SteveBz

One further point on the gif bit. My PC is a Linux-based PC with 16GB or RAM and 2 GB of swap. A couple of days ago, I increased the swap size to 40 GB and the gif convert function worked fine, so it's clearly a question of memory. I don't know what the cut-off is. Steve.

So I've tried it out. Again, as usual, I'm not sure I got the sign right and some of the code is a bit clumsy. Here's the code: # Define RV of 29.8 km/s rv = 29.8 * u.km / u.s H_FREQUENCY = 1420405000 c_speed = 299792.458 # km/s for coords, signal in sorted(data.items(), key=lambda x: x[0]): # Create Array of RAs raSig=signal[2] ras.append(raSig) # RA # Create Array of DECs decSig=signal[3] decs.append(decSig) # DEC # Create Array of Peak signals sigs.append(signal[0]) # peak dB value # Convert Frequency to velocity v_doppler = c_speed*(signal[1]-H_FREQUENCY)/H_FREQUENCY # Calculate adustment due to Earths rotation around the SUn. observation = ICRS(ra=raSig*u.deg, dec=decSig*u.deg, \ pm_ra_cosdec=0*u.mas/u.yr, pm_dec=0*u.mas/u.yr, \ radial_velocity=rv, distance = 1*u.pc) rvAdj = observation.transform_to(LSR()).radial_velocity # Adjust Doppler velocity v_doppler=v_doppler+float(str(rvAdj)[:5]) # Create Array of adjusted velocities vels.append(v_doppler) Please feel free to peer-review. Here's the output the velocity range seems greater. It was -20 to +60 now it's -50 to + 70: Kind regards Steve

ZiHao, nice to see you back. Impressive. I'll try it out. It doesn't look too difficult. Kind regards Steve.

OK, cool. I got the sign wong. It's always the way. I won't bother using abs() because it's just needless processing and complexity. RA_Obs is the same as the RA that we are looking at, but where is RA_sun? Do you think I can get it from astropy? Kind regards Steve.

In other words: Dec1=Dec RA1 = RA_Obs+90-RA_Sun Is that right? Steve

So I we subtract (or do I mean add?) that from the measured Doppler shift, don't we get the true radial velocity of the gas cloud from the Sun?

I can only say OMG. Isn't there some simpler formula like: If we are only interested in movedment in the plane of the Galaxy, so b=0. Vm = measured velocity in direction <l>; Vs = Velocity of Sun around Galactic centre; Ve = Magnitude of velocity of Earth aound Sun - 29.8 km/s; phi = angle of the Earth's orbit against the Galactic plane m = month number Vm = Vs + Ve . cos(phi) . cos (l) . sin (2.pi. m/12) I'm just guessing, I haven't derived it, but something like that? Regards Steve

My last question is this. What about planetary movement? The velocities I measure are about +20 km/s -> -60 km/s. Planetary rotation is about .5 km/s, so doesn't really matter, but revolution around the sun is a bigger deal: speed = 150e6*2pi/(365*24*3600) km/s speed = 30 km/s So really the velocities should be adjusted by the position of the Earth in respect to the Sun and I'm not sure how to do this. What do you think? Kind regards Steve.

Very nice, I totally agree. Can I make 2 observations:? 1) the gif-maker never works until I run Mogrify on it and reduce the size of the .png files, so obviously the automatic gif at the end of 24 hours also always fails. On my copy I've stripped that out and then I mogrify -resize 2000x585 *.png Before run my stripped-out vesion of 'gif' 2) Secondly, I love the debug data-dump, so I always save it in the 24 hr scan, then I have a second python program to extract the data and map it (as you saw). I also save many more parameters in the .json file than you do, eg datetime, l & b coords and some other stuff.

Hi Astronomers, Crawley Astronomical Society would like to invite you to a Zoom event ... yes we're still virtual. This Friday, the 15th of April, we are delighted to host Wolfgang Steinicke, to speak on William Herschel’s epochal Observing Campaign. William and Caroline Herschel discovered many deep-sky objects between observed 1774-1817. Most were discovered by William in the monumental sweep campaign (1783-1802), assisted by his talented sister. 2500 objects were published in three catalogues. The study of the sky from southern England also concerned double stars and the Solar System, yielding the Uranus discovery in 1781. This invitation is for this Friday, the 15th at 7:30. And as always, it's an opportunity to discuss what's on your mind astro-wise and chat to other members.   Continuing with Zoom, downloadable free on your mobile phone, your laptop, your PC or Mac, our Agenda for Friday 15th at 7:30, is: 1 – Get people connected. The link is: https://us02web.zoom.us/j/84453092128?pwd=QjZ0UDBFZTVqTjBOV1dVRTRScm9kZz09 (Meeting ID: 844 5309 2128, Passcode: 412277). I will start the session around 7.15 for a 7:30 start. 2 – Introduction. 3 – Wolfgang Steinicke on “William and Caroline Herschel”. 4 – Sky Diary & members photos. 5 – Virtual break for virtual tea and coffee (or something stronger) 5 – CAS News. 6 – AOB. More details and photos on the website: https://crawleyas.co.uk/meetings/ As always, please let me know if you would like to do a trial connection beforehand. Hope to see you there. Regards, Steve.

