Understanding Nebulae - what it is you are looking at.

[mental4astro]

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/image_tours/33-emission-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.

[mental4astro]

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... :sadeyes:

[Karlzburg]

I'm blind :lol: good write up Alex. Your sketches are amazing in detail

[xelasnave]

Wonderful posts Alex...you are the man.
Alex

[cubancigarman]

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)

[mental4astro]

G'day Roger!

:welcome: 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.

[mental4astro]

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! :D

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!!! :mad2: 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! :lol: 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! :D

Alex.

[Outcast]

This is awesome stuff Alex, thankyou for sharing.

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

Regards

Carlton

[croweater]

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 :)

[mental4astro]

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.

[iborg]

Hi Alex,



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


Philip

[Madanie7]

Really enjoyed this. Thanks for posting

[PCH]

Hi Alex,

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

Are you still making your telescopes?

[mental4astro]

I'm glad that this thread I started is being found helpful.

Paul, yes I am.

[mental4astro]

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.

[Nikolas]

This is a fantastic thread, thanks for all the information Alex great reading

[cubancigarman]

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

[mental4astro]

Filters...

Here I will again let an established site do some of the heavy lifting for me. There is no need for me to attempt to redo what has been well prepared by others as to what filters are best for what objects.

Guide to nebula and colour filters for astronomy (https://www.myastroshop.com.au/guides/filters.asp)

However, what I will do is offer some advice on how to select filters so that you make a better informed purchase.

There are four main nebula filters. Three of these, OIII, UHC, H Beta, are better suited to larger apertures. This is because they depend on a large aperture in order to make the transmitted light suitably strong enough to see. This is even more critical for the H Beta which is a very aggressive filter. These filters will perform BEST in apertures over 5", with the H Beta best over 10" it is so aggressive.

If your scope is 6" or below (no, I didn't make a mistake with the 6"), you may want to use a less aggressive filter, commonly known as a Broadband or Light Pollution Filter. These won't dim the overall image so much, but this also means that the contrast between nebulosity and surrounds won't be as stark. This is the tradeoff between the smaller aperture and wanting to more clearly see nebulosity.

There is a fifth type of filter. Narrowband filters can be expensive, and to purchase two or more even more so. One innovative company has produced a hybrid filter that combines the OIII and H Beta light bands in the one Hybrid filter. Omega Optical manufactures astronomical filters not just for themselves and its various subsidurary companies, but for some other high profile brands. Having all this sophisticated gear has also meant that they can fiddle around with innovative ideas, and produce very unique niche products. Their OIII + H Beta filter is one such product, and they provide it in both 1.25" and 2".

1.25": 1.25" OIII & Hb filter (https://www.ebay.com/itm/Filter-486-Astronomy-Hb-OIII-Nebula-II-28mm-1-25/311638720617?_trkparms=aid%3D222007 %26algo%3DSIM.MBE%26ao%3D1%26asc%3D 20131231084308%26meid%3D42272445db0 f4f949cd513ccc5d93687%26pid%3D10001 0%26rk%3D3%26rkt%3D7%26sd%3D3116537 32549%26itm%3D311638720617&_trksid=p2047675.c100010.m2109)

2": 2" OIII & Hb filter (https://www.ebay.com/itm/Filter-486-Astronomy-Hb-OIII-Nebula-II-48mm-2/311653732549?hash=item48900290c5:g: dWEAAOxyjPNREMZz)

This filter is not as aggressive as dedicated OIII or UHC or Hbeta filters, but these really are a great compromise filter if $$$ need to be watched. Being less aggressive, it is probably a better option to a Light Pollution Filter. I have one of these, and I've managed to see the Horsehead Nebula with it too. But remember, the Horsehead Nebula is NOTORIOUSLY difficult to see, and it DOES require an aperture LARGER than 10" in order to have any chance of seeing it, AND a very & transparent dark sky.

I'll talk about colour filters when I start a thread about viewing the Moon and Planets.

Alex.

[PSALM19.1]

:eyepop: What a smashing post, Alex! I've recently decided to go DSO hunting so your work here is inspirational ol' chap :)

[mental4astro]

Thanks Shaun! :)

One note about nebula filters - They will not work with galaxies! in the same way as they do with nebulae.

Galaxies, like stars, glow across the entire spectrum. As a percentage of their total light output, the OIII and Hydrogen spectrums form bugger all, and so using these filters with galaxies will only kill them stone dead.

