NUCLEAR POWER PLANTS

Introduction

Nuclear power is the fifth largest source of electricity in India after coal, gas, and wind power. A Nuclear reactor is a device used to initiate and control sustained nuclear chain reaction. Mainly they are used at nuclear powerplants for electricity generation and in propulsion of ships. Heat from nuclear fission is passed to a working fluid which runs through steam turbines. Just as conventional power stations generate electricity by harnessing the thermal energy released from burning fossil fuels, nuclear reactors convert the energy released by the controlled nuclear fission into thermal energy for further conversion to mechanical or electrical forms.

When a large fissile atomic nucleus such as Uranium-235 or Plutonium-239 absorbs a neutron it may undergo nuclear fission. The heavy nucleus splits into two or lighter nuclei (the fission products), releasing kinetic energy, gamma radiations and free neutrons. A portion of these neutrons later be absorbed by other fissile atoms and trigger further fission events release more neutrons and so on. This is known as nuclear chain reaction.

Methods to control nuclear fission

To maintain a sustained controlled nuclear reaction, for every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus. If this ratio is less than one then the reaction will die out; if it is greater than one it will grow uncontrolled (an atomic explosion). A neutron absorbing element must be present to control the amount of free neutrons in the reaction space. Most reactors are controlled by means of control rods that are made of a strongly neutron-absorbent material such as boron or cadmium.

In addition to the need to capture neturons, the neutrons often have too much kinetic energy. These fast neutrons are slowed through the use of a moderator such as heavy water and ordinary water. Some reactors use graphite as a moderator, but this design has several problems. Once the fast neutrons have been slowed, they are more likely to produce further nuclear fissions or be absorbed by the control rod.

Nuclear Power Stations:

1. KAIGA NUCLEAR POWER STATION

Kaiga power station is a nuclear power generating station situated at Kaiga, near the river Kali in Uttar Kannada district of Karnataka, India. The plant has been in operation since March 2000 and is operated by the Nuclear Power Corporation of India. The construction for Kaiga began in 1989. The reactor type is pressurized heavy water reactor. It has four units. The fourth unit went on critical on 27 November 2010. The two oldest units comprise the west half of the site and the two newer units are adjoining the east side of the site. All of the four units are small sized CANDU plants of 220MW.

2. TARAPUR ATOMIC POWER STATION

It is located in Tarapur, Palghar, India. It was constructed initially with two boiling water reactor (BWR) units built by Bechtel and GE under the 1963 123 Agreement between India, the United States and International Atomic Energy Agency. It was the first nuclear power plant in India. The construction of the plant was started in 1962 and the plant went operated in 1969.

3. KAKRAPAR ATOMIC POWER STATION

It is a nuclear power station in India, which lies in the proximity of the city of Vyara in the state of Gujarat which consists of two 220MW pressurized water reactor with heavy water as moderator (PHWR). The construction began in 1984 and the plant went operational in 1993. In 2003, this is declared as the best performing pressurized heavy water reactor.

4. RAJASTHAN ATOMIC POWER STATION

It is located at Rawatbhata in the state of Rajasthan, India. It was started in the year 1963 and the reactor type is pressurized heavy water reactor.

5. NARORA ATOMIC POWER STATION

It is located in Narora, Bulandshahar District in Uttarpradesh, India. The plant houses two reactors, each a pressurized heavy water reactor (PHWR) capable of producing 220MW of electricity. Commercial operation of NAPS-1 began on 1 January 1991, NAPS-2 on 1 July 1992. It is the first ISO-14001 certified atomic power station in Asia.

6. KALPAKKAM ATOMIC POWER STATION

It is located at Kalpakkam about 80km of Chennai, India; is a comprehensive nuclear power production, fuel reprocessing, and waste treatment facility that includes plutonium fuel fabrication for fast breeder reactors. It is also India’s first fully indigenously constructed nuclear power station, with two units each generating 220MW of electricity. The station has reactors housed in a reactor building with double shell contained improving protection also in the case of a loss-of-coolant accident.

7. KUDANKULAM NUCLEAR POWER STATION

It is the single largest nuclear power station in India, situated in Kudankulam in the Tirunelvelli District of Tamilnadu. Construction on the plant began on 31 March 2002. But found several delays due to opposition from local fisherman. KKNPP is scheduled to have six VVER-1000 reactors build in collaboration with Atomstroyexport, the Russian state company, Nuclear Power Corporation of India limited (NPCIL) with an installed capacity of 6,000MW of electricity.

