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Light relief for Cosmologists

'Calculating the Cosmos' by Ian Stewart and 'The Universe Next Door' a New Scientist compilation are both extremely enjoyable reads and have kept me going in between the'dark clear nights' here on the east coast.  So having time on my hands this summer, I prepared a digital image and poem in 'homage' to two of my favourite pursuits: reading books on cosmology I barely understand and eating shellfish most people tend to avoid.    'Winkles in the fabric of Space-Time' - mixed media - George Roberts - June 2018   "If there were winkles in the fabric of Space-Time At the Planck scale squid and plaice would rhyme If the Universe and Albert Einstein could spin on one sharp pin Might each sardine simultaneously be alive and dead in it's tin? Perhaps dark matter would even cease to matter? If cod, god and gravity were resolved in batter".   George Roberts from the book 'A Brief History of Gastropods'  




Gina's Ultimate All Sky Camera

I'm hoping this is my final and hence "Ultimate" generation of all sky cameras.  Based on the ASI185MC CMOS astro camera and Fujinon fish-eye lens of 1.4mm focal length and f1.8.  Image capture is provided by a Raspberry Pi 3 in conjunction with INDI drivers.  This is used with KStars/Ekos client software running on a Linux Mint desktop indoors.  Communication is via Wi-Fi.  The astro camera is an uncooled version but I have added a Peltier TEC cooler.  This cools the camera down to something like -15°C for night sky imaging with longer exposures of around a minute.  Daytime imaging is also covered using the camera's minimum exposure and gain.  The colour camera differentiates between dark clouds and blue sky and also shows the colours of stars at night. This Blog will describe the construction of the hardware and the special driver coding used to control dew heater, camera cooling and focussing.  




Creating a Pond Garden.

I'm starting with an empty area about 10 x 4 metres between sun lounge and observatory in front of living room window and facing roughly south.  I have killed off most of the weeds and grass by covering with an old tarpaulin for a year or so.  This has also stopped the ground from drying out and making it easier to dig.   In addition to providing a path to the observatory, this will provide flowers and shrubs to see from the living room window.  Plus a small pond and fountain.  The latter is something I have been working on in 3D printing and plan to have something unique.  Apart from the pond there will be planting areas and slabs and ornamental stepping stones. I have removed most of the tarpaulin and started digging a hole for the pond.  The latter is a pre-formed pond I bought from Amazon :-
Bermuda Sand Pre Formed Pond 128 x 84 cm. Here are some photos of pond hole digging and the general area.




The trip so far

Well I have been studying the various ways of looking at the night sky now for the last 9 months or so , after wanting some means to do this for a long time and finally  have the time to put some cash into it. So here in this blog I will attempt to document my path and try and keep myself on track. My main interest  is astrophotography so I will start with the equipment I have or intend to obtain , with comments Book: Make Every Photon Count: Bought on recommendation of folks in this forum , excellent read and will need to be read more times once my rig is complete. NEQ6 Pro Mount : Found one at a low price which needs some repair work and will be installing a belt drive mod into it. Decided to go right for a decently large mount so I'm not wishing in 6 months time I had done this in the first place. Camera: Canon D450 will be in my hands at the end of the month and I will be doing the IR modification on it. Still undecided on whether or not to do a cooling mod on it as well. Telescope: undecided upon right now and currently using my eyes to identify my way around the sky. Guide scope and guide scope camera: undecided . CAT5 fed USB hub system. EQMod PHD Backyard EOS : this will be setup once I have all the hardware. Assorted stuff : A lot of this I will 3D print I'm sure there will be some things that will be handy , will find out what these when they are needed Looking forward to fun and interesting times will update as we go .




