I’m very excited about this! I have finally taken the plunge and now have (or will have in early November) a remote imaging rig in Southern Spain. It is located at the PixelSkies remote hosting facility near Castilléjar in the province of Granada, Andalucia.
The imaging rig itself was originally built in 2020 and owned by First Light Optics, and it was used to capture images for a monthly image processing competition. I learned from Ian King that it was for sale and I couldn’t resist the opportunity to buy this, already proven, setup. Normally, one has to buy the kit and ship it out to the hosting location, all of which takes time, planning and money.
Here’s a picture of the whole system located in one of the roll-off roof sheds. More details and pictures are below.
The telescope itself is a StellaMira 104mm ED2 Triplet f/6.25 APO Refractor (with field flattener) and this rides on an amazing 10Micron GM 1000 HPS mount which has absolute encoders. The detector is a Starlight XPress TRIUS PRO 694 mono CCD camera which has 2750×2200 pixels in a medium format Sony chip. The resulting field of view is 66 x 53 arcminutes at a resolution of 1.44 arcseconds per pixel. To give an idea of what this means, the Moon would fit twice across the resulting images. The picture below shows the CCD camera connected to the telescope.
Also visible in the picture above is the 7-position filter wheel containing Optolong 1.25″ filters. The filters are the usual set of LRGB filters and the three 7nm narrowband filters for HA, OIII and SII. Notice also the Off-Axis Guider (OAG) with the Starlight Xpress LoadStar V2 guide camera siticking out to the right of the filter wheel. The pick-off prism for the OAG is in front of the filters so that unfiltered light always hits the CCD sensor of the LoadStar.
The picture below shows the 10Micron mount more clearly and also the Lakeside Astro motorised focuser. It is, of course, vital to be able to accurately focus remotely and the focus point will vary with temperature during the night, and is also different for each filter.
Also shown above is the mounting plate on top of the telescope cradles which has the red Hitec Astro Mount Hub Pro V4 control box. This has a full USB hub along with software controllable power ports and dew heater controller. This hub allows the cabling to be kept shorter and neater. Without a control hub like this, all the cabling would have to travel down to the PC on the floor and would create potential cable snagging issues as the telescope slews around. Here is a close up of the hub:
Another fantastic feature of this setup is the built-on flat panel. This Alnitak Flip-Flat will allow me to take my own flat-field images without asking anyone to arrange for a flat panel to be balanced on the telescope. This device can be seen at the front end of the telescope and it also acts as a lid for the telescope to prevent dust getting on to the objective lens. The opening and closing of the panel is software controlled as is the brightness of the flat panel. During cloudy nights I can also take bias and dark frames when the panel is in the closed position, but turned off. See the picture below which also shows the wide angle video camera (the red device below the flip-flat). This sensitive camera provides a wide view of the sky, useful for spotting clouds or generally admiring the constellations and the Milky Way.
Mounted on the mount pillar is a small Astromi.ch MBox device. This is a small, self-contained weather sensing device that delivers barometric pressure, temperature, humidity and dew point information with high accuracy. There are other bits and pieces (including the main Windows 10 control PC), but I have described the main components.
In due course I’ll share more information about how I get on with this fantastic system, and hopefully, lots of great images from this dark-sky site.
Finally, watch this video to see the system being assembled a year or so ago.
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.
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…
Since the early Summer of 2021 I have been building up a new deep-sky imaging setup based around the beautiful and venerable Takahashi FSQ-85EDX Refracting telescope. I’ve always wanted a ‘Tak’ and decided to go for this model known ad the ‘Baby-Q’. The optics are glorious and the focuser is incredibly rugged and can carry heavy cameras and filter wheels.
The idea, eventually, is to turn this setup into a fully robotic system which will be mounted low to the ground and housed in a simple box-like structure with a sliding roof. For now, I’m testing out the system to see how it performs.
Here is a small gallery of photos of the current system. I will add more details about the components below.
Here’s a list of the main components that you can see in the above photos:
Telescope: Takahashi FSQ-85EDX F/5.3 Apochromatic Refractor with 1.01x field flattener.
