Ed astro

Yes there is some green in the second picture, just above the clouds.

Managed to catch the northern lights for the second time this year from my home near Tiel in the Netherlands. This was between 22:15 and 22:45 UTC when geomagnetic activity was already declining. The northern lights were barely visible with the naked eye as a faint glow in the northern sky, but the camera picked it up easily. There was also some green towards the northern horizon, but this was difficult to see due to clouds and light pollution.

Hi, The 6 MHz bandwidth is of the Airspy SDR receiver I’m using. it is definitely possible to use the 22.2 GHz band for quantifying water vapor in the atmosphere; see for example this article: https://hal.science/hal-00224825/document An interesting aspect is that due to the effects of pressure broadening the water spectral line becomes narrower with increasing altitude; it is therefore possible to probe water vapor at different heights in the atmosphere by observing at different frequencies away from the rest frequency. not easy to do though with my dish, since I would need accurate calibration loads.

Hi Pete, Yes, water vapor in the atmosphere definitely has a noticeable impact on my observations but it is not a huge problem. The 22.2GHz line emitted by water vapor in the atmosphere is spread out over several GHz due to pressure broadening. With the 6 MHz bandwidth of the receiver you see an increased background noise instead of a line, and extraterrestrial signals appear weaker due to absorption losses. The atmosphere's background noise at 22.2 GHz is typically around 30- 40 kelvin near zenith, and path loss is around 10-20%. Atmospheric noise and losses get worse as you point the telescope lower due to the increased airmass, so it is best to observe a source when it is near its highest point above the horizon. With regards to variability: because the atmospheric water signal is so much wider than the bandwidth of the receiver and the width of the astrophysical maser lines, it should affect all peaks in the maser’s spectrum nearly equally. In W49 we see the peaks vary independently of each other, which can not be explained by variations in atmospheric conditions.

Hi Victor, the amplifiers inside the LNB already have plenty of gain, so adding an LNA would not be that useful. The 1420 MHz output frequency is intentional though, so that I could use an existing 1420 MHz filter if necessary. So far RFI at 22 GHz has been very limited, but with the growth of satellite megaconstellations and other services operating at cm- and mm- wavelengths the RFI situation could soon change….

Hi all, Here a little update on the water maser project: In February I opened up the LNB to adjust the frequency of the local oscillator (LO) by carefully tuning the frequency adjust screw. Now the LO frequency is changed to 20.814 GHz and the 22.235 GHz water line is converted down to 1421 MHz. This is well within the frequency range of my airspy mini SDR, which has a larger bandwidth compared to the nooelec SDR I was using before. I have also continued doing observations of the strong source W49. The variability is very obvious when looking through all the spectra collected over the past year. The features at -4 - -14 km/s seem to be particularly active. W51 decreased in brightness by two orders of magnitude since February 2022, and is no longer an easily detectable source. In February I therefore decided to pause monthy observations of this source in favour of other masers that are easier to detect now.

I'll second Robin's comment. At 1420 MHz (hydrogen line frequency, wavelength ~21 cm) the half power beam width of a 3 metre dish is 5 degrees- that means that if you are trying to detect a point source and your pointing is+-2.5 degrees off you receive half of the power of that source. Also note that the hydrogen clouds we typically observe at 1420 MHz are very diffuse and span several degrees in the sky, and are not really point sources even at very low (several degree) angular resolution. An accuracy of around 1 degree is therefore more than adequate for this purpose. For observations at the 1420 MHz hydrogen line with the 3 metre dish I made a rather crude and simple system for positioning using two degree arcs to indicate azimuth and elevation. Before starting an observation I calibrate these by pointing the dish at the sun. However, the radio spectrum extends way beyond 1420 MHz... Last year I started doing radio astronomy at 22.235 GHz (spectral line of water) with a 1 metre solid dish. At 22 GHz (wavelength of 13.5 mm) accurate pointing is much more critical, and the beam width of even the 1 metre dish is around 1 degree. Pointing deviations of as little as 15 arcmin already have a noticeable effect. I have therefore mounted the 1 metre dish on a HEQ5 mount and use a single point alignment on the Sun, Moon or the brightest radio source at 22GHz (W49). I have also attached a finder to the side of the dish and aligned it with where the dish is pointing using the Moon as a reference point, so I can also use bright stars for alignment of the mount at night. In summary, methods for pointing a radio telescope may vary greatly depending on the desired pointig accuracy, which in turn depends on the telescope's size and operating wavelength.

Last night it was also faintly visible here in the Netherlands (latitude 52 degrees north). The show only lasted for a very short time around 21:00- 21:30 UTC.

