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  #1  
Old 06-09-2018, 09:17 PM
mental4astro (Alexander)
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Understanding Nebulae - what it is you are looking at.

Nebulae can be beautiful stellar nurseries or the remnant ashes of a dying or dead star. In photographs they can also exhibit various colours, but mostly blue and red. And they can also exhibit a multitude of shapes and shades, from brilliant and colourful to dark and foreboding. Despite their many differences, what they all share is the forces of physics at play that form and mould them.

But what does it all mean?

One easy thing about understanding what you are looking at is you don’t need to have a degree in astrophysics, nor be a mathematics whizz. The concepts at play here are actually surprisingly easy to follow, and once you have the basic concepts figured out, then no matter what nebula you look at, you will be able to figure out what is going on with that nebula.

However, here I will let NASA do the heavy lifting for me in explaining nebulae! There is one NASA site that discusses the Eta Carina nebula using the images gathered of it by the Hubble Space Telescope. This Tour of Eta Carina will show you the structures and anatomy of a nebula, and by the end of the tour you will be able to recognise the various components and the forces at play. The greatest part of this is you will be able to use this knowledge with any other nebula you then look at.

What is especially good about this Tour is that the items being shown are ALL visible through amateur telescopes, depending on how large the telescope is, the bigger the aperture, the more details you will see. Yet even a modest 50mm telescope will reveal a lot that is mentioned in this NASA tour of the Eta Carina Nebula:

http://hubblesite.org/video/880/imag...ission-nebulae

BUT FIRST! Look at these sketches to prime you for your tour.

To help you along with your learning experience, below are two sketches I have done of the Eta Carina Nebula. Both were done from my home in Sydney. The first using an 8” scope, and the second a 17.5” scope. Please look at these pictures before you visit the NASA site. Then, AFTER completing the Tour, look at the sketches of mine again with your newly gained knowledge, and all of a sudden you will see so much more detail in the sketches that previously you had no idea what you were looking at! Two cosmic bubbles that have two different sources, dark pillars that resist erosion and hide protostars, brand new stars that have just kicked off their nuclear fires, glowing gas that is charged by the intense radiation of enormous stars, a myriad of details that are always on show, but hide from view only because of not understanding what you are looking at.

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Now, having armed yourself with a new understanding of what nebulae show in their appearance, you will now be able to identify these same characteristics in other nebulae. At little further education to some other nebula types, such as Super Nova Remnants (the glowing crap left over after a supergiant star explodes) and Planetary Nebulae (the glowing shell of material blown off by smaller stars that are dying (the way our own Sun will end)), yet they all show elements and features seen in the Eta Carina Nebula.


I have deliberately chosen to illustrate this whole document with my sketches in order to demonstrate that the features shown in that tour of Eta Carina are not invisible through a telescope, and very much within visual reach. And by all means, look up photographs of the items below and see for yourself that the view through a telescope can reveal a hell of a lot!

M16, the Eagle Nebula:
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M42, the Orion Nebula:
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The Veil nebula
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Thor's Helmet:
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The Helix Nebula:
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Thanks for looking,

Alex.

Last edited by mental4astro; 07-09-2018 at 09:11 AM. Reason: typo
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  #2  
Old 06-09-2018, 10:30 PM
mental4astro (Alexander)
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Why can't I see colour through my telescope?

We have all seen those marvelous and colourful photographs from the Hubble Space Telescope and in the imaging fora here in IIS. Yet when we look through our telescopes, NONE of those brilliant colours are visible!

What the heck is going on???

There are two categories of reasons why:

The primary reason is human eye physiology. Our eyes while exceptional at seeing detail and colour under brilliant light, in the dim light that we do our astro, our human eyes are very poor. The resulting image is a "default" one of black and white. In dim illumination, our colour sensitive cones are not fired up enough to trigger a response. The rods in our eyes are able to be fired, but the image they produce is essentially a black and white one.

However, colour can be seen in some deep sky objects, and namely nebulae, but the variety of colours and their brilliance has a lot of "depends" reasons. And these reasons are why some people can see colours in these DSOs, yet other people see no colours what so ever.

