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Farthest object I can observe in the Milky Way?

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#1 StarAlert

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Posted 23 September 2020 - 10:15 PM

I've been searching high and low for an answer to this question. But no luck. What is the farthest object I can observe within the Milky Way using a 4" refractor? Farthest star? Farthest glob? Given where we sit, I suppose the farthest objects are about 75,000ly away? Obviously, most of them will not be visible. M13 is about 23k ly. What's deeper? 

 

Thanks



#2 ismosi

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Posted 23 September 2020 - 10:32 PM

The farthest globular is NGC 2419 in Lynx. Also known as the 'Intergalactic Wanderer' and Caldwell 25, it is about 300,000 light-years distant. Should be doable in a 4-inch at mag 10.4 ..

 

https://www.nasa.gov...ard/caldwell-25


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#3 StarAlert

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Posted 23 September 2020 - 11:01 PM

The farthest globular is NGC 2419 in Lynx. Also known as the 'Intergalactic Wanderer' and Caldwell 25, it is about 300,000 light-years distant. Should be doable in a 4-inch at mag 10.4 ..

 

https://www.nasa.gov...ard/caldwell-25

How is this considered a part of the Milky Way? Our galaxy is only about 100,000 ly wide? 


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#4 gnowellsct

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Posted 23 September 2020 - 11:03 PM

How is this considered a part of the Milky Way? Our galaxy is only about 100,000 ly wide? 

It's part of the galactic halo, and the halo is considered a part of a galaxy.

 

=> Once upon a time it was not considered a part of our galaxy and was dubbed the "Intergalactic Wanderer."  However, the expansion of what we understand to be "the galaxy" coupled with revised estimates of NGC 2419's distance led to its inclusion in our galaxy as a high flying glob.  

 

This revision of status was, for some reason, considerably less controversial than Pluto.  (though I favor Pluto as a planet)

 

Greg N


Edited by gnowellsct, 23 September 2020 - 11:05 PM.

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#5 gnowellsct

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Posted 23 September 2020 - 11:11 PM

NGC 2419 is a good choice though I'm sure we're missing something further out that is within the galaxy's boundary.  It is Mag 10 so it should be fine in a four inch refractor--from a good site on a clear night.

 

The furthest Messier (inside our galaxy) is M54, a globular which is 88,700 light years from us.    There are a number of extra-galactic Messiers but they are other galaxies and far beyond our halo.

 

Greg N


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#6 StarAlert

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Posted 23 September 2020 - 11:29 PM

Ok... let's shift gears, then. What is the farthest observable star within the galaxy? Now, we're staying inside the main structure. From my Bortle 7 backyard, I can usually pick up about 10.5 mag. 

 

I was going to look for Alpha Centauri last night, but didn't realize it's only visible from the southern hemisphere. Looks like I need to take a trip down under. But that got me thinking about finding the farthest star. 



#7 No N in collimation

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Posted 23 September 2020 - 11:56 PM

Last night I saw a huge red star at 3 in the morning that I didn't recognize. Had to come in and find out what it was. It was Mars. Oh the shame! 


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#8 gnowellsct

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Posted 24 September 2020 - 12:11 AM

Ok... let's shift gears, then. What is the farthest observable star within the galaxy? Now, we're staying inside the main structure. From my Bortle 7 backyard, I can usually pick up about 10.5 mag. 

 

I was going to look for Alpha Centauri last night, but didn't realize it's only visible from the southern hemisphere. Looks like I need to take a trip down under. But that got me thinking about finding the farthest star. 

No the halo includes a lot of solo stars.  I was attempting to find a list of them but I was not successful.  Most halo stars appear to be studied by professional observatories who think nothing of taking a look at a 25th magnitude star.

 

Your idea of furthest observable star is not the same as my idea in my 14" or someone else's in a 25" etc.  Most nights your limiting magnitude is probably around 12 it might get up to 13 if you spend a lot of time at it and you have an excellent night.  Well the thing is as the ability to bring in dim stars increases you get into intense swarms of them.  I would hazard a guess that your best bet for "furthest" would be in the galactic plane to one side or another of the galactic center: enough to the side to "see beyond" the center but not so as to be blocked by it.

 

No one is going to be able to trot out a list under these conditions.  The number of stars in typical sky software is typically 15 million or more.  To pluck one out and say "this one is furthest" would be something of a chore.  

 

And it might not have any meaning.  There is no furthest star with any practical certainty due to measurement and brightness and other variables.  

 

In fact:  "Parallax angles of less than 0.01 arcsec are very difficult to measure from Earth because of the effects of the Earth's atmosphere. This limits Earth based telescopes to measuring the distances to stars about 1/0.01 or 100 parsecs away."   That's only 326 light years which isn't even 1% of the distance to the center of the Milky Way.    No one even knows the exact distances to all those stars swarming around the galactic center, or even the isolated ones in the opposite direction.