HOWEVER (there's always a "but"...), if your scope is BIG, over 14" in aperture, with a handful of galaxies the OIII and UHC filters are useful in showing up the BIG HII regions in some galaxies.

Two galaxies in particular are prime targets for this, M33 and M83. These two large face-on spiral galaxies have enormous glowing Hydrogen gas regions within their arms. A nebula filter can help reveal these strings of enormous star forming regions within these distant island universes. But, spotting these is an huge test on the quality of transparency of your DARK sky. Poor transparency will kill any attempt at seeing these difficult-to-spot regions, and poor transparency will also kill attempts to see galaxies at all. Maximizing your chances at seeing galaxies, nebulae and other DSO's is not just about "going bush", but the location where you set up is also vitally important. But this is another topic altogether.

I've so far made just one attempt as trying to see these regions in M83, but the location I was at, despite being dark, is plagued by poor transparency. I had no chance at seeing these Hydrogen regions despite the 17.5" scope I was using. I haven't given up and I now use another site that has much better transparency, and despite it being closer to Sydney, its location is such that the sky quality here makes the other site look like a foggy cemetery. The season for tackling M33 has started, so I'll be having a crack at it too. The Large Magellanic Cloud and Small Magellanic Cloud also have extensive glowing Hydrogen regions that benefit from using a nebula filter to search them out. M31, the Andromeda Galaxy, does not have vast enough Hydrogen regions to make them stand out with a nebula filter. Wait a billion years or two when our Milky Way galaxy and M31 begin their merry gravitational dance into merging, and then massive star forming regions will be triggered within M31!

I've mentioned galaxies here for two reasons: one they are not targets to try out nebula filters with; and two, that there IS a place for nebula filters with galaxies in trying to spot nebulous regions within them - you are NOT making the galaxies stand out here, just those glowing Hydrogen regions.

Alex.

[75BC]

Enjoy reading these observing lessons Alex.

I have a question or 2 about filters for nebulae. I have a cheap Kson 2” UHC filter that serves my purpose just fine. Only used it a couple of times so far but do they all give a colour tinge to what you’re observing as this one does?

A new shopping centre has been built about 1km from my house – getting bigger by the week – and they have installed those nice bright LED lights in the carpark that has noticeably brightened the sky from my backyard. Do I understand correctly that my filter will not be able to block this light as it is a full spectrum type of light being emitted?

Thanks in advance and looking forward to the upcoming planetary lesson as they are a favorite target for me. :thumbsup:

[mental4astro]

Hi Brendon,

Colour that you are seeing is no mistake. Two factors at play here, one is your eyes and their capacity to make out colours at low levels of light, and two is the actual colour/colours that these filters transmit. The light they transmit is not white. It is in the red and greenish range.

If you see an intense red red around individual stars this is an artifact of the way filters are produced transmitting internal reflections. Most obvious with brighter stars. A clue to their filter origin is this colour is too deep and intense, where actual red stars are more orange in appearance.

With respect to LED lights, what "light pollution filters" do is center their wavelength absorption around those of mercury vapour and sodium lights - older technology street lights. These broadband light pollution filters will still work, however their effectiveness is reduced because these LED lights transmit across the whole spectrum, as you said. Narrow band filters, OIII & UHC are less affected as they are more aggressive, but their effectiveness is still reduced in the Big Smoke.

It then becomes a balancing act between the light pollution vs aperture and filter you are using. While aperture is King, in the Big Smoke smaller apertures are the Knight in Shining Armour! ;) Telescopes collect light, and hence light pollution too. Me, from my home in Sydney I now never set up my 17.5", instead limit my aperture to no more than 8".

There's also another issue with Bigger Apertures - they are also more sensitive to the prevailing seeing conditions of the night. Particularly if you are maxing out the magnification. Dropping the aperture sometimes means the difference between a productive session or a night of frustration...

My last dark sky session, seeing was abysmal. Two of my mates had their 18" dobs, but I only took my 8" f/4 dobbie. They had a crap of a time as even their lowest magnification was too much for the conditions. Yet I was only doing low power wide field observing and the image I had was sensational! :D :D

For those of you not aware of this, ripping the maximum amount of magnification out of your scope is not the best use of any scope. There's a lot of factors at play, seeing (atmospheric stability), transparency (clarity of the sky, humidity, fog, smoke, etc), aperture size, object size andx brilliance. And it takes a bit of time to understand ho w they all come together to play nice or give you grief! :lol:

Alex.

