Radio Astronomy Galactic

Observing Galactic Radio Sources

Our galaxy contains many radio emitting objects that can be observed with Radio Telescopes. Most are too faint in radio to be observed with small radio telescopes. You may use your own or someone else’s radio telescope to make observations of sources within the Milky Way Galaxy. You may use online or collaborative resources, but you must obtain your own unique observations, and be actively engaged in the process.

I originally intended to use an SDR and make my own horn antenna lined with aluminum foil but eventually realized that it wouldn't work well. I abandoned the Radio Astronomy program for over a year until I stumbled on a solution: Green Bank NRAO's 40 Foot Radio Telescope – The National Radio Astronomy Observatory in Green Bank-West Virginia will make available a radio telescope for use by student groups, as well as other amateur science groups and organizations (e.g. scouts, 4-H, amateur astronomy clubs, etc.). The AL's Radio Astronomy web page describes the availability, but I had a number of problems.

My problems using Green Bank were:

(1). finding the correct contact person at NRAO (I'd seen mention of this on the AL's RadioAstronomy page but was unable to find a human to talk to.)

(2). getting trained to use the 40' dish,

(3). solving problems like driving the 700 miles to the facility, finding a place to stay, and logistics.

In the March of 2016 while searching the AL's web site I was able to find a member who'd successfully completed the Radio Astronomy program. I emailed him to ask how he'd completed the Galactic portion of the program. He replied that he'd used the 40' at Green Bank and had been trained to use it at one of the annual StarQuest star parties there. In the early April of 2016 my wife and I made one of our twice a year trips from Missouri to visit our son and his family in Maryland. On the way home we stopped by Green Bank for a visit. Unfortunately it was closed for the day, but I did get a good look around and decided to go to a StarQuest that summer. Doing some Goggling I came up with the particulars and attended the 2016 StarQuest. It was a most enjoyable experience and met a number of interesting people. While there I was trained to use the 40' and spent a night practicing. I later scheduled two nights (October 12/13, 2016) on the dish and in the residence hall. Knowing I would need help running the scope, I enlisted my son who has an interest in telecommunications. A few days before my time on the dish I drove to Maryland for a visit and we drove to Green Bank on October 12th. While there my son and I ran the scans needed to complete the Galactic portion of the program.

Using the 40' Dish:

The technology level of the 40 foot dish is straight out of the 1960s... drift scan at the meridian, manual control with push buttons, manual frequency changes, and paper strip chart recorder output. The process pretty much needs two people to run: one person to manually step through the desired frequency range and a second to control the paper output. It is almost like patting your head and rubbing your stomach at the same time. I know that I'm not coordinated enough to do them both at the same time. The dish needs to be positioned at the decimal altitude of the desired object and you then camp out until just prior to it crossing the meridian. The dish has a field of view of about 1 degree and the object will stay in the field for about four minutes (depending on the Dec). During that time one user first sends a 500 Jansky calibration signal to the recorder for 15-20 seconds. Once completed a 30 second baseline signal is recorded. At that point the other user presses a button to increment the scanned frequency by 0.01 Mhz every second for two minutes giving a scanned range from from 1419.8 MHz to 1421.0 MHz. During this period the first user marks the output every ten seconds so the frequency can later be determined.

The significance of this chosen frequency range is that it is centered around 1420.405 MHz or the frequency of the 21cm Hydrogen line produced when an electron in a ground state, neutral Hydrogen flips from a +1/2 to a -1/2 spin. This doesn't happen very often, but there is a lot of Hydrogen out there. The 40 foot dish detects this signal although it may be red or blue shifted as the Hydrogen atom either moves away or towards us. This red or blue shift can be measured and will be reported below. The signal strength is measured vs. the 500 Jansky calibration peak height. The frequency of the signal is measured by comparing to the ten second marks vs. the starting time. The data collected comes from information from the recorded strip chart output and notes on the chart as to object name, local sidereal time, set declination, date, and clock time.

Requirements:

Ten (10) observations must be made of at least three (3) different objects. The same object may be observed on different days. These observations may be made using equipment that you may or may not have built. Remote operation of radio telescopes is acceptable for the purposes of this requirement, as long as the applicant is an active participant manipulating the telescope, as

opposed to a passive observer, in the collection of data.

With the permission of the program's coordinator, I also scanned extra-galactic sources.

Note: The 40' dish is in a RFI quiet zone. Digital cameras, cell phones, laptops, tablets, and a long list of other things are not allowed. Any pictures below are the result of film exposures that have been scanned. All pictures and scans of strip chart recorder output were done by me.

Dish Altitude Meter

negative altitudes require a bit of thinking

Frequency scan controls

Strip chart recorder

I hadn't changed pens or paper in one of these since the 1960s!

My son at the strip chart recorder with the control rack in the background.

Green Bank StarQuest Observations

Obs # Data

1 Target Name: Random Location

Date: 7/6/2016

Time: 3:14 pm EDT

RA: 9h 55m 0sec

Dec: +9d 0m

Comments: This scan was done in a random part of the sky with no real target as part of StarQuest training on the 40' dish. The trainer called out the location. I ran the spectrometer for this "target" pressing the frequency increment button ever second for two minutes. The two people controlling the strip chart recorder kept the copy of the output. A small peak (2") was seen. Later looking at Stellarium I see that NGC 3049, a galaxy, should have been in the dish's FOV at that time.

