Comet meets Globular Cluster

 Comets, General Astronomy, Image Processing  Comments Off on Comet meets Globular Cluster
Dec 042021

Yesterday morning (3rd Dec 2021) Comet C/2021 A1 (Leonard) had a close encounter with the lovely globular cluster called M3. When I say ‘close’ I mean in an apparent way because the comet is in our Solar System and the globular cluster is about 34,000 light years away above the galactic plane!

I took this image with my remote telescope in Spain. It’s quite tricky creating a pretty image of the comet and the starry background at the same time because the comet moved slightly during the 20 minutes it took to capture all the images. This comet was aligned and stacked separately from the stars and then the two images were merged together.

 Posted by at 9:01 am

78.5 hours exposure on M81 and M82

 Deep Sky, Galaxies, General Astronomy, Image Processing  Comments Off on 78.5 hours exposure on M81 and M82
Nov 102021

This is the first image I have posted using data from my new remote telescope setup in Spain and it is, perhaps, the ‘deepest’ image I have ever processed. I have only recently taken over this system after I purchased it from First Light Optics who also kindly bequeathed me all their images taken over the last year or so that the system has been in operation. The images used to make up this image were taken over April and May 2021 when M81 and M82, both in Ursa Major, were higher in the sky. The larger galaxy on the left is M81 – Bode’s Galaxy and the smaller one is M82 – The Cigar Galaxy.

M81 and M82 were both discovered in 1774 by the German astronomer Johann Bode who reported his observation to Charles Messier who then added them to his famous catalogue. Both galaxies are about 12 million light years away (which is 114 million million km or 770,000 times further away than the Sun).

Here is the colour image; click on it to see a bigger version. More details follow the image below:

M81 and M82 in the Integrated Flux Nebula

What else can we see in this image? Directly above M81 is a blue patch – you can see it better in the full sized image. This is a satellite galaxy to M81 called Holmberg IX. This is a dwarf, irregular galaxy and based on the observed age distribution of stars it contains it is thought to have formed within the last 200 million years, making it the youngest nearby galaxy known. This would explain the blue colour as the stars within it will be young and hot.

The faint wisps all around the galaxies are all part of the Integrated Flux Nebula (IFN), so-called because it shines by the total (integrated) light of all the stars in our Milky Way Galaxy. The IFN lies beyond the main body of our galaxy, and is illuminated by the whole thing. It is incredibly faint and only recently discovered in 1984 by the IRAS satellite. To show it better, I have stretched the histogram of the luminance channel of the above image even more. This monochrome image is shown below:

For those interested in the technical details of the image acquisition and processing, the image contains a total of 78.5 hours of exposures made up as follows:

Red Filter112 x 5 minute exposures
Green Filter112 x 5 minute exposures
Blue Filter98 x 5 minute exposures
Luminance Filter287 x 5 minute exposures
H-Alpha Filter83 x 20 minute exposures

The above table shows the actual number of exposures that were used in the integration to make the final image. Many more were rejected because of satellite or plane trails, or thin cloud etc (for example 73 of 360 L images were rejected). All images were calibrated with bias, dark and flat frames and all processing was performed in the amazing PixInsight software.

 Posted by at 11:37 am

The Heart Nebula revisited

 Deep Sky, Image Processing  Comments Off on The Heart Nebula revisited
Nov 062021

A few posts back, I showed a narrowband image of IC 1805 – The Heart Nebula taken during the full Moon. It looked rather pink as the H-Alpha signal is so dominant and overpowers any greens and blues that the OIII signal might provide. Here’s a new, differently processed, version (note: I’ve also flipped it so that the heart is the right way up!). Read below to find out what I did differently.

Using the amazing PixInsight software, I split the R, G and B channels apart. This meant that the resulting red channel contained just the H-alpha signal, but the green and blue channels shared the signal from the OIII emissions. I then made a new O channel by combining the green and blue channels using a formula of (2*G + B)/3 which gave a bias towards the better image I saw in the green.

Calling the red ‘H’ and the new combine green and blue ‘O’, I stretched their histograms, but also used a range mask on the O to stretch it much more (the mask prevented the background from becoming too noisy). This was the key to getting more blue in the resulting image. Then I recombined using HHOO to correspond to LRGB. Now you know why these are called false colour images!. However, all the data is real, it’s just a personal preference.

I think the result has a more 3D effect.

 Posted by at 3:15 pm

The Orion Nebula and the Horse Head

 Deep Sky, Image Processing  Comments Off on The Orion Nebula and the Horse Head
Nov 052021

The Great Orion Nebula (M42) and the nearby Horse Head Nebula (IC 432) are amongst the most photographed objects in the deep-sky. Of all the images I have taken of these beautiful nebulae, this is my favourite because it encompasses both of them in a single wide image, but still has enough resolution to show the intricate details and also the darker dust clouds in the Orion Molecular Cloud Complex.