Taking it seriously

Having wanted to do astronomy properly for decades I finally took action late in 2017 and bought a pair of Canon 15x50 image stabilised binoculars.  I was absolutely blown away with what I could see using these from my garden with what I now know are Bortle 8 very light polluted skies. For the first time in my life I saw the Orion Nebula M42 - only as a small cloudy area but I knew there was more to see with better optics. 
When I saw the Pleiades, directly overhead, for the first time I knew I was hooked! I'd been reading posts here and on other sites and blogs and I knew that I'd need to think through what I wanted to achieve and what to spend my money on.  I used a strategy that has served me well over the years - Start from where you are!
That might seem obvious but I have read so many posts - facebook is the worst - where people go out and spend thousands of pounds on equipment because it is the 'best' but they don't know how to set it up never mind use it!  I experimented with what I had so that I'd know what I needed.  I started with my wife's Canon PowerShot SX730 which takes great pictures but isn't suited to astrophotography and then I got out my old Canon SX1.  That was a bit better and I used CHDK (Canon Hack Development Kit) to allow longer exposures.  I tried taking pictures through my binoculars but would have needed some precision DIY to hold the bins and the camera together.
I wasn't getting any good images, but I was learning about aperture, exposure length, ISO and the importance of keeping the camera still! My first purchase was a Canon EOS 7D Mark1 and a couple of lenses (18-55 and 75-300).  I got an Amazon Basics tripod - very well built for under £50 and set about trying to capture the universe. Using the 7D with Canons capture software I was taking lots of pictures and learning the hard way about star trailing.  With the 300mm lens fully extended the longest exposure I could manage which kept round stars was 0.8 seconds - so I took lots and lots of them and fed them to DSS. Of course DSS sometimes struggled to stack them and I couldn't see the results at first because the images were still extremely dim but I'll do a separate entry about software and how I got round these issues. It was clear I would need to buy a mount or a tripod mounted tracker if I was going to progress but first I had to think seriously about how I planned to use it long term. My Priorities - Transportable, sensibly priced, good quality. As mentioned, the sky where I live is Bortle 8.  I'm fortunate that I live on the southern outskirts of Glasgow and my back garden faces south so I can do a lot of practice and get some reasonable images but I really wanted to be able to pack my stuff up and drive to better sky.  20 minutes takes me to Bortle 4-5 so it's worth doing. I'm trying to do this as a hobby and not go overboard with the budget but I also don't want to waste my money on cheap stuff that doesn't perform well.  That's been great because it's forced me into researching options and being strict about what I need and what is just a 'nice to have'.  I don't buy stuff just for bragging rights! I'd thought seriously about getting an Ioptron Skytracker or Skyguider sized device but I didn't want to be too restricted on what I could mount on it, and I'm not likely to take my kit on a flight very often.  In the end I saw a 2nd hand Skywatcher EQ5 Goto mount at a reasonable price and I already knew it would do what I need for now.  I had originally planned to use the DSLR with a large zoom lens but when I costed these it was clear that I'd need to spend several thousands to get what I wanted.  That led me down the path of a short APO refractor.  Again, into the classified ads and someone here pointed me in the direction of a Skywatcher Esprit 80 which I am absolutely delighted with! So that's me got all of the hardware I need for now... but then I saw a 60mm Guide scope and Orion SSAG for a good price... So now I have everything I need for a while.  Why am I still looking at the classified adverts?  Just in case there's a bargain

My first astro photo

This was taken 8th April 2016 from an apartment in Hamilton Island, Australia.  The equipment I used was a Samsung Galaxy S5 and an old but good quality pair of binoculars left by the owners.  The skies were incredibly dark and we were able to attend a talk by a local astronomer who guided us around what could be seen with the naked eye. I was delighted last year when I used Stellarium last year to look at the view on that date and confirm that I had indeed captured Jupiter and 4 moons!

Improving An Aluminium Tripod

The aluminium tripods that come with a majority of beginner and mid-range scopes have had a bad name for years as being poorly made, sloppy and people have tried various ways to make them sturdier such as filling the legs with sand, lead shot, or even expanding foam. 
I just read an account the other day of where a person was fitting steel rebar into the legs to see if it will help…
The only problem with these solutions is that you end up with a very heavy cumbersome tripod that is really no better than what it was when the modifications were started. 
I will show you what I do with these to help take the shakes out of them. 
The tripod modifications can be done to any of these aluminium tripods and not limited to adapting the SLT mount.

Before starting the modifications, read the instructions thoroughly! If there is any part you are not sure of feel free to PM me.

The tripods are manufactured cheaply and are not a precision work of art but can be fixed to be quite usable for only a few dollars.
There are 3 different pivot points on the tripod that total 21 different places that the tripod can move so these can all be stiffened up.

Tools required:
Robertson or Phillips screwdriver
Drill and ¼” and 1/8” drill bits
Hacksaw or angle grinder
Fine flat file
White glue
Paint or varnish of choice
Socket/ combination wrench if using nylocks

All the needed supplies should be available at a local hardware store. 
18- #6 flat washers
18- #8 x 3/8” sheet metal screws
3- 1/4” x 3 1/2” bolts
3- 1/4” wing nuts or nylock nuts (preference)
6- 1/4” x 1” flat washers
6- 3/16” x 1” bolts
6- 3/16” wing nuts or nylock nuts
12- 3/16” x ¾ or 1” flat washers 
1- 1/8” x ¾” aluminium flat bar (need about 9”)
Container for all the old bolts and screws

Note: If you wish to paint your tripod and mount I recommend a degreaser and an aluminium etching primer to help the paint adhere to the aluminium parts. 

For this I will show what I did to adapt the aluminium tripod to a Celestron SLT hub/mount.

The supplied screws/ bolts holding everything together are cheaply made and it does not take much to strip these so all the hardware will be replaced with better quality. 

