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Dave Smith

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Everything posted by Dave Smith

  1. Lovely set of data. This one brings back memories. Many Moons ago I did the Open University practical course "Observing the Universe" in Majorca and this star we used as a team project introducing us to photometry using MaximDL on one of the nights. Dave
  2. Hi Billy. I have never had any concerns about atmospheric correction because my comparison stars have always been in the same field of view. If there are no "official" guide stars in the FOV I choose others using Guide software with the UCAC4 star database added. Mostly, however, I use the comparison stars given on an AAVSO chart. My FOV is around 30'. When I used my 90mm refractor the FOV was approx 1.5 degrees but had no problem with atmospheric correction. https://www.projectpluto.com/ Hope that helps Dave
  3. I can't get a direct link but the page I had in mind can be found by following the Beginners link on the BAA website. http://www.britastro.org/vss/ There is also much detail on visual observing on Gary Poyner's website http://variablestars.co.uk Gary has impressivly submitted more than a quarter of a million visual observations from light polluted birmingham. The Society of Popular Astronomy also have a guide to visual observing which is linked to on this page https://www.popastro.com/main_spa1/variablestar/ Hope they are useful. Dave
  4. Some valuable variable star results are produced by visual observers. There is a guide to visual observation of variable ststs on the BAA web site. I will post a link in the morning. Dave
  5. Observing Variable Stars Why observe variable stars? It is fascinating to directly observe the variation in brightness of a star and ponder as to why it is varying. Some vary because the star is intrinsically varying e.g. due to it regularly expanding and contracting and some vary because there are actually two stars eclipsing one another. Some variations are highly predictable while others are not. Professional astronomers who study stars are highly dependent on the results of amateurs which mean any observations are very useful. What equipment is needed? Stars can be observed with just the naked eye but to be of scientific use then the minimum requirement would be just a pair of binoculars. Many variable star observers make valuable contributions to the databases using binoculars or telescope by visually comparing the brightness of the star with that of nearby standard stars over a period of time. More precise estimates of brightness can be obtained with a telescope and camera (DLSR or CCD camera). Software (Free or paid for) is available to enable the measurements of variable stars compared with standard stars. Anyone who can take an astro-image and apply darks, bias and flats would be able to take useful variable star measurements. When starting out it is not necessary to purchase any filters. Once you are capable of taking a reliable set of readings the first filter to consider is a Johnson V filter. Even then a filter is not vital to make a valuable contribution. Which software? I started off using MaximDL simply because I already had it. I would not recommend buying it (it is very expensive) for this purpose as better free software is available. There are two free astronomy applications available and I have used both. Firstly Muniwin. It does the analysis on images and produces a spreadsheet ready for submitting to the BAA VSS database and the AAVSO database. I have found, however, that it sometimes rejects some of the data for no apparent (to me) reason. More recently AstroImageJ has become available and seems far more consistent. Both of these two packages come with help files. Collecting data My experience has been entirely using a CCD camera for variable star observations and so the descriptions that follow are biased towards that. There are links at the end which will give guidance on visual observing or using a DSLR camera. I am restricting the software description to using AstroImageJ Choosing a target star Fortunately there is much help on this on the BAA variable star section database. http://www.britastro.org/vss/ Follow the link to Observational Programmes – CCD Eclipsing Eclipse predictions. I would recommend as a first choice an eclipsing binary star as the variability is continuous which makes detection of some variability highly likely on first attempt. Finder charts Some are available on the BAA site but I find the aavso site more useful. https://www.aavso.org/ The charts that can be printed from there include comparison stars with their precise magnitudes. E.g. EG CEP Locating the star. Personally I think SGPro is superb for getting the star in the middle of the FOV especially if plate solving is used. There is no need to worry about orientation, just get the star centred in the FOV. Depending on your scope and mount guiding may be necessary to keep the star in position. The task is then to obtain images over a period of time such that the target star and comparison stars are not at or near saturation. Using AstroImageJ Download it from https://www.astro.louisville.edu/software/astroimagej/ On first use it is important to upgrade to the latest version by clicking on “help” “update” and then going up to “latest build”. To check that star image is not close to saturation Open the file to be checked and then place the cursor over star and ALT-CLICK. A profile of the star will appear. As long as the highest point on the graph is well below saturation point (around 65000 for a 16 bit camera) and the sky background level is reasonably below the signal level all is ok. It does not matter if there is a star in the field of view that is saturated as long as it isn’t being used as a comparison star. Data collection, calibration and photometry Once the data has been collected AstroImageJ can be used to do the calibration. Click the DP button and two windows will appear. You need the Data Processor window. The other can be closed. On the first line click the first blue folder symbol and navigate to where the light files are stored and click select. Then click on the second blue folder symbol and click on the first file in the series and click open. Further down do similar selections for your master dark and master flat. If you want to use AstroImageJ to construct the masters then please read the full AIJ instructions (see links) Once that is done click START at the bottom and the files will be calibrated and put into a sub-folder pipelineout. (You can change this name is you wish). Platesolving It is not absolutely necessary to plate solve the images but it can save a lot of trouble. If all the images are well aligned and there has not been a meridian flip then you may get away without the plate solving stage. I have found that plate solving the images leads to smooth running of AIJ in the photometry stage. It is also well worth installing a local version of astometry.net as explained on the AIJ forum (see references). It takes under 20 seconds per image with the local plate solver. If there are many images the computer can be left to itself while solving. To plate solve with AIJ proceed as follows. Import the calibrated files to AIJ and select the astrometry icon. Most of the selections are clear but it is important that you input the correct arcsec/pix for your scope camera and the R.A. and DEC of the target star (from the aavso finder chart). Then click START and if all is ok it will proceed with the plate solving. Running AIJ photometry Import the plate solved files into AIJ and click on the Multi-aperture-Measurements icon The following window will open. Tick boxes as shown and then click on the Place Apertures button. First left-click on the target star (the variable) and then the comparison stars. The variable will be labelled T1 and the comparison stars C2, C3 etc. When finished multiple windows will open including a plot and a measurements spreadsheet. The measurements spreadsheet needs to be saved as Measurements.txt The plot can be configured to plot any aspect from the Measurements file including the star magnitudes (if the box on the penultimate line of the Multi-aperture measurements is checked. Submitting results to the BAA and/or AAVSO databases. You do not need to be a member of the BAA or AAVSO but you do need to apply for a login. See the BAAVSS database or AAVSO website for details. To generate files in a format to upload to either organisation, the BAA Photometry Spreadsheet is required and can be downloaded from the BAA database. There is also a full guide to AIJ and the Photometry Spreadsheet available. I find it convenient to use Excel to plot a graph of magnitude against time as there is more flexibility with presentation. e.g. If you get stuck at any point and cannot find any help in the references then do not hesitate to contact me by pm on SGL. Dave Smith Feb 2019 References BAAVSS website http://www.britastro.org/vss/ There are many links there to VSS database Eclipse predictions Charts CCD (Target lists) and many more Beginners AAVSO website https://www.aavso.org/ AstroImageJ https://www.astro.louisville.edu/software/astroimagej/ AIJ user guide https://www.astro.louisville.edu/software/astroimagej/guide/AstroImageJ_User_Guide.pdf AstroImageJ Forum http://astroimagej.1065399.n5.nabble.com/ Astrodennis guide to exoplanet imaging using AstroImageJ http://astrodennis.com/ There is also much detail on visual observing on Gary Poyner's website http://variablestars.co.uk Gary has impressivly submitted more than a quarter of a million visual observations from light polluted birmingham. The Society of Popular Astronomy also have a guide to visual observing which is linked to on this page https://www.popastro.com/main_spa1/variablestar/
  6. Counter balance for my 250P Flextube GOTO Dobsonian. https://www.decathlon.co.uk/2-kg-coated-lead-diving-weight-id_8015197.html Does the job nicely. One luggage strap was secure but I'm just being careful. They also come in 1kg or 500g sizes. Dave
  7. You are correct, but to me it is using SkySafari that the big advantage. The Synscan app is ok but I wouldn't have bought the adapter just for that. The Synscan app does however have a better 2 star alignment with the scope pointing N and horizontal. Good for those who don't know star names. Dave
  8. The range is far more than you will ever need. I demonstrated it to our club last week and with the mount at the front and me at the back of the hall it still worked. At home it works from the next room. Dave
  9. No. It needs to be either SkySafari 5 plus or SkySafari 5 Pro according to the instructions in the Synscan app. Dave
  10. Very much so. Earlier I couldn't get it to work again but have now succeeded. It is important to have connection to the same IP address. So I am able to use my iPad as long as my Android phone is running Synscan. Phew ? Dave
  11. But it doesn't work the other way round, I.e. with Synscan on the iPad and SkySafari on the Android phone. So nothing is certain. Dave
  12. There is a good chance that will work. I have just used my Android phone to connect to the mount wirelessly with Synscan App and then ran SkySafari5 pro on my iP9ad and it worked!!! I have an old iPod touch but couldn't get Synscan app to run so you may need to be careful your old phone is not too old. Dave
  13. The Synscan app will run fine. I'm not so sure about SkySafari. It may be possible with two adapters but I don't know how. Simpler to get an Android phone. Dave
  14. OK I've plugged the wifi adapter in the handset but it doesn't power up so no go. I'm not too keen to experiment much as I can use an android phone and don't want to risk damaging the wifi adapter. Dave
  15. On my dob mount there isn't a multi-purpose port so if the hand set is plugged in then there is nowhere to possibly connect the wifi adapter. So I would agree with stash_old's conclusion. However with an android phone or tablet all is fine Dave
  16. Thanks for that. I have seen that as well, but where on earth you would plug a second adapter in, I do not know? The Synscan app does work fine on the iPad. In the instructions for an iOS device it says enter the IP address of the device that runs the Synscan App. I haven't a clue how to find that. Anyone any ideas? Not urgent for me but others may find it useful. Dave
  17. Funny you should say that Ed. I'm on Wednesday evening if it is cloudy. Dave
  18. I have recently purchased this in the hope that I could control my SkyWatcher 250P GOTO dob with SkySafariPro on my Samsung Phone. The provided handset does not seem to have a straightforward means of correcting an imprecise alignment without going through the whole alignment process again. In SkySafari the align button does this with just one press. The unit itself is quite small (see pic) and plugs in place of the handset. The app "Synscan" is needed from Android Play Store or the Apple App Store for any ALT-AZ mount. "SynscanPro" is needed for RA-DEC mounts. As long as the phone or device is set to connect via WiFi and the Synscan signal is chosen that is very straight forward and will connect readily. For me the "fun" started when attempting to connect via SkySafari. I did watch a couple of YouTube videos but the instructions given did not work for me. There are no instructions provided with the adapter but there are some within the Synscan App. (although not very obvious). The Synscan app needs to be active and connected to the mount and before trying SkySafari needs to have carried out an alignment. (This isn't necessary for testing purposes) The settings for SkySafari need to be as follows. Firstly choose the Scope type i.e SkyWatcher SynScan then the mount type - in my case Alt-Az GoTo Select Connect via WiFi IP address 127.0.0.1 Port Number 11882 SkySafari should then be able to connect to the mount via the Synscan App. In my case it did not. Much hair tearing (not that I have much!) and a few hours later it did connect and then later did not. Over the next 24 hours I managed to get connection twice but many times no connection. To cut a long story short it turned out that I had my phone using a battery saving mode and the two occasions it had worked was when the phone was connected to the charger. So out of battery saving mode and it works smoothly every time. Advantages of using the WiFi adapter. 1. Obviously no lead. It works at distances greater than you would need - I went into the next room and could still control the scope. 2. Much easier to read than the one line at a time on the handset. Particularly useful when choosing alignment stars - you can see a long list straight away. 3. The buttons on the Synscan App have more directions to choose (see pic) 4. Within the Synscan App there is a cool feature where the scope will goto the direction you are pointing the phone (or other controlling device) and you can then have all objects nearby listed for potential goto. 5. The Synscan App does also work on my iPad but have not yet managed to get SkySafari to connect yet. (I haven't tried very hard at this stage) 6. The sync facility in SkySafari is great e.g. on an open evening a child grabs the eyepiece and moves the scope off target, one button push and it will return. 7. The obvious advantage of using a star chart to choose an object. e.g. for finding things like the double cluster or double-double when you cannot remember the ngc or ic number. WARNING - Since getting the adapter to work on my phone I have not had the opportunity to test it under the stars. Should I find it does not perform as expected I will report back. At this stage I am delighted with my purchase. Dave
  19. Oh dear, the third eyepiece in a week! at least this time I managed to sell a couple of items to pay for it. I now have 10mm XW, 17mm hyperion, 24mm hyperion, 32mm TV plossl and 30mm Moonfish. Also 2x and 3x barlows so am now happy. There is an urgent need to now save as I would very much like to upgrade the focuser on my 250PX Flex tube dob and depending on how I get on with Barlowing the 10mm XW, may consider a 5mm XW. Dave
  20. I would love to have your 5mm and the other Hyperion but simply no funds at the moment. Fortunately the 10mm XW does Barlow well. Dave
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