66 replies to this topic

[Classic8]

Thanks guys for some really deep objects to try for from here in London with a little help of my Lodestar. I love these pre-solar system photons :-)

Make you feel young, don't they? 

[catalogman]

Attached is a list of 39 quasars brighter than mag 16 with a
redshift greater than 1, arranged by magnitude. The list is
extracted from the following catalogue:

 

http://vizier.cfa.ha...bin/Cat?VII/258

 

Just in case you're curious, the famous quasar APM 08279+5255
still tops the list at z = 3.911. However, another quasar
(B 1422+231) ranks close at z = 3.62 and is only half a mag
fainter (15.84).

 

A related thread (Post #45) compiles a list of brighter quasars with lower
redshifts:

 

http://www.cloudynig...-quazars/page-2

 

                                            -- catalogman

Attached Files

•  QSOs_z_more_than_1.txt   5.5KB   48 downloads
•  format.txt   3.97KB   34 downloads

Edited by catalogman, 10 April 2015 - 01:38 PM.

[quazy4quasars]

   @ Catalogman, you have not observed them;  that's clear enough.  1422 is 98 percent as distant and appears TWICE as bright as 5255,

   

   Stop quoting the misleading 15.2 in R and go look at them.  . The object 1422+231 is a much more accessible QSO  and since they are

 

   both lensed, their absolute brightnesses are somewhat irrelevant.   It is annoying to hear wrong information perpetuated.by the ignorant

 

   There. Now you can have the last word,  as usual.  and then, go educate yourself.  

[David Knisely]

Well, seeing at least three of the components of Einstein's Cross (25" f/5) I suppose kind of qualifiies as going pretty deep for me, although I kind of like observing things a little closer and brighter.  Clear skies to you.

[Dan Williams]

   @ Catalogman, you have not observed them;  that's clear enough.  1422 is 98 percent as distant and appears TWICE as bright as 5255,

   

   Stop quoting the misleading 15.2 in R and go look at them.  . The object 1422+231 is a much more accessible QSO  and since they are

 

   both lensed, their absolute brightnesses are somewhat irrelevant.   It is annoying to hear wrong information perpetuated.by the ignorant

 

   There. Now you can have the last word,  as usual.  and then, go educate yourself.  

 

Wow, did I miss something? It sounds like an episode on a t.v. show my daughter told me about called "Keeping Up With The Kardashians".  No wonder why I don't watch television.

 

 ~ Dan

[catalogman]

   <something quazy>

 

Gee. Thanks for the compliments, Quazy.

 

Now to address your main, um, points:

 

- No, Quazy, I don't have a scope. Bought three sets of mirrors
  from three different manufacturers (don't ask for company names)
  -- all have been certified as shaving mirrors or recyclable trash
  by the local astronomy club. Gave up building a scope -- now just
  collect atlases and catalogues instead (CN guidelines permit only
  posts from the large DSO database in Cartes du Ciel in Distro Astro 3.0).

 

- In the companion thread, Quazy, I did indeed note that the magnitudes
  posted from the original catalogue may not correspond to the visual
  band:

 

   http://www.cloudynig...-quazars/page-2

 

   (See Post #45.)

 

  You would have noticed this, Quazy, if you had bothered to, um,
  "educate yourself."

 

In closing, Quazy, I would like to note that your thoughtful and
insightful (inciteful?) post would have been more appropriate under
a different thread -- a good suggestion would be "Why people leave CN".

 

                                                                               -- catalogman

Edited by catalogman, 15 April 2015 - 03:18 PM.

[sgottlieb]

Catalogman, I've also made a little hobby out of collecting (print) catalogues and galaxy atlases, so I'm curious which ones you've acquired?

 

Feel free to PM, if preferred.

Edited by sgottlieb, 15 April 2015 - 09:08 PM.

[Dan Williams]

With any number attached to light-years we lose all sense of human proportion, but there's something magical to me about the 1 billion l.y. mark (maybe listening to Carl Sagan had something to do with that!). At the Golden State Star Party (GSSP) at Adin, California, I spent some time each night soaking up some 1 billion year old photons from a variety of galaxies and savoring some ancient light with my 18-inch Starmaster. SQM-L readings were in the 21.60-21.65 range.

 

 

I was afraid that I wouldn't be able to join the 1 billion light-year club with only 90mm, but I have become hopeful with 3C 273.  Burnham's Celestial Handbook has a nice chart showing location and magnitudes of surrounding stars.

 

I find it almost beyond comprehension that the image I will see is so far and so old.  I am really looking forward to Virgo coming into view.  Thanks for starting this topic!

 

 ~ Dan

[catalogman]

 

Catalogman, I've also made a little hobby out of collecting (print) catalogues and galaxy atlases, so I'm curious which ones you've acquired?

 

Feel free to PM, if preferred.

 

 

I started a new thread on it so that everyone can learn more:

 

http://www.cloudynig...our-collection/

 

 

                                                                                                 -- catalogman

[nytecam]

Great observations of these very remote objects - here's two of mine from this week - brightest 3C273 in Virgo @ 2BLY and my faintest to date in QSO 1011-017 in Sextans [m17.9] @ 10.7BLY - the latter appear double in my pic and Sloan DSS but may be a field star

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[theApex]

Risk drifting a bit off-topic, but still keeping to the concept of observational astronomy as a  "look into the past",  it's become natural to me (unlike what some posters have stated in this thread) to think it that way.

