SPACE RACE

The Space Race refers to the 20th-century competition between two Cold War rivals, the Soviet Union (USSR) and the United States (US), for dominance in spaceflight capability. It had its origins in the missile -based nuclear arms race between the two nations that occurred following World War II , aided by captured German missile technology and personnel from the Aggregat program . The technological superiority required for such dominance was seen as necessary for national security, and symbolic of ideological superiority. The Space Race spawned pioneering efforts to launch artificial satellites , uncrewed space probes of the Moon , Venus , and Mars , and human spaceflight in low Earth orbit and to the Moon.

The Space Race began on August 2, 1955, when the Soviet Union responded to the US announcement four days earlier of intent to launch artificial satellites for the International Geophysical Year , by declaring they would also launch a satellite "in the near future". The Soviet Union beat the US to this, with the October 4, 1957, orbiting of Sputnik 1 , and later beat the US to the first human in space,
Yuri Gagarin , on April 12, 1961. The "race" peaked with the July 20, 1969, US landing of the first humans on the Moon with Apollo 11 . The USSR tried but failed crewed lunar missions, and eventually canceled them and concentrated on Earth orbital space stations.

A period of détente followed with the April 1972 agreement on a co-operative Apollo–Soyuz Test Project , resulting in the July 1975 rendezvous in Earth orbit of a US astronaut crew with a Soviet cosmonaut crew. The end of the Space Race is harder to pinpoint than its beginning, but it was over by the December 1991 dissolution of the Soviet Union , after which true spaceflight cooperation between the US and Russia began.
The Space Race has left a legacy of Earth communications and weather satellites , and continuing human space presence on the International Space Station . It has also sparked increases in spending on education and research and development , which led to beneficial spin-off technologies .

Quantum mechanics

Quantum mechanics is the science of the very small. It explains the behavior of matter and its interactions with energy on the scale of atoms and subatomic particles .

By contrast, classical physics only explains matter and energy on a scale familiar to human experience, including the behavior of astronomical bodies such as the Moon. Classical physics is still used in much of modern science and technology. However, towards the end of the 19th century, scientists discovered phenomena in both the large ( macro ) and the small (micro) worlds that classical physics could not explain. [1] The desire to resolve inconsistencies between observed phenomena and classical theory led to two major revolutions in physics that created a shift in the original scientific paradigm: the theory of relativity and the development of quantum mechanics .  This article describes how physicists discovered the limitations of classical physics and developed the main concepts of the quantum theory that replaced it in the early decades of the 20th century. It describes these concepts in roughly the order in which they were first discovered. For a more complete history of the subject, see History of quantum mechanics .

Light behaves in some respects like particles and in other respects like waves. Matter—the "stuff" of the universe consisting of particles such as electrons and atoms —exhibits

wavelike behavior too. Some light sources, such as neon lights , give off only certain frequencies of light. Quantum mechanics shows that light, along with all other forms of

electromagnetic radiation , comes in discrete units, called photons , and predicts its energies, colors, and spectral intensities . A single photon is a quantum , or smallest observable amount, of the electromagnetic field because a partial photon has never been observed. More broadly, quantum mechanics shows that many quantities, such as angular momentum , that appeared continuous in the zoomed-out view of classical mechanics, turn out to be (at the small, zoomed-in scale of quantum mechanics) quantized . Angular momentum is required to take on one of a set of discrete allowable values, and since the gap between these values is so minute, the discontinuity is only apparent at the atomic level.

Many aspects of quantum mechanics are counterintuitive and can seem paradoxical , because they describe behavior quite different from that seen at larger length scales. In the words of quantum physicist Richard Feynman , quantum mechanics deals with "nature as She is – absurd".  For example, the uncertainty principle of quantum mechanics means that the more closely one pins down one measurement (such as the position of a particle), the less accurate another measurement pertaining to the same particle (such as its momentum ) must become.