Collected By:

Havyashree G P
Ivy Anjali D'Souza
Lekshmi Priya
Pallavi L

Source: Internet

RIPPLES IN SPACE TIME

Gravitational Wave

Introduction:
Gravitational waves are propagating fluctuations of gravitational fields, that is, “ripples” in space-time generated mainly by moving massive bodies. This distortion of space-time travel with the speed of light. Gravitational waves can be detected by devices which measure the induced length changes. The frequencies and the amplitudes of the waves are related to the motion of the masses involved. Thus the analysis of the gravitational waveforms allows us to learn about their source and, if there are more than two detectors involved in observation, to estimate the distance and position of their source and the sky.

Here space-time is any mathematical model that fuses the 3-dimensions of space and the one dimension of time in to a single four dimensional continuum. Space-time diagram is useful in visualizing and understanding relativistic effects such as how different observes perceive where and when events occur.

The idea of space-time continuum comes from the ground-breaking work of ‘Albert-Einstein’. One way of envisioning the space-time continuum is to think of a large piece of fabric, such as a sheet. Einstein realized that objects with mass, such as a person or planet earth, create wrinkles in space-time, which creates a dimple in a sheet. Einstein identified the curves in a space-time as ‘Gravity’ but he thought they would be too small to detect.

In February 2016 the direct measurement of gravitational waves are announced. This provides    us with a new method for exploring the universe.

From Prediction to Reality: A history of the search for gravitational waves

1915 -Albert Einstein publishes general theory of relativity, explains gravity as the warping of space-time by mass or energy.

1916 -Einstein predicts massive objects whirling in certain ways will cause space-time ripples—gravitational waves.

1936 -Einstein has second thoughts and argues in a manuscript that the waves don't exist—until reviewer points out a mistake.

1962 -Russian physicists M. E. Gertsenshtein and V. I. Pustovoit publish paper sketch optical method for detecting gravitational waves—to no notice.

1969 -Physicist Joseph Weber claims gravitational wave detection using massive aluminum cylinders—replication efforts fail.

1972 -Rainer Weiss of the Massachusetts Institute of Technology (MIT) in Cambridge independently proposes optical method for detecting waves.

1974-Astronomers discover pulsar orbiting a neutron star that appears to be slowing down due to gravitational radiation—work that later earns them a Nobel Prize.

1979 -National Science Foundation (NSF) funds California Institute of Technology in Pasadena and MIT to develop design for LIGO.

1990 -NSF agrees to fund $250 million LIGO experiment.

1992 -Sites in Washington and Louisiana selected for LIGO facilities; construction starts 2 years later.

1995 -Construction starts on GEO600 gravitational wave detector in Germany, which partners with LIGO and starts taking data in 2002.

1996 -Construction starts on VIRGO gravitational wave detector in Italy, which starts taking data in 2007.

2002–2010 -Runs of initial LIGO—no detection of gravitational waves.

2007 -LIGO and VIRGO teams agree to share data, forming a single global network of gravitational wave detectors.

2010–2015 -$205 million upgrade of LIGO detectors.

2015 -Advanced LIGO begins initial detection runs in September

2016 -On 11 February, NSF and LIGO team announce successful detection of gravitational waves.

Who has received the 2017 Nobel Prize for Physics?

The prize is shared by Rainer Weiss, Barry Barish and Kip Thorne “for decisive contribution to the LIGO detector and discovery of gravitational waves.”

Dr. Weiss- has born in Berlin and now a U.S. citizen- receives half the prize. The remaining half is shared equally by two Caltech scientists- Dr. Barish, Prof. of Physics and Dr. Thorne, Prof., Theoretical Physics.

WHAT DID THEY DISCOVER?
They are receiving the prize for the discovery of the gravitational waves released by violent events in the universe such as the mergers of black holes. First time this was detected on September 14^th, 2015, by the LIGO-VIRGO collaboration. Since then three more detections have been made, the last one on September 28^th, 2017.