[75BC]

Thanks Alex. Learning so much here and realizing I still have a lot to learn.
Even things that can seem obvious once you know such as why everything looked green through the filter I use.

Must be a common newbie mistake of cranking up the magnification but it took me a long time to learn, use less – see more. On planets this (eventually) became obvious. A bigger image does not equal more detail.

[stevous67]

Visual astronomy can really bore me, but this was great to read. :thumbsup: Thanks for the huge effort! :bowdown:

Regards

Steve

[mental4astro]

Thanks Brendon and Steve :)

I'm glad to read that you have found my work useful.

It occurred to me a few years back that there must be hundreds, if not thousands, of scopes sitting in boxes that haven't been used in years, and only pulled out of their boxes just two or three times because of the unrealistic expectations that people had, in not knowing how to handle their scope, not knowing about how seeing affects things, and impatience.

I've also rescued a couple of scopes from the Big Rubbish Council Cleanups, fixed them up, made a new dobbie mount for them and found new homes for these scopes that were on death row. I just couldn't bear the thought of just letting perfectly good scopes, however modest, be trashed. These little scopes have seen more use now than they ever did :)

Alex.

[mental4astro]

In my Observing the Moon & planets (http://www.iceinspace.com.au/forum/showthread.php?goto=newpost&t=170511) thread, I've provided a series of Challenges. I thought I'd do something similar here with this thread, but more along the lines of a theme than a Challenge. This is mainly because of the wide variety of apertures that scopes come in so I don't want to create a set of challenges that immediately excludes small scopes. Instead, it will be a series of themes with (I'm hoping) two or three different objects that will be as both examples, but also offer a range of difficulty so to test your visual acuity and yes your scope/aperture - some level of challenge is a good thing!

Theme No. 1

Dark pillars

1, The Fish Mouth in M42: With Orion making its way back into our evening sky, the easiest Dark Pillar to see is an excellent way to start out!

The "Fish Mouth" is the name of this dark pillar. It is seen as a dark "finger" that points towards the Trapezium. The Fish Mouth is held together by a bunch of protostars that are hidden deep withing this column of gas and dust, and the collective gravitational pull of these protostars is resisting the erosive power of the enormous energy blast that comes from the Trapezium. The Fish Mouth is not a dumb black lump either. It is very much a 3D cylindrical shape, and if your scope and eyes are up to the task it is possible to see the variation in shading that the Fish Mouth has.

Another great thing about the Fish Mouth is it can be easily seen under urban skies!

1A, The Trapezium. While we are looking at the Fish Mouth, lets look at the Trapezium - this pocket sized dynamo packs a real punch not just in terms of power output, but there are many more than just four stars that make up this small open cluster. Four stars are easily visible even in a 2" scope. 6 stars are visible in larger scopes from 4". Here's the real kicker - push your aperture to 14" and over, and you will be able pick out at least 10 component stars!

2, Eta Carina's skeletal fingers: In the very first post I made in starting this thread, both the NASA Tour and my sketches, show the skeletal-like fingers that are a couple of dark pillars in this huge nebula. These dark pillars are visible in scopes larger than 4", and if you are under urban skies they are JUST visible without any filters in an 8" scope. Under dark skies, these are easier to identify.

3, The Pillars of Creation of M16: Ok, this one is for BIG scopes! The dark pillars that form the Pillars of Creation, also known as the Eagle that gives the Eagle Nebula its name, is a real challenge to see. Aperture is one, but also good transparency is necessary. If transparency is not up to scratch, you will see the glowing mass that is this nebula, but the dark pillars will not be distinguishable. The night I first saw these I saw them through my 17.5" scope. Later on that same night I had a look at it through a 25" scope, and the pillars were totally invisible all because in the hour between my last view of them in my scope and looking through my friend's scope, the transparency of the sky went to pot!

I think this is a good start to this series of observation themes. If there is any theme or object you would like me to offer, please just ask! :D

[gjr80]

Thanks Alex, looking forward to running through this theme, but you do realise this is the equivalent of buying new equipment, I am now doomed to days (nights) of cloud...


