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