WHY DO GRAVITATIONAL WAVES MATTER TO US?
The discovery is due to an extremely delicate experiment. Gravitational waves were predicted by Einstein almost hundred years ago. After about 50 years of experimentation the waves were detected for the first time on September 2015.

The discovery and the repeated detection have made the possibility of gravitational wave astronomy very real. Gravitational wave astronomy is a way of mapping out some of the most violent processes in the universe such as black hole or neutron star mergers that cannot be detected with light or the conventional methods.

The discovery can prove the way of proving the general theory of relativity, so that we can look deeper and deeper in to the universe. It also throws up the possibility of detectors that can look at the begging of the universe.

Gravity is the weakest of the four fundamental forces so only the most extreme events Black holes colliding, Neutron star twirling and Supernova erupting produce detectable waves.

BLACK HOLE COLLIDING:
It is possible for two black holes to collide. Once they come so close that they cannot escape each other’s gravity, they will merger to become one bigger black hole. Such an event would be extremely violent. Black hole merger would produce tremendous energy and send massive ripples through the space time fabric of the universe. The ripples are called gravitational waves.

Neutron star twirling:
Neutron stars, the densest objects in the universe, can rotate up to several hundred times per second. If the star has properly spherical shape then it won’t emit gravitational waves as it spins. Only if the surface is bumpy, the spinning asymmetry would generate gravitational waves.

Supernova erupting:
The gravitational waves are emitted from deep inside the core of the star where no electromagnetic radiation can escape. This allows a gravitational wave detection to tell us information about the explosion mechanism that cannot be determined with other methods.

The gravitational waves that are detectible by LIGO will be caused by some of the most energetic events in the universe-colliding black holes, exploding stars, and even the birth of the universe itself. Detecting and analyzing the information carried by gravitational waves will allow us to observe the universe in a way never before possible. It will open up a new window of study on the universe.

LIGO:
LIGO is the world's largest gravitational wave observatory and a cutting edge physics experiment. Comprising two enormous laser interferometers located thousands of kilometers apart, LIGO exploits the physical properties of light and of space itself to detect and understand the origins of gravitational waves. 

Although LIGO will search for gravitational waves from space, and it is called an "Observatory", LIGO is not, strictly speaking, intended to be solely an astronomical facility. LIGO is truly a physics experiment on the scale and complexity of some of the world's giant particle accelerators and nuclear physics laboratories. Though its mission is to detect gravitational waves from some of the most violent and energetic processes in the Universe, the data it will collect will have far-reaching effects on many areas of physics including gravitation, relativity, astrophysics, cosmology, particle physics, and nuclear physics.
Three things truly distinguish LIGO from an astronomical observatory:

First, LIGO is blind. Unlike optical or radio telescopes, LIGO cannot see electromagnetic radiation (e.g., visible light, radio waves, and microwaves) nor does it have to because gravitational waves are not part of the electromagnetic spectrum

Second, LIGO is the opposite of round. Since LIGO doesn’t need to collect light from stars or other objects in the Universe, it doesn't need to be dish-shaped like telescope mirrors or radio dishes, which collect and focus electromagnetic radiation to produce images

Third, LIGO cannot function alone. While an astronomical observatory can function and collect data just fine on its own (some do not, by choice), gravitational wave observatories like LIGO cannot operate solo. The only way to definitively detect a gravitational wave is by operating in unison with a distant twin so that local vibrations are not mistaken for signals from gravitational waves.

How LIGO Works:
LIGO is the world's largest gravitational wave observatory. It consists of two detectors situated 1,865 miles (3,002 kilometers) apart in isolated regions in the states of Washington and Louisiana. Each L-shaped facility has two arms positioned at right angles to each other and running 2.5 miles (4 kilometers) from a central building. Lasers are beamed down each arm and bounced back by mirrors, essentially acting as a ruler for the arm. Sensitive detectors can tell if the length of the arms of a LIGO detector varies by as little as 1/10,000 the width of a proton, representing the incredibly small scale of the effects imparted by passing gravitational waves. LIGO has two observatories to act as a check on the other to rule out that potential gravitational-wave signal detection is not due to a local, terrestrial disturbance; both facilities will detect a true gravitational wave moving at the speed of light nearly simultaneously. Although the twin LIGO facilities act as a single observatory, they are not designed for "observing" in the conventional sense. Instead of eyes, the facilities can be thought more of as "ears" listening for gravitational waves, or even as a skin trying to "feel" the slightest of movements.

