Radio astronomy

RadioUniversePRO is the most advanced software ever developed for radio astronomy with compact radio telescopes: it gives you all the power to control the different components of your radio telescope with an immediate and easy-to-use interface. You do not have to worry about using different softwares, RadioUniversePRO is your intuitive control and data acquisition interfaces with the radio telescope. RadioUniversePRO is not sold separately and is supplied only with SPIDER radio telescopes.

 

Included with every SPIDER radio telescope, our RadioUniversePRO software allows you to control the antenna position and acquisition parameters of the receiver. This way you cannot only record data coming from the sky (deleting eventual artificial signal interferences) but also transits or radio-images of radio sources in the sky you want to study.

 

RadioUniversePRO radio astronomy software for SPIDER radio telescopes: key features

• Control software for SPIDER radio telescopes
• Intuitive and easy-to-use: in single a screen it shows all the controls of the radio telescope
• Mount control: it allows you to remotely control SPIDER 300A and SPIDER 500A radio telescopes with alt-az computerized mount, and SPIDER 230C radio telescope with german computerized equatorial mounts and ASCOM driver (it requires the installation of ASCOM platform)
• Receiver control: it allows you to connect and control H142-One receiver of SPIDER radio telescopes
• Data save in graphic format (PNG) and raw (FITS) compatible with NASA FITS Viewer.

 

RadioUniversePRO: IF Monitor

It displays the data coming from the radio telescope to the receiver in form of a Power Spectrum (upper row) and FFT Waterfall (lower row), both for Left and Right Polarization. Power spectrum is the graphical representation of the electromagnetic power distribution in the operative band, through the RF chain.

 

RadioUniversePRO: BBC Tool

BBC Tools window allow you to visualize in real time the uncalibrated power spectrum of the input signal in both IF left and right. RadioUniversePRO allows you to use a group of digital filters (16+16) fully tunable on the 2 Intermediate Frequencies. Every filter is identified by a BBC (Base Band Converter) label and a number from 01 to 16. Every filter can be set in frequency and bandpass.

 

RadioUniversePRO: Offset alignment

Offset alignments is the instrument that is used to synchronize the radio telescope on the radio sources position on the sky, by reducing the pointing errors on 2 axis of the mount. The radio telescope will perform automatic measurements of Total Power values by varying latitude and longitude offsets. When the procedure is completed, RadioUniversePRO will complete plotting of the graphs and calculate the best offsets to send to the mount electronics in order to better align to the pointed radio source.

 

RadioUniversePRO: Source visibilities

Source Visibilities tab lists the most powerful radio sources in the sky. This tab is designed in order to allow you to have a quick idea on the radio sources available that you can point and study with your radio telescope (detection level is different based on the SPIDER radio telescope model you use). In order to point the radio telescope to any of the listed radio sources, just make a mouse double click on the radio source row and the radio telescope will point it.

 

RadioUniversePRO: Gain calibration

Gain Calibration procedure executes Total Power measurements (by using the proper BBC filters the users selects) on a set of radio sources with a known radio flux by literature. During the Gain Calibration procedure, a proper polinome function allow RadioUniversePRO to calculate the theoretical flux in Jy the radio telescope would record without any atmospheric attenuation or any gain loss because of different factors (antenna deformation because of its weight for example).

 

RadioUniversePRO: OnOff

OnOff tab allows you to perform an ON-OFF recording on a radio source. The radio telescope is pointed to the radio source (ON position) and the data is collected. Then it’s moved in a position OFF the source and another set of data is collected and used to calibrate the previous one. This way you’re able to reduce the radio noise and the effect of external components (like the Earth atmosphere).

 

RadioUniversePRO: Spectrometer

During acquisition, every spectrum is shown in the “Spectrometer” tab, both for left and right polarizations. At the end of acquisition, RadioUniversePRO will automatically perform an average of the data and will display the spectrum. During data acquisition, you can zoom in the spectrum to better visualize parts of it.

 

RadioUniversePRO: Total Power Plots

Total Power Plots are the perfect instruments to easily visualize and record the variation of the radio signal flux over time. Just select the “Plot” option and you will see the value in counts for every BBC filter plotted over time. In the Total Power Plots tab you have the controls that allow the radio telescope to automatically perform a Cross Scan.