Start by taking the tripod legs off of the hub and set the hub aside as it will not be reused. 
Take the legs apart and remove all the factory screws/ bolts holding the cast metal pieces together. 
Check all of the plastic end pieces in the legs to make sure they are tight. 
If not they will need to be removed for now. You may wish to mark all the pieces so they go back together on the same leg but it is not essential. 

If you are going to paint your tripod/ mount now is the time to do it and give it a full day or two to properly dry. 
Use either #220 grit sandpaper or a course scotchbrite pad to scuff the metal to help it adhere to the parts. 
Do not forget to scuff the primer before painting! 

Now that you are ready to put the tripod back together we will stiffen up any of the plastic leg inserts if they were loose. 
The only piece you do not want to do this to is the top cap for the center leg. 
Do not install this cap or the center tray support brackets at this time. 

Put a bead of white glue around the inside of the leg where the insert goes and then push the insert into place. Using the new #8 x 3/8” (6 per leg set) screws, snug all the parts up. 

Picture 1:

Set aside and let the glue harden.
The #8 screws are slightly larger than the original size and will snug up nicely. You can see the difference in the photo above.

I tend to reuse the lower single leg bolts as they are usually fine for this job. I use the glue on the insert and then the bolt.

Before you reinstall the cast lower leg pieces run your finger around the hole that the center leg slides through, if there are any rough or sharp spots file them down smooth. 

Now that everything is dry start reassembly by installing the side legs and then slide the center leg up through the bottom. 
Set the legs aside for now. 

Now we get to the fun part, power tools!

Using the 1/4” drill bit enlarge the holes on the SLT mount hub to match the larger hole in the tripod legs. Once done set this part aside. 

The next step is modifying the center tray supports.
The supplied tripod tray is a flimsy piece of stamped metal and using the 3 original screws and wing nuts leaves much to be desired for tripod stability!
Using 6 bolts in the tray will hold the legs firmly in place and not allow any play.

Using the drill and the ¼” drill bit, drill a hole at the furthest end of the slot and another half the distance of the support. 

Picture 2:

Now to make the new center tray. This tray will spread the legs out a bit more making alarger ground triangle which helps with stability. 
I used a piece of 3/8” plywood with dimensions of 15 3/4” on the flat side and 13 5/8” flat to peak. Your 2 holes should be approximately 2 ½” and 5” from the peak. 
Drill ¼” holes and set aside for now.

TIP: Use the tray support as a template to mark out the holes to ensure alignment.

Picture 3:

Using the aluminium flat bar cut 3 pieces 2 3/4” long. Use the file to smooth and round off the edges of the piece. (I used the edge of a quarter as a template to round off the corners.)

Now to reassemble the tripod! 

Take a leg assembly and lay it flat on your work surface, insert the center leg cap at this time but do not screw it into place. 
Take one of the flat bar pieces and lay it across the legs butted up against the lip of the center cap and mark out the location of the screw hole on the flatbar. 
Using the 1/8” drill bit make a hole and then install this with the center cap.
If you have ever noticed on these tripods, as soon as you put some weight on them the center leg tends to slide/ lean inwards which causes only a small part of the leg to actually be making full contact. This flatbar brace will keep the center leg inline with the other legs when the scope is mounted. 

Picture 4:

Optional: I drill a second hole and rivet it into place so that the flatbar cannot loosen off and the cap can still be unscrewed and removed if needed. (3/16” drill bit and 1/8” rivet)

Once the flatbar is attached turn the leg section over and it is time to install the tray brace. 
Screw one of the pin brackets onto the leg and then insert the pin. 
Put 3 of the #6 flat washers on the pin and then slide the tray bracket on (flat side up). Install 3 more #6 flat washers and then the other pin bracket. Screw bracket into place. 
The tray support bracket should be nice and snug between the brackets now and there will be no slop for it to slide around on the pin. 
Repeat for other legs. 

Picture 5:

So now the tripod should almost be done, take the mount hub and install the new 1/4” x 3 1/2” bolt.
At a minimum you should have a flat washer under the bolt head and one under the wing nut.
Check the gaps between the legs and hub to make sure they are in full contact with each other. 
If there are gaps between the legs and hub use 1 or 2 appropriate thickness washers to fill the gap.
Plastic report covers can be cut to make washers if the gap is small.
You want the legs parallel but not squeezed to the point you cannot adjust the center leg smoothly.
Use a 1/4” x 1” flat washer and then your choice of either a wing nut or nylock to tighten things up.

Tighten until the leg is stiff but can swing without fighting it. 
Repeat for the other legs. 
You should now have a complete tripod minus the tray. 

Final step is to install the tripod tray using 2- 3/16” x 1” bolts and 4 flat washers for each leg. 
I use one washer on top of the tray and one underneath the bracket so you can tighten these up very well with the wing nuts or nylocks. 

Picture 6:

You should now be the proud owner of a very stiff aluminium tripod that no longer has a bad case of slop/ shakes when you put your scope on it. 




