Visible distance between stars
Discussion
I was looking up at the stars the other day, as I regularly do on a clear night, wondering what the f
k it's all about and considered the apparent visible distance between 2 stars.
I then thought: if we are as far away from the stars as they say (at least 6 light years) and that the average distance between stars is 4.5 LY, how come we can so many of them in our field of view making it look as though they are much closer together?
k it's all about and considered the apparent visible distance between 2 stars.I then thought: if we are as far away from the stars as they say (at least 6 light years) and that the average distance between stars is 4.5 LY, how come we can so many of them in our field of view making it look as though they are much closer together?
Might be of interest
https://www.space.com/3380-constellations.html
There's nearly 1000 light years between the stars of Orion.
https://www.space.com/3380-constellations.html
There's nearly 1000 light years between the stars of Orion.
The size and intrinsic brightness of stars varies wildly, so assuming that two stars of equal apparent brightness to your eye are equidistant gets you firmly into Father Ted / Father Dougal territory.
Also bear in mind that even in the least light polluted areas your naked eye can only see a tiny proportion of the stars that are potentially visible, even with just some minor assistance.
This is a slight crop of an image I took with a 135mm f/2.0 camera lens a couple of weeks ago (NGC7822 if you want to geek out)
The dimmest objects that you can see with a dark-adjusted naked eye in good conditions are typically magnitude 6.5 or brighter.
There are roughly ten stars in that picture with magnitude 6.5 or brighter. I'll leave it as an exercise for the reader to count the rest, but those are the ones you'd never see with unaided eyesight.
Also bear in mind that even in the least light polluted areas your naked eye can only see a tiny proportion of the stars that are potentially visible, even with just some minor assistance.
This is a slight crop of an image I took with a 135mm f/2.0 camera lens a couple of weeks ago (NGC7822 if you want to geek out)
The dimmest objects that you can see with a dark-adjusted naked eye in good conditions are typically magnitude 6.5 or brighter.
There are roughly ten stars in that picture with magnitude 6.5 or brighter. I'll leave it as an exercise for the reader to count the rest, but those are the ones you'd never see with unaided eyesight.
Edited by eharding on Tuesday 4th May 10:36
I've been thinking about all this before coming back and replying. I may have to think about it some more.
Damn it.
Imagine looking at 2 trees which are 100m away. Hold up your hands at arm's length with the tips of your thumbs together and the fingers of each hand held together, pointing upwards and your palms facing each other. If you can see both trees in the space between your palms surely this means that the distance from you to the trees must be much greater?
I have the image of an equilateral triangle in my mind with a star on 2 of the points and the earth on the other.
Can we identify 2 stars in an image like the one above which are the same distance from earth as from each other?
Damn it.
eharding said:
The size and intrinsic brightness of stars varies wildly, so assuming that two stars of equal apparent brightness to your eye are equidistant gets you firmly into Father Ted / Father Dougal territory.
Also bear in mind that even in the least light polluted areas your naked eye can only see a tiny proportion of the stars that are potentially visible, even with just some minor assistance.
This is a slight crop of an image I took with a 135mm f/2.0 camera lens a couple of weeks ago (NGC7822 if you want to geek out)
The dimmest objects that you can see with a dark-adjusted naked eye in good conditions are typically magnitude 6.5 or brighter.
There are roughly ten stars in that picture with magnitude 6.5 or brighter. I'll leave it as an exercise for the reader to count the rest, but those are the ones you'd never see with unaided eyesight.
OK I think I've found a way to express what I'm saying: So take any close pair of stars in that picture. Instinctively it would seem that the distance between them is far less than the distance from them to the telescope taking the picture. My logic says "surely the perspective would be different if this wasn't the case?"Also bear in mind that even in the least light polluted areas your naked eye can only see a tiny proportion of the stars that are potentially visible, even with just some minor assistance.
This is a slight crop of an image I took with a 135mm f/2.0 camera lens a couple of weeks ago (NGC7822 if you want to geek out)
The dimmest objects that you can see with a dark-adjusted naked eye in good conditions are typically magnitude 6.5 or brighter.