So here is the final image. About a week of scans. The top row and the bottom row seem to have a bit of a weaker signal. I think because of the roof at one side and the tree-line on the other. Also a few samples missing from the dec=61 degrees line. It would really benefit from running for another week in the middle of the garden, but I'm not sure I have the patience. What should I do next, do you think? I guess either try to plot the arms of the Milky Way or see if I can get a rotation curve. Not sure I have enough samples for either of these. I can probably only get about ten to 15 points where the signal intersects the plane of the Galaxy. Kind regards, Steve.

But is it the right way round?

Here's my sky-scan halfway through (3 days to go for the first pass - every 10 degrees from 10-60 inclusive) then maybe another five days to get it every 5 degrees 10-60. But the key question is, have I got it the right way round. Colour is velocity and length of vertical bar is intensity. So it seems that Cygnus at around RA=300 (and presumably therefore the Cygnus arm) is rotating away from us, and that the other arm (is it Perseus?) is rotating towards us. I'll update it in a few days when I get the other scans. Is this representation working for you? Do you think It's intuitive? I've also applied a little noise damping by averaging out the signal between RA=150 and RA=225, and DEC = 0-90 and subtracting it from everything. Anyhow, please let me know what you think. Kind regards, Steve.

OK, so I totally misunderstood this. Radial velocity is away from us and Doppler is towards us! Hmm. Perfect. I understand now.

Nice. So look at this: Versus this: It looks left-to-right. Steve.

Did you see this? mit_21cm_radio_telescope_JLExp_46.pdf Have you tied your own observations to the chart on page 7? Kind regards Steve.

I was using a compass, but as there is a lot of iron in it anyway, the compass may not be accurate 😅 Also, a little offset on the waveguide could throw the orientation. I'll check against Polaris on the next clear night. That's only 0.7 degrees out. I've run 51 degrees N, and now I'm running 41. I hope to run 31, 21, 11 and 61 all this week and map them. We'll see how it goes. I thought I'd try for a flattened rotation curve! Kind regards, Steve.

Here's a similar one, but this one is offset in the other direction. Just look at the main features.

Hi @Victor Boesen, I'm not sure that the image for the Milky Way is quite right. Is it a little offset to the right? My peak amplitude comes at about 10 degrees higher RA than indicated (ie 10 degrees leftward). I first thought my rig was a bit out, but actually, now I'm not sure of the map. Obviously my setup is rusty and shaky, but I think it's pointing more or less North. Maybe it's a bit of both. Could you check, do you think? Kind regards, Steve.

Sorry. I've just changed it 😅

I've just stretched the scale. Is this the right way round, do you think? I've put the colour scale between -50 and plus 30 km/s

Except if you look at this, the peak at 320 degrees should be a bit Blue and the peak at 75 should be a bit Red. I think I need to check again. The brown signal in the middle is definitely noise though. Steve.

I was just sitting here thinking that too.

Hi People, I've created a matplotlib version with velocity as colour, but I'm not sure it works. Does this makes any sense? It's supposed to be blue is negative (ie coming towards us) red is positive (ie going away):

Here's the code: import os import json # Main method # Generates and saves a GIF of 24H observations def main(): arr_txt = [x for x in os.listdir('Spectrums/clean') if x.endswith("json")] for fileName in arr_txt: path = f'Spectrums/clean/{fileName}' f = open(path) # Get RA sub1=fileName.find('ra=')+3 sub2=fileName.find('dec=')-1 ra=fileName[sub1:sub2] # Get DEC sub1=fileName.find('dec=')+4 sub2=fileName.find(',.json')-5 dec=fileName[sub1:sub2] # returns JSON object as # a dictionary record = json.load(f) data_dict=record['Data'] freqs=data_dict['Freqs'] values=data_dict['Data'] maxValue=max(values) print(ra, dec, maxValue) if __name__ == "__main__": main()