Advanced LIGO (aLIGO):
The initial technology deployed for LIGO was sensitive to movement of 1/1000 the diameter of a proton, but with an upgrade begun in the 2010s, LIGO's sensitivity was boosted 10-fold. The many enhancements included increasing the power of the lasers from 10 watts to 200 watts and mirror seismic isolation technology improvements. Overall, aLIGO will be able to detect possible gravitational wave-producing events three times farther away than the initial LIGO setup. Accordingly, a far larger volume of space will now be within "earshot" of the LIGO project, with the opportunity to catch far more potential sources of space-time ripple.

The overall performance of Advanced LIGO is dominated at most frequencies by the quantum noise of sensing the position of the test masses, with a contribution at mid-frequencies from the internal thermal noise of the test masses. This design, with modest enhancements after it enters scientific use, should take this interferometer architecture to its technical endpoint; it is as sensitive as one can make an interferometer based on familiar technology: a Fabry-Perot Michelson configuration with external optical readout using room temperature transmissive optics. Further advances will come from R&D that is just beginning, such as the exploration of cryogenic optics and suspensions, purely reflective optics, and a change in the readout to one which fully exploits our understanding of the quantum nature of the measurement (e.g., quantum non-demolition speed meters). These later developments will be timely for instruments to be developed in the second decade of this century.

Collected By:

                       Prajna

                       Preethi Salyan K S

                       Rachana K

                       Rashmitha H

         Source: 

                       Internet

Astronaut Selection and Training

History of Astronaut Selection

Man’s scope of space exploration has broadened since the first U.S. manned space flight in 1961. But the nation will never forget the original seven pilots who focused our vision on the stars. In 1959, NASA asked the military services to list their members who met specific qualifications. In seeking its first astronauts, NASA required jet aircraft flight experience and engineering training. Height should be no more than 5feet 11 inches because of limited cabin space available in the mercury space capsule being designed. After many intense physical and psychological screenings, NASA selected seven men from an original field of 500 candidates. They were Air Force Captains   L. Gordon Cooper Jr., Virgil “Gus” Grissom and Donald K. “Deke” Slayton, Marine Lieutenant Colonel John H. Glenn Jr., Navy Lieutenant M. Scott Carpenter and Navy Lieutenant Commanders Walter M. Schirra Jr., Alan B. Shepard.

By 1964, prime emphasis had shifted away from flight experience and toward superior academic qualification. Applicants were invited on the basis of educational background alone. These were the scientist astronauts, so called because, as a minimum, applicants were required to have a doctorate level degree equivalent experiences in the natural sciences, medicine or engineering.

Since selection of the first class of astronauts, many men and women have pursued and realized their dreams of flying in space. Thus all began by submitting their applications to become astronauts.

Basic Qualification Requirements

The Astronaut Candidate selection process was developed to select highly qualified individuals for human space programs.  Astronaut Candidates are selected on an as needed basis. Both civilian and military personnel are considered for the program. Applicants, all of whom must be citizens of the United States, must meet a series of minimum requirements.

          

The requirements for Astronaut Candidates are a bachelor degree from an accredited institution in engineering, biological science, physical science or mathematics. Quality of academic preparation is important. Degree must be followed by at least 3 years of related, progressively responsible, professional experience or at least 1,000 hours of pilot-in-command time in jet aircraft. An advanced degree is desirable and may be substituted for experience as follows: master’s degree 1 year of experience, doctoral degree 3 years of experience. Teaching experience, including experience at the k-12 levels, is considered to be qualifying experience for the Astronaut Candidate position: therefore, educators are encouraged to apply.

Additional requirements include the ability to pass the NASA long-duration space flight physical, which includes the following specific requirements: Distant and near visual acuity must be correctable to 20/20 in each eye, blood  pressure not to exceed 140/90 measured in a sitting position, and the candidate must have a standing height between 62 and 75 inches.

