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Distance between stars

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#1 phottomatt

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Posted 16 June 2024 - 09:28 PM

Is there a way to determine distance between starts without special equipement? I was star hoping with my Binos the other night, sketching an area and I'm not sure my Binos have the advertised FOV. If I could find the distance between 2 stars I could "calibrate" my FOV. If I get a chance I'll aim at a known pair but until then I was hoping to figure it out on my own.

#2 Keith Rivich

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Posted 16 June 2024 - 10:01 PM

Most Planetarium programs, Stellarium being the most obvious, has a function to get the distance (in degrees, minutes, seconds) between any two points in the sky. Find a pair of stars that fit your FOV edge to edge and use the program to get you your separation. 

 

Only other way is to do the drift method. I'll let you do the homework here!


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#3 TOMDEY

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Posted 16 June 2024 - 10:07 PM

Your bino on a tripod and a stop watch >>> Aim at a star near the celestial equator south meridian. Pan west to put the star just outside the east side of the field and lock Az. Time its path across the field. Multiply the seconds by 15. That is the field diameter in arc-sec.    Tom


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#4 CarolinaBanker

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Posted 16 June 2024 - 10:17 PM

When you say distance do you mean angular distance? A tracking scope with an astrometric eyepiece would work. 


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#5 Tony Flanders

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Posted 17 June 2024 - 05:13 AM

As Keith has said, almost all planetarium programs have this capability.

 

If you use a paper star atlas you can use the Dec ticks as a scale.


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#6 Sebastian_Sajaroff

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Posted 17 June 2024 - 06:35 AM

For objects closer than 10°, you can use this formula :
D = SQR(Δδ ^ 2+ (cos(δ) * Δα) ^ 2)

Δδ is the difference in declination between both objects
Δα is the difference in right ascension between both objects (converted to degrees by multiplying by 15)
δ is the average of both declinations
SQR means square root

For objects close to the equator (|δ| < 10°), you can use the drift mode : a star takes 4 minutes to cross 1°
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#7 MikiBee

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Posted 17 June 2024 - 11:47 PM

If you hold one finger in front of your binoculars that is one degree, just kidding it wouldn't work. But having slightly illuminated circles or a cross showing the angular distances in the field of view of a pair of binoculars would be a cool feature. Not sure how to google it and see if anyone has done it.


Edited by MikiBee, 17 June 2024 - 11:48 PM.

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#8 JoeFaz

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Posted 18 June 2024 - 08:36 AM

If you hold one finger in front of your binoculars that is one degree, just kidding it wouldn't work. But having slightly illuminated circles or a cross showing the angular distances in the field of view of a pair of binoculars would be a cool feature. Not sure how to google it and see if anyone has done it.

There are hunting oriented binoculars with this feature built in. The problem with an aftermarket solution for this is that the reticle/circles/etc, has to exist or be projected at or very near the image plane to be visible, which is a tall order for an aftermarket modification.


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#9 aeajr

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Posted 18 June 2024 - 08:54 AM

Most binoculars provide a spec of Degrees FOV at a certain distance.  They often also offer the field of view as feet, yards or meters at a specific distance.   If you want to compare your binos to the spec, this would probably be a better way to do it. 

 

This question might be better discussed in the binocular section.  Others may have the same binoculars and already know the answer. 


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#10 phottomatt

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Posted 18 June 2024 - 09:14 AM

Most Planetarium programs, Stellarium being the most obvious, has a function to get the distance (in degrees, minutes, seconds) between any two points in the sky. Find a pair of stars that fit your FOV edge to edge and use the program to get you your separation. 

 

Only other way is to do the drift method. I'll let you do the homework here!

I got this working, thank you, note just need to convert from arcminutes/seconds to angle for FOV.

 

If you hold one finger in front of your binoculars that is one degree, just kidding it wouldn't work. But having slightly illuminated circles or a cross showing the angular distances in the field of view of a pair of binoculars would be a cool feature. Not sure how to google it and see if anyone has done it.

LOL good one! 

 

Most binoculars provide a spec of Degrees FOV at a certain distance.  They often also offer the field of view as feet, yards or meters at a specific distance.   If you want to compare your binos to the spec, this would probably be a better way to do it. 

 

This question might be better discussed in the binocular section.  Others may have the same binoculars and already know the answer. 

Good point, I'll try there,  my main objective was to learn how to measure the distance on my own not specifically for the Binos.


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#11 aeajr

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Posted 18 June 2024 - 10:20 AM

This is the tool you would use with a telescope.  

https://www.telescop...ce/p/113822.uts

 

Otherwise I would use the timed method.  Run it several times and average them out.


Edited by aeajr, 18 June 2024 - 10:20 AM.

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#12 MikiBee

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Posted 18 June 2024 - 06:02 PM

This is the tool you would use with a telescope.  

https://www.telescop...ce/p/113822.uts

 

Otherwise I would use the timed method.  Run it several times and average them out.

This is nice for measuring double stars' distances. Wonder if there is a bino version of this or maybe for a finderscope? 



#13 CarolinaBanker

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Posted 18 June 2024 - 07:33 PM

This is nice for measuring double stars' distances. Wonder if there is a bino version of this or maybe for a finderscope?


Yes, they’re called reticle binoculars, Oberwerk makes a pair.
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#14 gwd

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Posted 20 June 2024 - 05:18 AM

This is the tool you would use with a telescope.  

https://www.telescop...ce/p/113822.uts

 

Otherwise I would use the timed method.  Run it several times and average them out.

The website says the product is no longer available.   I'd like to have one.  



#15 Jon Isaacs

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Posted 20 June 2024 - 05:47 AM

Just to be clear, Matt is hoping to measure the TFoV of his binoculars. 