Okay, it's a much smaller scale (also shorter time span), but I even got into the habit of making use of that train of thought to, for instance, induce non-conversant star party guests (perhaps looking through a telescope for the first time in their lives) to also think it that way; as I invite them to observe stars placed at specific distances (in light years) to then reveal (usually to their astonishment) the light reaching their retinas has left its mother star at specific years (historical events, their own births, etc.)

So I personally find it odd some quite experienced astronomers declare they've never given this a further thought.

[Galaxy_Mike]

Interesting thread, probably inspired me to try 3C 273 with my 4.5 " dob.

It's interesting, higher magnification allows you to see dimmer stars according to

http://www.cruxis.co...ngmagnitude.htm

And I think I was at 70x before I could see the SN in m82 last year

[Galaxy_Mike]

Interesting thread, probably inspired me to try 3C 273 with my 4.5 " dob.

It's interesting, higher magnification allows you to see dimmer stars according to

http://www.cruxis.co...ngmagnitude.htm

I think it would apply to quasars, which are stellar? I think I was at 72x before I could see the SN in m82 last year

Edited by Galaxy_Mike, 20 April 2015 - 04:47 PM.

[Starman1]

That calculator assumes:

refractor 99% transmission x 4 surfaces

That's a little low for multi-coatings and a little high for MgFl2 coatings

 

reflectors 88% reflective x 2

This is pessimistic for a new coating

 

compound scopes 99% reflective x 2

the corrector is ignored, as is the diagonal.

Unless you know how to modify the html code, then I recommend:

 

This calculator, on the other hand:

http://www.scopecity...-calculator.cfm

(the company no longer does any commercial business)

assumes:

refractor: 98.5% x 4 surfaces transmission (MgFl2 coatings)

reflector: 96% x 2 surfaces (enhanced coatings)

compound scope: 98.5% x 2 AND 94% times 2 (MgFl2 corrector and semi-enhanced mirrors.

the diagonal is ignored.

 

If you can modify the html code, then find the entry for your type of scope and change the percentages to match your particular scope.

Use .985 for MgFl2 lens coating, .995 for full multi coating

Use .91 for standard aluminum coating, 0.94 for semi-enhanced coating, 0.96 for enhanced aluminum and 0.98 for dielectric coating

Make sure to add a diagonal if using a compound scope.

[Galaxy_Mike]

Thanks Don, that calculator gives a few tenths more, maybe I can get it. I remember getting the code, don't remember if I modified it, probably a tutorial online somewhere.

I still haven't done NELM and don't know my pupil size. So that probably throws it off more. Any tips on finding pupil diameter? I don't think they're normal size.

An interesting thing I noticed with the first calculator was that NELM didn't matter much at high magnifications. So it might be possible with the moon out, since it's stellar, not an extended dso. Does that sound right in your opinion?

[Starman1]

For stars, I think what matters is contrast with the sky and a small size to the spurious disc.

That means a limit is more likely to be reached between 25x/inch and 50x/inch.

One odd thing about the calculator is it suggests a fainter limit as we age.  There are reasons for that, but i think it's true only up to a point.

Past age 65, I doubt that's the case.

 

As for a pupil gauge, see:

http://duchekconsult...pupil_gauge.htm

 

As for NELM, remember it's with averted vision and the star won't be continuously visible.

And you have to be dark adapted--preferably outside for at least an hour.

And you want to look near the zenith, so get a good comfortable chair.

See, to learn about the limit of your eyes:

http://freescruz.com...o/how_faint.htm

and then see for charts:

http://www.imo.net/v.../observation/lm

Edited by Starman1, 21 April 2015 - 12:34 AM.

[Sasa]

An interesting thing I noticed with the first calculator was that NELM didn't matter much at high magnifications. So it might be possible with the moon out, since it's stellar, not an extended dso. Does that sound right in your opinion?

 

The magnification helps only up to a certain point. If you look at the original paper, Schaefer assumed that the resolution of eye in averted vision for faint object is 15'=900''. Once the star (its size is given by the seeing parameter in the calculator) is bloated above this size, the contrast between the star and the background does not improve. So, for 2'' seeing, the limit improved up to power of 450x.

 

Concerning various differences of reflectivity for refractors/reflectors, one needs to keep in mind the scale: 10% light loss means 0.1 loss in limiting magnitude. I doubt that the calculation is that precise. If I remember well the paper, once the "experience level" is taken into  account, the spread of LM between the observers was about 0.5 magnitude (i.e. 2/3rd of the observers were within +/- boundary from the calculator prediction). Without "experience level" tweaking, the spread was 1.5.

 

For me, the value of the calculator comes with understanding various effects and their estimate. Once you "calibrate" your experience level, the calculator gives pretty good feeling what would be your LM in other telescopes, what happens if you go under darker sky (this is interesting, the limit improves much slowly than the naked eye LM - my experience confirms it) or what happens if you push the magnification higher.