 

RadioUniversePRO: Mapping

Mapping tool lets you scan a sky area and convert it into an image map. Select the Mapping tab to reveal Mapping options in the Setup Map area. You can set Width/Height (the side of the Map you want to create), Delta (a moltiplicative factor of the HPBW of your radio telescope, this is the distance from pixel to pixel of the map RadioUniversePRO will create), Average(number of seconds the antenna has to track every pixel and average values).

 

RadioUniversePRO: Envirnomental data

Environmental data tab shows all the data related to environmental conditions and coming from the external sensors of the radio telescope. Here you can connect to the Ultrasonic Wind Sensor and monitor wind speed, check for internal temperature of the WP-100 and WP-400 mounts, and connect to the All Sky Cam and see in real time, inside of the RadioUniversePRO software, the radio telescope you’re controlling.

 

RadioUniversePRO: Dark and Light mode

In order to improve visibility of displayed graphs and recorded results, RadioUniversePRO has a Dark Mode that also makes it easier to stay focused on data coming from the SPIDER radio telescope. You can always come back to the Light mode by selecting View -> Light.

 

RadioUniversePRO: FITS format

RadioUniversePRO lets you save recorded data in graphical format (PNG) as visualized on the user interface but you can also save raw data in FITS format compatible with NASA FITS Viewer, the same software often used by professional radio telescopes. This way users can quickly open and view their data and export them to process with other softwares.

 

RadioUniversePRO: system requirements

• Operative system: Windows 10 (suggested: 64 bit version)
• Screen resolution: at least 1920 x 1080
• RAM memory: 4 GB (suggested: 8 GB)
• Processor: i3 (suggested: i5 or i7)

Would you like for us to build a radio telescope at your location? Our  team is able to ship to you and install one or more of our radio telescopes – here what you need to know beforehand.

 

Radio telescope schematics

Radio2Space radio telescopes are composed of components to be installed outside (radio telescope antenna and mount) and others to be installed inside (receiver, antenna control unit, other accessories and control software). All elements must be properly powered and must be connected to each other with special data cables provided with the radio telescope. Here you can see the general schematics of the elements composing Radio2Space radio telescopes.

 

 

Power and data cables

The antenna has to be connected to the radio telescope control room with an underground pipe where power and data cables have to be inserted. In order to avoid too high gain losses, we suggest having the control room closer than 50 meters from the radio telescope antenna. If you have longer distances, we recommend the optional Radio over Fiber Optics kit.

 

 

Concrete base

In order to guarantee utmost safety and stability, it is necessary to install the radio telescopes (except for the SPIDER 230C model that comes with a field tripod) on a reinforced concrete base that has to be prepared by the customer (we can provide the concrete base suggested design to the customer). The radio telescope is equipped with a dedicated column for ground anchorage to support the forces generated by large antenna.

 

 

In the control room

In the control room, receivers and various devices can be set on a table or in a standard 19″ rack. If you haven’t a rack, we can supply you our RK19 rack that comes with fans for temperature control and remote power on/off. The entire radio telescope is controlled with our RadioUniversePRO software that has to be installed on a Windows computer that is not included with the radio telescope. If you haven’t a PC, we can provide you with our CMP-19 computer for radio telescopes.

 

 

Security and environmental control

Radio2Space radio telescopes (except for 230C model) are designed to be functional also in bad weather and windy conditions. However, the radio telescope has to be parked in Stow position (with the antenna facing the Zenith) when the wind exceed 50 km/h. The optional UltraSonic Wind Sensor continuously monitor the speed and direction of the wind and, if the wind speed exceeds 50 km/h, automatically parks the radio telescope in safety position (thus reducing the wind load on the antenna).

 

If you like for us to build a radio telescope at your location and you want more info, click here to contact us.

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Affordable radio interferometry

Radio interferometry is the technique used by professional radio astronomers to create a single large radio telescope using multiple smaller antennas. Radio interferometry allows radio astronomers to obtain radio pictures with higher angular resolution, but up until now this technique has been used only in very expensive research instruments….

Today we present our next challenge – To develop the first affordable radio interferometry system for SPIDER radio telescopes!

 

 

Radio interferometry and angular resolution

Exploring the Universe by means of detecting radio waves has many advantages, like performing radio astronomy during daytime and in adverse weather conditions. However, since the angular resolution of a telescope is directly proportional to the wavelength, a radio telescope has an angular resolution much smaller than an optical telescope. For example, the angular resolution is calculated by this formula:

θ = 2.5 x 10⁵ * (λ/D)

where θ is in arcseconds and λ (wavelength) and D (telescope diameter) are in meters.

