Jump to content


Photo

How to describe what is visible?

  • Please log in to reply
7 replies to this topic

#1 ggalilei

ggalilei

    Apollo

  • *****
  • Posts: 1067
  • Joined: 01 Sep 2011
  • Loc: Kentucky

Posted 14 August 2014 - 01:53 PM

I think it's very difficult to convey usable information on how well any target will show, because it depends on many factors. I wish though that a little more guidance were provided in the General Observing and Beginners forums by experienced observers so that beginners don't get frustrated when they cannot see what they read was readily visible. Not the best example for sure, but the most recent one: I recently read of an observation of the central star in the Cat's Eye nebula at about 135x when the full Moon was out. Last night I gave it my first attempt with a 10" reflector and the Moon still below the horizon. I had never looked for that nebula before: it's small, and difficult to find by star hopping because in a mostly empty field. It took me a while to even find the nebula. I could see no trace of the central star up to 250x. I'm not doubting at all the report, I just wish we could take the time to give more information to the beginners who browse these forums when we report a generally challenging observation, not a "disclaimer," just a bit of advice, because someone will in fact try to follow through and look for these targets. I know I will try to keep this in mind next time. But maybe it's just me whining and no one is getting frustrated? Share your thoughts?

Thanks, Tonino.



#2 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 22873
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 14 August 2014 - 02:20 PM

The problem is that we cannot know all the circumstances under which someone may try to observe the object (or detail in an object).

For instance, in order to say, "You should be able to see this.....", we'd have to know:

--the experience of the observer

--the size of the scope

--the magnification used

--the cleanliness of the optics

--the quality of the optics

--the quality of the seeing conditions

--the level of collimation in the scope

--the cooling of the scope (closeness to ambient)

--the altitude of the object above the horizon when viewed.

--the brightness of the night sky at the site

--the color of the star or object

--the transparency (i.e. extinction) of the sky at the site

--the exit pupil produced by the eyepiece

--the type of scope

--the age of the coatings and the type of coatings

--the age of the observer

--the quality of the eyesight of the observer

--whether or not the observer had drugs (prescription or otherwise) or alcohol in his system

--when during the night the observation took place

--whether the Moon was in the sky or not

--whether the observer was using a laptop/tablet/cell phone program to find an object

--whether the observer was completely dark adapted

--whether any direct lighting was visible at the site

--how tired the observer was

--whether the scope tracked or had to be manually moved

 

Where I grew up, the skies were modestly dark in my back yard.  I had no trouble seeing all the Messier objects and hundreds of NGC objects

with a 4.25" reflector.  Yet, I read of people having a hard time seeing this or that Messier object with a 10" scope!  The difference is almost certainly

the darkness of the sky, so could I say all the Messier objects would be visible in a small 2" or 4" scope (they're all visible in a 50mm finder at a dark site)?  

Well, certainly in dark skies, but many modern observers don't observe in dark skies and have to travel hundreds of miles to get to them.  

So I don't think I can safely say that all the Messiers are visible in scopes of that size.

 

So perhaps we should say, "This is what I saw," and try to specify the scope and conditions so others may relate.

I know if I could ONLY observe in my backyard in L.A., I'd be a lunar/planet/double star specialist and simply stop observing anything else.

I live in a White White Zone, where the night sky is kind of like a permanent twilight and never gets dark.

I have access to dark skies by driving, though.  Should I assume that someone else does not?

Should I assume the individual asking about the visibility of a particular object is living under skies as bright as mine?

Or should I assume the observer CAN get his scopes to dark skies?

 

All these factors will influence the relevance of a reply.

 

The one thing I always tell newbies is this:

"You will never see less than you see right now.  As you gain experience, you will see more--more details, more faintness, more objects.  There is no experience

in which you can participate that will teach you how to observe a deep-sky object through a telescope other than observing through a telescope.  Observe,

and observe again, and observe some more.  A year from now you will go back to view the objects you could *barely* see when you started out, and you

will find them bright and detailed.  Were you blind?  No.  You were just inexperienced."