Jocular: a preview

I've been mainly working on the stack inspector this week. The idea is to be able to quickly inspect the entire stack, rejecting bad subs (this also applies to calibration frames, though fuller support for calibration is the main task for next week). The stack inspector also allows animation of the subs and/or stack, making it easy to diagnose tracking issues etc. There's the option to restack based on an arbitrary sub in case the keyframe chosen isn't too good. One thing I'm finding a great surprise when going back through some of my old captures is the proportion of 'bad' subs that nevertheless get stacked into something reasonable.

Martin Meredith

Martin Meredith


Water Cooling for 3D Printer High Power Hotends

Having played with water cooling for astro cameras and seen this applied to 3D printers instead of fan and fins for cooling hotends but at high cost, I though I would like to try myself.  I have reasonable DIY skills   Some filament types benefit from a heated chamber and warm air is not so good for cooling.  This is one example where water cooling is particularly beneficial.  Another benefit should be reduced weight for the X carriage permitting faster acceleration and deceleration for fast printing.




Jocular -- a new tool for EAA

Since shortly before xmas I've been developing a piece of software to support electronically-assisted astronomy (EAA). Realistically it is still some months away from release, but the main design elements are getting close to being fixed so I think now is a good time to document what I'm doing in the hope that any comments or suggestions might be taken on board before the thing fossilises too much. The tool -- codenamed Jocular -- aims at promoting observation, but getting the most out of the limited number of photons we EAA-ers typically collect for each object we observe. The interface will be kept as simple as possible, but in spite of this I'm planning to implement a fair bit of AP-like functionality, adapted to the EAA use case where nearly all processes have to be handled semi- or fully-automatically. In a sense the tool was motivated by a desire to experiment with just what is possible to accomplish in near real-time and minimal user intervention. So there will be support for a full calibration scheme but operating silently where possible, as well as various luminance-chrominance manipulations, gradient removal and advanced stacking and stretching options. I'm attempting to operate by the principle of least commitment, which is especially important for EAAers, whereby it shouldn't be necessary to take decisions in advance that limit later options and potentially waste photons. For example, it will be possible to reject subs from any earlier point in the stack, or change the stacking mode, or choose a different key frame for star registration, or re-assign incorrect subs to the appropriate type or to a different object -- at any point during the observation of that object. Currently, live mode operates via a 'watched folder' approach in which an arbitrary capture program dumps .fits into that folder. These can be darks, bias frames, flats or lights, or short captures used for FAFing (focus-alignment-framing); a user-defined naming template enables the program to sort out the type of each sub. However, I am one small step away from complete integration with Nebulosity, which will enable capture control for any cameras/filterwheels supported by Nebulosity, but all done via a simple interface. The Nebulosity option will also allow scripted captures, again heavily simplified e.g. click RGB to have the program capture N subs of duration D from each of RGB, rinse-and-repeat (assuming the user has an electronic filter wheel). I hope to support INDI-based capture/control at some point and would like to track down some compatible open-source capture options as this is one area I really don't have the time or inclination to work on. It is possible to use the tool both live and offline in much the same way. The tool will provide easy access to previous observing sessions, enabling a user to revisit and re-process the data in a 'what if' fashion. It will support observation planning and logging as well as image annotation.  The program is being written in Python. In principle it can be ported to all OSs, including iOS and Android, but I'm developing first and foremost for the Mac where there is a shortage of EAA tools. The software will be open source. Here's a shot of the current interface during a recent test session observing the polar ring galaxy NGC 660 in Pisces. 

Martin Meredith

Martin Meredith


Meeting an Astronaut -International Space School Educational Trust (ISSET)

Toot and I had a great time in Norwich last night. Dr Michael Foale CBE gave a talk about his life as an astronaut to a packed audience at the University of East Anglia. What an accomplished, kind and measured man. A couple of hours in his company passed very quickly. He has great interpersonal skills and although we only spoke to him very briefly, both my partner and I felt we had 'met him' rather than just 'heard him' speak.  What an exciting, if not at times scary, life and career he has had? Highlights include: a spacewalk to upgrade the Hubble Space Telescope's computer from a 386 to a 486 ( I had one of each but I only had to fetch them from Currys) stopping the MIR space station from spinning out of control after it had been hit by a supply vessel commanding the International Space Station There were many children in the audience who were very interested in space and science. Dr Foale encouraged them to do what they were good at, pursue their dreams and not to be deterred by setbacks.  He paid particular care to encourage girls to pursue careers in science and aerospace. He very kindly - let anyone who wanted to - have their photograph taken with him. A long queue of excited children formed down one side of the Lecture Hall. "Dr Foale, I could tell you that the photograph is for my grandchildren, but really its for me"  said a very excited and pleased old man. If you get a chance to hear him speak and/or go to events organised by ISSET or a 'Pint of Science'  - go for it!