Considering an optical telescope with 50cm diameter (0.5m) with medium value of 550nm of λ (5,5×10-7 m), the theoretical angular resolution is:

θ = 2.5 x 10⁵ * (5.5×10^-7 / 0,5) = 0.275 arcseconds

If we want to have the same angular resolution with a radio telescope recording 21cm wave length, we’ll need to solve this equation:

0.275 arcseconds = 2.5 x 10⁵ * (0.21 m /D)

And this bring us to a diameter of 190909 meters. This means, in order for a radio telescope to have the same angular resolution of a 50cm optical telescope, the antenna would need to be 191 km in diameter, far too large to actually build! However, by using radio interferometry we can effectively create a single telescope as large as the distance between the two farthest radio telescopes composing the array.

 

 

The advantage of radio interferometry with compact radio telescopes

Many radio telescopes are designed as an array of more compact antennas instead of a single massive instrument. Examples can be found at the new Atacama Large Millimeter Array (ALMA) in Chile, composed of many 7 and 12 meter diameter antennas as well as the Very Large Array (VLA) in New Mexico (USA) that uses 27 antennas, each 25 meters diameter. SPIDER radio telescopes use smaller antennas, with diameters ranging from 2.3 to 5 meters – This is one of the reasons that makes the SPIDER so affordable, even within the reach of schools, universities or a science museum budget.

As you begin building an antenna with a diameter larger than the 5 meter model used in the SPIDER 500A, the costs of the radio telescope increase dramatically due to the massive mount that would be required not only to precisely move such an antenna (precise movement is critical in radio astronomy applications) but to also safely handle any adverse weather conditions, like the more compact SPIDER radio telescopes. When we studied the possibility of developing a larger radio telescope, we found that the manufacturing costs of a 8 meter model would be more than 3 times that of the SPIDER 500A radio telescope… Clearly radio interferometry is the solution.

 

 

Today we embark on our next challenge: radio interferometry

When we developed the SPIDER line of radio telescopes, we brought to market the first line of affordable, professional, compact radio telescopes developed specifically for radio astronomy. Now we want to extend this development to radio interferometry to create complete arrays of radio telescopes, allowing you to do radio interferometry with ready-to-use SPIDER systems! In order to accomplish this, there are different goals we will need to meet:

1. Development of a Fiber Optic Device that, by replacing standard RF cables, will maximize the signal from the compact antennas capable of sending data over medium/long distances between the LNA and the receiver, allowing flexibility in the interferometer design.
2. Development of the BKND-Pro Professional Backend that, not only will provide very high spectral resolution for single dish radio astronomy and SETI applications, but it will also be designed to sample the signal in the time domain in preparation for data correlation from multiple SPIDER telescopes.
3. Development a Synchronization Device for the different clocks of the radio telescopes and for the acquisition system.
4. Development of the Correlator that will acquire data coming from the different SPIDER radio telescopes and merge all of the signals to create a single high resolution radio map of the Universe.

We’ll publish all these developments on our website so please subscribe to our newsletter or to our Social Media channels to be sure and get the latest updates!

 

If you like to know more about our affordable radio interferometry system for SPIDER radio telescopes, contact us.

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What are the results you can record with a radio telescope? In this article you can see spectra, cross-scans and radio maps you can record with SPIDER radio telescopes. When we record a picture of an Universe object, we usually use a digital camera that has many pixels (typically several millions). This way, when we record the picture, the light we receive “lighten” many pixel at the same time and each pixel records light coming from different sky areas. But, when we use radio telescopes, we record the signal from a single area of the sky (only large professional radio telescopes may have more LNA units), just as if our camera had only one pixel.

 

 

If the instrument is equipped with a precise automatic pointing and tracking system, and you have the coordinates of Universe radio sources in the sky (as in our SPIDER radio telescopes), you can point the antenna to the correct direction, and then record the radiation flux coming from the object itself. This is relates to the power of the signal emitted by the radio source. The type of data obtained depends on the receiver characteristics and by the fact that the measure could be calibrated or not. That’s why, in general, the first result you get radio telescopes pointing the sky is a number.

