There has been a slight gap between my last blog and this one. The purpose of this blog is to take me, as a total radio astronomy novice on a journey into the wonders I have been told exist out in the far depths of space. So why have I suddenly come to a juddering stop?
I have been trying to get my head round what my radio telescope actually does. I say my radio telescope, I mean the one at Mansfield and Sutton Astronomical Society. Over the last few weeks I have discovered in general terms what radio astronomy is and the basics of how it works. I have talked briefly about huge professional dishes and how to make a home made aerial. So now is the big moment where my home radio is switched on. The monitor is recording the signals and the speakers are giving me my long anticipated feedback. Yay I can see a blip on my monitor and can hear static through my speakers. All very exciting, but it’s not going to hold my attention for long. Is this it? Time to do a bit more digging.
Having sat and thought about it, I think the problem may be in the wording of the title, specifically the word “radio”. Despite my earlier blogs where I discussed what radio waves are, I still think of radio as sound. Whilst space is something that we look up at, isn’t it? Does that mean then that radio astronomy is adding a very crackly soundtrack to our visual observations? Well actually in some cases the answer is yes. In fact the society is actively looking at combining Camera’s with the radio telescope so we can both see and hear those meteors as they fly across the sky. But not in every case.
Going back to the basics of radio I discussed how it is a wave in much the same way that light and infa red are waves. So when a meteor emits waves, it emits a whole spectrum of waves, some of which we can detect with our eyes, light waves, and some we can’t, radio waves for example. It’s called the electromagnetic spectrum. What we can do is take those radio wave signals, process them with our computer, add a little bit of wizardry, and produce a visual representation of those waves. We can see space via those radio waves.
By detecting the electromagnetic spectrum of an object we can see it in different ways.
The below images are of our Milky Way galaxy in a 360 degree map view in both visible light (left) and radio radiation (right – 408 MHz). Pictures from Radio-astronomy.org.
By comparison the below image is taken in infrared.
Why then do we concentrate on radio waves and not infrared or X-rays? It is down to the earths atmosphere. Since rays from space have to pass trough our atmosphere it affects the images we can obtain, thats why we get better pictures from space telescopes such as Hubble, than ground based telescopes.
The radio window
The above figure shows the amount of transmission through the earth’s atmosphere as a function of wavelength.
According to Cardiff University, clear areas mean the atmosphere is transparent. Shaded areas mean no radiation gets through the atmosphere at those wavelengths. There are two prominent windows through which to make earth based observations, the optical and radio windows with the radio window covering a much larger wavelength band than the optical. The window’s width varies slightly depending upon atmospheric conditions but is generally from 1 cm to 10 m. Wavelengths greater than 10 m are reflected by the ionosphere, the amount of reflection being a function of the electron density. The short wavelength limit is due to atmospheric absorption and depends on atmospheric composition such as the presence of cloud cover.
To sum up radio astronomy is not necessarily listening to the stars as such, rather it is detecting that range of the electromagnetic spectrum that falls within the radio wavelength. These wavelengths can be analysed to discover what is happening in the universe around us and processed into optical images.