D7500 has high thermal pattern noise

In an earlier post I examined the noise in single dark frames over a range of exposure times.  My conclusion was that the Nikon D7500 was a lower noise camera than the D5300.  This was also backed up by an examination of master bias frames that again strongly favoured the D7500. However ... The first image I attempted to produce with the D7500 exhibited very strong streaks in the noise. I had been in the habit of not using dark subtraction with the D5300 as it has very low thermal pattern noise.  Accordingly, I again only used bias and flat frame calibration in the workflow that produced the above images.   Whilst the streaks are due to patterns in the noise being spread across the image due to errors in the application of dithering during tracking, it did indicate that the D7500 did have significant thermal pattern noise.  I found this surprising because the noise in individual frames ( when looked at in isolation ) seems to be completely random.  I thought that perhaps my memory had failed me and maybe the D5300 has the same level of pattern noise but my memory was being tricked.  That is, all my recent images with the D5300 were taken at lowish air temperatures ( ~5 deg or so ) whereas the image above was captured on warm nights ( low 20s ) and so maybe the D5300 would be just as bad at higher temperatures.    To test this I produced bias corrected master darks for both the D7500 and D5300 from images all taken at around 20 deg or just over.  The images below have all been stretched using the same screenTransferFunction applied to the Pixinsight histogram tool.  The results are striking ... D5300 master dark ( 47 subs, bias corrected ) - red channel: D7500 master dark ( 281 subs, bias corrected ) - red channel: D5300 master dark 100% centre crop - red channel: D7500 master dark 100% centre crop - red channel: And the histograms of the full size images ( red channels ) ... D5300 master dark ( red channel ) histogram: D7500 master dark ( red channel ) histogram: The Pixinsight statistics tool calculates the following: D5300:  mean 2.3,  standard deviation 9.3
D7500:  mean 7.5,  standard deviation 20.8 ------------- Analysis: The images and histograms clearly show that the D7500 has higher pattern noise than the D5300.  In particular, from the histograms, 0.1% ( 6,286 ) of D5300 pixels are more  than 44 ADU whereas, for the D7500 this figure is 27 times as great at 2.7% ( 141,305 pixels ).  Furthermore, the master dark for the D5300 was only produced using 47 images -v- 281 for the D7500 so I would expect that this difference would be even higher with more D5300 frames.  On the other hand, whilst not shown in the histograms above, my D5300 does have more 'very hot' pixels than the D7500 ( 579 pixels greater than 400 ADU -v- 10 pixels greater than 400 ADU ).  However, these hot pixels are very easily removed via dithering during tracking and sigma clipping when integrating.  The very large number of warm pixels however are very difficult to remove as dithering just places different warm pixels on top of each other. I went back and examined the 'random' noise seen in the individual D7500 dark frames ... and yes they do look random when seen individually, however, when flicking between a number of frames it is clear that the 'random' pattern is repeated in each frame!  Conclusion: My D7500 has very significant thermal pattern noise, albeit randomly distributed in a fixed pattern.   ............   Next steps (?) - I could use in dark subtraction during calibration to reduce the impact of pattern noise - however, as my camera is not cooled and the night's temperatures are constantly changing, any master dark will not closely align to the actual thermal pattern noise and as such dark subtraction may help but will not solve the problem - Using in-camera dark subtraction ( Nikon's long exposure noise reduction feature ) would almost completely remove the pattern noise from each frame.  However, due to the extra random noise being introduced by subtracting another noisy dark frame from each light frame, as well as the reduction in total light frames by 2, the resultant images will suffer from higher levels of random noise.  So whilst this would be an improvement with respect to the pattern noise, it is not a complete solution. - Third option, sell the D7500 and go back to using the D5300 ... 





Christmas upright Armchair Astronomer 'transforms' into horizontal Settee Astronomer without any visible expenditure of energy as Moon obliges by rising almost directly in front of his sitting room window. I could get to like this 'indoor astronomy' as it offers a warmer winter alternative for the older stargazer.




John Herschel in South Africa ( NGC 253, Sculptor Galaxy )