 

 

 

Another result type that can be obtained with radio telescopes is a cross-scan. This technique consist in pointing the radio telescope to the selected target and command data acquisition by moving the antenna in azimuth and elevation, this way creating a cross section centred on the target with the antenna tracking system, with a faster speed than sidereal rate. We can thus record a curve of values and, if the radio source is perfectly centred, the resulting central peak has a direct correlation with the radio emission coming from the source. This type of result is very interesting since it allows to evaluate also antenna parameters such as the resolution capabilities of the antenna and is also used to verify performance of radio telescope.

 

 

By using a specially designed receiver and backend, like our SPIDER radio telescopes, the captured signal coming from a precise area of the sky may be sampled with a digitiser. This way the radio telescope is able to detect also the spectrum of the target. This is particularly interesting when the user wants to detect particular emission lines like the neutral Hydrogen line emitted by the Milky Way.

 

 

If the radio telescope has a precise tracking and automatic pointing system, we can record a radio map of the object that we want to study. This allows us to record an image of the object radio emission. In order to do so, the radio telescope is continuously moved by scanning the desired sky area and recording the radio emission which comes from each pixel that compose our image. Some pixels will record a different quantity of radio waves from the adjacent ones and each number is then associated with a color, this way generating a radio image of the object! Our SPIDER radio telescopes allow the user, in a very simple way, to obtain these results with a compact radio telescope by using the RadioUniversePRO software. In the image below, you can see a radio map of the Cassiopea A supernova remnant recorded with SPIDER 300A radio telescope.

 

Radio interferometry is an advanced technique, developed by professional radio astronomers, that allows to use many smaller antennas instead of a too large one. In fact, when we think of a radio telescope, we imagine an instrument of enormous dimensions, equipped with a very large parabolic antenna that collects radio waves coming from space. By using many compact radio telescopes, radio interferometry improves results in radio astronomy research and allows the use of more affordable radio telescopes. For example, by using this technique the Event Horizon Telescope (an international collaboration of multiple radio telescopes from all over the world) recorded, in April 2019, the first radio map of a black hole inside the M87 galaxy, with an incredible resolution of 25 microarcseconds!

 

Radio interferometry: basics

When we look at a point source, such as a star, with a telescope, a point image will not form on the focal plane since the circular aperture of the instrument causes diffracted rays to generate a particular “pattern” on the focal plane, first explained by George Airy in 1835 with his “wave theory of light”: this pattern consists of concentric light regions alternating with dark ones. These rings, increasingly weaker as you move away from the center of the pattern, are the product of diffraction and have a peak in the central area, called “Airy disk”.

 

 

The optical resolving power of a telescope is related to the size of the Airy disk which depends on the wavelength λ of the observed radiation and the diameter D of the instrument. Using the approximation for small angles, Airy’s disc has an angular size given by the equation θ ≈1.22 λ/D: the larger the diameter of the instrument, the greater the theoretical resolution. If we now assume to observe a celestial object formed by 2 or more stars arranged very close to each other, Airy’s discs will overlap on the focal plane of the telescope, therefore it will be possible to “resolve” each of the stars only if the peaks the centers of each pattern won’t be added destructively, that is when their focal plane distance is no shorter than the radius of Airy’s disc (this rule known as Rayleigh’s condition).

 

 

This applies not only to optical telescopes but also to radio telescopes which, due to the longer wavelength they record to “observe” the sky, have a much lower resolution capability than the optical ones, given the same diameter. For example, in order to match the resolution of Hubble Space Telescope (2.4 meters in diameter), ALMA, one of the most modern radio telescopes recording millimeter radio waves, would need a 5 km diameter parabolic antenna.

 

First interferometers

Michelson’s interferometer is based on the interference properties of light: a beam of electromagnetic waves coming from the same source (in the case of a radio telescope, from a celestial object) is divided into 2 parts on different paths and subsequently reconverted. If the 2 paths have different lengths or move through different materials, there is a phase shift in their optical path. We will obtain maximum light intensity when the angle θ formed by the direction of the star with respect to the optical axis of the instrument is such that the difference between the paths of the 2 beams is an integer number of wavelengths (with respect to the center of the passband). If the angular dimensions of the star are small compared to the space between 2 adjacent interference maxima, the image of the star will be crossed by a clear pattern of alternating dark and light bands, known as interference fringes. Conversely, if the angular dimensions of the star are comparable to the spacing between the maxima, the image will be the result of the superposition of a series of patterns along the star, where the maxima and the minima of the fringes do not coincide and the amplitude of the fringe will be attenuated, as shown in figure below (b). Thanks to this technique, in 1920 Albert Michelson and Francis Pease created the first “stellar interferometer” and by using it they measured that the diameter of the Betelgeuse star was equal to the Mars orbit.