Eid al-Fitr

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Eid al-Fitr (Arabic : ﻋﻴﺪ ﺍﻟﻔﻄﺮ ʻĪd al-Fiṭr) is an important religious holiday celebrated by Muslims worldwide that marks the end of Ramadan , the Islamic holy month of fasting (sawm ). This religious Eid ( Muslim religious festival) is the first and only day in the month of Shawwal during which Muslims are not permitted to fast. The holiday celebrates the conclusion of the 29 or 30 days of dawn-to-sunset fasting during the entire

month of Ramadan . The day of Eid, therefore, falls on the first day of the month of Shawwal. The date for the start of any lunar Hijri month varies based on the observation of new moon by local religious authorities, so the exact day of celebration varies by locality.

Eid al-Fitr has a particular salat (Islamic prayer) consisting of two rakats (units) and generally offered in an open field or large hall. It may be performed only in congregation ( Jama’at ) and has an additional extra six

Takbirs (raising of the hands to the ears while saying "Allāhu Akbar" which means "God is the greatest"), three of them in the beginning of the first raka'ah and three of them just before ruku' in the second raka'ah in the

Hanafi school of Sunni Islam . Other Sunni schools usually have twelve Takbirs, seven in the first, and five at the beginning of the second raka'ah. According to Shia Islam, it has 3 Takbirs in every Rakat.  This Eid al-Fitr salat is, depending on which juristic opinion is followed, Fard ﻓﺮﺽ (obligatory), Mustahabb ﻣﺴﺘﺤﺐ (strongly recommended, just short of obligatory) or Mandoob ﻣﻨﺪﻭﺏ (preferable).

Muslims believe that they are commanded by Allah, as mentioned in the Quran , to continue their fast until the last day of Ramadan and pay the Zakat al-Fitr before offering the Eid prayers .

History

Eid al-Fitr was originated by the Islamic prophet Muhammad . It is observed on the first of the Islamic month of Shawwal at the end of the month of Ramadan, during which Muslims undergo a period of fasting. [6]

According to certain traditions , these festivals were initiated in Medina after the migration of Muhammad from Mecca . Anas reports: When the Prophet arrived in Madinah, he found people celebrating two specific days in which they used to entertain themselves with recreation and merriment. He asked them about the nature of these festivities at which they replied that these days were occasions of fun and recreation. At this, the Prophet remarked that the Almighty has fixed two days [of festivity] instead of these for you which are better than these: Eid al-Fitr

General rituals

See also: Eid cuisine

Main article: Islamic calendar § Astronomical considerations

Traditionally, it is the day (beginning at sunset) of the first sighting of the crescent moon shortly after sunset. If the moon is not observed immediately after the 29th day of the previous lunar month (either because clouds block its view or because the western sky is still too bright when the moon sets), then it is the following day.

Eid al-Fitr is celebrated for one, two or three days. It is forbidden to fast on the Day of Eid, Also the specific prayer is nominated for this day. As an obligatory act of charity, money is paid to the poor and the needy (Arabic:

Zakat-ul-fitr ) before performing the ‘Eid prayer . As another rituals, Muslims recite the following incantation in a low voice while going to the Eid prayer: Allāhu Akbar, Allāhu Akbar, Allāhu Akbar. Lā ilāha illà l-Lāh wal-Lāhu akbar, Allahu akbar walil-Lāhi l-ḥamd . Recitation ceases when they get to the place of Eid or once the Imam commences activities.

Eid al-Fitr mass prayer in Istiqlal Mosque, Jakarta , Indonesia

Eid prayer and eidgah

Further information: Eidgah

The Eid prayer is performed in congregation in open areas like fields, community centres, etc. or at mosques. No call to prayer is given for this Eid prayer, and it consists of only two

units of prayer with an additional six incantations . The Eid prayer is followed by the sermon and then a supplication asking for Allah's forgiveness, mercy, peace and blessings for all living beings across the world. The sermon also instructs Muslims as to the performance of rituals of Eid, such as the zakat . Listening to the sermon at Eid is not required and is optional, a Sunnah i.e. while the sermon is being delivered. After the prayers, Muslims visit their relatives, friends and acquaintances or hold large communal celebrations in homes, community centres or rented halls. 

