering of moonlight by the atmosphere and the light from the moon preventing your eyesight adapting to full dark conditions. The closest comparison to the lunar surface conditions would be a clear night, no moon, no city lights, stadium lights pointing only down. This would minimise light pollution while still leaving the eyes adapted to the stadium lights rather than the sky.

[skinbath]

Thanks for the clarifying the above...

[Bob B.]

phantomwolf said:

It's not Light Pollution. Light Pollution is when light reflects off of air molecules and reflects back down thus making the sky brighter and blocking stars. What PeterB is talking about is being in a brightly lit area that would be the equivilent of daytime, but having a night sky, that the eyes cannot see the bright area you are in and the dim stars at the same time. The difference would be in trying to view the stars above a city and not being able to see through the orange glow compared to having all the patio lights on about the yard and trying to see the stars.

Both conditions can be considered a form of light pollution. What you describe as light pollution, PhantomWolf, is know as sky glow. The other condition is called light trespass, which is when a nearby light source shins directly on the observer causing glare and loss of dark adaptation.

[PhantomWolf]

I think that what skinbath was describing and pointing out that Astronomers were worried about is the "sky glow" though rather then direct light from being in a brightly lit area as mosty of us head out into the countryside to observe.

[skinbath]

phantomwolf said:

I think that what skinbath was describing and pointing out that Astronomers were worried about is the "sky glow".

Yes this is what is spoken of....the fact that there`s so much ground based light.

Regarding the two definitions of light pollution given....Don`t they both have the same effect?....i.e. an impairment of vision of the night sky.....I`m taking a guess that the lack of stars visible from the moon is so caused by light trespass...the reflection of the sun from the moon surface?

[gwiz]

That's right. The astronomical camera on Apollo 16 was able to take star pictures as there was no sky glow to interfere with the necessary long exposures. The astronauts eyes were adapted to the sunlit surface and the general still and cine photography used short exposures appropriate to the surface brightness.

[skinbath]

::)Heh,heh...full circle...now I see what peterb was saying...cheers all...