Click on the image below to see a bigger version.

I took this image in January 2016 whilst Sue and I were renting a rural house in Southern Spain for the Winter months. The skies were lovely and dark at the house which was in the Cabo de Gata region of Andalusia.

More remarkably, I used a non-cooled DSLR camera in the form of my modified Canon 6D. Modified means that the filter that blocks the deep red part of the spectrum has been removed which makes the camera more sensitive to the Hydrogen Alpha emissions in these nebulae. Astronomers call this a filterectomy!

I took 60 x 4 minute exposures and then 30 or so shorter exposures of 30 and 15 seconds for the brighter core of M42. The shorter exposures where blended in to the rest of the longer, deeper exposures making this image and example of an High Dynamic Range (HDR) image. Without blending in the shorter exposures, the core would appear completely blown out and the finer structures would have been lost.

All processing was performed in PixInsight, including the initial calibration using bias, dark and flat frames.

 Posted by at 1:34 pm
Oct 222021

Following on from my last post with the Andromeda Galaxy, here is another beautiful galaxy which is also part of a group of galaxies known as the Local Group. The Andromeda Galaxy and our own Milky Way are the two largest in the group and this one known as the Triangulum Galaxy is third.

Why the Triangulum Galaxy? This is simply because it can be found in the small constellation of Triangulum – the Triangle! Just about any group of three stars might do, but this particular triangle is found above Aries and below Andromeda.

Again, as with my M31 image, the Optolong L-Extreme filter was used to collect the H-Alpha data which was then blended into the red channel. This enhances the pinky-red regions on nebulosity in the spiral arms of the galaxy.

As usual, click on the image below to see the full-size version.

For the technically-minded, this article shows the equipment used to take this image.

I acquired the images using N.I.N.A. software. I took 72 x 300s exposures with the QHY268C camera for the RGB and 17 x 600s exposures using the L-Extreme dual-narrowband filter to get the Ha data which I combined with the red channel from the RGB. All processing with PixInsight.

 Posted by at 11:24 am

M31 – The Andromeda Galaxy

 Deep Sky, Equipment, General Astronomy, Image Processing  Comments Off on M31 – The Andromeda Galaxy
Oct 132021

Messier 31, the great galaxy in the constellation of Andromeda is one of the most photographed night-sky objects of all, probably second only to the Orion Nebula. Every few years I get an itch to image it again. Most astro-photographers like to revisit old targets once in a while, and this often happens when new telescopes and cameras have been purchased, and this is the reason why I’m having another go at this beautiful object. I showed off my new kit in my previous post.

It is often said of M31 that it is the furthest away object that can be seen with the naked eye. This is an amazing thing when you think about it! This galaxy is about 2.5 million light years away and it is the nearest large galaxy to our own Milky Way galaxy which is not too different in structure from M31 itself. In a dark, moonless sky, M31 looks like a fuzzy blob to the naked eye. Some people say they can also detect another nearby galaxy called M33 – The Triangulum Galaxy with the naked eye. I personally can’t see M33, but it is further away from us than M31 at around 2.75 million light years, so M33 really does represent the furthest thing anyone can see without optical aid of any kind. I’ve asked a lot of people if they can see M33 in a good, dark sky in the UK, but I’ve never found anyone who can, so I’m happy that those photons that left the Andromeda Galaxy when Homo habilis first walked the Earth, enter my eye and are detected by my retina represent the most ancient particles of light that can ever stimulate the human consciousness.

Here is my latest image of M31. Click on the image below to view a much larger version (4000 pixels across). Next, I will describe some more details of how this image was acquired and processed.

Firstly, what are we looking at here? The first thing to realise is that we are viewing this spiral galaxy from an angle of about 45 degrees. If we could fly over the galaxy and look directly down on it, we would see a vast spiral shape. Another thing to understand is that all of the distinct, bright stars in the image are all relatively close-by stars in our own Milky Way – in other words we are looking through a ‘curtain’ of nearby stars to see outside our own galaxy. We should understand that galaxies are vast islands of stars, separated by huge distances of near-empty space. The Andromeda Galaxy contains about a trillion stars (that’s a million, million stars) which is about twice the number in our own Milky Way galaxy. So, you are looking at all of these trillion stars in this image which are too far away to see them individually, so they glow like a huge mass.

