Star visibility

[An amateur]

How bright does a star have to be for it to be visible at 10, 20 30 or 40 degrees from the full moon?

 

[Catastrophe]

Hi. Interesting question. Why do you ask? Best choose another night?

 

[Wolfshadw]

I would also think that the answer would vary based on the amount of light pollution you have in your viewing area.

-Wolf sends

 

[An amateur]

Hi. Interesting question. Why do you ask? Best choose another night?

In ancient China and India the path of the moon was mapped and the months were identified/named by the stars in the vicinity of the full moon. To identify these stars it is necessary know which stars would have been visible close to the full moon.

 

[An amateur]

I would also think that the answer would vary based on the amount of light pollution you have in your viewing area.

-Wolf sends

Little of no light pollution, remote but low altitude site.

 

[Catastrophe]

In ancient China and India the path of the moon was mapped and the months were identified/named by the stars in the vicinity of the full moon. To identify these stars it is necessary know which stars would have been visible close to the full moon.

Thank you for your interesting reply.
Do you not wish to get this information from any astronomy magazine?

Maybe in ancient times they were well aware of how much the moon moved each day and perhaps measured in hand widths to where the full moon would be and looked at the stars in that position?

 

[Helio]

In ancient China and India the path of the moon was mapped and the months were identified/named by the stars in the vicinity of the full moon. To identify these stars it is necessary know which stars would have been visible close to the full moon.

Weren't they using a new moon instead?

 

[Eva Braun]

I don't know if it's worth to trust google, but I found that it should be 30 degrees from the full moon.

 

[Helio]

I don't know if it's worth to trust google, but I found that it should be 30 degrees from the full moon.

I wouldn't mind seeing the link so I can see what they are saying. It doesn't make that much sense because they well knew the location of bright stars by the use of constellations and coordinates, I assume. Why use the Moon when a horizon only should suffice? Curious.

 

[serhiy1635]

How bright does a star have to be for it to be visible at 10, 20 30 or 40 degrees from the full moon?

I guess that it depends on the clouds in your area in that particular time. And as it has been already mentioned it might depend on how polluted air in your town . Because today air in most big cities are very polluted so it might be even smoke from cars and factories that it might seem that it is a haze .

 

[vincenzosassone]

In my opinion the bright of the stars in a place is determinated only by one thing: the light pollution. The moon and clouds are only natural factors, and we can't say anything about them. Somethimes there is the full moon that deny us to watch the stars around them, the same for clouds, and there will be, thus, many days in which you can only see a part, or nothing, of our night sky. But light pollution, istead of previous element, is permantent in a place, just for this reason in my opinion had to be taken in consideration. Finally, speaking about the altitude, I really don't think that change a lot if you watch the stars near to a beach, or near to the Everest mountain.

 

[serhiy1635]

In my opinion the bright of the stars in a place is determinated only by one thing: the light pollution. The moon and clouds are only natural factors, and we can't say anything about them. Somethimes there is the full moon that deny us to watch the stars around them, the same for clouds, and there will be, thus, many days in which you can only see a part, or nothing, of our night sky. But light pollution, istead of previous element, is permantent in a place, just for this reason in my opinion had to be taken in consideration. Finally, speaking about the altitude, I really don't think that change a lot if you watch the stars near to a beach, or near to the Everest mountain.

But still it would be better to have a look at them in the open area. Light pollution might also be caused from buildings and from advertising boards which can hinder you. I am not claim that my point is right! If you have some ideas about that, please share

 

[vincenzosassone]

Light pollution might also be caused from buildings and from advertising boards which can hinder you.

Yeah, you're right, in the light pollution we have to concern also the object that hinder our visibility, I forgot that point because I live in a countryside and I have never had this problem. But this is one of the element that take the name of light pollution.

 

[serhiy1635]

Yeah, you're right, in the light pollution we have to concern also the object that hinder our visibility, I forgot that point because I live in a countryside and I have never had this problem. But this is one of the element that take the name of light pollution.

Yeah, I know that there other light pollution aspects that can cause problems with visibility of stars but I assume that one that I`ve mentioned previously is the most important and influences the most.

 

[vincenzosassone]

Yeah, I know that there other light pollution aspects that can cause problems with visibility of stars but I assume that one that I`ve mentioned previously is the most important and influences the most.

Well... I don't know. If you lived in a bright city you can see nothing, whereas if you lived in a city in which there are many palaces, you can see something, at least the your zenon point. But these things go together, so isn't possible by us to be aware of this

 

[serhiy1635]

Well... I don't know. If you lived in a bright city you can see nothing, whereas if you lived in a city in which there are many palaces, you can see something, at least the your zenon point. But these things go together, so isn't possible by us to be aware of this

Would you be so kind to name me please other aspects of light pollution that can influence the same as light from the buildings of big cities)

 

[vincenzosassone]

Would you be so kind to name me please other aspects of light pollution that can influence the same as light from the buildings of big cities)

Well, in many aspects I have already aswered you...

