Active and Adaptive optics and Creating an Artificial Star
♤ The radiations emitted by distant stars are analysed by astronomers to understand the complexities of universe.
♤ These radiations travel a long way through the thick atmosphere and thus get distorted which might not provide required data.
♤ Expensive telescopes like Hubble space telescope have been sent into space for better observation. Establishing a telescope in outer space is very costly and therefore scientists focused on mountaintops in Hawaii, Chile etc. to establish powerful telescopes and have adopted cheaper technologies like Active optics and Adaptive optics for sharp and steady images.
♤ Active optics corrects the changes in shape of primary mirror used in telescopes from phenomenon like uneven expansion (due to heat during day and cold during night) or distortion of mirror due to gravitational pull, violent rush of wind etc.
♤ Adaptive Optics:
o Light is affected by the medium in which it propagates, so turbulence in the atmosphere distorts signals from astronomical objects. (A good example is twinkling stars).
o Thus rapid changes in the orientation of mirrors are required with dynamic conditions of atmosphere, which might not be easy by using active optics techniques. Adaptive optics is used to correct these changes.
o Adaptive optics uses a flexible mirror which adjusts its shape under computer control. However this method requires a special star called reference star. This reference star must be located in the same field of view as distant objects under study. Using this method results into sharp images as if the atmosphere were not present.
♤ Why Artificial stars?
o Adaptive optics is a complicated process as it requires a nearby reference star for observation which might not be available for many astronomical objects under observation.
o To overcome this limitation astronomers artificially create a suitable star according to the requirement.
o With the use of a powerful LASER a bright spot light can be created which is known as artificial star.
o With the help from this artificial star the mirrors of telescope can be adjusted accordingly and we can know about the true shape of the signal coming from the target star.