Eid gifts, known as Eidi , are frequently given at eid to children and immediate relatives. 

Performing Eid-ul-fitr prayer

Eid al-Fitr prayer (Salat al-Eid) or Eid al-Fitr Namaz is performed on the occasion of Eid. The Prayer of Eid al-Fitr is performed in two different ways by Sunni and Shia Islam.

Sunni procedure

There are two Rak'ah (Rakaat) performed in the Eid al-Fitr prayer. The prayer of Eid al-Fitr starts by doing "Niyyat" for the prayer and then Takbeer (Allahu Akbar) is said by the Imam and all the followers. The next is to recite "Takbeer-e-Tehreema" in first Rakaat. Then the congregation says Allahu Akbar seven times, every time raising hands to the ears and dropping them except the last time when hands are folded. Then the Imam reads the Surah-e-Fatiha and other Surah. Then the congregation performs Ruku and Sujud as in other prayers. This completes the first Rak’ah. Then the congregation rises up from the first Rak'ah and folds hands for the second Rak’ah. In the next step the Imam says five takbirat, followed by the congregation, every time raising the hands to the ears and dropping them except the last time when the hands are folded. Again the Imam reads the Surah-e-Fatiha and another Surah followed by the Ruku and Sujud. This completes the Eid prayer. After the prayer there is a khutbah.

Big Bang theory

 

The Big Bang theory is the prevailing cosmological model for the univers from the earliest known periods through its subsequent large-scale evolution.  The model describes how the universe expanded from a very high-density and high-temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of

light elements , the cosmic microwave background (CMB), large scale structure and

Hubble's law . If the known laws of physics are extrapolated to the highest density regime, the result is a singularity which is typically associated with the Big Bang. Physicists are undecided whether this means the universe began from a singularity, or that current knowledge is insufficient to describe the universe at that time. Detailed measurements of the expansion rate of the universe place the Big Bang at around 13.8 billion years ago, which is thus considered the age of the universe . After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles , and later simple atoms . Giant clouds of these primordial elements later coalesced through

gravity in halos of dark matter , eventually forming the stars and galaxies visible today.

Since Georges Lemaître first noted in 1927 that an expanding universe could be traced back in time to an originating single point, scientists have built on his idea of cosmic expansion. The scientific community was once divided between supporters of two different theories, the Big Bang and the Steady State theory , but a wide range of empirical evidence has strongly favored the Big Bang which is now universally accepted.In 1929, from analysis of galactic

redshifts , Edwin Hubble concluded that galaxies are drifting apart; this is important observational evidence consistent with the hypothesis of an expanding universe. In 1964, the cosmic microwave background radiation was discovered, which was crucial evidence in favor of the Big Bang model, since that theory predicted the existence of background radiation throughout the universe before it was discovered. More recently, measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating , an observation attributed to dark energy 's existence.  The known physical laws of nature can be used to calculate the characteristics of the universe in detail back in time to an initial state of extreme density and temperature .

General relativity of Black hole

General relativity of Black hole

Slow motion computer simulation of the black hole
binary system GW150914 as seen by a nearby observer, during 0.33 s of its final inspiral, merge, and ringdown. The star field behind the black holes is being heavily distorted and appears to rotate and move, due to extreme gravitational lensing , as
spacetime itself is distorted and dragged around by the rotating black holes .

General relativity ( GR , also known as the general theory of relativity or GTR ) is the geometric theory of gravitation published by
Albert Einstein in 1915 and the current description of gravitation in modern physics . General relativity generalizes special relativity and Newton's law of universal gravitation , providing a unified description of gravity as a geometric property of space and time , or spacetime . In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the
Einstein field equations , a system of partial differential equations .