Applicants for the Astronaut Candidate Program must meet the basic education requirements for NASA engineering and scientific positions, specifically, successful completion of standard professional curriculum in an accredited college or university leading to at least a bachelor’s degree with major study in an appropriate field of engineering, biological sciences, or mathematics. The following degree fields, while related to engineering and the sciences, are not considered qualifying: degrees in technology (engineering technology, aviation technology, medical technology, etc.); degrees in psychology (except for clinical psychology, physiological psychology, which are qualifying); degrees in nursing; degrees in exercise physiology and similar fields; degrees in social sciences(geography, anthropology, archaeology, etc.); and degrees in aviation, aviation management or similar fields.

Astronaut selection and training

Following the preliminary screening of applications, a week long process of personal interviews, medical screening, and orientation are required for both civilian and military applicants under final consideration. Once final selections have been made, all applicants are notified of the outcomes.

Selected applicants are designated Astronaut Candidates and are assigned to the Astronaut Office at the Johnson Space Centre (JSC) IN Houston, Texas. The Astronaut Candidate undergo a training and evaluation period lasting approximately 2 years. During this time they will participate in the basic Astronaut Candidate training program, which is designated to develop the knowledge and skills required for formal mission training upon selection for a flight. Military proficiency in NASA aircraft during their candidate period.

As a part of Astronaut Candidate training program, candidates are required to complete military water survival before beginning their flying syllabus, and become SCUBA qualified to prepare them for spacewalk. Consequently, all Astronaut Candidates are required to pass a swimming test during their first month of training. They must swim 3 lengths of a 25-metre pool without stopping, and then swim 3 lengths of the pool in a flight suit and tennis shoes with no time limit. They must also tread water continuously for 10 minutes wearing a flight suit.

Candidates are also exposed to the problems associated with high (hyperbaric) and low (hypobaric) atmospheric pressures in the altitude chambers and learn to deal with emergencies associated with these conditions. In addition, Astronaut Candidate are given exposure to the microgravity of space flights in a modified jet aircraft as it performs parabolic manoeuvres that produce periods of weightlessness for about 20 seconds. The aircraft then returns to the original altitude and the sequence is repeated up to 40 times in a day.

Final selection as an astronaut will depend upon satisfactory completion of the training evaluation period. Graduation from the Astronaut Candidate Program will require successful completion of the following: International Space Station systems training, Extravehicular Activity skills training, Robotics skills training, Russian Language training, and aircraft flight readiness training. Civilian candidates who successfully complete the training and evaluation and are selected as astronauts become permanent Federal employees. Civilian candidates who are not selected s astronauts may be placed in other positions within NASA, depending upon agency requirements and workforce constraints at that time. Equal opportunity in employment means opportunity not just for some but for all. NASA provides equal opportunity in Federal employment regardless of race, colour, gender, national origin, religion, age, non-disqualifying physical or mental disability, genetic information, sexual orientation, status as a parent, or gender identity.

Pay and Benefits

Salaries for civilian Astronaut Candidates are based on the Federal Government’s General Schedule pay scales for grades GS11 through GS14, and are set in accordance with each individual’s academic achievements and work experience. Selected military personnel will be detailed to JSC, but will remain in an active duty status for pay, benefits, leave, and other similar military matters.

Astronaut Responsibilities

Astronauts are involved in all aspects of on-orbit operations of the International Space Sation (ISS). This includes extravehicular activities (spacewalks), robotics operations using the remote manipulator system, experiment operations, and onboard maintenance tasks. Astronauts are required to have a detailed knowledge of the space station systems, as well as detailed knowledge of the operational characteristics, mission requirements and objectives, and supporting systems and equipment for each experiment on their assigned missions. Long-duration missions aboard the space station generally last from 3 to 6 months. Training for long-duration missions is arduous and takes approximately 2 to 3 years beyond the initial training and evaluation period. This training requires extensive travel, including long periods in other countries training with our international partners. Tips to and from the space station will initially be aboard other future spacecraft presently being developed.

Astronaut Formal Training

The astronaut begin their formal training program during their year of candidacy by reading training manuals and by taking computer-based training lessons on the various vehicle systems.

The next step in the training process involves the spacecraft systems trainers. The astronauts are trained to operate each system, to recognize malfunctions, and to perform corrective actions if needed.