Gary

[mental4astro]

Theme No. 2

Nebulous Extensions

This might seem like an odd theme, but it brings into play a whole bunch of ideas that have been discussed here: the human eye, experience, sky conditions and filters.

If you don't have any nebula filters, don't despair! These are not mandatory. Helpful, sure, but not mandatory.

First a little background as to why I've come up with this theme, and it will then make much more sense.
While I was thinking about what theme to offer, I looked at the picture I posted Thor's Helmet, and it reminded me of the two very important experiences I had with it - my first and second views of it. And this in turn what I've also come to learn with using my scopes, and why I don't use a tracking scope when I do any DSO observing.

What Thor's Helmet taught me about the sky - I first saw Thor's Helmet at the IIS Astro Camp some 6 years ago. I didn't know about it, and it was suggested to me as a target by a fellow Camper. And when I saw it through my 17.5" dob I thought it was freaking AWESOME!

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Well, it was a great first time view, but what I did not know was how the site we were using for the camp was crushing the quality of our sky - in a lush valley in the middle of agricultural/dairy country. A couple of years later I revisited Thor's Helmet from the Blue Mountains west of Sydney. The conditions here were totally different - on top of a bone-dry sandstone ridge 1000m above sea level. What the difference in location and the sky conditions it provided just blew my socks off when I looked at Thor's Helmet once again with the same scope.

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What also influenced my view was how I used my scope. I was now aware that our eyes quickly lose their sensitivity at low levels of illumination, and that they need to be tricked up again to restore their maximum sensitivity, and this needs to be done constantly. And this is done by my constant nudge-nudge-nudging of my push-to scopes. A static image provided by a tracking scope will not provide this physiological trigger to refresh our eyes. So if you are using a tracking scope, YOU NEED TO PROVIDE THIS REFRESH MECHANISM by constantly tapping the side of the scope to induce a damn good vibration!

And the difference this will make will blow your socks off too! It really will now that you are aware of what doing this does to your eyes, either the constant nudge-nudge or the strong tap of the scope! Those oh-so-faint extensions of a nebula will all of a sudden just keep on going and extending!

There's a bunch of great nebulae that have fantastic extensions that at first glance just don't stand out, and if you rush you just won't see, and you don't need a 17.5" scope either! Sometimes a smaller aperture is a better bet too. Now, if you are already familiar with the objects listed below, do revisit them now that you are armed with new insight on how to best exploit your eyes and scope. And BE PATIENT! DAMN IT!!!

* NGC 2359 - Thor's Helmet - well of course... :rolleyes:

* M42 - The Orion Nebula

* NGC 3372 - Eta Carina Nebula

* The LMC - not a nebula, but a galaxy, and a face-on spiral galaxy whose two faint arms can be traced with fast f/ratio scopes and dropping the magnification as low as possible/practical. The first pic below shows how the arms are orientated in the sky when you look up at the LMC. The second pic is my sketch of it using a 4" f/5 refractor so the image is flipped left-to-right. The LMC is an amazing task-master that is all too often ignored, and it hides it true treasure in plain sight from impatient eyes! And the third image is a close up of that sketch which was done on an A1 size sheet of paper - a BIG sketch!

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* M17 - the Swan Nebula, a winter nebula

* M8 - the Lagoon Nebula, also a winter nebula

* NGC 3576 - the Statue of Liberty Nebula. This one is really difficult unless you are using a BIG scope, say 12" and BIGGER. You NEED to be particularly patient with this small but oh-so-intricate nebula in order to really get to see its full extent, which is enormous really! Below is my sketch of it from a site with poor transparency. I can't wait to revisit it from the Blue Mountains site I use. Can't see the Statue of Liberty here? Do a google search for it! :)

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~x.X.x~

What all of the above require is PATIENCE! It is the only way that you will actually get the most out of the object, your scope & your eyes. Rush, and you will only cheat yourself. The reward comes from slowing down, understanding the way our eyes work, and using your scope in such a way that it will work best for your HUMAN eyes.

I mentioned earlier a little about site selection. It is something that next to no amateur astronomers ever give more than just finding an open grassy field. But the truth is that open grassy field is actually the worst that we can use for astro!!! If you would like to read more on how to find the best site for astro, have a read of the article I wrote on the subject:

Selecting A Site For Astronomy Purposes (http://alexanderastrosketching.blogspot.co m/p/selecting.html)

This is a topic all of its own. I had submitted the above article for inclusion here in the Articles section of IIS, but nothing came of it. That's why the link to my own blog.