The secondary reason for colour perception:

* Gender: 1/3 of all males have some degree of colour blindness, from oh-so-slight through to no colour perception at all (very rare). Yet colour blindness is rare in females.

* Age: Colour perception at low levels of illumination can change with age. I can atest to this! When I got my 17.5" scope about 8 years ago, the very first object I looked at was M42, the Orion nebula, I was able to see pinks, blues and greens in it! Yet today, same scope, and even better eyepieces, yet I have lost those lovely pinks, and the blues and greens are much less vibrant. Yet there are some lucky individuals whose colour perception doesn't change. <sigh>

* Health: Whole of body health can affect eye health and vision. Diabetes, smoking, excessive alcohol consumption, drugs (perscribed or illicit), and a myriad of other health complications can all work against not only colour perception, but also visual acuity.

* Genetics: One card we have no control over, and have mum and dad to thank for. There are some genetically inherited traits that mean some individuals have exceptional low light colour pereption, yet others struggle to see much at all little lone colour.

And of course, the whole lot of the above varies between individuals!

But all is not lost!

So, if at first you don't see colour, be patient. Looking through a telescope is a very different experience that our "daylight" accustomed eyes are used to. It takes a little time to re-train your eyes to see under these unique conditions. One part of this re-training process is to use "averted vision" in order to maximize detail perception. I'll elaborate a little more on averted vision in a following post here.

DON'T RUSH! Take your time, and be calm at the eyepiece, and you will allow your eyes to adapt. Rush, and you are only cheating yourself.

Do these things, and if you are one of the fortunate individuals with good low light colour perception, and you will be rewarded. There are not very many objects that do show us colour through the telescope, so if you cannot see colour, don't be disappointed. Heck, I've lost my ability to see those vivid colours in M42...

Last edited by mental4astro; 08-09-2018 at 10:12 PM. Reason: typo
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  #3  
Old 06-09-2018, 11:56 PM
Karlzburg (Karl)
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I'm blind good write up Alex. Your sketches are amazing in detail
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  #4  
Old 07-09-2018, 10:51 AM
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Wonderful posts Alex...you are the man.
Alex
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Old 07-09-2018, 12:14 PM
cubancigarman (Roger)
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this is excellent for newbies like me, thank you!

question, what eyepiece would you recommend using for observing these nebula? (mind you i only have a 25mm and 8mm)
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  #6  
Old 07-09-2018, 12:34 PM
mental4astro (Alexander)
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G'day Roger!

to IIS!

I suggest you start with the 25mm. It will concentrate the image and will give a wider field of view and allow for a larger overview of the object. Of course, this depends on the size of the nebula, but start with the 25mm, then switch to the 8mm as it will help darken the background and help with contrast, but the trade-off is a smaller field of view due to the magnification.

Something like a small planetary nebula a 25mm EP won't help you very much, but it can help make it stand out so you can identify it. You can then switch to the 8mm.

What scope do you have? Also, from where are you doing most of your observing - urban skies or dark?

Have you had the opportunity to spot the Lagoon Nebula (M8) and the Triffid (M20)? Both are very close to each other, and pretty much dead overhead at this time of year. M8 is better with the 25mm, and as M20 is smaller, it does well in the 8mm. But try both eyepieces and see how each nebula responds through each EP. Don't be affraid to switch between EPs no matter what you are looking at!

Alex and Karl, thanks you for your kind words

Alex.

Alex.
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  #7  
Old 08-09-2018, 09:12 PM
mental4astro (Alexander)
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Getting the MOST out of your HUMAN eyes

Ok, we now know that our eyes are not the best at low levels of light. But, did you know that our eyes also have different areas that are more and less sensitive in low levels of light? That the less sensitive area to light holds both the greatest number of colour receptors and is also where we see things with the greatest detail - central vision. That the area that is most sensitive at low levels of light is also the area where less detail is seen - peripheral vision. AND that there is a sweet-spot between these two areas of our vision where we get both detail and light sensitivity!