 

"I was star hoping with my Binos the other night, sketching an area and I'm not sure my Binos have the advertised FOV."

 

Drift timing with binoculars is so time consuming as to be impractical.  For pair of binoculars with a 6 degree field of view, that would require 24 minutes.. and it you missed it, you have to start over.  And you want to average a few readings.  

 

I use SkySafari for my measurements, it's on my phone and tablet and I can get precise numbers in the field.. 

 

Another technique that is reasonably accurate for wide field views is to use a digital level.  A digital level in an angle gauge, it measures the elevation.  The one I have reads to 0.05 degrees, is accurate to 0.1 degrees. 

 

  The binoculars must be mounted and the digital level mounted to the binoculars..  Choose a star on the meriden so it's motion has no vertical component.. then place the star at the bottom of the field of view, record the altitude, place the star at the top of the field of view, record the altitude.  The TFoV of the binoculars is the difference between them.  

 

This is the digital level I use, it is white characters, black background, I tape red film over the window so it is red on black.  Comparing it to Sky Safari, the altitude is quite accurate, usually about 0.1 degree.

 

https://www.amazon.c...1zcF9hdGY&psc=1

 

Jon


Edited by Jon Isaacs, 20 June 2024 - 05:48 AM.

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#16 gwd

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Posted 20 June 2024 - 06:16 AM

I don't see among the tools in Stellarium that you can input two arbitrary positions on the celestial sphere to get the great circle distance between them.  I see the planetary calculator for the degrees between many solar system objects.  I see the phenomenon calculator for separations between some objects.  

 

I've attached spreadsheets where you can enters arbitrary locations and see the degrees separation between them and also the position angle and number of fields of view.   

Attached Files



#17 Jon Isaacs

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Posted 20 June 2024 - 06:39 AM

I don't see among the tools in Stellarium that you can input two arbitrary positions on the celestial sphere to get the great circle distance between them.  I see the planetary calculator for the degrees between many solar system objects.  I see the phenomenon calculator for separations between some objects.  

 

I've attached spreadsheets where you can enters arbitrary locations and see the degrees separation between them and also the position angle and number of fields of view.   

 

I do not use Stellarium, as I said I use SkySafari.. Maybe the desktop version of Stellarium has something similar.. 

 

The first step is to choose a star or object.  Then in the Selection Menu, one of the options is "Measure a distance."

 

I choose the second objects and SkySafari shows the angular separation and position angle as well as the actual 3 dimensional distance if it has the information available..  

 

Jon



#18 aeajr

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Posted 20 June 2024 - 08:00 AM

In Stellarium the distance tool is only on the desktop version. It is an add in tool you have to select to be loaded at startup. I use it a lot.
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#19 ChristianG

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Posted 20 June 2024 - 10:51 AM

Hi all.

 

Just as a reminder, I suppose most folks here know this... One thing that should not be done is to point the binoculars at a brick wall and count bricks in the field of view (say). That's because astronomical field of view is with instrument focused at infinity, and looking at something significantly closer puts the eyepiece's fixed-size field stop further from the objective, thus capturing less angular field of view. Cheers!

 

--Christian


Edited by ChristianG, 20 June 2024 - 10:53 AM.


#20 Jon Isaacs

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Posted 22 June 2024 - 07:32 AM

Hi all.

 

Just as a reminder, I suppose most folks here know this... One thing that should not be done is to point the binoculars at a brick wall and count bricks in the field of view (say). That's because astronomical field of view is with instrument focused at infinity, and looking at something significantly closer puts the eyepiece's fixed-size field stop further from the objective, thus capturing less angular field of view. Cheers!

 

--Christian

 

I calculate that for a pair of 10x50s with a wall 50 feet away, the error is about 1%... 

 

Jon



#21 Tony Flanders

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Posted 22 June 2024 - 08:04 AM

ChristianG said:
 

One thing that should not be done is to point the binoculars at a brick wall and count bricks in the field of view (say). That's because astronomical field of view is with instrument focused at infinity, and looking at something significantly closer puts the eyepiece's fixed-size field stop further from the objective, thus capturing less angular field of view.

 
And Jon responded:
 

I calculate that for a pair of 10x50s with a wall 50 feet away, the error is about 1%...


I agree with Jon that while the error due to close focus can be significant for instruments with long focal lengths, it's likely negligible for hand-holdable binoculars.

In my experience, a much bigger problem with brick walls is that it's hard to make sure that your line of sight is perpendicular to the wall, and that bricks are not in fact evenly spaced.
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#22 ChristianG

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Posted 24 June 2024 - 01:13 PM

Yes of course.

 

In my post: "... looking at something significantly closer ..." only meant that there would be some kind of error if you just stand a few feet away from a wall.

 

And for a 50 feet object distance (15240 mm), a 200 mm f/4 objective lens typical of 10X50 binoculars puts the image at 202.7 mm, so indeed about a 1% error. If that's acceptable, so be it! Cheers.

 

--Christian



#23 Dave Mitsky

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Posted 25 June 2024 - 03:05 PM

Angle Measure Plug-in

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  • Angle Measure Plugin Screenshot 2024-06-25 Processed.png


#24 phottomatt

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Posted 30 June 2024 - 11:14 AM

Great stuff, thank you everyone. I made a sketch the other night from the view with my 20x80 Orion Binos making sure to note the stars on opposite sides. Then went to Stellarium and using the Ocular view I input my Bino specs to compare with my sketch. Then I found the stars in my sketch and used the measure tool to verify. It was exactly as advertised, which I assumed it would be but thought the process to verify in real life would be fun, and it was.

Edited by phottomatt, 30 June 2024 - 11:17 AM.

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