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Dew forms on a surface when the temperature of that surface falls below the dew point. A surface exposed to the clear night sky cools by radiating heat out into space which is only a few degrees K (This is an over simplification of course as the atmosphere blocks the radiation at some wavelengths but you get the idea). A dew shield works by limiting the angle over which the heat can be radiated away. Cooling still takes place but more slowly. There may be other effects. For example some people swear by rolled up newspaper or other absorbing material which perhaps preferentially absorbs the moisture in the air close to the optics.
Cheers
Robin
Hi Eric,
If you were transmitting you might want to tune it more precisely to provide a better match to the transmitter but a 3 element yagi antenna tuned for 144-148MHz should work ok at 143MHz for receiving. (It would be difficult to retune in any case as you would need to increase the length of the elements slightly). For example there is an article on the BAA radio astronomy website showing a 7 element yagi centred on 143 MHz with a flat response over +-7MHz bandwidth, fig 2.9 on page 8 here
https://www.britastro.org/radio/projects/Antennas_for_meteor_radar.pdf
Robin
Hi Eric,
Is this specifically using the Graves transmitter on 143MHz ? If so a small 2m amateur band yagi could be a good choice. Like these perhaps
https://www.radioworld.co.uk/hygain-2m-3-el-beam-500w—vb-23fm
https://hamradiostore.co.uk/cushcraft-a148-3s.html
Cheers
Robin
Hi George,
The fits file is 2 column data table (wavelength and flux) not an image so Maxim does not understand it. You can view the data in a free general fits data viewer like NASA’s fv for example or alternatively download the dat file version and view it in notepad, excel etc. Better though is to view it in a free dedicated spectroscopy program like Visual Spec or ISIS etc. I have also loaded it into the BAA spectroscopy database so you can view it there too.
https://britastro.org/specdb/data_graph.php?obs_id=3607
Cheers
Robin
Hi George,
There is another one classified by me last October which was then also confirmed by professionals
https://britastro.org/node/15857
but I dont know of any others.
It would be nice to have a higher SNR spectrum to confirm the presence of other features (eg Fe curtain or He, N lines) but that would need a larger telescope. The spectroscopic evolution of an initial blue continuum with a strong H alpha emission emerging over time with around this velocity is characteristic of a nova though.
Cheers
Robin
The spectrum has now developed sufficiently to attempt a classification.
It shows a clear broad (~1600km/s FWHM ) Ha alpha emission line and an H beta emission line at the expected radial velocity for this region of M31 so in the absence of any professional spectra, I have classified it as a Nova in TNS.
Robin
I spent 2 more hours on the spectrum last night but no better. (The “light pollution” from the galaxy is just too much. The sky background in the slit is ~8x the star signal) so no spectroscopic confirmation yet I am afraid. If there is still no confirming pro spectrum I might try again in a few days when any characteristic spectral features should have developed more.
Robin
Very noisy at an SNR of just ~3-4. A blue continuum with no obvious features (though they would have to be very strong to show at this SNR) There is an emission feature at H alpha at the expected local velocity (-500km/s) but it could equally well be just noise.
Robin
On it now with the ALPY 600. It is there but barely above the background. Perhaps a hint of broad H alpha. Rain is due in 10 mins so an hours worth is all I am going to get tonight.
Nice find George/Nick !
I saw this pop up on my TNS alert yesterday but the skies had just clouded over. You are probably right though unless it brightens a bit. mag 17 is extremely marginal for me for a spectrum with enough resolution for a firm confirmation (ALPY 600) and as you say, the bright background wont help. It is on my list though. (I am starting to look at the potential to confirm M31 novae spectroscopically so if you like, you can contact me direct for a confirming spectrum if you find something interesting. The M31 season is probably closing for this now though as I need at least a couple of hours fully dark and at good altitude)
Cheers
Robin
A spectrum from last night with the ALPY 600 compared with a best match type Ia near maximum from GELATO
Peter Somogyi has now posted an amateur spectrum on the ARAS forum using an ALPY 600
http://www.spectro-aras.com/forum/viewtopic.php?f=38&t=2205#p12098
He has also posted a spectrum of sn2018hna which I classified as a type II when discovered back in October 2018 at mag 16 but strangely has been rising steadily since it was discovered and is currently mag 13.7
http://www.spectro-aras.com/forum/viewtopic.php?f=38&t=2214
The differences in the spectrum between the two (Ia and IIP) are very obvious
Cheers
Robin
Hi Paul,
It has not maxed out yet so if it follows the normal Ia light curve will likely be around mag 16 in a month’s time so still an easy imaging target.