Mount: Skywatcher AZ-EQ6 Pro
Camera: QHY268C cooled CMOS camera (one-shot colour, full 16-bit)
Filter Wheel: Starlight Xpress 5 x 2″ filter wheel
Guide Scope: ZWO 60mm. Focal length is 280mm, F/4.67
Guide Camera: ZWO ASI290MM Mini mono
Auto Focuser: Pegasus Astro FocusCube2
Power, Dew Heater and USB Hub: Pegasus Ultimate Powerbox V2
Dew Heater bands on both scopes
Windows Computer: Beelink Mini PC (in the plastic box on the ground running N.I.N.A.)
If you look at the photos with all the cabling, you will see a plastic box on the ground below the mount. This contains a ‘headless’ mini PC running Windows 10. Think of an Intel NUC and you will get the idea, but this is a Beelink with an Intel i5 CPU which comes cheaper than a NUC. This computer has all of the software installed to control the rig. I’m using the free N.I.N.A. software here and the little PC is connected to the wireless router I have in my dome just a few feet away. This allows me to use remote desktop from the comfort of my dome, office or house.
The thing that really was a ‘game-changer’ for me is the Pegasus Powerbox which is mounted just below the lens of the main scope. This provides all of the 12-volt power ports I need to run the various bits of kit and also has a USB hub with 6 ports. Additionally it can power and control the heat of three heater bands and can detect the dew-point so that it can intelligently adjust the power to the bands to keep the lenses free from dew. Because nearly everything connects to this hub, there are only two cables that need to be connected to the big plastic box on the ground. One is the 12V power to the hub and the other is the USB3 port to the Beelink mini PC.
I run the amazing free N.I.N.A (Nightime Imaging ‘N’ Astronomy) software on the mini PC and the recently added Advanced Scheduler is amazing allowing me to power up the system before dark and set up various targets to image during the night. The system will do everything such as cooling the camera, auto-focusing, slewing and centring targets, flipping across the meridian and shutting down at dawn. It can also deal with re-focusing during the night if the focus drifts and re-centring after a cloudy spell.
Assuming I get some clear nights over the Autumn months, I will hopefully be posting some new images soon.
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.
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.
It’s about time I got my astronomy blog going again so I thought I’d start by explaining what I’ve been up to over the past two years or so in an area of study on the possible existence of exoplanets around a certain type of binary star system known as Post Common Envelope Binary (PCEB) systems.
I got into this area of research after meeting fellow Selsey astronomer John Mallett in 2019. John is part of a small group of amateur astronomers who have been researching in this area for a few years and I was recruited into their number almost straight away. The group goes by the name of ALTAIR Eclipsing Binary Research Group and here is a link to the about page of our website which is written and maintained by myself. The site is private to the four of us who are currently members, but the about page is publicly accessible. You can access all the published papers from the ALTAIR group on the About page – I have only been involved in the most recent one, but I am very busy writing parts of a new paper which is in progress.
The technique used to determine if an unseen third body (an exoplanet or perhaps a brown dwarf) might be orbiting one, or both of the stars in the PCEB system is called the method of Eclipse Time Variation (ETV). The rest of this article explains this in more detail.
Let’s clear up some terminology…
Exoplanets are planets that orbit stars other than the Sun. It is an amazing fact that we had no evidence of the existence of any exoplanets until 1992, although it was widely assumed that the Sun could not be unique in having a family of planets (and other smaller bodies) in orbit around it. Such are the vast distances between the stars, it is only in these past few decades that the technology has existed to detect the existence of exoplanets, and it is only very recently that any exoplanets have been directly observed – most are detected by more subtle, indirect means – more about this shortly as it is pertinent to this story. To put it into perspective, there are now well over 4000 ‘confirmed’ exoplanets, and the number has been doubling every 27 months. However, only 16 exoplanets have been discovered using the ETV method that we, the Altair Group, are studying.
Binary stars are extremely common in the universe. A binary star system consists of two stars in a common orbit around each other. Star systems with three or more stars also exist. The specific type of binary systems that we are interested in are known as PCEB systems and evolve in a particular way, which I will briefly describe.
