In this page we present a short introduction with links to optical interferometry, the technique where our schools focus. The level is very simple in order to make it understandable by everyone.
Optical interferometry is an astronomical technique that combines the light from different telescopes. When the light from two sources is combined it produces interference fringes. In the optical the wavelength of the light is very small, of the order of a thousandth of a millimeter. Therefore the paths that the light travels from each telescope to the interference chamber must be equilibrated to a precision comparable to the wavelength of the light. This is a formidable technological task because the telescope separation if of the order of 100 meters. It is also the reason why astronomical interferometry has only become a mature technique in the last decade.
Another problem that makes optical interferometry difficult is the atmosphere. The atmosphere is turbulent and this is the cause of the twinkling of the stars. An astronaut in space would see the stars as fixed and stable as a street lamp. Turbulence therefore causes the interference fringes to wobble back and forth very quickly, typically at one twentieth to one hundredth of a second. This is very fast and the fringes then become blurred when recorded. But there is a solution, the optical paths of each telescope can be corrected in real time at a speed faster than turbulence – this is what is done by modern systems.
You might now ask, if optical interferometry is so challenging why bother? It turns out that astronomers are interested in optical interferometry because it is the only way to measure very small angular sizes. Let's consider the Sun, we can easily measure the Sun's disk diameter (not directly because would damage our eyesight). But it turns out that most of the stars that we can see in the night sky are so small that we cannot measure it's diameter. Even with the Hubble Space Telescope the stars would look like a point. But with an optical interferometer the diameters of many stars can be measured.
The Very Large Telescope Interferometer (VLTI) is the most powerful interferometer on the planet and was built by the European Southern Observatory. The goal of the ONTHEFRINGE project is to train young European astronomers (PhD students and Post docs) in optical interferometry and related sciences with a series of four two week long schools.
To know more about the VLTI have a look at the following links:
Telescopes and technologies
1. The mechanisms that maintain the lights paths equal for each telescope are called delay lines, The VLTI delay lines are quite a piece to technology.
2. Adaptive optics is an important element of the chain that corrects the atmospheric turbulence effects in an interferometer.
3. The first time the VLTI obtained interference fringes
4. The VLTI combines not only the light of huge 8m diameter telescopes but also the light from quite big 1.8m telescopes
Astronomical results
5. The VLTI measures the diameter of star
6. Eta Carina is the biggest star in the Milkyway, the VLTI measured it's strong wind.
7. Newborn stars are surrounded by very small disks that give birth to planets. The VLTI has detected the first step in this process.
8.A Cepheid is special kind of star that enables astronomers to measure distances the universe. The VLTI has detected the change in diameter of these stars when they pulsate allowing more precise cosmological distances
9. A special issue of an astronomical professional journal is dedicated to astronomical results from the VLTI
The professional astronomers optical interferometry page
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