Is it Abstract Art or Science?

Many cosmological questions about the early universe are on the horizon of scientific discovery at this time. Theorists have come up with a time line that shows the development from the Big Bang to the present gigantic and complex universe. Can we prove what the theorists have predicted? Perhaps – but with every measurement there is some amount of error and uncertainty. Unfortunately, the uncertainty that can be tolerated in our group’s experiments to be able to state definitively, “We know when the first stars and black holes formed” is ridiculously small. The project that I have been working on for the last year set out to find the error related with using an antenna at varying locations on the Earth and different times during the day to make accurate measurement of the radio spectrum. Every antenna has a beam pattern – which is the area that an antenna can collect information from, and each beam pattern has places that are more sensitive and less sensitive to incoming signals.
By projecting these beam patterns onto a temperature coded map of the sky, an estimate of what that antenna can “see” at that time, frequency, and location on the globe can be made – but if you ask me, most of the information I get resembles a painting I would love to hang on my wall.

Figure 1- Sky Map at 408 MHz

Figure 1- Sky Map at 408 MHz


Figure 2-Beam in Azimuth and Elevation

Figure 2-Beam in Azimuth and Elevation


Figure 3 - Beam in Right Ascension and Declination

Figure 3 – Beam in Right Ascension and Declination


Figure 4 - Beam Projected on the Sky Map

Figure 4 – Beam Projected on the Sky Map

Figure 1 shows the temperature coded map of radio emission from our own Milky Galaxy in the sky – red is hot and blue is cold. Figures 2 and 3 above show how the modeled beam pattern looks for a physical antenna in two different astronomical coordinate systems. Figure 4 filters the beam pattern, modeled on the data set generated for the antenna beam pattern filtered by RA/DEC, against the sky map. On the color scale, red is the strongest signal and blue is the weakest signal. So as the earth rotates, the sky over the antenna will change and the red, or strongest collecting point, will hit different parts of the sky. In Figure 4, the beam pattern was projected on the galactic sky map at an arbitrary latitude, longitude, and time on earth (in this case a location in Australia).

After this projection, the temperature of the projected map was summed at each frequency. Once this was coded, I add a series of “for” loops in my software to change the antenna’s latitude from -90˚ to 90˚, the time from hour 0 to 24, and the orientation azimuth from phi of 0˚ to 360˚. After plotting as a function of frequency, the curves were fitted with a second order power curve with the form: Ax^B+C. All of the curves and the corresponding residuals were plotted on the same figure for better comparison (Figure 5 and Figure 6 below). Once on the same plot, the curves that had an error larger than 0.05 K were eliminated. The last step was changing the time and the location simultaneously to determine the best combination of data collection of those two parameters – this can be seen in Figure 7. So far, our experiment site in Western Australia at -27 latitude is looking pretty good (at least for part each day)!

Figure 5 - Temperature Sum For Different Latitudes

Figure 5 – Temperature Sum For Different Latitudes


Figure 6 - Residuals for Best Latitudes

Figure 6 – Residuals for Best Latitudes


Figure 7 - Best Latitude and Time to Collect Data

Figure 7 – Best Latitude and Time to Collect Data

This process, although easy to write out step by step, was quite particular. Taking hundreds upon hundreds of data points from an antenna and figuring out how to adapt the program that was written for the theoretical case was less than straight forward.

So, is it abstract art or science??

Plot of the Coordinates - This one is fun to look at!

Plot of the Coordinates – This one is fun to look at!

Another plot of the coordinate system that is just fun to look at!

Another plot of the coordinate system that is just fun to look at!

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