Some predictions of general relativity differ significantly from those of classical physics , especially concerning the passage of time, the
geometry of space, the motion of bodies in free fall , and the propagation of light. Examples of such differences include
gravitational time dilation , gravitational lensing, the gravitational redshift of light, and the gravitational time delay . The predictions of general relativity have been confirmed in all observations and experiments to date. Although general relativity is not the only relativistic theory of gravity , it is the simplest theory that is consistent with experimental data . However, unanswered questions remain, the most fundamental being how general relativity can be reconciled with the laws of quantum physics to produce a complete and self-consistent theory of quantum gravity .

Einstein's theory has important astrophysical implications. For example, it implies the existence of black holes—regions of space in which space and time are distorted in such a way that nothing, not even light, can escape—as an end-state for massive stars . There is ample evidence that the intense radiation emitted by certain kinds of astronomical objects is due to black holes; for example,
microquasars and active galactic nuclei result from the presence of stellar black holes and
supermassive black holes , respectively. The bending of light by gravity can lead to the phenomenon of gravitational lensing, in which multiple images of the same distant astronomical object are visible in the sky. General relativity also predicts the existence of gravitational waves , which have since been observed directly by the physics collaboration LIGO . In addition, general relativity is the basis of current cosmological models of a consistently expanding universe.

Widely acknowledged as a theory of extraordinary beauty, general relativity has often been described as the most beautiful of all existing physical theories.

Standard Model of particle physics

The Standard Model of particle physics is the theory describing three of the four known fundamental forces (the electromagnetic , weak , and strong interactions, and not including the gravitational force ) in the universe , as well as classifying all known elementary particles . It was developed in stages throughout the latter half of the 20th century, through the work of many scientists around the world, [1] with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks . Since then, confirmation of the top quark (1995), the
tau neutrino (2000), and the Higgs boson (2012) have added further credence to the Standard Model. In addition, the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy.
Although the Standard Model is believed to be theoretically self-consistent and has demonstrated huge successes in providing experimental predictions , it leaves some phenomena unexplained and falls short of being a complete theory of fundamental interactions . It does not fully explain baryon asymmetry , incorporate the full theory of gravitation as described by general relativity , or account for the accelerating expansion of the Universe as possibly described by dark energy . The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology . It also does not incorporate neutrino oscillations and their non-zero masses.
The development of the Standard Model was driven by
theoretical and experimental particle physicists alike. For theorists, the Standard Model is a paradigm of a
quantum field theory, which exhibits a wide range of physics including spontaneous symmetry breaking ,
anomalies and non-perturbative behavior. It is used as a basis for building more exotic models that incorporate hypothetical particles , extra dimensions , and elaborate symmetries (such as supersymmetry ) in an attempt to explain experimental results at variance with the Standard Model, such as the existence of dark matter and neutrino oscillations.

Atmosphere of Earth

The atmosphere of Earth is the layer of gases , commonly known as air , that surrounds the planet Earth and is retained by Earth's gravity . The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface , absorbing
ultraviolet solar radiation , warming the surface through heat retention (greenhouse effect ), and reducing temperature extremes between day and night (the diurnal temperature variation ).
By volume, dry air contains 78.09% nitrogen , 20.95% oxygen,  0.93% argon , 0.04% carbon dioxide , and small amounts of other gases. Air also contains a variable amount of water vapor , on average around 1% at sea level, and 0.4% over the entire atmosphere. Air content and atmospheric pressure vary at different layers, and air suitable for use in
photosynthesis by terrestrial plants and
breathing of terrestrial animals is found only in Earth's troposphere and in artificial atmospheres .
The atmosphere has a mass of about 5.15 × 10 18 kg, [3] three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space . The Kármán line, at 100 km (62 mi), or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km (75 mi). Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition.
The study of Earth's atmosphere and its processes is called atmospheric science (aerology). Early pioneers in the field include
Léon Teisserenc de Bort and Richard Assmann .