But these things go together, so isn't possible by us to be aware of this

Maybe I didn't mean just this, and you are right, the same light of the buildings can interefere with the vision of the sky. But I also said that when there are many buiding, there is also much light. In these cities, obviously, there is also the smog! You're right, but I want to find the most right answer to this question: where is the highest light pollution?
If you agree, I would say that the light pollution is in the most developed cities. In fact in them there are all the things, maybe there aren't these aspects in the same amount, but the difference is unimportant.

 

[Helio]

The key issue boils down to contrast. Pollution, daylight, cloud haze, moonlight, air mass (due to altitude) all contribute to our ability to see dim stars.

I've forgotten what the contrast values are to see the dim stars, but that should be easy to find.

I mention daylight as an issue, but some celestial objects can be seen in broad daylight if you know exactly where to look. For instance, Venus is the easiest of those objects, not counting the Sun and Moon, of course.

One of the reasons we can do this is because the daylight is additive in light to Venus. So when you look at, say, Venus, then you are getting all the light from Venus plus the scattered light from the Sun that is coming from out atmosphere. This improves the contrast level between Venus and the blue sky.

 

[vincenzosassone]

cloud haze, moonlight

I really don't think that these aspects could be considered as light pollution, in fact these change everyday instead of the conditions that are always the same as the bright of the city and its buildings...

 

[Helio]

I really don't think that these aspects could be considered as light pollution, in fact these change everyday instead of the conditions that are always the same as the bright of the city and its buildings...

The OP is really a question about visibility. The ability to see a dim star, say 40 deg., from the Moon will become a question of the contrast between the star and the surrounding medium. Pollution plays a big role since our eyes struggle in seeing the contrast the dimmer things get, IIRC.

Contrast is the dominant issue worth understanding when it comes to observations.

When we can't read what we see in dim light, we apply more light which boosts the contrast between the black ink, or other color, and the paper.

 

[vincenzosassone]

The OP is really a question about visibility. The ability to see a dim star, say 40 deg., from the Moon will become a question of the contrast between the star and the surrounding medium. Pollution plays a big role since our eyes struggle in seeing the contrast the dimmer things get, IIRC.

Contrast is the dominant issue worth understanding when it comes to observations.

When we can't read what we see in dim light, we apply more light which boosts the contrast between the black ink, or other color, and the paper.

Yeah, I know that the contrast is an important feature. In the light pollution, in fact, I treated also the light of the cities that works in the same way of your contrast between the Moon and the dimmer star. This is a particular feature of this aspect of the light pollution, for this reason I wouldn't take in account this because is only a consequence of the real phenomenon: the bright of the sun, of the moon, of the cities, etc...
Said that, now I want to say you that the light pollution, always in my opinion, contains only the phenomenon that characterize the place everytime as the buildings that can't go away as the moon all the moonless night. This is only my opinion, because I have never heard someone speaking in a precise manner of the light pollution, in fact I'm here to learn, as you!

 

[Helio]

Right. Light pollution is really the lights from the ground that have some of their light reflected back to the observer. This is what happens in daylight --our atmosphere scatters sunlight toward the ground.

So it becomes just how polluted the sky is from pollen, dust, aersols, water vapor, etc. However, the best way, IMO, to treat it is to determine how bright the sky is relative to the brightness of the object. This will produce the level of contrast, and at some point the contrast washes out the object.

The sky brightness can be expressed in magnitude per sq. arc minute. The human eye sees, on average, about one square arc minute. So, for a typical star, whatever the star's apparent magnitude is, so too is its effective surface brightness. This makes it easy to get the ratio of the two magnitudes (in unit area) to calculate the actual contrast.

 

[vincenzosassone]

Right. Light pollution is really the lights from the ground that have some of their light reflected back to the observer. This is what happens in daylight --our atmosphere scatters sunlight toward the ground.

So it becomes just how polluted the sky is from pollen, dust, aersols, water vapor, etc. However, the best way, IMO, to treat it is to determine how bright the sky is relative to the brightness of the object. This will produce the level of contrast, and at some point the contrast washes out the object.

The sky brightness can be expressed in magnitude per sq. arc minute. The human eye sees, on average, about one square arc minute. So, for a typical star, whatever the star's apparent magnitude is, so too is its effective surface brightness. This makes it easy to get the ratio of the two magnitudes (in unit area) to calculate the actual contrast.

I tried to read it twice, I wanted to find something that touched my speech but there isn't anything about it. But thanks to you I understood something of worth: we have also to take in account the same sky with the same stars! Many thanks, now I understand what is truly the light pollution and what aspects are important to take in account.