The Sonny Carter Training Facility, or Neutral Buoyancy laboratory (NBL), provides controlled neutral buoyancy operations in the facility water tank to simulate the zero-g or weightless condition that is experienced by the crew during space flight. It is an essential tool for the design, testing, and development of the International Space Station and future NASA programs. For the astronaut, the facility provides important preflight training in becoming familiar with planned crew activities and with the dynamics of body motion under weightless conditions in order to perform spacewalks.

Several full-scale mockups and trainers are also used to train astronauts. These mockups and trainers are used for onboard systems orientation and habitability training. Astronauts practice meal preparation, equipment stowage, trash management, use of cameras, and experiment operations.

Astronauts, who are pilots maintain flying proficiency by flying 15 hours per month in NASA’s fleet of two-seat T38 jets. Non-pilot astronauts fly a minimum of 4 hours per month. The T38 is used for flight readiness training to help the astronauts become adjusted to the flight environment, including the g-forces experienced on launch.

The astronaut training is designed to prepare personal for space flight on the International Space Station, Russian Soyuz spacecraft, NASA’s Orion vehicle, and future spacecraft.

International Space Station Program Description

The International Space Station is the largest international scientific and technological endeavor ever undertaken. The space station is a permanent scientific laboratory in which gravity, temperature and atmospheric pressure can be manipulated for scientific and engineering pursuits impossible in ground-based laboratories.

The International Space Station marked its 10^th anniversary of continuous human occupation on Nov.2, 2010. Since Expedition 1, which launched in October 2000, the space station has been visited by more than 200 individuals, travelled more than 1.5 billion miles (equivalent to eight to the Sun) and orbited the Earth more than 60,000 times.

NASA and the world have learned much about building in space and about how humans and spacecraft systems function on orbit. But there is much more to do and learn. The voyage of research and discovery is just beginning as NASA shifts its focus from assembly to scientific research, technology development, exploration, commerce, and education.

Aboard the orbiting laboratory, crew members pursue novel avenues of research and development that impact medical research, advance materials and processes to benefit industries on Earth, and can accelerate breakthroughs in technology and engineering that have proven themselves as practical applications for life on Earth.

The station continuous to expand the boundaries of space research. The unique capabilities of its laboratories will lead to discoveries that will benefit missions farther into outer space. Using the station to study human endurance in space and test new technologies and techniques, NASA will prepare for longer journeys to other destinations, such as Mars and beyond.

21^st Century Astronauts

The astronauts of the century will continue to work aboard the International Space Station in cooperation with the international partners; help to build and fly a new NASA vehicle, the Orion Multi-Purpose Crew Vehicle (MPCV) designed for human deep space exploration; and further NASA’s efforts to partner with industry to provide a commercial capability for space transportation to the space station.

The Orion MPCV draws from more than 50 years of spaceflight experience and is designed to meet the evolving needs of our nation’s future human space exploration program. Orion features dozens of technology advancements and innovations that have been incorporated into the spacecraft’s subsystem and component design and includes both crew and service modules, a spacecraft adaptor, and a revolutionary launch abort system that will significantly increase crew safety. Its life support, propulsion, thermal protection, and avionics systems, in combination with other deep space elements, will enable extended duration deep space missions. These systems have been developed to make possible the integration of new technical innovations as they become available.

Orion will be capable of carrying astronauts on diverse expeditions beyond Earth’s orbit-ushering in a new era of human space exploration.

NASA is in the process of identifying possible near-Earth asteroids to explore with the goal of visiting an asteroid in 2025. With that goal, and keeping in mind that the plan is to send a robotic precursor mission to the asteroid approximately five years before humans arrive, NASA will need to select the first set of targets to explore within the next decade.

INDIAN ASTRONAUTS

During the mid-80’s Rakesh Sharma proved to be a pioneer in the field of piloting. He was the first Indian to venture in to the space and bring a new perspective to the country. Though it is long ago Rakesh undertook the Historical journey to space, it is still remembered among the people. Owing to his dedication and struggle, he became a part of most distinctive space program that involved only best military cadets. The Inter cosmos Research Team was a program conducted by Soviet Union and included active participation from allied countries such as India, Syria and France. Rakesh Sharma was now chosen for this assignment and ever since he has been an inspiration to upcoming cosmonauts.