Hi all, It has been a while since I posted an update on this project. In the past few months I have detected two more water maser sources: Cepheus A and G37.403+0.232 Cepheus A was observed on October 9 and 10. Interestingly, this star forming region has a characteristic double peaked spectrum. The two peaks could be originating from two different maser spots within the star forming region, moving at slightly different velocities. In the period November 2022- January 2023 five observations have been done pointing the dish at the star forming region W44. The water maser emission from this region is an average velocity of 60 km/s relative to the local standard of rest (LSR) according to the data published on the MaserDB database. Shown below is the averaged spectrum from all five observation sessions (approximately 8 hours of total observing time). A vey faint signal was indeed detected, but it was at -56 km/s, so a bit too low for W44. In fact, the velocity is more consistent with another source, G34.403+0.232, which is located just 10 arcmin north of W44.

Hi, The OP has not replied anymore to this thread, but it seems there are still a lot of other folks who are interested in radio astronomy here on this forum. This evening I had some time to put together a simple hydrogen line "cantenna" from parts I had already sitting around, as an example of what a beginner could easily make. It is effectively a metal can, 15 cm wide and 27 cm long. I made it from a thin sheet of galvanized steel, but one can also use something like a paint bucket of approximately the right dimensions (width should be 15 plus or minus 1 cm, the length is not very critical). Inside the can is a small, 4.9 cm long monopole antenna (the probe), which was made from a piece of 7 mm wide copper rod soldered to an N-connector. The probe length is somewhat critical, the width is not as important but should be atleast 3 millimeter. The distance between the probe and the bottom of the can should be close to 8.3cm. The antenna was placed outside on a spot away from trees or buildings which could block my view of the sky. The hydrogen line signal is rather weak compared to the noise of the receiver, so a low noise amplifier (LNA) must be used. I used a nooelec SAWbird HI LNA, which also includes a filter for blocking unwanted signals at frequencies away from the hydrogen line. The LNA is connected to the antenna via a N-to-SMA adapter and a short piece of SMA cable (the cable between the LNA and the antenna should be kept as short as possible to reduce cable losses!). After the LNA cable losses are not as important, so several metres of coax cable can be used between the LNA and the SDR receiver and computer. In fact it is better to keep at least a few metres distance between the antenna and the computer in order to prevent interference. An RTL-SDR receiver was used with the SDR# program and the IF average plugin to detect the hydrogen line. The hydrogen signal is weak, so you need to average the spectrum over several seconds to minutes with a program like IF average to get a good signal-to-noise ratio. Even then the hydrogen line is often only visible as a very small bump in the spectrum near 1420.4 MHz. The larger bumps and crests in the spectrum are artifacts of the SDR, which make it more difficult to recognise the hydrogen line. Unfortunately there were also some troubles with the power cirquit in my old LNA, so the results were not as nice as I hoped. To get rid of the SDR artifacts, a "dark" spectrum whithout the hydrogen line signal needs to be made and subtracted from the spectrum. This can be done by shifting the frequency 1- 2 MHz away from the hydrogen line and clicking "background" in IF average. When the background is corrected the spectrum can be centered at 1420.4 MHz again to record the hydrogen line. The spectrum can also be exported as a text file containing the frequency and intensity values. These can then be copied over to for example Excel for further analysis and plotting.

Hi all, Besides the regular observations of W49 and W51 I have also observed some other maser sources in the last few months. In August I managed to detect W75N in Cygnus. The detected peak has an LSR velocity of 11 km/s, which matches quite well with the LSR velocities of this object reported in the maser database MaserDB. The star forming region G25.649+1.050 was observed on three evenings, and a weak peak was detected around the expected LSR velocity of +43 km/s. However, the signal-to-noise ratio was too low to call this a positive detection. The peak was also very close to the midpoint of the spectrum where artifacts of the SDR receiver often occur. This source has to be observed another time. Finally, the Westerhout 3 star forming complex has been observed again for about 1.5 hours yesterday evening. The W3 region contains two water maser sources: W3(OH) and W3(2). W3(OH) is usually the strongest of the two. To my surprise, there was no peak in the spectrum at -48- -50 km/s where I would have expected a strong signal of W3(OH). Instead, three weak peaks are detected at -37, -39 and -41 km/s, which is more consistent with W3(2). Maybe W3(OH) is just unusually weak now, or my frequency or velocity correction is off. However, W51 was also observed the same evening (as part of the monthly observation program on W49 and W51) and the LSR velocity of the peak seemed to be right, so a mistake in the frequency or velocity correction seems less likely. Anyway, the unexpected results are often also the most interesting and fun.

