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Astronomy/Idea for a telecope

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QUESTION: Hello Phillip,

I thought of a great idea.  At night, can a solar heating array, such as this one in Spain: http://en.wikipedia.org/wiki/Gemasolar_Thermosolar_Plant, reflect cosmic radio waves to a collector for astronomical observations?

The surface area of all those mirrors is massive, so if these can can reflect light, radio, microwaves etc. this may enable a dual use for these types of power plants.  The controls used to track the sun is the same for any object in space.  I would imagine that the quality of the signals may not be as precise but this still may be useful in a more generalized application/study.

I think that a conversion from a power plant by day to an observatory by night would be relatively easy.

What are your thoughts?

Thanks,
Allen

ANSWER: Hello,

An interesting idea but I don't think it would work, for several reasons.

First, solar radiant energy, i.e. for solar power consumption isn't the same as detecting -collecting radio waves for analysis or observation.

One thing we learn in radio astronomy are some of the basic properties of radio waves, as they pertain to the plasma in which they originate. These properties are what make radio waves susceptible to detection.

To be specific, the plasma conditions associated with the motion of charged particles, that actually give rise to radio wave propagation are based on the fundamental equation of motion: m (dv/dt) = q(v X B) where q is the charge, and the cross product is for velocity and magnetic induction. The motion is such that the velocity v is always perpendicular to the force acting on the particle, so that:

 dv/dt = q/ m [v X B] is a centripetal acceleration.


Meanwhile, (v⊥ )2 / r = q/ m [v⊥ B]


The quantity r is none other than the gyro-radius. Solving for it one finds:


r = m/ q [v⊥ / B] = v⊥ / (qB/m)


for which one can have either the electron, or ion gyro-frequency.

These equations  are critical because they explain the physical basis for the origin of a preponderance of radio waves (i.e. gyro-magnetic emission).  

There is no analog for this using a solar collector, designed for energy collection which may also lack the design attributes, needed to say pick iup a distant pulsar, or exploding galaxy in the radio spectrum

What sort of attributes are we looking at?


The essentials of assorted radio telescope properties, especially for antennas, entail the practical design of **specific antennas** matched to the known properties of the object. Thus, we would need to have a certain design in order to detect an object of given flux, and spectral output.  For example, we'd need to distinguish between the flux emitted for an isotropic (lossless) antenna, and an anisotropic antenna with the gain (g) subject to particular constraints.

This is why one of the problems in a typical radio astronomy course involves working out the beam width and beam efficiency of a given antenna, as well as computing the 'brightness temperature' for a localized source.  Sensitivity of the antenna must also be considered, as well as other details such as the amplification of high frequency signals

In addition, we will want to know the antenna temperature, in terms of the brightness temp. for the specific type of object we seek to detect.

A single use solar collector, for all these reasons, simply cannot work as a radio telescope unless the design is altered in major ways, i.e. to accommodate the diverse radio wavelengths peculiar to different radio objects.


---------- FOLLOW-UP ----------

QUESTION: Thank you for the explanation but this was well over my head.   I am disappointed that this may not work.  

Just another thought.  Would it be possible to add an electomagentic backing /reflective material or coating to the enhance mirror's EM capability?  If this was a an independent backing, it could then be slightly curved to better better focus the energy at the antenna. This may then aid in the choice in antennas.

I do not have enough knowledge of astronomy to specify the type of attributes that one would desire.  I would think that there could be some sort of application, even if it was not for high end astronomical uses.  

Some ideas that I came up with: spotter for better telescopes, conducting general sky surveys, planet spotting in nearby galaxies or making observations of Jupiter and Pluto.   I just don't know.

Thanks Again.

Allen

Answer
Antenna pattern
Antenna pattern  
Hello,

Please understand that the problem we have is that while you have an idea that looks reasonable (and it does) you are not familiar with the specification and requirements for radio telescope antennas, say to detect assorted cosmic radio sources. The difficulty is in communicating those to you without going into too much technical detail.

Let me try here using a diagram, which shows the response of a radio telescope antenna as a function of direction. We agree here that an antenna can be a collector of radio waves and that in some ways it's similar to a solar energy collector. However the similarity ends with the need for rigorous design specs.

These are embodied in the antenna pattern, such as shown. So the key questions are: a) whether any theoretical design can attain such a pattern for the objects that need to be detected, and b) is the design also meeting the other specs such as I briefly described in the previous post.  (One also wants to pay attention to things like 'noise levels' and how to reduce them to a minimum).

Other aspects that pertain to the pattern include whether the antenna is linearly polarized in one of the principal planes. (The mutually perpendicular patterns you see through the main lobe axis are called principal plane patterns. Linearly polarized means the electric vector, associated with an EM wave is confined to one linear vibration dimension.)  One example of a complexity that might arise in a given antenna design is that the dominant radiation might be linearly polarized in one principal plane, but the radiation from some minor lobes might be cross -polarized.

All of these need to be taken into account if a radio telescope is to be functional.


I hope you can see from this that attaining a workable radio telescope antenna isn't as simple as inserting backing /reflective material or coating to the enhance the reflector's EM capability.

The reason is that this is likely to have no net effect on the antenna pattern needed for detection.

I do think there might be a possible application for uses that are not high end, but I would have to invest a lot more time looking at those issues, and right now I am unable to devote that much time to it.

I suggest maybe sending your basic idea to an amateur group that is interested in radio astronomy and seeing what they think. You might be able to find a number of them by googling.

Sorry I can't be of more help!

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Philip Stahl

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I have more than forty years of experience in Astronomy, specifically solar and space physics. My specialties include the physics of solar flares, sunspots, including their effects on Earth and statistics pertaining to sunspot morphology and flare geo-effectiveness.

Experience

Astronomy: Worked at university observatory in college, doing astrographic measurements. Developed first ever astronomy curriculum for secondary schools in Caribbean. Gave workshops in astrophysics and astronomical measurements at Harry Bayley Observatory, Barbados. M.Phil. degree in Physics/Solar Physics and more than twenty years as researcher with discovery of SID flares. Developed of first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Develop first ever loop solar flare model using double layers and incorporating cavity resonators.

Organizations
American Astronomical Society (Solar Physics and Dynamical Astronomy divisions), American Mathematical Society, American Geophysical Union.

Publications
Solar Physics (journal), The Journal of the Royal Astronomical Society of Canada, The Proceedings of the Meudon Solar Flare Workshop (1986), The Proceedings of the Caribbean Physics Conference (1985). Books: 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level'. 'Astronomy and Astrophysics: Notes, Problems and Solutions'.

Education/Credentials
B.A. Astronomy, M. Phil. Physics

Awards and Honors
American Astronomical Society Studentship Award (1984), Barbados Government Award for Solar Research (1980), Barbados Astronomical Society Award for Service as Journal Editor (1977-91)

Past/Present Clients
Caribbean Examinations Council, Barbados Astronomical Society, Trinidad & Tobago Astronomical Society.

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