What else can we see here? Well, you will see the dark regions in the galaxy. These are huge lanes of cosmic dust which are obscuring the light from stars behind them. Also, if you zoom in to the big image you will see the disk of red regions that glow around the galaxy. Here’s a zoomed in region that shows the red regions nicely. Each of these red areas shines be the light of Hydrogen-Alpha. All of them would be seen as nebulae to any inhabitants of planets orbiting the stars in M31 and any of them could be the equivalent of, say, the Orion Nebula that we see locally here in our region of the Milky Way.

Lastly, there is a bright elliptical blob showing below M31 in the main image. This is a dwarf elliptical galaxy called M110 which is a satellite to M31 itself. We have similar objects associated with the Milky way and they are known as the large and small Magellanic Clouds.

So, how did I create this image? I used the telescope and camera system I showed in my previous post. Over four clear nights in October 2021, I took lots of long exposure photographs of M31. The telescope was guided very accurately by the separate guide scope that was checking the guiding accuracy every 2 seconds throughout the whole time, and instructed the mount to make tiny corrections to keep the galaxy perfectly still on the chip of the sensitive camera. Eventually I had about 22 hours of exposures stored on my imaging computer. By the time I weeded out the poorer frames, I had 10 hours of data from my broadband luminance filter, and about 7 hours of data from my narrowband filter.

The narrowband filter I used was the 2″ Optolong L-Extreme filter. This passes light from both H-Alpha and Oxygen-III sources, both with a passband of 7nm wide. In this image I only wanted the H-Alpha data, so I extracted the red channel from the narrowband images and threw away the green and blue which shared the OIII signal. Then I merged the H-Alpha signal with the red channel from the broadband RGB images. This enhanced the red emission nebulae in M31 beautifully.

I’ll write a more detailed blog about my process next…

 Posted by at 2:13 pm

The Veil Nebula – a mosaic

 Deep Sky, General Astronomy, Image Processing  Comments Off on The Veil Nebula – a mosaic
Sep 292021

The beautiful Veil Nebula in the constellation of Cygnus (the Swan) covers a large apparent area of the sky. When I say ‘large’ I mean it in a relative way. It covers a large enough area to make it hard for the average telescope to cover in one frame. To put this into perspective, the full Moon (or the Sun) is about half a degree across, but we need a field of view (FOV) of about 3 by 3 degrees to encompass the whole of the Veil Nebula. Thus, we can say that the full Moon would fit about 6 times across the apparent span of the Veil Nebula.

I have a lot of different telescopes and cameras! Some telescopes, such as the popular Schmidt Cassegrain design, are good for viewing the planets and small galaxies, but these typically have very small FOVs because they have long focal lengths to provide the high magnification which we need to see the belts on Jupiter, the craters on the Moon, or the rings of Saturn. Think of these telescopes as the telephoto lenses of the astronomer’s toolkit. Then there are the shorter focal length, smaller telescopes. These are the type (typically small refractors) that can give a wider view of the starry sky and they are ideal for delivering a larger FOV on to the camera’s sensor. However, only the smallest of these could cover the 3 by 3 degrees we require, and so I have resorted to the technique of imaging one half of the Veil Nebula on one night, followed by the other half on another night! I used an using an 85mm F/5.3 refractor. The two sets of images are ultimately processed and seamlessly joined together in a mosaic to show the Veil Nebula in one final image. Although this sounds complicated, there are advantages to this approach as the final image provides a much higher resolution of the target than could been obtained with a telescope that could fit the whole thing in in one go. The final image ends up with more pixels too.

The Veil Nebula is a Supernova remnant. The star that blew itself to pieces was 20 times more massive than the Sun and was just over 2,000 light years away. This cataclysmic event happened about 10,000 years ago. The remaining remnant structure is about 110 light years across and contains the beautiful glowing filaments that you can see in the image. The red colour is caused by ionised Hydrogen atoms, and the green from doubly ionised Oxygen atoms. The filter that I used to capture this image allows light of these two colours (wavelengths) to pass through, but cuts off everything else, including general light pollution and moonlight etc. Astronomers call this narrowband imaging.

Click on the image below to see a full-sized version.

 Posted by at 9:48 am

Three new images from the summer

 Deep Sky, General Astronomy, Image Processing  Comments Off on Three new images from the summer
Sep 282021

Here, on the south coast of England, the nights get very short indeed for a couple of months around the Summer Solstice. In fact, there are several weeks where theoretical ‘astronomical twilight’ never ends and the Sun never drops below 18 degrees below the horizon. I normally abandon deep-sky imaging but, this year, I was testing out a new system and decided to have a go at a few easy and classic Summer deep-sky targets.

The main thing that helped my productivity during these short nights was a new dual-band narrowband filter from Optolong called the L-Extreme. These multi-band filters are becoming very popular with deep-sky imagers these days. The pass-band spectrum graph is shown below, and you can see that there are two peaks – one centred on H-Alpha and the other on OIII and both are 7nm wide.