Hi, as Robin already stated, the design of the radio telescope or antenna really depends on what you aim to observe. For a beginner I think that detecting the hydrogen line at 1420 MHz is a good starting point. You could start by making a simple “cantenna”, once you have detected the hydrogen line with it you can mount the antenna in the focal point of a dish for more serious hydrogen line astronomy. If you are interested I can give more details on how to make a relatively simple setup for hydrogen line detection.

Hi all, I have done new observations of W49 and W51 on July 14 and August 8. With six observations in total now, the plots where all the spectra are plotted together are starting to look rather messy and confusing. Therefore, I was experimenting with different ways to visualise the changes in the spectra over time using Matplotlib/Pyplot. First I tried to make "stacking graphs". The nice thing about this type of graph is that the shape of the peaks is still visible. On the other hand, it is difficult to avoid too much overlap between strong peaks while also showing the weaker features. Another way to display the changes is by plotting a heatmap of all the spectra. What I like about this type of diagram is that changes in the peaks are very well displayed. However, the shape of the peaks is not shown of course. The peak at -6 km/s in the spectrum of W49 was in outburst around May 28, and it is now back at the same intensity as before the outburst. Furthermore, a new weak feature emerged at +11 km/s. The intensity of W51 decreased more than 10-fold in the period February- April, but it did not change much since then. Last night I also tried to detect another maser (OH43.8-0.1), but this attemt was not successful.

Hi all, Last night there were some noctilucent clouds visible above the northern horizon here in the Netherlands. In the past, these clouds were rarely seen, but nowadays they are a yearly recurring phenomenon. Last nights display was not particularly spectacular compared to previous years but I still got some nice pictures.

Hi Victor, I have not published the code yet, there is no GitHub page or anything for this project. For LSR correction I have not written any code myself but I just use the online LSR calculator from ATNF (https://www.narrabri.atnf.csiro.au/observing/obstools/velo.html) Programming is really not my expertise though… Eduard

Hi all, For comparison I have plotted the most recent spectra of W49 and W51 together with the earlier observations. Because I did not have a reference signal during the earlier observations I just tried to align the peaks (note that this may not be entirely correct). The wide peak at -6 km/s in the spectrum of W49 has significantly increased in intensity over the last two months compared to the narrower peak at 5.5 km/s. W51 on the other hand does not seem to have changed very much since last month apart from a slight increase in intensity.

Hi all, I realised that this thread has slowly turned into a monthly update on the variable masers in W49 and W51... This time, I have of course new observations of these sources, but I have also something new to share about this project. Recently I have tried using the 28th harmonic of a Leo Bodnar GPSDO (GPS-disciplined oscillator) as a reference signal for correcting the frequency drift and offset of the LNB. I made a small waveguide antenna out of a piece of copper tube with an inner diameter of 8mm (this antenna is essentially a miniaturized version of the "cantenna" design commonly used for 1420 MHz hydrogen line feeds). The cutoff frequency of this waveguide is about 11 GHz, so any unwanted harmonics below that frequency should be filtered out. I also added a conical horn section with an opening of 35mm to make the antenna more directional. The 28th harmonic is of course extremely weak and can only be detected at short distance, but that is actually desirable for my project (a stronger signal would disturb the observations). Recently I did some observations of W49 and W51. Thanks to the reference signal I was able to compensate the frequency offset and drifting of the LNB. It was also finally possible to calculate radial velocity (doppler shift). This will make it easier later on to compare my own spectra from different observations to each other and to spectra published in the scientific literature. To be continued... Eduard

Hi Victor, Most of these masers vary irregularly. Usually there is always some maser emission detected from these strong sources, but individual peaks in the spectrum can emerge and disappear in a few months to several years. Sometimes one of these peaks increases rapidly in brightness and fades away again in only a few months or weeks. Such flares are unpredictable and are still not very well understood There are also examples of masers which vary periodically, such as the OH- masers in the atmospheres of Mira variables and OH/IR stars. Anyway, I think it is great to see that some of this variability is detectable with my amateur setup. After all, if you can only “see” a handful of “maser stars” with your small radio telescope then these stars better be very interesting, otherwise you will soon get bored… Eduard

Hi all, This morning I observed W51. Its brightness seems to have significantly decreased again since my last observation five weeks ago. Some of this decrease may be due to less favourable observing conditions (W51 was lower in the sky and there was a thin layer of clouds). However, it is unlikely that such a large decrease in intensity (>10-fold since february) is only the result of variations in gain or moisture, given that I get more or less the same numbers each time I point my dish at the sun or W49.