Sir John Herschel at the Cape of Good Hope Having spent the years 1825 to 1833 cataloguing the double stars, nebulae and clusters of stars visible from Slough, in the south of England,  John Herschel, together with his family and telescopes,  set sail from Portsmouth on the 13th of November 1833 bound for Cape Town.   As detailed below, in an extract from his book, the family enjoyed a pleasant and uneventful voyage and arrived some 5 months later at Table Bay with all family and instruments in good condition.  Reading on however, one might very well think that it might not have ended so well had they but left shortly after ... “... (iii.) Accordingly, having- placed the instrument in question, as well as an equatorially mounted achromatic telescope of five inches aperture, and seven feet focal length, by Tulley, which had served me for the measurement of double stars in England; together with such other astronomical apparatus as I possessed, in a fitting condition for the work, and taken every precaution, by secure packing, to insure their safe arrival in an effective state, at their destination, they were conveyed (principally by water carriage) to London, and there shipped on board the Mount Stewart Elpliinstone, an East India Company's ship, Richardson,Esq. Commander, in which, having taken passage for myself and family for the Cape of Good Hope, we joined company at Portsmouth, and sailing thence on the13th November, 1833, arrived, by the blessing of Providence, safely in Table Bay, on the 15th January, 1834, and landed the next morning, after a pleasant voyage, diversified by few nautical incidents, and without seeing land in the interim. It was most fortunate that, availing himself of a very brief opportunity afforded by a favorable change of wind, our captain put to sea when he did, as we subsequently heard that, immediately after our leaving Portsmouth, and getting out to sea, an awful hurricane had occurred from the S. W. (of which we experienced nothing), followed by a series of south-west gales, which prevented any vessel sailing for six weeks. In effect, the first arrival from England, after our own, was that of the Claudine, on the 4th of April, with letters dated January 1st.(iv.) ...” “Result of Astronomical Observations, Made During the Years 1834, 5, 6, 7, 8, At the Cape of Good Hope ... “ by Sir John Herschel, 1847 John Herschel rented a property and set up the twenty foot reflector near Table Mountain, at a site, that was then, just outside of Cape Town. The Twenty Feet Reflector at Feldhausen, Cape of Good Hope, South Africa, 1834 This telescope was made by Herschel in England and transported, along with his other instruments, by ship to Cape Town and then inland to Feldhausen.  The telescope is a Newtonian reflector, built to William Herschel’s design, with a focal length of 20 feet and clear aperture of 18 1/4 inches ( f13 ). The location of the telescope was established by careful survey to be: lat 33d 55’ 56.55”,  long 22h 46’ 9.11” W ( or 18.462 deg E ).  The site of the great telescope was memorialised by the people of Cape Town by the erection of a granite column that is still there today.   ............. Observations of the Sculptor Galaxy Amongst his many thousands of observations made from Cape Town, of nebulae, clusters of stars, double stars, the sun, etc., Sir John Herschel records that he observed V.1 ( CH10 - Caroline’s Nebula - the Sculptor Galaxy ) during two different “sweeps” and gave it the number 2345 in his South African catalogue. Sweeps:    646 -  20th November 1835;   733 - 12th September 1836 At the latitude of Feldhausen, and on these dates, the Sculptor galaxy would have been at an altitude around 80 degrees above the northern horizon when near the meridian ( which was where the telescope was pointed during Herschel’s “sweeps” ). The sight afforded from this location, with the Sculptor Galaxy almost at the zenith, must have been significantly brighter and clearer than the Herschels had thus far been granted from its location way down near the horizon south of Slough. .......... Other Obsevations by John Herschel from Cape Town Also observed by John Herschel in 1835 were the people and animals that inhabit the moon ... The Great Moon Hoax of 1825 - “Lunar Animals and other Objects, Discovered by Sir John Herschel in his Observatory at the Cape of Good Hope ... “  




