John's Astronomy Pages

You could see it previous nights' images so I had to select it for a target tonight.  Main emphasis here is on what appears to be a giant flame in the sky. Of course it is not alight. It is part of the Orion Giant Molecular Cloud region and is an emission nebula. Light from Alnitak is energising the atoms within and causing the electron to become exited. Most of the appearance actually comes when these electrons re-combine with molecular hydrogen. There is a big dust lane across the front.

I have doctored this picture a little by reducing the size of the bright star Alnitak. This is a common procedure in astro photographs where a subject would otherwise saturate the image. The smaller star is from a shorter duration frame that is patched in using graphical editing software..

It seems I am becoming a collector within my hobby as I now own another telescope.  This one is a self build from components bought individually on Ebay.  It is an 80mm APO refractor, i.e. smaller but higher quality than the 6 inch refractor I already own.  I have assembled a lens made of Japanese FL-53 (the best), tube with baffles, 2 inch Crayford Focuser, Mount rings and Dovetail bar.  It is little over half a metre in length and quite lightweight and would classify as a "grab-and-go" telescope.  Focal Length is 600mm (distance from primary lens to point of focus) and Focal ratio is F/7.5 which is medium speed.  Original intention was to build a guide scope which this will indeed perform  but also produces cracking good pictures of it's own!

Tonight I am going to be very ambitious.  I'm going to test it on the beloved Horsehead Nebula.  This is very close to the bright star Alnitak, in Orion's belt, and as we know such a star would soon saturate and test a refractors optics. Here is a single 10 minute self guided exposure with the Starlight MX7C single shot colour camera.

Indeed Alnitak did saturate as expected but there is nothing like the blue halos being experienced by the 6 inch scope.  Not only do we have the (bloated) star Alnitak but also we can spot the Horesehead nebula as well as the Flame nebula below the primary star.  Alot of information in this one picture.

 

 

So let's reposition the scope and aim directly at the Horesehead aiming to get Alnitak out of the field of view.

Here is the result of stacking 6 shots of 10 minutes each. The stars are nice and round (good tracking) and the colours are good too. Only problem is with shadows of (probably) dust motes on the lens. I can remove these by way of sky flats.  These are images of an evenly illuminated background, in my case I use the sky as it brightens in the morning!  However I wasn't aiming to stay up this late to obtain said flats.

 

Indeed I turned my attention to another object as the night was still young, only 2am.

The night is still young and although Orion is heading west Leo is lining up towards the south.  This is constellation with several bright galaxies.  The 80mm APO I am using has a reasonably large field of view and can capture three of these galaxies in a single frame.  This is quite a common group of galaxies for Astro-photographers and hence the name Leo Triplet.

 

Another small problem is showing up.  Hot pixels. Nearly every CCD camera has a few (or many) hot pixels that show up as one of the primary colours (red, blue or green).  Now I am getting a bit too clever for my boots as my tracking skills are improving.  Problem now is that a hot pixel will appear in each stub at the same place.  With accurate guiding the target is in the same place on each frame and hence so are the hot pixels.  Taking an average of many frames will not remove such hot pixels.  The technique is to use dithering.  This means the camera must be very slightly shifted between frames.  When the images are aligned on the target the hot pixels will be in a different place each time and will thus have little or no consequence on the final image when averaged.

So we see it is a continuous learning curve!

The rain has gone, the sky is clear and all looks set for a full night of stargazing. It is always a good sign when the skies clear after some substantial rain. It usually means the air has be cleaned of that interfering dust and gives best chance of dark skies. Tonight I will try my EOS filter which fits inside the Canon DSLR. The features of this filter are to reduce light pollution which comes from things like sodium street lighting, sky glow and moon glow. It does this by filtering frequencies associated with these solution effects, most notably Sodium lighting (orange colour).

 

For the moon I have to reduce the iris in front of the objective lens otherwise it will be much too bright. This also changes the focal ratio from F12 to F22 which is good for a lunar/planetary object. Quite a surprise it has given the image is nice and sharp but it is tinted blue! Now in hindsight that is to be expected as the filter is designed to remove light pollution as well a moon glow!

 

 

 

For the rest of this evenings viewing click here:A-full-night-of-stargazing

Long spells of dull weather between these rare clear nights but it looks like an all-night session tonight. I thought I'd have a bash at M33 the Triangulum galaxy, named because it is in constellation called Triangulum. It is a face-on spiral with low surface brightness. This means one needs some really long exposures to capture it in full glory. I am using my Canon DSLR at prime focus on a 6" achromatic refractor. A feature of refractor telescopes is that red, green and blue light comes to focus at different points from the lens. This means if you focus on green then you may see blue, red or violet fringes around bright stars. An Achromatic refractor goes some was to reducing this effect, known as chromatic aberration by introducing two lenses (doublet). Also the choice of glass, e.g. crown and flint with differing refractive index. More recently a new type of refractor has been introduced called an apochromatic that has the newest and highest quality of glass yet known.  It may also be a triplet lens (three lenses in combination).