 

And it will be of no interest to anyone.  Because you're not really asking about the furthest star but the furthest star (in our galaxy) that you can see in YOUR telescope.  That will in theory be a bit further/dimmer than someone with a 3 inch telescope but not as far as someone with a $200 six inch dob. Your question implies the existence of lists of stellar distances organized by aperture detectability.  We don't have those lists.  Geometry limits the measurements to a few hundred light years.   Other measurement techniques are not as precise and so not suitable for naming the "furthest star" in your four inch aperture.

 

Greg N


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#9 kel123

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Posted 24 September 2020 - 12:11 AM

Ok... let's shift gears, then. What is the farthest observable star within the galaxy? Now, we're staying inside the main structure. From my Bortle 7 backyard, I can usually pick up about 10.5 mag.

I was going to look for Alpha Centauri last night, but didn't realize it's only visible from the southern hemisphere. Looks like I need to take a trip down under. But that got me thinking about finding the farthest star.


You cannot possibly see it by this time of the year.

#10 gnowellsct

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Posted 24 September 2020 - 12:12 AM

If you want an interesting star check out UY Scuti.  It's currently one of the top contenders for "biggest star that we know about."



#11 Sleep Deprived

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Posted 24 September 2020 - 12:20 AM

If you want an interesting star check out UY Scuti.  It's currently one of the top contenders for "biggest star that we know about."

Astronomy Magazine has an article TODAY on their website about the most extreme stars, and UY Scuti is in the article as the largest star that we know of (with a few asterisks after it).  Anyway:

 

https://astronomy.co...in-the-universe


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#12 Redbetter

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Posted 24 September 2020 - 12:29 AM

I was going to look for Alpha Centauri last night, but didn't realize it's only visible from the southern hemisphere. Looks like I need to take a trip down under. But that got me thinking about finding the farthest star. 

 

FYI-- 

 

Alpha Centauri is at nearly -61 deg, but can be seen from the northern hemisphere.  I observed the pair the first time I went to Hawaii (~21 N latitude.)   Should also be visible in southern Florida and Texas when the southern horizon is clear to the ground. 

 

As with Canopus (which is further north), you have to catch it at the right time of year.  Ignoring refraction and altitude, Canopus is less than 1 degree from the horizon at my primary observing spot at elevation.  But I catch it just above ground level between some trees a few times per year (as well as driving back down the mountain where things open up over the valley.)  


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#13 Tony Flanders

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Posted 24 September 2020 - 05:41 AM

Ok... let's shift gears, then. What is the farthest observable star within the galaxy? Now, we're staying inside the main structure. From my Bortle 7 backyard, I can usually pick up about 10.5 mag.


10.5 is pretty dismal for a 4-inch refractor! You should be able to go considerably fainter than that, even from Bortle-7 skies. High magnification and averted vision.

Off the top of my head, a 4-inch refractor under pristine skies should be able to detect stars roughly to mag 13.0-13.5, depending on the observer. Yet another quick mental calculation tells me that should show supergiant stars out to a distance of at least 100,000 light-years -- flat across the disk of the Milky Way.

Alas, the problem is that supergiants are necessarily young, and all of the Milky Way's star-forming regions lie close to its plane, where the views end up being blocked by dust in almost all directions. The parts of the distant Milky Way that are readily visible, including globular clusters and the central bulge, consist entirely of old, and therefore much fainter, stars.
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#14 StarAlert

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Posted 24 September 2020 - 03:04 PM

Tony, I'm referring to direct vision, but I can certainly use averted vision if needed. 

 

10.5 is pretty dismal for a 4-inch refractor! You should be able to go considerably fainter than that, even from Bortle-7 skies. High magnification and averted vision.

Off the top of my head, a 4-inch refractor under pristine skies should be able to detect stars roughly to mag 13.0-13.5, depending on the observer. Yet another quick mental calculation tells me that should show supergiant stars out to a distance of at least 100,000 light-years -- flat across the disk of the Milky Way.

Alas, the problem is that supergiants are necessarily young, and all of the Milky Way's star-forming regions lie close to its plane, where the views end up being blocked by dust in almost all directions. The parts of the distant Milky Way that are readily visible, including globular clusters and the central bulge, consist entirely of old, and therefore much fainter, stars.

 

So maybe this is a better a question.

What is the most distant star you've seen in your refractor? 


Edited by StarAlert, 24 September 2020 - 03:05 PM.


#15 Dave Mitsky

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Posted 24 September 2020 - 03:19 PM

Alpha Centauri is at nearly -61 deg, but can be seen from the northern hemisphere.  I observed the pair the first time I went to Hawaii (~21 N latitude.)   Should also be visible in southern Florida and Texas when the southern horizon is clear to the ground.

I can attest that Alpha Centauri is indeed visible from southern Florida.  I've seen it from the site of the Winter Star Party in the Florida Keys.


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#16 StarAlert

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Posted 24 September 2020 - 05:34 PM

I live in the LA area. I think it's too far north. SkySafari says it never rises and sets. I wonder if San Diego is far enough south. hmmmm. 


Edited by StarAlert, 24 September 2020 - 05:35 PM.


#17 Tony Flanders

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Posted 25 September 2020 - 05:11 AM

So maybe this is a better a question.
What is the most distant star you've seen in your refractor?