How do you get to Carnegie Hall?  Practice. :grin:


  • Carol L likes this

#3 Kevdog

Kevdog

    Apollo

  • *****
  • Posts: 1276
  • Joined: 11 Jul 2012
  • Loc: Desert Hills, AZ

Posted 14 August 2014 - 04:24 PM

Generally the best way to get a good idea of what objects should look like it to look at sketches and not photos.  Search around for a sketch of your target made by a similar sized telescope and it'll be pretty close to what you will see.

 

The book "Turn Left at Orion" is good for this as they have sketches of the objects in the book rather than photos.  They usually have 2-3 depending on visibility of the object: one for binoculars, one for a small refractor (80mm or so) and one for a 10" dob.

 

 

The one thing I always tell newbies is this:

"You will never see less than you see right now.  As you gain experience, you will see more--more details, more faintness, more objects.  There is no experience

in which you can participate that will teach you how to observe a deep-sky object through a telescope other than observing through a telescope.  Observe,

and observe again, and observe some more.  A year from now you will go back to view the objects you could *barely* see when you started out, and you

will find them bright and detailed.  Were you blind?  No.  You were just inexperienced."

How do you get to Carnegie Hall?  Practice. :grin:

 

Knowing where to look, but also knowing how to look makes a big difference.  I'm still building those skills, but I definitely notice a huge difference from when I first started.  The same objects in the same scope now show a lot more detail.

 

I remember a great tip for training your eye.  Stare at a blank wall and really look for details.  Soon you'll notice small cracks, discolored patches, stains, cobwebs, etc.   Eeking out those details is the same skill you use when viewing through a telescope.  Low contrast, minute details.

 

Also recently when looking at Saturn I realized something.  I saw 5 non-twinkling dots nearby.  I checked SkySafari and sure enough, those were 5 of the moons circling Saturn.  Until that time I had been too busy looking at the moons to notice!  Details!   



#4 Philler

Philler

    Messenger

  • -----
  • Posts: 480
  • Joined: 15 Jul 2013
  • Loc: Kansas, USA

Posted 14 August 2014 - 07:03 PM

I did a web search on sketches of DSO's, specifically "Sketches of Galaxies" recently. I found lots of sketches and descriptions done with a variety of scopes. Most of the sketches and descriptions were good and useful and gave basic information on the DSOs.  But one thing was really frustrating on several sketches/descriptions: the observer failed to identify the object with NGC or Messier or whatever designation. I am not sure if this was just overlooked, or the observer just did not know what the object was, or we are supposed to know, or they just did not care. But to me, identifying the object is just as important as the description. They would give detailed info on other things like sky transparency, magnification, time in UT and date, aperture,even brand of eyepiece, and even how tired they were, but we are left with a mystery galaxy.  Go figure?

 

I also hate it when an observer will shun the more well known NGC designations and instead only give the Hickson, or Arp, or UGC or other designation.


Edited by Philler, 14 August 2014 - 07:09 PM.


#5 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 22873
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 14 August 2014 - 10:58 PM

One thing I can generally say about sketches posted: you WILL see more of the object than the sketches.

 

I view Astronomy Sketch of the Day every day, and I often marvel at how little each sketcher has seen in the object.

Most observers must observe in heavily light-polluted areas or have vision problems.

 

While that may be partially true, in reality most have sketching problems.  Were I to attempt, with chalk and black paper, to sketch, for example, the Regio Centralis

(center) of the Orion Nebula, said drawing would take two whole nights just to begin to record the small details and stars seen there

in a 12.5" scope.  Photos are only a *little* more detailed than what can be seen with the eye, and, in some cases, less.

Yet most drawings, with just about any scope size, seem to show less than I saw back in 1963 with a 4.25" scope.

 

There are a few sketchers whose drawings come close to what can be seen in the scope, but, by and large, most sketches should make

just about any visual observer feel great because they display so much less detail than can be seen in a scope.

 

Having said all that, I would STILL refer a lot of newbies to sketches rather than photos, because sketches will be better at representing what may be seen.

And if the observer sees MORE than the sketch, how bad is that?  Delivering more than expectations?  How many things in life can we say

that about?