There are roughly ten stars in that picture with magnitude 6.5 or brighter. I'll leave it as an exercise for the reader to count the rest, but those are the ones you'd never see with unaided eyesight.
Edited by eharding on Tuesday 4th May 10:36
Imagine looking at 2 trees which are 100m away. Hold up your hands at arm's length with the tips of your thumbs together and the fingers of each hand held together, pointing upwards and your palms facing each other. If you can see both trees in the space between your palms surely this means that the distance from you to the trees must be much greater?
I have the image of an equilateral triangle in my mind with a star on 2 of the points and the earth on the other.
Can we identify 2 stars in an image like the one above which are the same distance from earth as from each other?
Edited by Driller on Thursday 6th May 20:03
This was answered in the first response to your OP. You have no perspective whatsoever at these distances, it’s impossible to know whether a star is big and big and bright and 1000 light years away or small and dim and 10 light years away.
In your analogy imagine a bonsai tree 10 meters away and an identical looking oak tree 100 meters away, both looking the same size to you, how does your triangle work now. In this scenario you MAY still know which is nearest as you will have some 3D perspective. With the stars it would be impossible.
In your analogy imagine a bonsai tree 10 meters away and an identical looking oak tree 100 meters away, both looking the same size to you, how does your triangle work now. In this scenario you MAY still know which is nearest as you will have some 3D perspective. With the stars it would be impossible.
Green1man said:
This was answered in the first response to your OP. You have no perspective whatsoever at these distances, it’s impossible to know whether a star is big and big and bright and 1000 light years away or small and dim and 10 light years away.
Add to this your perspective on just how fast/slow the speed of light actually is.https://www.youtube.com/watch?v=2BmXK1eRo0Q
Driller said:
Great replies, thanks. All fascinating stuff and that video is brilliant!
So if the closet star is Alpha Centuri and it's 4.37 light years from earth, can we find another star which is equidistant from earth and Alpha Centuri forming an equilateral triangle?
If AC is the closest start to earth, why do you think there's be another equally close?So if the closet star is Alpha Centuri and it's 4.37 light years from earth, can we find another star which is equidistant from earth and Alpha Centuri forming an equilateral triangle?
sociopath said:
Driller said:
Great replies, thanks. All fascinating stuff and that video is brilliant!
So if the closet star is Alpha Centuri and it's 4.37 light years from earth, can we find another star which is equidistant from earth and Alpha Centuri forming an equilateral triangle?
If AC is the closest start to earth, why do you think there's be another equally close?So if the closet star is Alpha Centuri and it's 4.37 light years from earth, can we find another star which is equidistant from earth and Alpha Centuri forming an equilateral triangle?
MiniMan64 said:
sociopath said:
Driller said:
Great replies, thanks. All fascinating stuff and that video is brilliant!
So if the closet star is Alpha Centuri and it's 4.37 light years from earth, can we find another star which is equidistant from earth and Alpha Centuri forming an equilateral triangle?
If AC is the closest start to earth, why do you think there's be another equally close?So if the closet star is Alpha Centuri and it's 4.37 light years from earth, can we find another star which is equidistant from earth and Alpha Centuri forming an equilateral triangle?
sociopath said:
Driller said:
Great replies, thanks. All fascinating stuff and that video is brilliant!
So if the closet star is Alpha Centuri and it's 4.37 light years from earth, can we find another star which is equidistant from earth and Alpha Centuri forming an equilateral triangle?
If AC is the closest start to earth, why do you think there's be another equally close?So if the closet star is Alpha Centuri and it's 4.37 light years from earth, can we find another star which is equidistant from earth and Alpha Centuri forming an equilateral triangle?
The second star wouldn't have to be exactly the same distance from earth, just similarly close enough to illustrate the point of an equilateral (ish then in this case) triangle.
Eric Mc said:
There are no other stars as close as the Alpha Centauri group. The next closest is Sirius at about 10 light years.