Cashing in on Photons - Auction prize

Every Autumn our local pub organises a charity auction evening.  As one of the lots I offer a voucher for 'An evening of Astronomy'.  This blog shows the outcome of the last winning bid as posted on the local website, warts and all. Cashing in on photons   A short article on an outreach at the Bishop Monkton observatory   Sunday the 22nd of October 2017, a week after the annual auction at the Lamb and Flag, the owners of the Astronomy Evening voucher from 2016 made it to the observatory.  It may have taken a year to arrange but that’s nothing to the 2.3 million year old photons hitting our eyes from M31, the Andromeda galaxy.   The author’s own image of M31, the Andromeda galaxy.   This was just one of the sights I was able to show to my guests, Carole, David, Stancey and Olly.  What great companions they were too being very patient as I waffled on about the secrets Andromeda gave up to Edwin Hubble and the scientific community in the early 1920s.  Showing the attentive audience how to star hop just with their eyes from the great square of Pegasus to a large fuzzy patch overhead was all it needed. Until then most astronomers believed everything we could see was contained within our own galaxy, the Milky Way.  How much further from the truth could that have been, as we now know it is merely in our backyard in astronomical terms.   Testing the sky was also on the agenda for the evening and the conditions were such that we could just make out the seven main stars of Ursa Minor with normal vision.  That equates to a magnitude 5 sky so not too bad but how much better it could be without all the untamed light around us.  Olly, pointing at the Pleiades, remarked that he always thought that was Ursa Minor. An open cluster, number 45 in Messier’s catalogue, known as the Seven Sisters or Subaru in Japan is a very young, close group of hot white/blue stars formed from the same cloud of gas.     The author’s own image of the Pleiades (M45).   We had to crack on though and put to use the short, telescope driving lesson undertaken under red light and over a glass of wine earlier in the kitchen.  I wanted to make sure we didn’t miss a chance to view M13, the Great Hercules globular cluster before it sank below the rooftops.  It proved a bit of a tough nut to crack because to get the most out of it we had to use a technique called averted vision.  David realised that the large fuzzy ball in the eyepiece was made of thousands of stars, bound together by their own gravity like a swarm of bees around a honey pot.  These 12 Billion year old stars though take us back to the very start of the Universe.   M13, the Great Hercules globular cluster (Wikipedia commons credit; rawastrodata.com).   It was time to move on to some other deep sky objects so we dipped into the space between Perseus and Cassiopeia to sample the double cluster that is pretty in itself but I wanted my audience to look a bit deeper.   Our eyes are poorly equipped compared to cameras but obvious to all is a rich, orange star apparently visiting the cluster of younger members.    Colour tells us so much about a star and so we chased Cygnus the Swan across the Milky Way with both ‘scopes to pinpoint Alberio, the star designating the swan’s head.  In the ‘scope everybody detected Alberio as two stars of sharply contrasting colours, an optical double, often described as indigo and gold telling us immediately that they have markedly different surface temperatures and characteristics.  Are they gravitationally bound as a binary system? Well the jury is out on that one but current estimates have one third of all stars in the Milky Way to be true binaries.   Getting towards the end of the evening it was time for a couple of more challenging objects.  Number 57 in Messier’s catalogue is described as a planetary nebula purely because when viewed in the 18th century it resembled a view of the know planets, small, round (ish) and some colour.  These objects have nothing to do with planets but are the result of the after effects of a dying star that has puffed off its last layers of gas leaving a white dwarf at the centre.  The gas is energised by the radiation from the star and takes on colours that are determine by its composition, very often the green of triply ionised oxygen.   M57, the Ring nebula (NASA/ESA public domain)   I tried hard to answer and fulfil the questions and requests from my guests and one of the first queries raised before we left the kitchen, was “Can we see any planets?”.  Unfortunately it’s pretty poor times in the UK right now for the top targets and will be for some time.  However, the two ice giants are in the southern sky so in theory are visible but crikey they are a long way off.    With Olly’s help and whilst the others warmed up in the kitchen we changed to my old Schmidt Cassegrain telescope that has a focal length of 2.3 metres to attempt this feat.  This also meant realigning the telescope mount. That took a few minutes but it was then possible to pick out Uranus, which is about 4 Earths wide at a distance of nearly 3 billion miles! It is obviously a disk that has a slight green tinge.  We also tried to view Neptune, which is a massive 4.5 billion miles away but the view was slightly obstructed by my roof!   Uranus and Earth comparison (NASA public domain).   Visitor comments   Carole kindly remarked about the group’s experience of the evening and her words are below.   “We had been looking forward to this evening ever since we bid for it in the auction. It took a while for us to find a time that was good for everyone and for the skies to be clear and not moonlit.  It was well worth the wait and a huge thanks to Chris for offering the event and putting on such an amazing evening.    Having only a very limited knowledge of astronomy, it was great to have Chris enthusiastically explaining to us what we were seeing.  He has an array of different telescopes and he patiently set them up in his observatory for us to get the best view of the various stars and planets. Seeing the telescopes and learning about how they are controlled to lock onto coordinates in the sky is fascinating in itself.    Chris has already described above the range of astronomical bodies we focused on in just a couple of hours. Before the evening I don’t think any of us had heard of Messier’s catalogue! There is just so much to observe and it was a treat to see two remote planets. Neptune was a bit naughty trying to hide behind the house chimney but we just about saw it. We also saw Uranus, which was a bonus. Everything else was good to see and the evening was very enjoyable so we hope to see some more at a future date.”




Nikon D7500 -v- D5300 Dark Frame comparison ( Astrophotography )

Below is a comparison between single dark frames taken with the Nikon D7500 and D5300 with exposure durations varying from 1 sec to 240 sec ( my usual main light frame exposure ) all at ISO400. Firstly a graph of the standard deviation of the noise in the dark frames versus exposure time: The standard deviation of the noise is a fairly constant 2 ADU less for the D7500 compared to the D5300 ( pretty much the difference in the read noise between the two ) However, the difference is not just in absolute terms but also in the quality of the noise ... Below are the dark frames -  ranging from 240 sec exposures at the top to 1 sec at the bottom:                                      D7500                                                                              D5300     The D5300 dark frames clearly show the pattern in the read noise ( banding down the bottom ) and also have far more chrominance noise compared to the D7500. At 240 seconds ( the main exposure I have been using ) the difference is starkly different; the D7500 produces images with much lower noise that is significantly more even and random and hence more likely to be reduced during integration.