It is likely, in a binary system, that one of the stars will be more massive than the other. The more massive the star, the faster it ‘burns’ through the various stages of stellar fusion, and the faster it evolves. In this way, the more massive ‘primary’ star in the pair more quickly evolves into its red giant phase and expands enormously. (Our Sun will become a red giant in about 5 billion years). The primary star expands to the point where matter in its outer layers starts to overflow and transfers to the smaller secondary star. Thus, a common envelope of material is formed between the two stars. The secondary, typically a main-sequence star at this point (like our Sun), cannot cope with all this material that is being donated to it by the primary partner and, eventually, the common envelope is ejected from the star system altogether. The key here is that the departing envelope material takes angular momentum away with it, and the law of the conservation of angular momentum dictates that the two stars must be left with less angular momentum. This they achieve by moving closer together, which also causes their orbital period to decrease to the point where they spin around their common centre of gravity in a stunning, but typical time of two or three hours! During this process, the primary star will evolve on and will become either a white or red dwarf, whilst the secondary star stays as a main sequence star for a long period due to the fact that it started life as a fairly low mass star.
First, I should mention that it is generally not possible for us to make out the two separate stars using a telescope from here on Earth – certainly not with an amateur telescope, and this means we just see a single resulting point of light. So where does the eclipsing bit come in?
If the stars are aligned, even roughly, to our line of sight such that during their orbital dance, the stars move in front of each other, we will notice the following effects:
When the stars are side by side, the combined point of light that we see will be at its brightest
When the fainter of the stars moves in front of the brighter, we will see a larger dip in brightness (the primary eclipse)
When the brighter of the stars moves in front of the fainter, we will see a smaller dip in brightness (the secondary eclipse)
These effects are clearly illustrated in the graph of brightness (magnitude) over time shown below. We call this a light curve. I made these measurements at my observatory here in Ham of brightness (a process called photometry) of a star called HS0705+6700 (aka V0470 Camelopardalis) over a 4.5 hour period. The big dips are the primary ‘minima’ and the small ones are the secondaries. The binary orbital period of this star system is about 2.3 hours. The strange time scale at the bottom is in Julian Days with a correction for differences in the Earth’s position with respect to the barycentre of the Solar System. See here for more details about BJD, but know that this is the standard way astronomers in this field represent the date and time of the measurements. You can see on the graph that the primary dips are separated by just under 0.1 of a day which is where the 2.3 hours comes from.
Rotating Like Clockwork?
We might expect that the resulting whirling pair of stars will eclipse each other repeatedly and accurately, like celestial clockwork, and this would be true if we just considered the Keplerian equations of celestial mechanics. It would mean that, if we can measure the time of the minima with sufficient accuracy, we can work out the binary period and therefore we should be able to predict the time of any eclipse into the future (or back into the distant past).
This does actually hold accurately to a certain degree. We do indeed predict when eclipses should occur so that we can observe and measure them over the months and years after we have established the exact date and time of the first observed eclipse, and we are able to do this because, although the period is not exactly following Keplerian clockwork, it does so to a very high degree of accuracy – easily enough to pin down the time so that we can go out on the predicted night and be sure of capturing the minimum dip so that we can re-measure and refine the date and time once more.
However, in the real world there are several other known physical effects that can very slightly change the orbital period of the two stars. I will go into this shortly, but first let me introduce the tool we use to highlight any differences that might be seen in the binary period over time. The graph is called the O – C (pronounced “O minus C”) which stands for the Observed minus Calculated (or Computed) graph. An example taken from within our ALTAIR website for our friend HS0705+6700 is shown below:
What we see in the O – C chart above is the Cycle or Epoch number of the eclipse plotted on the horizontal x-axis. The number of seconds difference from the expected calculated date and time of each minimum point is plotted on the y-axis. The different colours illustrate that the measurements were made by different groups of observers and research teams over the years (the legend is not shown here for clarity). The red group to the right has been made members of our ALTAIR group in the past few years (we try to observe this star every month if we can). As mentioned above, the period of HS0705+6700 is about 2.3 hours, so 80000 orbital cycles represent roughly 21 years of measurements. The zero Epoch is normally defined and agreed to be a certain historical observation and sometimes a measurement prior to this is found in the literature as is the case with the blue measurement with a negative cycle number at far left. The error bars tend to become smaller as time goes on due to improvements in technology. Some of the measurements on the left will have been made from photographic plates and photomultiplier detectors, whilst CCD cameras will have been used in more recent years.
