Adaptive Optics
while searching on web i came across below picture.
that's the observatory but what so special about the picture. well that encourage me to find the answer. that's a laser guided observatory.it uses Adaptive optics to correct the distance object images.
while looking at a night sky we observe that stars are twinkling.star are twinkling because of the turbulance in the atmosphere.that's the big problem the astronomer faces while studying the distance galaxy,star,planets etc...while looking through the ground based telescope the images we see are blurry or distorted and cant able to study.
so how to solve this problem? one solution is to place the telescope where atmosphere turbulence is minimum or nearly zero.that's lead NASA to place the telescope out of the reach of the atmosphere.one of the extraordinary work of nasai s The HUBBLE Space Telescope(HST) located above 530 kms from the earth.images taken by the HST is extremely clear cause there is no atmosphere means no air for turbulence.
below is the some images taken by HST.
Spiral Galaxy
but one problem with space base telescope is its very expensive.(includes space shuttle launch,deployment, maintenance, up gradation cost,not everyone can access the telescope)
so astronomers come across the idea of Adaptive Optics.
Adaptive optics measures
the atmospheric distortions in the incoming light from a star or other object
and sends electronic signals to a deformable mirror that can change its shape
rapidly to correct for the distortions. In the system built for the 100-inch
telescope, the light reflected from the telescope mirror is divided into
several hundred smaller beams or areas. Looking at the beam of light from a
star, the system sees hundreds of separate beams, some of which have been deviated
because of atmospheric turbulence. The electronic circuits in the system
compute the altered shape of a mirror surface that would realign the separate
beams so that they are all going in the same direction. Then a signal is sent
to the deformable mirror to change its shape in accordance with these
electronic signals, resulting in an undistorted beam.
Thus images formed with the
100-inch telescope using adaptive optics are as sharp as those from NASA's
Hubble Space Telescope. This is the most revolutionary technical development in
astronomy since Galileo first used an astronomical telescope in 1609.
Below is the diagram of how adptive optics works.
YouTube link easy to understand how AO works.
but also one problem with AO is that there should be a enough light source (bright star) near the observe region.not every region of space have enough light source so,here we came above 1st picture at the starting of the blog.the laser guide observatory.
There are two main types of laser guide star
system, known as sodium and Rayleigh beacon guide stars. Sodium beacons are
created by using a laser specially tuned to 589.2nm to energize a
layer of sodium atoms which are
naturally present in the mesosphere at an altitude of
around 90 kilometers. The sodium atoms then re-emit the laser light, producing
a glowing artificial star. The same atomic transition of sodium is used to
create bright yellow street lights in many cities.
Rayleigh beacons rely on the scattering of light by the molecules
which make up the lower atmosphere. In contrast to sodium beacons, Rayleigh beacons
are a much simpler and less costly technology, but do not provide as good a
wavefront reference as the artificial beacon is generated much lower in the
atmosphere. The lasers are often pulsed, with measurement of the atmosphere
being time-gated (taking place a few microseconds after the pulse has been
launched so that scattered light at ground level is ignored and only light
which has traveled for several microseconds high up into the atmosphere and
back is actually detected
Below are without AO and with AO images.