Hi all, Another month has now passed since my previous observations, so I decided it was time to check W49 and W51 again. This morning W49 was observed for about an hour. I also plotted todays spectrum over my previous spectra from March and February. Overall, the intensity of the main peaks seem to have increased compared to the earlier observation in March, but it is unclear whether this is a real change of the source itself or if it is due to more favourable conditions (less clouds/ moisture in the atmosphere). However, it is also clear that the peaks are changing in intensity relative to each other- likely due to the intrinsic variability of the source. The fact that changes can be detected in the spectrum over a period of a few weeks or months means that the source itself must be quite small (at most a light-month across). I will try to observe W51 again this weekend. Eduard

Hi all, More observations have been done at 22.2 GHz over the past two weeks. I have pointed the dish at a number of different sources: NGC 2071, NGC 7129, W75, Cepheus A, IRAS 06053-0622 and G25.8-0.18. Unfortunately, none of these sources were detected, they are probably too weak right now for detection with a small 1 metre dish. W49 and W51 were successfully observed again. It seems like both sources have become weaker since the first observations 5- 6 weeks ago. However, since the vertical axis is not calibrated it is hard to tell which part of the change is real, and what part is due to pointing errors or gain variations. On the other hand, the different maser features (peaks) in the spectrum of a source usually vary independently of each other, while gain variations or pointing errors should influence the measured intensity of all the peaks equally. I plotted my most recent spectrum of W49 (from March 26) over an earlier spectrum made on February 12. The strongest feature has significantly decreased in intensity, while the weaker peaks have remained almost the same. It is therefore likely that the decreasing intensity of the main peak is (mostly) due to the intrinsic variability of the source. The same was done for W51. However, W51 lacks any sufficiently strong peaks besides the main peak to compare with. It would be interesting to observe these sources again in one or two months.

Hi Victor, That filtered LNA could be really handy- there is often quite a bit of RFI above 1.7 GHz which can cause some problems when trying to detect weak signals. What is the noise figure of your LNA? Low system noise is really important for this kind of work. I have detected four OH masers with my 3 metre dish over the past few years: these were the red giant stars NML Cygni, OH26.5+0.6 and V669 Cas at 1612 MHz, and the star forming region W3(OH) at 1665 MHz. I used a G8FEK LNA and homemade filters for 1612 and 1665 MHz. These observations were quite challenging, it required tens of minutes to several hours of data recording to get good results.

Hi Victor, These look like some really nice dishes to play around with! As mentioned before water masers are difficult to observe due to their high frequency (you need really accurate pointing and tracking) but there are other options at lower frequencies as well. OH (hydroxyl) has four maser lines at 1612, 1665, 1667 and 1720 MHz. These frequencies are quite close to the hydrogen line, so you could use the same SDR receiver and LNA, and probably even the same feed that you use for hydrogen line observations if it performs well enough at 1.6 GHz. OH masers are generally a lot weaker than water masers though, but with a 3 metre dish you should be able to detect a few of them.

Hi Victor, I am using the SDR# IF average plugin for averaging the spectrum over a longer time period. The methods for making spectra of these masers are very similar to hydrogen line observing- you can use the same software and observation routine. The main difference is that the maser lines are usually 10- 100 times weaker, so you need to integrate a lot longer to get good SNR. Typically I make tens of spectra with each an integration time of a few minutes, and average them all afterwards. I keep the resolution low at 256 bins (12 KHz for an SDR with a bandwidth of 3 MHz, just enough to resolve the lines while keeping the noise low. Observing these water masers is challenging but also rewarding, they are bright and variable radio sources but they are rarely observed by amateurs. So if you are done with hydrogen line observing at some point this might be an interesting project.

Well Marv that is mostly my fault since I did not even really try to explain this 😉 What you are seeing are spectra of water masers. When water molecules in a gas cloud are subjected to strong infrared radiation or collisions with other molecules, they can emit strong microwave radiation at a frequency of 22235 MHz (wavelength of about 13.5 millimeters.) These conditions are usually found inside star forming regions. When we point a radio telescope at a star forming region and plot the intensity of the received microwave radiation against frequency, we see a spike at or near 22235 MHz. Due to Doppler shift, this spike is usually a few MHz above or below the rest frequency depending on how fast the source is moving towards or away from us. In many cases we see a number of different spikes in the spectrum, these all correspond to different sources within the same star forming region, which are moving at different velocities. I hope this makes things a bit more clear! Best regards, Eduard