Happy, and patient, hunting!

Alex.

[mental4astro]

Nebula Challenge No. 1

The Homunculus Nebula

The massive nebula complex of Eta Carina gets its name from the star Eta Carina. As I mentioned earlier, this star is in its death throes. Having exhausted its fuel, it is in its final stage of its existence as it struggles to maintain that fine balance between the energy output and its massive gravitational pull upon itself. In a way, it is having fits and spasms as this supermassive star stuggles to keep itself going. And eventually, the energy output of the core won't be able to resist the massive crush of the main body of the star, the star will then collapse on itself, and this monumental implosion will result in one almighty supernova explosion.

But for all this drama, what is most fascinating about the star Eta Carina is this very pre-supernova stage that it is currently in. These jitters and spasms at one time saw Eta Carina as the second brightest star in the sky around 150 years ago - which most likely wasn't Eta Carina itself throwing this massive wobbly, but its invisible binary companion that had its own fit of blowing material it has absorbed from its supermassive parent. The material that's been ejected by Eta Carina we can actually see through even modest scopes. AND then, the complex gravitational and magnetic interplay between these two stars has sculpted this cocoon into a most gorgeous bipolar nebula - the Homunculus Nebula.

For all the terrifying violence happening with this supermassive star, the Homunculus itself is only a very small structure within the giant Eta Carina Nebula complex. It is no larger than Saturn through a scope. But its delicate double-lobe structure can be seen even in small scopes. When you first look at Eta Carina, you will first notice its distinct red colour. You will then notice that it is somehow fuzzy, curiously "resisting" to come to focus. But this is because of the influence wee bipolar nebula.

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The Challenge

This is one challenge that will test your visual acuity, your patience, your scope, seeing and transparency, and depending on your scope the need for a dark sky or an urban sky this is possible.

As the Homunculus is a small sucker, you will need to ramp up the magnification, and thankfully it takes magnification very well. How much magnification depends on your aperture.

The first part of this challenge is to identify the two lobes. You will see one love quite clearly, the one that points more towards us. The second lobe points away, and it is a little dimmer. The lobes themselves show a fine, very delicate, almost filigree structures within them. Identifying the individual lobes and their striated structure is the first part of this Challenge.

The second part is identifying the most illusive and yet striking third structure of the Homunculus - the skirt of material that fans out between the two lobes, somewhat like a ballerina's tutu. It was the unexpected spotting of this skirt just last week that not only left me gasping with amazement, but is also the inspiration for this challenge. This skirt I had only ever seen in Hubble photos of the Homunculus, and never, EVER expected that this skirt was even a visual possibility! Yet there it was, plain as day!

Note that the skirt is a most illusive structure. While seeing the two lobes is relatively easy, the skirt is another matter altogether. Seeing conditions, transparency, visual acuity, scope quality, all coming into play.

I saw it through a 10" scope from an apartment block rooftop from inner Sydney. I didn't have my sketching materials with me as I wasn't expecting to see anything so breathtaking. I'm glad that I didn't have them either as I would not have been able to reproduce the Homunculus with the necessary colour.

However, this vista was the necessary inspiration for me to raid my other kit of soft pastels to have a practice at reproducing what I saw through the eyepiece. The sketch below is the test piece I did, attempting to emulate the various structures and colours that I saw, including the skirt.

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Happy hunting!

~x.X.x~

This test sketch also gives an insight to how I work. I often practice my sketch technique, not only to keep in touch with it, but to experiment with new ideas and trying different techniques and also following up inspirations that have pricked my attention and curiosity. These inspirations can be anything, from cloud formations to the drawing done by a little kid, and then trying to work out how to adopt that effect into my sketching repertoire. Trying these things out at the eyepiece is neither the best place nor where to experiment - the eyepiece is where you need to be confident with your technique, and concentrate wholly on the task at hand.

Alex.

EDIT: I've reloaded the sketch pictures because for some reason they didn't show up in the first instance.

Alex.

[Wavytone]

Alex that third sketch is pretty much how it appeared on Saturday night at Blackheath, at 300X... maybe a bit more pinched in on either side.

[Joves]

Inspiring post, Alex. Thanks for taking the time to write it.