 

 

The first radio interferometer dates back to 1946 when it was used by Ryle and Vonberg for the study of radio emissions from space that a few years earlier had been first discovered by Jansky, Reber and others. This interferometer was formed by an “array” (a group) of 2 dipole antennas operating at 175 MHz frequency and having a baseline D (distance between the antennas) varying between 17 and 240 meters.

 

 

It was a so-called “transit interferometer”, a diffused type in the 50s and 60s of the last century, that needed antennas to be pointed to the local meridian, at a certain elevation, and wait for the earth’s rotation to move the object along the Right Ascension. If θ is the zenithal angle of the object to be observed and is different from zero, the electromagnetic waves will reach antenna B first (see figure above) and subsequently antenna A with a delay τ=(D/c) sin⁡θ, where c is the speed of light. The detector of the receiver, integrated over time, will generate a response proportional to the square sum of the voltages of the 2 signals similar to the trace in picture below.

 

 

Modern radio interferometry

The countless technological advances of recent years have led to a large use of interferometry in radio astronomy. Just think of the large networks of professional radio telescopes that form the VLBI, Very Long Baseline Interferometry, which has been operating since the late 1970s by connecting several instruments distributed in several parts of the world, with the aim of creating a single large instrument with an equivalent diameter of thousands of kilometers. Among the most sensitive and performing networks in the world there is the EVN, Europe VLBI Network, which uses the largest European radio telescopes for periods of a few weeks a year.

 

 

Among the most famous networks we also remember the VLBA, Very Long Baseline Array, which uses 25 radio telescopes located along the American continent; ALMA, an array of antennas that rises on the Chilean plateau at 5000 meters above sea level and that since 2013 observes the sky in wavelengths from 0.3 to 9.6 mm; LOFAR, an interferometer managed by ASTRON in the Netherlands capable of mapping the universe at frequencies between 10 and 240 MHz; SKA, the Square Kilometer Array, an ambitious project currently under construction that will see the creation of 2 arrays ensuring constant coverage of frequencies from 50 MHz to 14 GHz.

 

 

Radio interferometry with small instruments?

Although some experiments of amateur radio interferometry date back to the 80s of the last century, it was with the advent of the Sat TV systems at the end of the last century that we a progressive increase in amateur experiments, however always by few electronics experts.

 

 

The challenge of creating a radio interferometer that was within the reach of research groups, schools and universities was taken by PrimaLuceLab that, after the development of the Radio2Space SPIDER radio telescopes for radio astronomy (with parabolic antennas up to 5 meters in diameter and receivers to capture the n neutral hydrogen wavelength at 21 cm) has now presented the project of its radio interferometer with the installation of the first array of 3 radio telescopes, 5 meter diameter each, at the Sharjah Academy for Astronomy, Space Sciences & Technology near Dubai (UAE).

 

 

The difficulties in the realization of an interferometer project are many: first of all the antennas that compose the array must have very high mechanical precision, with a mount for radio sources pointing and tracking ff the large antennas equipped with a precision similar to the one of an optical telescope. SPIDER radio telescopes are in fact equipped with ultra-low backlash alt-az mounts and with encoders capable of reading few arc seconds errors. They are also equipped with an specially designed feed for 21cm wavelength, with double polarization, connected to very low noise LNAs that amplify the signal before it reaches the receiver. For the operation of the interferometer, PrimaLuceLab is developing a device that transforms the radio frequency output from the LNA into an optical signal over fiber, even at distances in kilometers. This eliminates the normal coaxial cables and therefore the losses in the signal between antennas and receivers.

 

 

In the control room, on the other end of the optical fiber, the signal will be transformed in the RF band and connected to the receiver (one for each antenna). To maintain adequate time consistency, a synchronization device will also be developed for the timing of radio telescopes and for the acquisition system. Then, signal will be digitized by means of an extremely performing backend and which will save the data on disk for subsequent processing. Finally, signals from each antenna will be sent to the digital correlator that, based on the Fourier transform, will perform the calculations necessary for the signal correlation and will output the visibility functions for each baseline of the antennas array.

