Robin Leadbeater

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Viewing 20 posts - 701 through 720 (of 1,188 total)
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  • in reply to: Winchester weekend sold out #580727
    Robin Leadbeater
    Participant

    I thought this was a BAA meeting

    in reply to: Sirius B #580694
    Robin Leadbeater
    Participant

    I’ve just seen there is now a revision to the path noted at the bottom of the page.  (The original track was calculated based on the position of the centre of mass of the A-B system rather than Sirius A !

    I hope you have not already made your travel plans !

    Robin

    in reply to: Sirius B #580693
    Robin Leadbeater
    Participant

    Just spotted this on the S&T website

    https://www.skyandtelescope.com/observing/will-sirius-disappear

    “Monday night, February 18th. That evening around 10:30 p.m. MST (5:30 UT February 19th), there’s a good probability that the 17th-magnitude 4388 Jürgenstock will occult the sky’s brightest star for up to 1.8 seconds.”

    The event is not visible from the UK but anyone on the narrow path though North America could get (very a brief) view of Sirius B free from the glare of its bright companion. (Sirius is predicted to be totally eclipsed for just 0.2sec !)

    Robin

    in reply to: Dew shields #580682
    Robin Leadbeater
    Participant

    I’ve not done any scientific measurements but when I made mine I read that most dew shields are too made short and they should be 3x the aperture. This does look rather long though and gives  problems with the mount in a breeze.  

    I first saw the newspaper trick on a small refractor at a sky party in Denmark. Most people who did not have heaters were struggling with dew but not this guy. (I think perhaps he changed it once during the night when it got too soggy)

    Robin

    in reply to: Dew shields #580681
    Robin Leadbeater
    Participant

    As an aside,  dew is less of a problem in breezy conditions as the airflow is constantly removing the cooling boundary layer of air over the surface where dew is forming. (Which is just as well as my dew shield acts as a sail !)

    in reply to: Dew shields #580679
    Robin Leadbeater
    Participant

    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

    in reply to: Meteor back scatter radio antenna #580657
    Robin Leadbeater
    Participant

    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

    in reply to: Meteor back scatter radio antenna #580654
    Robin Leadbeater
    Participant

    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

    in reply to: Possible nova in M31 #580653
    Robin Leadbeater
    Participant

    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

    in reply to: Possible nova in M31 #580647
    Robin Leadbeater
    Participant

    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

    in reply to: Possible nova in M31 #580644
    Robin Leadbeater
    Participant

    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

    in reply to: Possible nova in M31 #580625
    Robin Leadbeater
    Participant

    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

    in reply to: Possible nova in M31 #580615
    Robin Leadbeater
    Participant

    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

    in reply to: Possible nova in M31 #580614
    Robin Leadbeater
    Participant

    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.

    in reply to: Possible nova in M31 #580610
    Robin Leadbeater
    Participant

    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

    in reply to: potentially bright supernova in NGC3254 #580607
    Robin Leadbeater
    Participant

    A spectrum from last night with the ALPY 600 compared with a best match type Ia near maximum from GELATO

    in reply to: potentially bright supernova in NGC3254 #580570
    Robin Leadbeater
    Participant

    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

    in reply to: potentially bright supernova in NGC3254 #580567
    Robin Leadbeater
    Participant

    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

    in reply to: Dslr camera and reflector telescope #580559
    Robin Leadbeater
    Participant

    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

    in reply to: Dslr camera and reflector telescope #580558
    Robin Leadbeater
    Participant

    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

Viewing 20 posts - 701 through 720 (of 1,188 total)