Note my original comment on mag 18 being out of range for amateurs referred specifically to spectroscopy, not imaging. With my ALPY 200 the target has to be about 6.5 mags brighter for spectroscopy than for a conventional photometry image. The big advantage with slit spectroscopy though is most of the sky background is kept out by the slit so you can get away with much higher levels of light pollution. My limiting spectroscopic magnitude is ~17.5 which corresponds to mag 24 for photometry. I would need much darker skies to do photometry that deep in a conventional image though.
Cheers
Robin
And of course you can also use your DSLR with your Star Analyser to do some simple spectroscopy that you asked about
https://britastro.org/node/16809
There are some tips on how to do this on Christian Buil’s page here
http://www.astrosurf.com/buil/staranalyser/obs.htm
(Don’t worry about the wedge prism or focal reducer he uses there, just screw the Star Analyser on the front of the nosepiece adapter)
Robin
Hi Garion,
DSLR are very popular for astrophotography and it is possible to produce some stunning deep sky images with a DSLR used at prime focus (eg using a T ring and eyepiece adapter in place of the lens and mounting the camera in place of the eyepiece)
eg this website picked at random from the many out there
http://ried-sternwarte.de/dslr-galerie.html
You ask if it will work with your reflector and there are two potential issues that you will need to check with your particular setup.
If you plan to use it at prime focus, you will need to check that you can reach focus. (This can be a problem with Newtonians and DSLR as you might not be able to wind the focuser in far enough to place the camera sensor at the telescope focal plane) You can add a Barlow lens to get round this but this increases the focal length, making the stability and tracking capability of the mount more critical.
You will need to test the stability of your mount and how well it will track. You might struggle with your Meade Polaris 130MD with its EQ3 mount and simple motor drive, but the best way to find out is to try it.
Cheers
Robin
I see this website which plots the VIIRS satellite data also accepts SQM readings, though they are rather sparse
https://www.lightpollutionmap.info/#zoom=6&lat=7401398&lon=-432104&layers=B0FFTFFFFFT
The string of readings up the M6/A74 is interesting. Perhaps I should mount a one on the roof of the car, coupled with a GPS logger.
Robin
Yes possibly of not much scientific value unless you can get a large enough number of observers in a given location and over a reasonable length time to beat down the variability (The key to success in citizen science projects) but I suspect this project by CPRE is more about public awareness of the issue and to get a conversation going than the actual quality of the measurement. Hence the use of an instantly recognisable constellation. Interestingly I met a casual observer from a nearby village the other day who had been lent a sky quality meter to monitor their skies by the Friends of the Lake District.
Robin
It depends on your budget and what else you plan to do with the camera really. There is a lot of choice out there. Simple CMOS mono cameras with 1/3 size sensors typically used as guiders work ok with the SA, can be used for simple imaging of planets and brighter deep sky objects and can be bought from around £150-180. If you want a camera which can take spectra and images of faint objects or do photometry though then a camera with a larger size cooled sensor would be better and more versatile but are more expensive, typically ~£800 to the skies the limit. Good value can sometimes be found second hand though as people trade up. I have bought through Uk AstroBuySell for example.
It looks like some extra characters got attached to the spectroscopy section link – fixed now.
perhaps the webmaster can move this thread there ?
The Starshoot might work to get you started but I have heard reports that it goes completely blank on fainter objects (even Saturn!) rather than show a noisy image so it might not work so well. In any case a mono camera would be much better for science (including spectroscopy and photometry) so that could be the way to go if that is where your interests lie.
I see from your own page on here you have a small Newtonian on a driven mount. That will work well with the Star Analyser. For starters, just focus the Star Shoot on Betelgeuse, then screw the SA on the front of the camera nosepiece, refocus slightly to pick up the features in the spectrum and see what you get. (There will be two spectra, one either side of the star image, go for the brighter one and adjust the exposure so it is not over exposed). You should be able to see something like this spectrum of Delta Virginis on my website, though perhaps without the extended range into the IR as your camera probably has an IR blocking filter built in. The broad bands are from TiO molecules which form in the atmosphere of cool stars.
http://www.threehillsobservatory.co.uk/astro/spectra_14.htm
Good Luck!