Kalpana Chawla an Indian-American astronaut and the first Indian woman in space was the one of the seven astronauts who lost their life in the space shuttle Columbia disaster on Feb1, 2003. A role model for many young for her incredible journey from Karnal, where she was born, to NASA where she become an astronaut to fulfil her dream of reaching the stars.  

 

Collected By:

                          Sindhhu D G

                          Tashhreefa

                          Vidya Saraswathi A

                          Vinutha

Source: Internet

EYE TO THE SKY

Physics Behind the Wonders.....!

Sometimes we get caught up in the day-to-day grind that we forget how amazing and at times mysterious and terrifying the world around us really is .It is easy to take nature for granted,   its many unfathomable wonders. In this article, a selection of the most compelling and occasionally haunting optical illusions and atmospheric phenomena that the natural world has to offer are explored. When light from the Sun and the Moon enters our atmosphere, it is sometimes reflected, refracted and dispersed by tiny ice crystals, water droplets and dust to produce a whole host of fantastic atmospheric visions. Some are even more common than we realise.

Rainbow

A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.

Rainbows can be full circles. However, the observer normally sees only an arc formed by illuminated droplets above the ground, and centered on a line from the sun to the observer's eye.

In a primary rainbow, the arc shows red on the outer part and violet on the inner side. This rainbow is caused by light being refracted when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it.

In a double rainbow, a second arc is seen outside the primary arc, and has the order of its colours reversed, with red on the inner side of the arc. This is caused by the light being reflected twice on the inside of the droplet before leaving it.

Aurora

An aurora , sometimes referred to as polar lights, northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in the Earth's sky, predominantly seen in the high-latitude regions (around the Arctic and Antarctic).

Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere) due to Earth's magnetic field, where their energy is lost.

The resulting ionization and excitation of atmospheric constituents emits light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes.

Aurora came from the Latin word for "dawn, morning light", since auroras were formerly thought to be the first light of dawn.

Halo

Halo is the name for a family of optical phenomena produced by light interacting with ice crystals suspended in the atmosphere. Halos can have many forms, ranging from coloured or white rings to arcs and spots in the sky. Many of these are near the Sun or Moon, but others occur elsewhere or even in the opposite part of the sky. Among the best known halo types are the circular halo (properly called the 22° halo), light pillars and sun dogs, but there are many more; some of them fairly common, others (extremely) rare.

The ice crystals responsible for halos are typically suspended in cirrus or cirrostratus clouds high (5–10 km, or 3–6 miles) in the upper troposphere, but in cold weather they can also float near the ground, in which case they are referred to as diamond dust. The particular shape and orientation of the crystals are responsible for the type of halo observed. Light is reflected and refracted by the ice crystals and may split up into colours because of dispersion. The crystals behave like prisms and mirrors, refracting and reflecting light between their faces, sending shafts of light in particular directions.

Sun dog

A sun dog or mock sun, formally called a parhelion is an atmospheric optical phenomenon that consists of a bright spot to the left and/or right of the Sun Two sun dogs often flank the Sun within a 22° halo.

The sun dog is a member of the family of halos, caused by the refraction of sunlight by ice crystals in the atmosphere. Sun dogs typically appear as a pair of subtly colored patches of light, around 22° to the left and right of the Sun, and at the same altitude above the horizon as the Sun. They can be seen anywhere in the world during any season, but are not always obvious or bright. Sun dogs are best seen and most conspicuous when the Sun is near the horizon.

Sun dogs are commonly caused by the refraction and scattering of light from plate-shaped hexagonal ice crystals either suspended in high and cold cirrus or cirrostratus clouds, or drifting in freezing moist air at low levels as diamond dust. The crystals act as prisms, bending the light rays passing through them with a minimum deflection of 22°. As the crystals gently float downwards with their large hexagonal faces almost horizontal, sunlight is refracted horizontally, and sun dogs are seen to the left and right of the Sun. Larger plates wobble more, and thus produce taller sundogs.

Sun dogs are red-coloured at the side nearest the Sun; farther out the colors grade through oranges to blue.