 

 

Thanks to the radio interferometry technique, we are developing an affordable interferometer system to simultaneously use many radio telescopes and obtain high resolution radio maps of radio sources in the Universe. The system will be configurable with a variable number of antennas and it will also allow the user to increase their performance by installing more antennas in a later moment. Thanks to this system, universities, scientific museums, planetariums, research institutes but also groups of amateurs will have at their disposal a scientific instrument, ready to use but very powerful, that up to yesterday was available only to professional researchers.

Salvatore Pluchino
Filippo Bradaschia

Radio astronomy is a fascinating science and it studies the Universe by detecting radio emission from many objects like the Sun, the Milky way, planets, galaxies and nebulas. In this presentation Filippo Bradaschia, PrimaLuceLab president and co-founder, gives an overview on radio astronomy history and basic physics. Then he introduces the most important radio sources in the Universe and the SPIDER affordable radio telescopes developed by PrimaLuceLab with Radio2Space brand. These instruments allow any school, university, museum or science institute to make real radio astronomy with powerful but affordable, compact and easy to use radio telescopes.

In this presentation:

1. Introduction: discovery of the invisible Universe
2. How radio waves are generated in the Universe
3. How the Universe appears in radio waves
4. Radio astronomy with SPIDER radio telescopes

 

 

By today, radio astronomy can be performed not only by professional radio astronomers. In fact PrimaLuceLab builds complete radio telescopes ready for use for educational (schools, universities, science museums) and research (science institutes, space agencies) markets at an affordable price. This way you no longer need to study how to build a radio telescope but you can use a certified and powerful instrument, and focus your attention in getting data and make real radio astronomy!

 

 

SPIDER radio telescopes are turnkey systems composed of the antenna, mount, pier, receiver and software, ready to capture radio waves coming from space. Antenna diameters range from 2.3 to 5 meters with different types of mounts, also weatherproof in order to allow the radio telescope to be installed in the field without the need of a protection structure. Every SPIDER radio telescope is designed to be remotely operated from a control room where the H142-One 1420 MHz receiver with computer and RadioUniversePRO software are installed.

 

If you want to know more about our SPIDER radio telescopes, you can click here and discover all the available models. In order to allow everyone start his project, PrimaLuceLab also offers design, shipment, installation and training services. Thanks to our team specialized in radio telescopes, we can support you from design to shipment, from installation to on-site training.

The Sun is one of the strongest radio sources in the sky: if the part of the Sun emits more in the visible wavelengths is called photosphere, the radio frequencies born in the chromosphere and in the corona, the solar atmosphere. The solar surface has a temperature of about 6000K, and even if the gas at this temperature emits more wavelengths in the frequencies of visible and ultraviolet light, because of its proximity we can also record the radio emission.

 

 

The Sun emits radio waves since it’s hot hot (it is said that it is a thermal source and then emits radio waves more at high frequencies) but there is a strong emission even at lower frequencies (in the field of non-thermal sources) for the mechanism of  synchrotron radiation which derives from the movement of high speed electrons around the magnetic field.

If we analyze the flux density (in simplified terms, the amount of radio waves arriving from the Sun) emitted as a function of frequency, we can highlight a second peculiarity: at wavelengths greater than 1 cm the curve is divided into two cases identified as “quiet Sun” and “disturbed Sun”. The first is defined from normal Sun activity while the second depends on the sunspots activity.

 

 

In reference to “quiet Sun” emission , the solar disk has a different diameter in function of study frequency.

• At very low frequencies (below 0.1 GHz) and therefore at very long wavelengths (> 3m) the solar disk appears much bigger and brighter in the center, and its brightness gradually decreases and vanishes after several solar radii.

• For frequencies between 0.1 GHz and 3 GHz, the Sun is still larger than its optical counterpart and a radio peak intensity near the edge called limb brightening is noticeable.

• For frequencies above 3 GHz the Sun appears similar (though still greater in size) to its visible counterpart and its brightness is uniform.

From these considerations it is possible to verify that higher frequency radio waves originate closer to the photosphere, the ones with lower frequency in the corona, which then gives the Sun a greater dimension in the sky.