I’ve been imaging with Ha, OIII and SII narrowband filters for many years, but so often in the past I have been unable to capture a full set of sub images due to poor weather or lack of time, and this filter brings the possibility of acquiring more finished images as these three testify. By the way, the SII band is not included with this filter but, so often, the SII signal is so weak it rarely adds much to an image. However, since I have this filter in my filter wheel (so that I can use a Luminance filter for RGB imaging) I still have the option of adding my SII filter into the mix if I so desire.

I should mention that these narrowband filters are generally used with one-shot colour cameras. The Ha signal ends up in the red channel and the OIII signal is often mixed between green and blue. My new system includes the amazing QHY268C one-shot colour cooled CMOS camera which is very sensitive and has 16-bit resolution.

I will add a separate article showing the new setup, but it includes the superb Takahashi FSQ-85EDX APO refractor working at f/5.4 riding on a Skywatcher AZ-EQ6 Pro mount. The field of view is 179′ x 120′ which is 3 x 2 degrees (1.72 arc-seconds per pixel).

All three images consist of just over 2 hours of exposures – that’s all the darkness I had on each night! I took 600 second exposures throughout and calibrated with dark, flat and flat-dark frames.

Please click on each image below to see the full size of the images (which are only 50% of the originals).

The first image is the North America Nebula in Cygnus (NGC7000)

The second is IC1396 in Cepheus which contains the Elephant Trunk Nebula near the middle.

Lastly, NGC6888, The Crescent Nebula in Cygnus which is sometime referred to a van Gogh’s Ear!

Hopefully, my next article will not be too long coming. Thanks for reading.

 Posted by at 11:00 am
Sep 112015

Here are three different versions of M16, The Eagle Nebula in the constellation of Serpens Cauda. Interestingly, the constellation of Serpens is unique in that it is the only one that is split into two distinct pieces, namely Serpens Caput (the head) and Serpens Cauda (the tail). All of these images have been recently taken using the amazing telescope that I co-share with Australian amateur Jason Jennings. This scope is hosted in the ‘barn’ at the Siding Spring Observatory, Coonabarabran, NSW, Australia. I’ll write another post about the scope soon, but it is an amazing 16″ f/3.5 astrograph.

This first version is a ‘traditional’ LRGB image, meaning it has been made by taking separate images using Clear (Luminance), Red, Green and Blue filters and then combining those to make a final colour image. This should be close to how the eye would perceive the colour because the R,G and B filters pass frequencies of light similar to the sensors in our tri-colour vision system. The clear filter is used as a luminance channel and is where most of the sharpened detail resides.

As with all the images, please click on them to see a full-sized version.

M16 LRGB Version

This next version is taken using three narrowband filters. These are H-Alpha (Ha), OIII and SII. The wavelength of these filters are commonly used by astronomers because there are a lot of emission nebulae that have excited atoms in them that emit light in these wavelengths (especially Ha which is nearly always the strongest). So, to produce an ‘RGB’ image from them requires that they are mapped to the Red, Green and Blue channels of the image. I have chosen to use the ‘Hubble Palette’ which maps the SII to Red, Ha to Green and OIII to Blue. Here is the result:

M16 Narrowband Version

You will notice that the star colours are not good in the narrowband version and this is a consequence of the filter mapping and also because of the relative strengths of the three channels. So, in the third image below, I have combined the stars from the RGB image with the nebulosity from the narrowband image. Here it is:

M16 – NB with RGB stars

I’m not sure which version I prefer!

Finally, a 4th image (I lied!) taken last year with a longer focal length instrument (12″ f/9 RCOS) which shows the ‘Pillars of Creation’ in more resolution. This was also taken using the Hubble Palette which is appropriate because the iconic pillars were made famous by those fabulous images from the Hubble telescope.

The heart of M16

 Posted by at 2:13 pm

An Old Favourite Reprocessed – The Pleiades

 Deep Sky, Image Processing  Comments Off on An Old Favourite Reprocessed – The Pleiades
Dec 072012

From time to time it becomes apparent that your image processing skills have improved to the point where you become convinced that it would be possible to reprocess old data and stun the world with the results!

I often find, however, that the improvements are minimal, and that is probably the case here, but I still find this target fascinating. Here is a re-processed image of M45 – The Pleiades, which is currently well placed in Northern Hemisphere skies. Jupiter is not too far away too.

I captured this data in September 2011 using a QHY-8 one-shot colour CCD camera (which I have since sold!). The telescope was my little 75mm Pentax APO refractor. I took 20 exposures each of 10 minutes and combined them to produce this.

 Posted by at 3:35 pm