સૂર્ય: આવૃત્તિઓ વચ્ચેનો તફાવત

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૦૬:૧૯, ૧૪ જાન્યુઆરી ૨૦૧૧ સુધીનાં પુનરાવર્તન

સૂર્ય
સૂર્ય
દાર્શનિક તથ્યો
પૃથ્વી થી શરેરાશ અંતર 149.6×106 km
(92.95×106 mi)
magnitude (V) −26.8m
Absolute magnitude 4.8m
Orbital લાક્શનિક્તા
Mean distance from
Milky Way centre
2.5×1017 km
(26,000 light-years)
Galactic period 2.26×108 a
વેગ 217 km/s
ભૌતિક characteristics
વ્યાસ 1.392×106 km
(109 Earths)
Oblateness 9×10-6
Surface area 6.09 × 1012 km²
(11,900 Earths)
Volume 1.41 × 1018 km³
(1,300,000 Earths)
Mass 1.9891 × 1030 kg

(332,950 Earths)

ઘનત્વ 1.408 g/cm³
સપાટી પરનુ ગુરૂત્વાકર્ષણ 273.95 m s-2

(27.9 g)

Escape velocity
from the surface
617.54 km/s
સપાટી પરનુ તાપમાન 5780 K
કોરોનાનુ તાપમાન 5 MK
કેન્દ્રનું તાપમાન ~13.6 MK
તેજસ્વીતા (L) 3.827×1026 W
Mean Intensity (I) 2.009×107 W m-2 sr-1
Rotation characteristics
Obliquity 7.25?
(to the ecliptic)
67.23?
(to the galactic plane)
Right ascension
of North pole 1
286.13?
(19 h 4 min 31.2 s)
Declination
of North pole
63.87?
Rotation period
at equator
25.3800 days
(25 d 9 h 7 min 12?8 s) 1
Rotation velocity
at equator
7174 km/h
Photospheric composition
હાઈડ્રોજન 73.46 %
હીલિયમ 24.85 %
ઑક્સીજન 0.77 %
કાર્બન 0.29 %
લોહ 0.16 %
નીયોન 0.12 %
નાઈટ્રોજન 0.09 %
સીલીકોન 0.07 %
મેગ્નેશ્યીયમ 0.05 %
સલ્ફર 0.04 %

સૂર્ય આપણા સૂર્યમંડળના મધ્યમાં આવેલો તારો છે. પૃથ્વી તથા અન્ય ગ્રહો, એસ્ટેરોઈડ, ધૂમકેતુઓ સૂર્યની આસપાસ પરિભ્રમણ કરે છે.

પ્રાથમીક તારો જેની આસપાસ પદાર્થો ભ્રમણ કરે છે તેને પણ તે સૂર્યમંડળનો સૂર્ય કહેવાય છે. ક્યારેક બહુ તારા મંડળ જેમાં બે કે વધુ તારાઓ હોય તેમા આવા તારાઓને સૂર્યો પણ કહેવાય છે.


સામાન્ય માહિતી

સૂર્ય આપણી આકાશગંગાનો (સામાન્ય કક્ષાનો) (main sequence) તારો છે. તેનો સ્પેક્ટરલ વર્ગ G2 છે- એટલે કે - સૂર્ય સરેરાશ તારાથી ભારે તથા ગરમ પણ બ્લુ જાયન્ટથી નાનો છે. સામાન્ય કક્ષા ના G2 તારાઓનો સરેરાશ જીવનકાળ આશરે ૧૦ બિલીયન વર્ષ (૧૦ Ga) હોય છે. સૂર્ય ન્યુક્લિઓકોસ્મોક્રોનોલોજી પ્રમાણે લગભગ ૫ બિલીયન વર્ષ પહેલા રચાયો હોવાનુ મનાય છે. સૂર્ય આપણી આકાશગંગાના કેન્દ્રથી ૨૫,૦૦૦-૨૮,૦૦૦ પ્રકાશવર્ષના અંતરે આવેલ છે. કેન્દ્રની આસપાસ પરીક્રમણ કરતા સૂર્યને ૨૨૬ મીલીયન ૨૨૬ Ma વર્ષ લાગે છે. સૂર્યની કક્ષામાં ભ્રમણ ગતિ ૨૧૭ કી.મી/સેકન્ડ છે (એટલે કે, ૧૪૦૦ વર્ષમાં ૧ પ્રકાશવર્ષ , અને ૮ દિવસમાં ૧ એયુ).

ખગોળશાસ્ત્રમાં સૂર્યને દર્શાવવા () સંકેત વપરાય છે.