2 Target Name:: Random Location

Date: 7/6/2016

Time: 3:22 pm EDT

RA: 10h 05m 0sec

Dec: -7d 0m

Comments: We then moved the dish in Dec to a second location and did a second scan with me controlling the strip chart recorder and one of the other trainees sequencing the spectrometer. The trainer called out the location. After the two scans, two other people in the group of 20 trainees took over our jobs. When completed I felt pretty confident that I could do the procedure at the practice time that night. Stellarium showed that the dish was pointing at NGC 3115.

3 Target Name:: Random Milky Way

Date: 42557

Time: 11:20 PM EDT

RA: 18 h 07m 29 s

Dec: -20 d 0m

Comments: Practice session that evening. There was heavy (but very impressive) lightning in the area that evening and only four of us did the 1/2 mile walk to show up for practice.

One of the things in the packet we were given that afternoon was a plot of the Milky Way's position showing RA and DEC. Knowing the LST (displayed on the computer) we found the coordinates and moved the dish to the correct Dec. We picked a random location in the Milky Way and did a scan. I moved the dish to the location and sequenced the spectrometer. We were all pretty happy to see a 3" spike on the strip chart showing Hydrogen. The others in the group kept the scan.

4 Target Name:: 3C 380

Date: 7/6/2016

Time: 11:46 PM EDT

RA: 18 h 28m 13 sec 48d 42m 41s

Dec: 48d 42m 41s

Comments: There were also a number of NRAO recommended radio targets in our training materials. As the night progressed we located a six of these targets. I've only included the targets that I actively participated in scanning. I ran the strip chart recorder for this target that gave a small hump. The others in the group kept the scan.

5 Target Name:: NRA0 5790

Date: 7/7/2016

Time: 00:00 AM EDT

RA: 18 43 30

Dec: -2d 46m 39s

Comments: I ran the sequencer for this target that gave a slightly larger hump. The others in the group kept the scan.

6 Target Name:: NRAO 5890

Date: 42558

Time: 00;16 AM EDT

RA: 18 59 16

Dec: 01 42 31

Comments: I ran the strip chart recorder for this target that gave a hump about the size as 3C 380. Because of the continuing lighting and threat of rain we packed up and headed up the hill. We were all confident that we knew what we were doing. The others in the group kept the scan.

After attending the StarQuest 2016 I knew that I wanted to return to Green Bank and give it a shot on my own. I reserved two nights on the dish in October. As mentioned above, I also managed to talk my son, who has an electrical engineering background, into assisting me. Little did I know what a good idea that was.

We arrived in Green Bank around 3:30 p.m. on Oct. 12th to check into the Residence Hall and killed a bit of time. Around 5 p.m. we drove to Henry's for dinner. We then returned to Green Bank and walked down to the dish. From then on everything was an disaster. First, I was having major tendonitis problems with my hands and hips. The 1/2 mile walk to and from the dish to the gate was a painful experience. During the hour training and two hour practice sessions at the Green Bank StarQuest 2016 everything worked flawlessly. All the plotter had paper and ink while the knobs, dials, buttons, etc. were set correctly. The only things needed to do were to find the correct declination and follow the directions. No time during training was devoted to diagnosing problems. The first time out for our October visit resulted in pretty much nothing! Without the help of my electrical engineer educated son, our two nights at Green Bank would have been totally wasted. Whether it was a dial setting (and there are lots of dials), button off (again lots of buttons), or bad cable, the first night's spectrographs other than the calibrations were all flat lines. We knew we'd followed the correct procedures, but just no data. After my son looked at the system for three hours the first night and about two hours the second night we got our first real data. Along the way we ran out of paper and ink and had to search for more. Since we'd picked a Tuesday and the facility was technically closed, nobody was around for help. I found out the next day my contact person was out on vacation. If we were to get things operational, it was up to us.

On 10/12 we repeated the cycle below at least 20 times but got no good data. Around midnight we packed up and up the hill.

My son reading the directions again.

Read directions
Make a change
Move dish to new object
Wait until object crossed the meridian--sometime as long as 30 minutes
Start a scan
See if we got a signal (and we didn’t)
Search instructions, bits of papers, post-it stuck to walls or equipment and “wiggle wires”

The control rack with lots of knobs and dials!------>

(mosaic of two images)

After touring Green Bank on the October 13th we returned to the 40' dish's control room about 6:30 that evening expecting the worst. Once again we struggled for almost three hours until we finally found the last piece of the puzzle scrawled on a piece of paper that had fallen to the floor under the left rack. A button on a unit on the cart that was to send the signal to the spectrometer was off. We corrected the problem and were finally able to get data.