This sweet-spot around our central vision is the area that we as observers need to use to maximize our capability at the eyepiece.

Here's an everyday example to demonstrate what I'm talking about. You are in your bedroom at night with all the lights off. Only a feeble light is visible illuminating the room. Have you noticed that when you look around the room in the dark, when you look directly at something that it somehow "disappears", but as soon as you look away to one side of that thing it somehow "reappears"!? The good news is two fold - 1, you are not going mad - it's how our eyes actually do work; 2, it is this very feature of our eyes that we use at the eyepiece!

Looking at things this way, just to the side and not directly, is called AVERTED VISION. It is using that sweet-spot area around our central vision where there is a rich mix of both rods and cones as the central vision transitions to our peripheral vision. It is this area where there is that all important low light area of our vision where we get both detail AND low light sensitivity.

THIS is the one trick to maximizing our experience at the eyepiece!

Do not look directly at the object, but just to one side of it!

The good thing about using AVERTED VISION is it takes only an instant to learn, and only moments to master! You've been using averted vision all your life in dark rooms/environments, and you've never been aware of it!

Below is a little example of how to utilize averted vision. The object in question is a globular cluster. Our immediate response is to look at it directly. That is fine with this sketch. But through the eyepiece, so see a globular cluster in all its splendor with its many thousands of stars all so clearly visible and individual, you DON'T LOOK AT IT DIRECTLY, but just to one side as indicated by the X. It can be to the left or right of the object, it doesn't matter. It just needs to be just off to one side.

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Tip in locating objects

You may have also noticed another VERY ANNOYING thing when using your scope. When you are trying to find a faint object you are panning the scope from side to side, and you catch a glimpse of something faint and fuzzy out of the corner of your eye, but when you pan the scope back to that faint thing YOU CAN'T FIND THE BLASTED THING!!! This is because you are now using your central vision to spot that faint thing, when it was your peripheral vision - your most light sensitive vision - that spotted that thing.

The solution is an easy one, but a bugger of one to learn - DON'T LOOK FOR THE OBJECT while you pan the scope back!

This is a really easy thing, but a bugger of a trick to remember, and it still catches me out after 35 years of using telescopes! It is also totally counter intuitive to how we use our eyes everyday. But it all has to do with the way our eyes work that I described above. If it was your peripheral vision that spotted that faint thing, then it must be your peripheral vision that needs to be used to reacquire it!

~x.X.x~

I hope these three article specific posts have been helpful to you as you start on your astro experiences. Many people become frustrated with astronomy because they don't understand how our eyes work, how to exploit their strengths, and the unfortunate expectations that the pretty pictures create in our minds. But astro can be a very satisfying experience. Just that as with all things we do, such as walking, driving, playing a sport, it takes time and understanding to make the most of these. Astro is also a quite pursuit, not a "smash'n'grab" one. Like a said earlier, rush things and you will miss things. Slow down, calm your heart, and the Universe will reveal itself to you!

Alex.

PS, The sketching technique I use at the eyepiece was taught to me by the late Scott Mellish. While Scott demonstrated the technique he developed, one thing he said to me was "if you need averted vision to see an element, you should use averted vision to lay it down on the paper". And this was said to me in a very matter of fact way! And the thing is, it works too!

Alex.

Last edited by mental4astro; 08-09-2018 at 10:18 PM. Reason: typo
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  #8  
Old 08-09-2018, 09:21 PM
Outcast (Carlton)
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This is awesome stuff Alex, thankyou for sharing.

Perhaps it could be added as a pinned post for ease of future reference.

Regards

Carlton
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Old 08-09-2018, 09:43 PM
croweater (Richard)
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Great stuff Alex. Really well written. You don't need to be a newbie to get something out of it. Thanks for the effort you put in. Cheers Richard
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  #10  
Old 10-09-2018, 01:06 AM
mental4astro (Alexander)
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Thanks for the comments!