Making sense of the O – C curve
The simplest way to compute the time of any epoch is to measure the period to the best accuracy possible and then add integer multiples of it to the date and time of the first epoch. If we call the Epoch number E, we can write a formula like this:
JDE = JD0 + E x Period
This is called the linear ephemeris. JD means Julian Date which is just a way of representing a date and time as a number. As I type this, the Julian Date is 2459444.8958333335. There are many on-line Julian Date converters available to try. They are handy because you can find differences between dates by subtracting them and calculate future dates by adding days to them. This is why it is common practice to quote the period of binary stars in days. For example, the period of HS0705+6700 is 0.09564668 days and the linear ephemeris for this star system is as follows:
JDE = 2451822.75964598 + E x 0.09564668
The value of the reference Julian Date of the JD0 in the above equation is a date back in October 2000. With this, you can now calculate the date and time of any epoch in the future, or past. If everything was purely working to Keplerian celestial mechanics, every point in the above O – C plot would be on the zero line and each point would be exactly 0.09564668 days apart, so we now must address why this is not the case.
Mechanisms that can Change the Binary Period
There are three mechanisms that are known to have an effect on the period of this kind of PCEB system and these are:
The Applegate Effect
Angular momentum loss
The presence of a third, unseen body (or more than one unseen body).
Before I briefly explain these effects, I think you will be able to imagine that if we can calculate the sizes the first two effects, and we still find that they cannot account for the full magnitude of the O – C variations seen, then we are left with the conclusion that some unseen body must be the cause. This is the reasoning used so far by researchers in this field, and it is the way that those 16 ETV exoplanets mentioned above have been ‘discovered’.
Another thing that makes the above argument more convincing is that, when all other known effects have been subtracted from the O – C plots, what is often left over is a cyclic variation. Surely an exoplanet would leave a cyclic, periodic fingerprint behind as it goes around in its orbit?
Just a few words about the first two effects in the list above:
The Applegate Effect
A mechanism to potentially explain the eclipse time variations seen in O – C diagrams was proposed by Applegate in 1992. This process relies on the secondary star being magnetically active, undergoing solar-like magnetic cycles which are strong enough to redistribute the angular momentum (AM) within the star. No loss of AM from the system is required. This leads to shape changes which affect the gravitational quadrupole moment. Since the orbits of the stars are gravitationally coupled to variations in their shape, this effect could explain the small changes that are observed in the orbital period. We can calculate the magnitude of the AM variations seen in the O – C plots and then compute the size of the Applegate effect. Generally, it is found that the Applegate effect is at least an order of magnitude too small to explain the O – C variations (at least this is the case with the PCEBs that we are currently studying).
Angular Momentum Loss
Note that we are talking about a loss of AM, not a cyclic variation in AM. This means that there should be a gradual decrease in the period over time as the AM is lost. There are two causes of AM loss.
The first is caused by Gravitational Radiation. This is a consequence of Einstein’s General Theory of Relativity. Accelerated masses cause ripples in the geometry of space and time and carry energy away from the binary system.
The second effect is known a Magnetic Braking which is a theory explaining the loss of stellar AM due to material getting captured by the stellar magnetic field and thrown out to a great distance from the surface of the star.
The sizes of both of these effects can be calculated. Often, like the Applegate effect, their contributions are not enough to explain the O – C variations seen.
Once this work has been done and the known effects have been subtracted, the remaining job is to calculate the number, mass and orbits of potential exoplanets that could explain the cyclic variations in the O – C. As you can imagine, this is not an easy task!
Our current work focuses on following up with lots of new eclipse timings for the 18 stars in our canon. We are interested in how the proposed exoplanets are faring against our new timings.
This blog article is an overview of our work. I have not explained any details about how we observe and measure the brightness of the stars, nor how we analyse the light curves to calculate the times of minima. We have written several Python tools to do all this and maybe the next blog will go into a bit more detail.
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 iTelescope.net ‘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 possible nova with the catchy designated name of PNVJ20233073+2046041 has now officially been named as Nova Delphini 2013.
It was clear here last night for an hour or so just as the sky was dark enough for me to make out the stars in Delphinus and Sagitta, so I took this shot of the new star with a 50mm lens on a Canon 60D. I’ve annotated the image so that you can where to find the Nova.