My original plans were to have been to sample a variety of deep sky object including open clusters, globular clusters, planetary nebula, dark nebula, and galaxies. With the time constraints of getting the system to produce data late in the evening on 10/13/2016, we decided to take what we could get as any kind of object crossed the meridian. We stopped after Cassiopeia A* (RA 23h 23min 26sec). The next target we considered was to be M32, M32, M110 (RA 00h 40min). Because of the known blue shift we knew we'd need to increase the scanned range and had worked out how to do it. Realizing that faced with the walk back up the hill and that we'd need to wait for over an hour for it to cross the meridian, we wimped out, shut everything down, and headed up the hill

7 Name: NGC 7293

Helix Nebula

Date: Oct. 13, 2016

Time: 10:27:30 EST

RA: 22h 29m 38.55s

Dec: −20° 50′ 13.6″

Dish Alt: -20.83°

Signal Strength: 200 Janskys

Red Shift: 0.000134

8 Name: NGC 7380

Wizard Nebula

Date: Oct. 13, 2016

Time: 10:45:00 pm EST

RA: 22h 47.0m

Dec: 58° 06′

Dish Alt: 58.14°

Signal Strength: 2170 Janskys

peak 1 2400 Janskys (est)

peak 2

Red Shift: 0.000021

peak 1 -0.00013

peak 2

I kind of like my friend Dan Crowson's LRGB image of the WIzard Nebula a bit more than my radio scan...definitely more color and considerably more pixels.

9 Name: Cas A

Date: Oct. 16, 2016

Time: 11:20:30 PM CST

RA: 23h 23m 26s

Dec: +58° 48′

Dish Alt: 58.80°

Signal Strength:

peak 1 1410 Janskys

peak 2 1350 Janskys

peak 3 937 Janskys

Red Shift:

peak 1 -0.00023

peak 2 -0.0003

peak 3 -0.00037

SNR the brightest extrasolar radio source in the sky

10 Name: UGC 12138

Date: Oct. 13, 2016

Time: 10:38:00 pm CST

RA: 22h 40m 17s

Dec: +08° 03' 14"

Dish Alt: +08.05°

Signal Strength:

peak 1 647 Janskys

peak 2 127 Janskys

Red Shift: 7.74E-05

11 Name: NGC 7469

Date: Oct. 13, 2016

Time: 11:01:30 PM CST

RA: 23h 03m 15.6s

Dec: +08° 52′ 26″

Dish Alt: 8.87°

Signal Strength: 521 Janskys

Red Shift: 0.000204

Seyfert-1 Galaxy

Modified instructions from Terry Trees:

V. USING THE HI SPECTROMETER

The Milky Way is full of neutral hydrogen atoms - especially in the plane of the galaxy - and it happens that neutral hydrogen (HI) emits radio waves at a frequency of 1420.41 MHz. This is well within our passband of 1350-1430 MHz.

But, using the telescope in normal continuum mode does not allow us to observe this narrow spectral line. The HI contribution to our received signal occurs over such a narrow frequency range that is masked by radio waves coming in at all other frequencies in our passband. In order to detect HI we need to block out all of those radio waves and just look at those coming in at the frequency of HI.

We accomplish this at the 40 foot by combining a very narrow bandpass filter with a tuner that allows us to sweep over the frequencies of HI emission. The tuner is our main Local Oscillator which is mixed with our RF signal- giving us an IF signal of 100 MHz. This signal is mixed a second time with a signal centered at 110.7 MHz and then passed through a filter. The filter is a bandpass filter with a 10 KHz wide passband centered at 10.7 MHz. Refer back to Figure 2 to see what this system looks like. The following page shows a table to illustrate how the frequencies mix.

Observing Procedure:

1. Switch to spectral line mode on the IF drawer panel.

Left rack, 4th console down.

2. Reduce the “Input Level” to 0.4 or so

Left rack, 3rd console down

3. Check the Square Law Detector to be sure that it reads 40 or so.

Left rack, 2nd console down

Also check your filter bank to be sure that you have chosen 10 KHz bandwidth.

Left rack, 9th console down

4. Position the telescope to the proper declination.

Right rack, 4th console down

FIRST, power-on this console

SECOND, Make sure Coordinate Selector is set to elevation

LAST, power-off console at completion of entire observing session

5. Set your paper speed to 60 mm/minute.

6. Set your start frequency on the Local Oscillator (LO) to 1319.8 MHz.

(100MHz lower than the expected observing range as explained above.)

Right rack, 3rd console down

Push “FREQ”

Punch in 1319.8

Push “MHZ”

7. Set your tuning step size. On the main LO, push the "Step" button. Then select ".01 MHz".

NEW: Right rack, 3rd console down

Press the Incr Set button

Key-in .01

Press the MHz button

8. Start the chart recorder (paper feed). Write down the Declination.

9. Calibrate.

Left rack, 3rd console down, Zero Offset knob for blue/black pen

Left rack, 6th console down, Zero Offset knob for red pen

Write down the Right Ascension.

10. Run the “Timed Event Marker” (NEW: PC Metronome program) set for 1 second ticks to time your tuning steps.

11. Change the LO frequency from 1319.8 MHz to 1321.0 MHz in .01 MHz steps.

Do so every 1 second. (Press the up arrow button.)

12. Push the printer’s “Event Marker” button every 0.1 MHz. (10 seconds).