In the case of a ‘disturbed Sun’, it is possible to delineate a low variability component, ranging from days to months, which is evident at wavelengths from 3 to 60 cm and a high variability component characterized by strong emissions of radiation in time intervals from seconds to hours. The first component is closely associated with the presence of sunspots even when not directly visible because they are beyond the edge of the Sun. Then this radio emission originates in regions above the photosphere.

The second component (with high variability) instead is linked to strong emissions that follow the occurrence of flares, violent matter explosions initially visible in the visible band of H-alpha (for example with specialized solar telescopes).  Flares can be divided into impulsive or eruptive. The former have a short duration, from seconds to minutes, and develop only in the lower layer of the solar atmosphere. The latter have longer life, from minutes to hours, and can generate huge amounts of energy and matter ejected into space. Flares are caused when charged particles are suddenly accelerated. The energy required for this acceleration is derived from the magnetic field around the most active areas of the solar surface. During the impulsive phase of the flare, there is a fast increase in the intensity of radio waves with centimeter or decimetre wavelengths. The most powerful eruptive flares emit radiation for several hours.

The radio activity bound to these phenomena is classified (Wild, Smerd, Weiss , 1963) in function of the characteristics of this emission:

• Type I: short events that occur in large numbers associated with a continuous emission (duration: from hours to days)
• Type II: strong events with frequency shift from high ​​to low values ​​(duration: minutes)
• Type III: strong events with short duration with frequency shift from high to low values ​​(duration: seconds)
• Type IV: continuous emission (duration: from hours to days)
• Type V: continuous emission associated to type III, recorded in frequencies lower than 100 MHz (duration: 1-2 minutes)

The characteristics of these types are well illustrated when considering the events that follow a solar flare.

 

 

In phase 1, there is a strong type III emission immediately after the onset of a flare visible in the H-alpha line. There is a very strong radio emission that ends quickly and that, it is believed, is derived from the oscillations of the plasma associated with the expulsion of electron beams in response to flare. Sometimes, especially at frequencies below 100 MHz , the flare is associated with a more continuous and long lasting emission, the type V. The electromagnetic waves of this type are generated by the acceleration of electrons along the magnetic field lines in the corona.

In events strongest , ie in the eruptive ones, there is also the phase 2 which begins with short and net signals peaks which often also include a second repeat (harmonic). This emission comes by the shock wave front to the gas cloud above the flare. At times, immediately after you can record a weaker but continuous signal that can last from hours to days and that is called type IV . The latter is related to the synchrotron emission coming from the gases above the flare and it can have short and strong signal peaks classified as type I.

Among the radio burst type IV there is one type , called “mu-burst type IV” , in which the signal is emitted, with wavelengths from 30 cm to 1 cm, so even above 10 GHz. This allows us to understand that the Spider230 radio telescope can also be used for studies of thesesolar atmosphere phenomena, possibly associated with a H-alpha solar telescope to study simultaneously the different components of the electromagnetic spectrum coming from the same phenomenon, namely a flare.

 

 

Sometimes, during the most intense phenomena, high energy cosmic particles are emitted from the Sun and, when they encounter the Earth’s magnetic field, they generate magnetic storms and auroras.

Largest radio telescopes in the world are used by professional radio astronomers, and often you can also visit them. Radio telescopes are extraordinary instruments, equipped with giant parabolic antennas or other, designed to work as single instruments or as interferometers. They are used to study objects in the Universe in radio waves frequencies but often are also used for satellite communication or studies of Earth’s atmosphere. Here you have a list with some of the largest radio telescopes in the world and a brief description for each instrument.

 

Very Large Array – VLA (USA)
Probably one of the most famous radio telescopes in the world thanks to films like “Contact”, it uses 27 Cassegrain antennas each 25 meters diameter that can be moved along a Y shaped rail system.

 

Arecibo (Puerto Rico)
Up to 2016, it was the largest parabolic antenna in the world, thanks to its 305 meters diameter. The antenna was placed on a natural depression in the ground and it has no mount: the radio telescope can point different sky regions moving the central feedhorn.

 

GBT (USA)
The Robert C. Byrd Green Bank radio telescope has a parabolic antenna with asymmetric surface and an off-axis illumination. In Green Bank there are also other large radio telescopes such as the 43-meter diameter one with equatorial mount.

 

Atacama Large Millimeter/submillimeter Array – ALMA (Chile)
The ALMA radio telescope includes many 7 and 12 meters diameter parabolic antennas that have been installed in Atacama desert in Chile, about 5000 meters above sea level. Thus, it will study also the high radio frequencies usually blocked by the atmosphere.