In that case Eric, can we find 2 stars that are approximately 10,000 light years from earth with the same distance between themselves? I think you can see what I'm trying to do and I'm interested in the result.Driller said:
In that case Eric, can we find 2 stars that are approximately 10,000 light years from earth with the same distance between themselves? I think you can see what I'm trying to do and I'm interested in the result.
Why bother. If you know already that two stars are the same distance from each other - what is the point of your experiment if the purpose of that experiment is to tell you something you already know.In reality, there are a number of methods used to gauge stellar distances. The most reliable is using parallax. This involves looking at a star's position in relation to background star on a particular date in the year. Exactly six months later, when thee earth has travelled to the opposite side of its own orbit around the sun, take the same measurement. The star you will be looking at will have shifted slightly against the background of the other stars. If you have measured this "shift" accurately, using trigonometry, you can triangulate and work out the distance from the earth to that star.
This system works very well but is only accurate for fairly close stars i.e a couple of hundred light years at most. Most stars in the sky are much further away than that so alternative methods need to be used.
The next method is to identify what type of star you are looking at. Stars belong to types or families of types. The type of star you are looking at can be determined by looking at its overall colour, its visible spectrum and perhaps other types of radiation it emits, such as infra red, ultra-violet or x-ray. If you can identify the type of star, then you can gauge its overall size and, most importantly, its true luminosity (as opposed to its apparent luminosity). If you can get a handle on all these factors, then you can gauge how far away the star really is.
This second method is not as accurate as using parallax but it does give a reasonable idea of the distance. Our knowledge of stars is always evolving so this means that stellar distance using luminosity as the main measurement can vary over time. For instance, a few months ago we saw massive brightness changes in the red giant Betelgeuse. How significant these changes were depended on how bright and big Betelgeuse really is - and working that out means having a reasonable idea as to its distance. Unfortunately, you are trying to measure two slightly unknown variables and the distance measurements for Belegueuse have ranged from about 200 to 650 light years.
Wacky Racer said:
Bit off topic, but am I right in thinking if the Sun is around 93 million miles away, and the speed of light is 186,000 miles per second, when you look at the sun you are seeing it as it was roughly eight minutes previously?
It's about 150 million kilometers (1AU) and 8 minutes 20 seconds but yes. MiniMan64 said:
I think your main problem is that the human brain just cannot really get its head around the distances involved. We have no reference point to process on that scale.
^^^THIS.Most people just can't grasp it. Most people hear talk of large numbers on the news, in terms of debt, but still don't truly get it. £10m of debt, or was is £10bn of debt, it's just a lot. But 10m seconds is about a week short of 4 months, whereas 10bn seconds is 317 years!!!
I understood OP’s question a little differently, which is “if two stars formed an equilateral triangle with Earth, how would they appear in the sky?”.
See if this helps: it’s a map of stars within 12 light years of the Sun. The diamond is where they would be on the plane, the other end of the line is the absolute distance (so the relevant one here). The circles are 0.5 light years apart.
So two stars at the distance of Alpha Centauri (4 LY) in an equilateral triangle would appear about 1/12th of the sky apart. At the distance of Procyon (12 LY) about 1/2 the sky.
In terms of a visible pair, Lalande 21185 & Sirius are both around 8.5 light years from us, and about the same apart. From Earth they’d appear about a 1/3 of the sky apart. You’d need binoculars though, as although Sirius is very bright (at magnitude -1.5 the brightest in the Northern Sky), Lalande is only magnitude 7.5.
See if this helps: it’s a map of stars within 12 light years of the Sun. The diamond is where they would be on the plane, the other end of the line is the absolute distance (so the relevant one here). The circles are 0.5 light years apart.
So two stars at the distance of Alpha Centauri (4 LY) in an equilateral triangle would appear about 1/12th of the sky apart. At the distance of Procyon (12 LY) about 1/2 the sky.
In terms of a visible pair, Lalande 21185 & Sirius are both around 8.5 light years from us, and about the same apart. From Earth they’d appear about a 1/3 of the sky apart. You’d need binoculars though, as although Sirius is very bright (at magnitude -1.5 the brightest in the Northern Sky), Lalande is only magnitude 7.5.
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