And of course, if you have any questions, I'm only too happy to answer them. The only dumb question is the one that isn't asked. You might have an observing question, an object specific question, how you can further improve how you see things through your scope, could be for further help, telescope specific (all scopes have unique pros and cons), anything. If I have sparked a question from what you have encountered so far, that is good, and ask.

While I try to be comprehensive, I may overlook something, or may not have been too clear in some other.

Using a scope for astro means re-learning how to use your eyes and how to see things. While my eyes are not as "good" as a 17 year old's, my experience makes up for that, and a bit more. And at the same time, my experience can also mean I can forget certain difficulties new comers have, so any questions you may have will also help me improve what I cover when I write pieces like this.

Oh, in just writing the above I've just remembered something else - while Deep Sky Objects have a very specific set of observing requirements, the Moon and Planets have another set all together! And for these, I'll look at starting another thread specific to these.

Alex.
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Old 10-09-2018, 02:21 PM
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iborg (Philip)
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Hi Alex,



Thank you for putting these notes together. Well thought out and written.


Philip
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Old 10-09-2018, 09:48 PM
Madanie7 (Brendan)
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Really enjoyed this. Thanks for posting
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Old 11-09-2018, 09:13 AM
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Hi Alex,

A very enjoyable read thank you, and once again your sketches are amazing.

Are you still making your telescopes?
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Old 11-09-2018, 10:02 AM
mental4astro (Alexander)
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I'm glad that this thread I started is being found helpful.

Paul, yes I am.
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Old 11-09-2018, 10:51 AM
mental4astro (Alexander)
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It is all done with magents...

There is one final part that needs clarifying with nebulae, the odd appearance of most planetary nebulae and some other exotic types that are associated with an odd type of star called Wolf-Rayet stars, and also supermassive stars that are just about to go supernova.

The one an only astro-physics lesson here. I promise!

Single stars like our Sun, are more of an exception than the norm. Most stars are actually in pairs (binary systems), trios (tertiary) and sometimes higher.

This means that several stars can be orbiting around each other. In some cases, some stars are so big that they have smaller stars orbiting around them just like planets!

The closest star to us (apart from the Sun), Alpha Centauri, is a tertiary system. The brightest star in the sky, Sirius, is a binary with a big parent and a wee companion (affectionately known as "The Pup", and being able to separate the pair is a good test of telescope optical quality).

When one of these stars starts to die (usually the larger one first - stars live the rock'n'roll lifestyle!), they throw off their outer layers of their structure, becoming what is called a planetary nebula (PN). However, ALL stars have very strong magnetic fields around them. This magnetic field influences the appearance of the PN - to a point. It is the complex magnetic, orbital and gravitational interplay between the various component stars that then gives rise to the really odd appearance of so many nebulae!

Here endth the lesson...

With the complex interplay between the various component and ACTIVE stars, the expanding shell/shells of glowing gas and material is then rearranged into some very curious and beautiful shapes and forms.

The Helix nebula has a massive spiral-like structure:

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The Spiral Galaxy Nebula in the constellation Musca resembles a barred spiral galaxy:

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Thor's Helmet surrounds one of these Wolf-Rayet stars:

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The Homunculous Nebula is created by the interplay of the pre-supernova parent star shedding material and then formed with the interplay of the parent star's massive magnetic field and with the much smaller and invisible binary companion. It is invisible because it lies deep inside the nebula and orbits very close to the parent star:

NASA image
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Alex.

Last edited by mental4astro; 15-09-2018 at 11:59 AM. Reason: Typo
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Old 12-09-2018, 09:19 AM
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This is a fantastic thread, thanks for all the information Alex great reading
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  #17  
Old 15-09-2018, 11:22 AM
cubancigarman (Roger)
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Quote:
Originally Posted by mental4astro View Post
G'day Roger!

to IIS!

I suggest you start with the 25mm.
Something like a small planetary nebula a 25mm EP won't help you very much, but it can help make it stand out so you can identify it. You can then switch to the 8mm.

What scope do you have? Also, from where are you doing most of your observing - urban skies or dark?

Alex.
I have an 6SE and its been a blast. I will check out your recommendations. Thank you!!!!!
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