Edited by Starman1, 14 August 2014 - 10:59 PM.


#6 David Knisely

David Knisely

    Hubble

  • *****
  • Posts: 15549
  • Joined: 19 Apr 2004
  • Loc: southeastern Nebraska

Posted 16 August 2014 - 12:57 PM

I think it's very difficult to convey usable information on how well any target will show, because it depends on many factors. I wish though that a little more guidance were provided in the General Observing and Beginners forums by experienced observers so that beginners don't get frustrated when they cannot see what they read was readily visible. Not the best example for sure, but the most recent one: I recently read of an observation of the central star in the Cat's Eye nebula at about 135x when the full Moon was out. Last night I gave it my first attempt with a 10" reflector and the Moon still below the horizon. I had never looked for that nebula before: it's small, and difficult to find by star hopping because in a mostly empty field. It took me a while to even find the nebula. I could see no trace of the central star up to 250x. I'm not doubting at all the report, I just wish we could take the time to give more information to the beginners who browse these forums when we report a generally challenging observation, not a "disclaimer," just a bit of advice, because someone will in fact try to follow through and look for these targets. I know I will try to keep this in mind next time. But maybe it's just me whining and no one is getting frustrated? Share your thoughts?

Thanks, Tonino.

 

 

With central stars in many planetary nebulae, atmospheric seeing may be one primary factor in whether they are visible or not.  I have had times when I have caught the 11th magnitude central star in the Cat's Eye (NGC 6543) in an 8 inch at between 114x and 230x without a lot of trouble, simply because the seeing was fairly stable (better than a couple of arc seconds for an extended period of time).  If the seeing is bad of the scope is not cooled-down, the central star will get blurred enough to blend into the glowing central region of the nebula, making it difficult or impossible to see.  As for finding the Cat's Eye, I find it fairly easy anymore.  I form a  narrow "X" with the stars 27, 28, 32, and 46 Draconis with NGC 6543 almost in the middle of the "X".  Each of those stars is 5th magnitude and brighter, so I can see any of them either in my 9x50 finderscope or with averted vision and just my unaided eye.  Clear skies to you.



#7 David Knisely

David Knisely

    Hubble

  • *****
  • Posts: 15549
  • Joined: 19 Apr 2004
  • Loc: southeastern Nebraska

Posted 16 August 2014 - 01:06 PM

I did a web search on sketches of DSO's, specifically "Sketches of Galaxies" recently. I found lots of sketches and descriptions done with a variety of scopes. Most of the sketches and descriptions were good and useful and gave basic information on the DSOs.  But one thing was really frustrating on several sketches/descriptions: the observer failed to identify the object with NGC or Messier or whatever designation. I am not sure if this was just overlooked, or the observer just did not know what the object was, or we are supposed to know, or they just did not care. But to me, identifying the object is just as important as the description. They would give detailed info on other things like sky transparency, magnification, time in UT and date, aperture,even brand of eyepiece, and even how tired they were, but we are left with a mystery galaxy.  Go figure?

 

I also hate it when an observer will shun the more well known NGC designations and instead only give the Hickson, or Arp, or UGC or other designation.

 

 

Yes, the drawings should provide some very basic information about the observation, but a lot of people fail to do this unfortunately.  However, as for the Hickson, Arp, or UGC designations, UGC numbers are often primary identifiers, as the objects may either not have an NGC designation or are multiple objects that are much better known by their Hickson or Arp number.  Years ago, finding out what these objects are or where they are was a problem unless more common designations were used.  However, today, a quick on-line querry will reveal everything needed about them to find them on any deep star atlas regardless of  how they are identified.  Clear skies to you.



#8 ggalilei

ggalilei

    Apollo

  • *****
  • Posts: 1067
  • Joined: 01 Sep 2011
  • Loc: Kentucky

Posted 17 August 2014 - 07:56 AM

I'll try the "X" with mag-5 stars to locate NGC6543, that should help. Thanks David,

Tonino.

P.S. In retrospect, my Dob was not quite well collimated that night.








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics