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robin_astro

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About robin_astro

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    http://www.threehillsobservatory.co.uk

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  1. For (a), if this was a real situation and not a typical simplistic course question, then you would also need to consider the solar spectral energy density, the atmospheric transmission and the efficiency of the solar cells with wavelength. (Not sure why they have given you the diameter of the sun, except that with this and the luminosity, you could estimate the temperature and hence the spectral energy density, though I doubt that is what they intended. Cheers Robin EDIT: Holy thread resurrection batman!
  2. How does it look from the back? (Mirror slits are normally back surfaced so you dont get ghost spectra from internal reflections reflected into the spectrograph) Cheers Robin
  3. Hi Eric, That's a nice build and first light results. You can get to impressively high resolution to with the 1800 l/mm grating. There are some recent results with this grating on the VdS forum, for example splitting the binary components of Mizar in the H alpha line https://forum.vdsastro.de/viewtopic.php?f=24&t=5685 Cheers Robin
  4. No it doesn't. As well as your schoolboy error mixing radians and degrees, You can measure the position of the star ie the centroid of the star image to much greater precision than the resolution
  5. A spectrum last night https://britastro.org/specdb/data_graph.php?obs_id=3925 Robin
  6. Depending on what lines you are looking for you dont need to go that far into the IR. For example at high redshifts the Lyman jump in the UV at 1216A is shifted into the visible eg as here at z=3.87 http://www.threehillsobservatory.co.uk/astro/spectra_22.htm and at low redshifts the H Balmer lines are still measurable without an order filter eg as here http://www.threehillsobservatory.co.uk/astro/spectra_12.htm (bottom of the page) http://www.threehillsobservatory.co.uk/astro/spectra_21.htm Robin
  7. Alternatively you can use a wedge prism to separate the orders vertically (like an echelle spectrograph) This does have the disadvantage that the spectrum is slightly curved though Robin
  8. Hi Vlaiv There is no light in astronomical spectra below 3100A (The atmospheric ozone cut off) so you can go for a higher cut off than that if you like . I used a 610nm Baader filter which I happened to have which has the advantage that the Sodium light pollution is kept out of the IR spectrum. http://www.threehillsobservatory.co.uk/astro/Classifying_red_stars_using_a_Star_Analyser_VdS_poster.pdf In practise though you can typically measure up to ~7000A with the Star Analyser unfiltered as the signal in the second order is very low below ~3500A because of the low sensitivity of the camera and the high blaze efficiency of the grating Cheers Robin
  9. The M42 spectrum is impressively clean considering your light pollution. Did you subtract a sky background spectrum ? Cheers Robin
  10. Hi Tobias, Are you planning to use use a solar analogue to divide the lunar spectrum by to calculate the lunar reflectance spectrum and how are you correcting for atmospheric extinction? Cheers Robin
  11. As a practical introduction to one aspect by Carl Reade. (Milky Way Hydrogen line observations) I can suggest this thread. Initially with the helical but later in the thread much better with a small dish I think my dad put a soldering iron in my hand when I was born and helped me pass my RAE back in 1964 aged 14. Still hold a ticket (G8DVW) but not been active for many, many years
  12. In the UK the best price for the Star Analyser will likely be direct from the manufacturer https://www.patonhawksley.com/gratings Robin
  13. Hi Gav, The focal length of the Cooke will be too long to give decent resolution used with the small sensor ASI camera I think but might possibly work with the modded DSLR where you can spread the spectrum out further. (The maximum resolution of the spectrum is effectively defined by the size of the star image relative to the length of the spectrum, then there are some additional aberrations due to the simple converging beam arrangement which ultimately limit it) . You could try a focal reducer but I suspect this setup will show significant chromatism though in any case, losing focus at the blue/UV end, seen as a "fishtail" at the end of the spectrum. The 200mm f5 Newtonian though would be an excellent choice if you can set that up. (You could almost piggyback it and use it as a finder/guidescope for the Cooke. The mount might not notice the small extra weight ? ) I dont know the Chamelion 3 I'm afraid. A quick google suggests it comes with various sensors so you would need to plug the appropriate numbers into the calculator. Does it have any long exposure capability ie a few seconds at least ? If so, it could be a better choice than the ASI 120. Room for experiment there I suspect Cheers Robin
  14. Christian Buil has some nice images and tips for using the SA with a DSLR (The wedge prism it is not needed) http://astrosurf.com/buil/staranalyser/obs.htm It helps extend the wavelength range if the IR blocking filter has been removed as here, also for the ASI120MC if it can be removed. Robin
  15. Did somebody Call ? ? Hello Gav, Yes either camera can be used with the Star Analyser but I would suggest the ASI120 for starters. A mono camera if available would be better though for the various reasons I outline here https://groups.yahoo.com/neo/groups/RSpec_Real_Time_Spectroscopy/conversations/messages/6782 To use the SA100 with the ASI120, you just screw it onto the nosepiece and use it pushed into the eyepiece holder as you would for normal imaging. You might want to add a spacer or two. For best resolution check the calculator and keep increasing distance from the sensor until the calculator starts complaining. https://www.rspec-astro.com/calculator/ Exposure times depend on how faint the target is (Anything from less than a second for the brightest stars to tens of minutes for mag 12 quasars or supernovae) but there is no need to guide, just align and stack shorter exposures. (An SA100 spectrum is typically about 6 mag fainter than the equivalent star so if you can record a mag 16 star say in a normal image say, you should be able to record a spectrum of a mag 10 star) For example there are many examples on my website taken using a mono modified webcam which should give some idea of the performance with the ASI120. The 10 inch Cooke refractor is a spectacular instrument but may not be the best choice. (What is the focal length? The SA works best with shorter focla lengths provied the focal ratio is higher than ~f5) What other scopes do you have? I would say the sweet spot for the SA is something like an f6 6-8 inch newtonian or a 100mm f6-8 apochromat. At larger apertures/longer focal lengths you can go fainter but resolution suffers Note that the Star Analyser is a very low resolution device, typically around 30-50A resolution so will not show fine details but works best on objects showing bold spectroscopic features. Cheers Robin
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