Also on the agenda tonight is M45 or the Pleiades and also known as The Seven Sisters. As mentioned before this cluster is a good test of eyesight. Typically 5-7 stars can be seen by the average naked eye. There are in fact at least 500 stars in this cluster. The aim in photographing this cluster is to capture some of the nebulosity that still surrounds some of the stars as they awake from their cocoon. Again long exposure is required but this leads to saturation on the main stars. Here is my best attempt so far but still leaves a level or more to aim for.

 

 

So much for great expectation for clear nights! Must seriously consider moving to the mountains. Only a short period of clear skies expected tonight so let's keep it simple. M31 is a sister galaxy to our Milky Way galaxy and along with some smaller galaxies is known as The Local Group.

M31 is very similar in structure to our galaxy in that both are large spirals. Indeed M31 had alway been considered much the larger of the twins but recent discoveries put our own galaxy possibly 50% lager then previously believed. Not so easy to measure from the inside. For this photo I am using the Canon Rebel/350 DSLR at prime focus. The Canon has a CLS filter that should remove skylight pollution especially from the street lights around my area. This seems to work but it tends to remove so much red that it leaves a blue hue as seen in this image. I was able to bring this more in-line with what I have in the past using a photo editing suite. Still this was an interesting effect which I will use again.

Now is the time dust down the scopes, collimate the lenses and generally get prepared for dark night ahead. End of September now and Outdoor Bowls are in their bag and only the Prize awards to look forward to. So time to turn my attention to Stargazing. Well deep space astronomy is my preferred topic. I tried some early evening shots of M33 Galaxy but quality of seeing was not really good enough to present the results. But during the wee hours of the morning, getting on for 3am now, I could see our beloved Orion Nebula rising. Well this is normally a target in January - February when it is high in the sky towards the south-west. So it was a novelty I couldn't resist now. This photo is using the Starlight Xpress MX7C single shot coloured camera and is the sum of several 5 minute shots. I normally use my DSLR camera on this object but the outcome using the smaller sized but more sensitive camera.

Now looking forward to darker skies.

Full Moon tonight and not much chance of any reasonable deepsky images. So let's turn a hand to capturing the Moon in it's full glory. The Full Moon can be somewhat difficult to image simply because it is too bright! As we are seeing it full on we are not able to appreciate the mountains, valleys and plains. Normally it is best to image when a thin crescent. At this time we can see the separator line, border between day and night, where mountains cast their shadows. It is interesting to note the Moon does not rise so high in the sky during summer. Although this would suggest better viewing of deepsky objects in summer it is countered by the fact we have fewer hours of darkness. Whereas in Winter with the longer hours of darkness the Moon rises so high it is almost daylight at Full Moon. Images of the Moon take a lot of tweaking and invariably always need improved contrast adjustments. This one is not so bad and is a composite of about a dozen images. The Software has a some difficulty auto aligning these and hence were manually aligned before stacking.

Compare this version of Globular Cluster M13 with that taken a few nights ago.  We have much improved focus and colour resolution. This is given it is late July, i.e. middle summer here in the northern hemisphere.

I am getting some practice in with a 6 inch refractor. It is a completely different beast to the 8 inch Cassegrain. Firstly it weighs nearly a ton. Well at least that is the feeling lifting it onto the mount. Not just the weight but also the optical system. Of course it uses lenses rather than mirrors. First impression through the lens was of the moon and notice the field of view is very similar to that of the 8 inch SCT. Visually it compares favourably.

Getting a camera attached proved testing as even when the focuser is fully drawn it could not focus at infinity. Since I didn't have an extender I fitted a 6.3 Focal reducer instead. Here are some results.

Double star Albireo, also known as Beta Cygni, is a favourite for small telescopes and binoculars. To the naked eye it appears as a single star. Under moderate magnification one can identify the two component stars. These two stars are gravitationally bound and about 400 light years away.  

Here is the Globular cluster M13 which is also known as the The Great Cluster in Hercules. Probably the best known globular cluster in the Northern hemisphere.The colours are all wrong here and you can clearly see red/blue halos around some stars. This is an artifact (aberration actually) that plagues early design refractors. It is the result of red and blue light being focused at different points by a glass lens. More study needed here.

Opposite to Globular Cluster here is an Open Cluster.  This is not such a large one and might be hard to recognise as such. At first sight this looks quite a good image but again it is lacking the correct colours.

Overall a pleasing night of subjects and interesting information gleaned from the scope. It is a case of reading up alot on refractors to learn how to improve these images.

Clearskies