D7500 - Read noise and patterns in bias frames ( Astrophotography )

The Nikon D5300 has a well-earned reputation as one of the lowest noise DSLR cameras used for Astrophotography.  Now that I have a new Nikon D7500, I was keen to see how it compared to the D5300 in terms of the level of read noise and the extent to which that read noise is non-random ( and thus needs to be removed using a Master Bias frame to prevent it summing up during image integration).    So here goes ... ......... A single bias frame Nikon D5300: ISO400, 1/4000th second: This may look pretty bad but really the extreme stretch is bringing out the very small variations across the frame:

Standard Deviation:     3.53 ADU ( note: in this context,  3.53 ADU means 3.53 "units" on a real number scale ranging from 0 to 16,383 ( ie. a real conversion of a 14 bit digital scale ))   The master bias frame looks like this: Nikon D5300: ISO400, 1000 x 1/4000th sec frames Standard deviation: 0.48 ADU The bands at the bottom are each 1 ADU brighter than the one above.   Now for the D7500 ... A single bias frame from the Nikon D7500: ISO400, 1/4000th second: It is immediately clear that the single bias frame is cleaner.  The statistics confirm this:

Standard Deviation:     1.37 ADU   And the master bias ... Nikon D7500: ISO400, 1000 x 1/4000th sec frame Standard deviation: 0.07 ADU The band at the bottom is 1 ADU brighter than the background.   The improvement is very obvious Std. Deviation single bias frame:  1.37 versus 3.53 Std. Deviation master bias ( 1000 frames ):  0.07 versus 0.48   In graphical form ...   Conclusion: The read noise in a single frame from the D7500 is around 40% of that in one from the D5300.  This should give me greater flexibility to reduce exposure times and still ensure that the read noise is only an insignificant component of the overall noise. I will need to consider further the impact of the very low level of pattern noise in the Master Bias; it is so low that I will think about whether or not I still need to calibrate my lights with a Master Bias ( particularly for long exposures when the noise is dominated by light pollution and thermal noise ).      




My new love - the Nikon D7500

It was love at first sight when I first laid eyes on the gorgeous noise curves of my dear Nikon D5300; young and beautiful with a great body and a large sensor, I was smitten.  Now, well, what can I say... my roving eye has spied a new beauty; younger with heaps of energy that should go all night and , whilst I do prefer larger sensors, I can’t stop thinking about the noise curves hidden beneath that lovely new body...   I struggled with my guilt for ages, I really did, but the time has come - I’m dumping the D5300 for the new love of my life; the Nikon D7500.    




Aurora Reykjavik October 2017

Just got back from Iceland having enjoyed a few days sploshing about in the geothermal waters, looking at waterfalls and geysers and eating lots of cod. As you can imagine, we were very excited at the prospect of seeing the Aurora Borealis.  Unsurprisingly, nights went by under a dense blanket of cloud. Then, on the morning of the last full day of our holiday, the sun came out and so did we.  After a full 10 hours traipsing about a glacier and investigating basalt columns on a black beach we returned to our hotel in Reykjavik.  Night fell - clunk!  One by one all the light pollution came on all over the city - but what was that faint sepulchre glow advancing from the far North across the slate grey Arctic Ocean?  Hurrah at the twelfth hour we got to see the Northern Lights. An excellent display it was too - lasting for about three hours. With the naked eye we could clearly distinguish green , magenta and blue light and we managed to take some photographs. Our astronomical cup overflowed. I have attached a rough and ready annimation which gives some impression from the early moments of the display.  




All Sky Camera Mark 7

This is my latest generation of all sky cameras and based on the ASI178MM followed by ASI185MC CMOS astro camera and a Fujinon fish-eye lens of 1.4mm focal length.  Although rated at f1.8, this lens lets a lot more light through than this would imply.  Image capture is provided by a Raspberry Pi 3 in conjunction with INDI software.  This is used with KStars/Ekos client software running on a Linux Mint desktop indoors.  Communication is via Wi-Fi.  The Mark 6 ASC has proved inadequate after being in use for some time.  This blog will describe the problems of the Mark 6 and report my progress in developing this new version.




Dream of clear skies

So what have I seen through my scopes since the last blog..............zip.........nothing.....nowt....zero The wonderful Cornish skies have been full of clouds, when I've been awake anyway, and now the howling gales prevent even standing my scopes upright even if the clouds clear. I had one glorious night of dark skies while on a work trip to central Germany, the sky lit up with stars, unfortunately my scopes were back in Blighty. Still just staring upwards can be so rewarding.....I highly recommend it! So short and sweet (as my father used to say "like a roasted maggot") but I live in hope of nights out with my scopes, I did manage to buy a new 8mm BST EP which I can't wait to use.......reviews seem pretty good Clear skies to all




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