Ah, that is a different question. The most distant stars I have seen through my 4-inch refractor are roughly 160,000 light-years (160 kly) distant, in the Large Magellanic Cloud. In fact some of those are likely visible even in 10x50 binoculars.

But there is no dust-free path more than a few thousand l-y long to an OB-region in the northern 2/3 of the celestial sphere.

For a reasonable approximation, let's say that the most distant northern stars I have seen through my 4-inch refractor are the brightest star of Messier 3, some 34 kly distant. But M3 is exceedingly hard to resolve in a scope that size. Messier 13, at 22 kly, is much easier to resolve.


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#18 StarAlert

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Posted 25 September 2020 - 07:26 AM

Ah, that is a different question. The most distant stars I have seen through my 4-inch refractor are roughly 160,000 light-years (160 kly) distant, in the Large Magellanic Cloud. In fact some of those are likely visible even in 10x50 binoculars.

But there is no dust-free path more than a few thousand l-y long to an OB-region in the northern 2/3 of the celestial sphere.

For a reasonable approximation, let's say that the most distant northern stars I have seen through my 4-inch refractor are the brightest star of Messier 3, some 34 kly distant. But M3 is exceedingly hard to resolve in a scope that size. Messier 13, at 22 kly, is much easier to resolve.

You’re able to resolve an individual star from the Large Magellanic Cloud with a 4”? 
What do you mean by OB-region? 



#19 Tony Flanders

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Posted 25 September 2020 - 01:35 PM

You’re able to resolve an individual star from the Large Magellanic Cloud with a 4”?


Easily. The LMC is undergoing explosive star formation, so it is awash in ultraluminous young stars.
 

What do you mean by OB-region?


Sorry, I have my nomenclature crossed, as it were. I should have said either H-II region or OB association. They are different life stages of the same phenomenon.

The Orion Nebula is an H-II region. Orion's Belt is an OB association. Both contain stars luminous enough to appear bright to the unaided eye despite their roughly 1500 l-y distance. The three bright belt stars are all roughly magnitude 2. Move them 100 times farther from Earth, to the distance of the LMC, and they would still be magnitude 12, well within the range of a 4-inch scope. However, the Orion Nebula is a pipsqueak compared to the LMC's Tarantula Nebula.


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#20 Starman1

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Posted 25 September 2020 - 05:44 PM

I live in the LA area. I think it's too far north. SkySafari says it never rises and sets. I wonder if San Diego is far enough south. hmmmm. 

Southern horizon at 29° N (that's down in the Baja) is required to see α Centauri for a few seconds as it culminates.

It's not possible in CA.


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#21 BillP

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Posted 25 September 2020 - 10:38 PM

For stars inside the galaxy proper and not outside the disk, Rho Cassiopeiae is usually mentioned as the furthest naked eye star.  Mag 4.6 and about 3000-4000 LY distant.

 

But Phi Cassiopeiae is listed at Mag 5 with a SIMBAD parallax of only 0.2460 (2018 Gaia DR2 data) so about 13,000 LY distant.

 

Uncertainties in the Gaia DR2 data are typically around 0.04 for sources brighter than ~14 mag.  If we do a SIMBAD search for stars with a more reasonable parallax of around .08 and <=mag 10, a nice candidate is HD 208275 in Cygnus (21 54 10.2680 +39 52 37.927).  It is mag 9.4 and using a 0.08 parallax the distance should be around 41,000 LY distant.


Edited by BillP, 25 September 2020 - 11:04 PM.


#22 StarAlert

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Posted 25 September 2020 - 10:48 PM

For stars inside the galaxy proper and not outside the disk, Rho Cassiopeiae is usually mentioned as the furthest naked eye star.  Mag 4.6 and about 3000-4000 LY distant.

But Phi Cassiopeiae is listed at Mag 5 with a SIMBAD parallax of only 0.2460 (2018 Gaia DR2 data) so about 13,000 LY distant.

Thanks Bill,

Those are the two stars that seem to come up most often when I do a google search. I'll start with them and see if I can find any single stars farther away. 

 

Tony's suggestion is interesting. I'll be putting the LMC on my list as well. 

 

And it looks like I'll be making a trip south see our closest neighbor. 


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#23 Ohmless

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Posted 25 September 2020 - 11:04 PM

don't know about the most distant star, but NGC 7006 is 135,000 light-years away at mag 10.6 in Delphinus.  I've seen it with my 4" achromat at a dark site.  Not the most distant but still remarkably far away.



#24 StarAlert

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Posted 25 September 2020 - 11:18 PM

Ok... so it turns out the Large Magellanic Cloud is only visible from the southern hemisphere. Yet another reason to take a trip to South America or New Zealand. 



#25 StarAlert

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Posted 25 September 2020 - 11:23 PM

don't know about the most distant star, but NGC 7006 is 135,000 light-years away at mag 10.6 in Delphinus.  I've seen it with my 4" achromat at a dark site.  Not the most distant but still remarkably far away.

Thanks,

135k ly is certainly far away. From what I've read, though, its' going to take a lot more than a 4" refractor to resolve a star from this cluster. 


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