 

FAST (China)
The Five-hundred-meter Aperture Spherical radio Telescope (FAST)) is a radio telescope located in southwest China. It consists of a fixed 500 m  diameter dish constructed in a natural depression in the landscape and it is the world’s largest filled-aperture radio telescope.

 

Effelsberg (Germany)
Thanks to the huge 100 meters diameter parabolic antenna, this is one of the largest radio telescopes in the world. This radio telescope weighs 3200 tons and it takes 12 minutes to make a complete 360 degrees rotation.

 

Medicina (Italy)
Near Bologna there are two radio telescopes: the “Northern Cross” that consists of an array of antennas in two perpendicular arms and a 32 meters diameter parabolic antenna which is also used in interferometric observations.

 

Sardinia Radio Telescope (Italy)
This radio telescope, built 35 kilometers away from Cagliari, uses a 64 meters diameter parabolic antenna designed with high accuracy (among the best of several radio telescopes in the world) in order to allow recording at high frequencies (up to 100 GHz).

 

Lovell Radio telescope (England)
With its 76 meters diameter antenna, this instrument is one of the largest radio telescopes in the world with movable reflector. It is located in Jodrell Bank (England) and it’s part of English MERLIN interferometer system.

 

Parkes (Australia)
Parkes Observatory is located in the south-eastern Australia and it uses a great 64 meters diameter parabolic antenna. In addition to radio astronomy, it was also used to collect the Apollo 11 transmissions coming from the Moon.

 

Square Kilometer Array – SKA
Currently under study, it uses a network of thousands of antennas installed both in Australia and in South Africa. Combining the recorded signals, it will be possible to obtain a collecting area equivalent to the one of 1 square kilometer parabolic antenna.

Radio astronomy is a young science, born at the beginning of 20th century. There are two figures that have historically contributed to birth of this science: Karl Jansky and Grote Reber.

Jansky was an engineer that, at the end of 20s, worked at Bell Labs in New York society where, in particular, he were dedicated to recording of atmospheric interference at shortwave. From summer of 1931, Jansky built an instrument and he began to record an inexplicable signal whose origin was not clear. In 1932 he realized that the signal had every day a small advance over time and so Jansky concluded that it had to come from outside the Solar System. He became so famous in newspapers and on radio, but despite trying to attract attention of astronomers, his discovery was not followed. Jansky did not even have to any scientific recognition for his discovery and he died in 1950.

 

 

Grote Reber was only to deepen Jansky results building an instrument in order to receive waves from space. He built it in his house garden, the first radio telescope with parabolic antenna in the world. His instrument was equipped with a parabolic dish with a diameter of 9.6 meters and an altazimuth mount. From 1937 he began reception attempts at 3300 MHz but got nowhere until, in 1939, he began to record signal coming from Milky Way lowering frequency at 160 MHz. He began to realize first maps of sky radio emission and, with the construction of new and more sensitive receiver at higher frequency, he gradually improved resolution capacity.

 

 

After these initial and fantastic discoveries, few were interested in radio astronomy until the end of Second World War during which immense development of radar techniques allowed for the first time to build sensitive instruments to record faint radio signals also from more distant objects in the Universe.

Is the world exactly as we see it? It is not so simple. For example, some animals, such as bees, can see parts of electromagnetic spectrum that we can not see (such as ultraviolet light or infrared): the world does not appear to them as to us. Our eyes are in fact sensitive to wavelengths between 400 and 700 nanometers (1 nanometer is one millionth of a millimeter). Instead electromagnetic spectrum is made up of many types of waves of which the visible is only a small area:

 

 

Radio waves: are characterized by higher wavelengths, greater than 1 millimeter. Higher frequency radio waves are called microwaves.

Infrared: with a wavelength between 700nm and 1mm, we humans we can not see it but we perceive it as heat on skin.

Visible light: with a wavelength between 700 and 400 nm, it is the part of electromagnetic spectrum that we can see and which is expressed through rainbow colors.

Ultraviolet: it has a wavelength between 400 to 10 nm and it is responsible for our tans.

X rays: characterized by a wavelength between 10 and 0.01 nm, they are very important for medical application because they are used for medical diagnostics.

Gamma rays: with a wavelength less than 0.01 nm, are those with greater energy.