Corona

A corona is an optical phenomenon produced by the diffraction of light from the Sun or the Moon by individual small water droplets and sometimes tiny ice crystals of a cloud or on a foggy glass surface. In its full form, a corona consists of several concentric, pastel-coloured rings around the celestial object and a central bright area called aureole. The aureole is often (especially in case of the Moon) the only visible part of the corona and has the appearance of a bluish-white disk which fades to reddish-brown towards the edge. The angular size of a corona depends on the diameters of the water droplets involved: Smaller droplets produce larger coronae. For the same reason, the corona is the most pronounced when the size of the droplets is most uniform. Coronae differ from halos in that the latter are formed by refraction (rather than diffraction) from comparatively large rather than small ice crystals.

Pollen corona: - Each year trees of the Northern forests release copious clouds of pollen. The pollen grains from a given tree variety usually have very similar sizes - ideal for corona formation. 

Unlike water droplets, pollens are non spherical. Many have air sacs to assist wind dispersal and they are consequently become specially oriented as they drift in the air. The result is elongated coronae, sometimes with bright patches on their rings.

Pollens are comparatively large and so their coronae are small. Look close to a well shielded sun  or, preferably, search for them in the reflection of the sky in a pool or dark glass.

Mirage

A mirage is a naturally occurring optical phenomenon in which light rays bend to produce a displaced image of distant objects or the sky. The word comes to English via the French mirage, from the Latin   mirari, meaning "to look at, to wonder at". This is the same root as for "mirror" and "to admire".  In contrast to a hallucination, a mirage is a real optical phenomenon that can be captured on camera, since light rays are actually refracted to form the false image at the observer's location. What the image appears to represent, however, is determined by the interpretive faculties of the human mind. For example, inferior images on land are very easily mistaken for the reflections from a small body of water.

For exhausted travelers in the desert, an inferior mirage may appear to be a lake of water in the distance. An inferior mirage is called "inferior" because the mirage is located under the real object. The real object in an inferior mirage is the (blue) sky or any distant (therefore bluish) object in that same direction. The mirage causes the observer to see a bright and bluish patch on the ground in the distance.

Light rays coming from a particular distant object all travel through nearly the same air layers and all are bent over about the same amount. Therefore, rays coming from the top of the object will arrive lower than those from the bottom. The image usually is upside down, enhancing the illusion that the sky image seen in the distance is really a water or oil puddle acting as a mirror.

Diamond ring effect 

The Baily's beads effect, or diamond ring effect, is a feature of total and annular solar eclipses. As the Moon covers the Sun during a solar eclipse, the rugged topography of the lunar limb allows beads of sunlight to shine through in some places while not in others. The effect is named after Francis Baily, who explained the phenomenon in 1836. The diamond ring effect is seen when only one bead is left, appearing as a shining "diamond" set in a bright ring around the lunar silhouette.

Lunar topography has considerable relief because of the presence of mountains, craters, valleys, and other topographical features. The irregularities of the lunar limb profile (the "edge" of the Moon, as seen from a distance) are known accurately from observations of grazing occultations of stars. Astronomers thus have a fairly good idea which mountains and valleys will cause the beads to appear in advance of the eclipse. While Baily's beads are seen briefly for a few seconds at the center of the eclipse path, their duration is maximized near the edges of the path of the umbra, lasting 1–2 minutes.

Red moon

The moon does not have any light  its own ,it shines because its surface reflects sunlight. During a total lunar eclipse, the earth moves between the sun and the moon and cuts off the moon’s light supply. When this happens ,the surface of the moon takes the reddish glow instead of going completely dark.

        
The red colour of a totally eclipsed moon has prompted many people in recent years to refer to total lunar eclipses as Blood Moon.

        
The reason why the Moon takes on a reddish colour during totality is a phenomenon called Rayleigh scattering.  It is the same mechanism responsible for causing colourful sunrises and sunsets and the sky to look blue.

            
When sunlight entering the Earth's atmosphere strikes the particles that are smaller than the light's wavelength, it gets scattered into different directions. Not all colours in the light spectrum, however, are equally scattered. Colours with shorter wavelengths, especially the violet and blue colours, are scattered more strongly, so they are removed from the sunlight before it hits the surface of the Moon during a lunar eclipse. Those with longer wavelengths, like red and orange, pass through the atmosphere. This red-orange light is then bent or refracted around Earth, hitting the surface of the Moon and giving it the reddish-orange glow that total lunar eclipses are famous for.

Collected By:

                          Reshna K

                          Sahana H

                          Shilpa M P

                          Sinchana K P

Source: Internet