ચેતવણી: સૂર્યની સામે જોવાથી આંખના રેટીનાને નુકશાન પામે છે તથા અંધ્તવ આવવાનો ભય પણ છે. વધુ વિગત માટે નીચે જુઓ.

સૂર્યનુ બંધારણ

સૂર્ય એક લગભગ ક્ષતિરિક્ત(ચોક્કસ)ગોળાકાર તારો છે. તેની ઉપવલયતા-ગુણોત્તર (oblateness) 9×106 છે. આમ તેનો તેના ધ્રુવ પાસે નો વ્યાસ તેના વિષુવવૃત્તીય વ્યાસ થી ૧૦ કી.મી. નાનો છે. આનુ કારણ તેનું ખૂબ મંદ કેન્દ્રત્યાગી ભ્રમણ છે. સૂર્યનું ભ્રમણ તેની સપાટીના ગુરૂત્વાકર્ષણથી ૧૮ મીલીયન ગણું ઓછું છે. સૂર્યના ગ્રહોની Tidal effects તેના કદને અસર પાડતી નથી. પરંતુ સૂર્ય સૂર્યમંડળના કેન્દ્રથી છેટે barycenter ની આસપાસ ફરે છે જેનુ કારણ ગુરૂનો ગ્રહ છે.

અન્ય ગ્રહો ની જેમ સૂર્યને ચૉક્કસ બાહ્ય સપાટી નથી. પરંતુ તેમાં રહેલા density of gases comprising the Sun drops off following an exponential relationship with distance from the centre of the Sun. Nevertheless, the Sun has well defined interior structure, described below. The Sun's radius is measured from centre to the edges of the photosphere.

The solar interior is not accessible directly and the Sun itself is opaque to electromagnetic radiation. Humanity's knowledge of the solar interior comes from a combination of analytic and computer modeling of stars, and helioseismology, the study of sound waves that travel through the Sun's interior.

કેન્દ્ર

સૂર્યના કેન્દ્રમાં, જ્યાં તેની ઘનતા ૧૫૦ ગ્રામ/સેમી (એટલેકે પૃથ્વી પર પાણી કરતા 150 ગણી), થર્મોન્યુક્લીયર પ્રક્રિયા (ન્યુક્લીયર ફ્યુઝન) દ્વારા હાઇડ્રોજન નું હીલીયમ માં રૂપાંતર થવાથી પ્રઞટ થતી ગરમી વડે સમગ્ર તારો ધગધગે છે. દર સેકન્ડે આશરે ૮.૯×૧૦૩૭ પ્રોટોન હાઇડ્રોજન ન્યુક્લીયસનું હીલીયમ ન્યુક્લીયસમા રૂપાંતર થાય છે. જેનાથી ૪.૨૬ મિલિયન (૪૨.૬ લાખ) ટન/સેકન્ડ અથવા ૩૮૩ yottawatts (૯.૧૫5×૧૦૧૬ ટન ટી.એન.ટી / સેકન્ડ) પદાર્થ-ઊર્જા જેટલી પરાવર્તીત ઊર્જા ચૂંબકીય-મોજાં, રૂપે સૂર્યના અન્ય સ્તરો વટાવી બાહ્ય અવકાશમાં વછુટે છે, (સૂર્ય પ્રકાશ) અને ન્યુટ્રીનો (and to a smaller extent as the ગતિ અને thermal energy of સૂર્ય પવનો plasma and as the energy in the સૂર્યનું ચૂંબકીય ક્ષેત્ર). A ફ્યુઝન રીએક્ટર, which some physicists believe may one day provide power for human use, would use a similar process to extract atomic energy.

The core is the only part of the Sun where an appreciable amount of heat is produced by fusion: the rest of the star is heated by energy that is transferred outward. All of the energy of the interior fusion must travel through the successive layers to the solar photosphere, before it escapes to space. The core extends from the center to about 0.2 solar radius.

Radiative zone

From about ૦.૨ to about ૦.૭ solar radii, the material is hot and dense enough that thermal radiation is sufficient to transfer the intense heat of the core outward. In this zone, there is no thermal convection: while the material grows cooler with altitude, this gradient in temperature is not strong enough to drive convection. Heat is transferred by ions of hydrogen and helium emitting photons, which travel a brief distance before being re-absorbed by other ions.

=Convection zone

From about 0.7 solar radii to 1.0 solar radii, the material in the Sun is neither dense nor hot enough to transfer the heat energy of the interior outward. As a result, thermal convection carries the heat to the surface as thermal columns carry hot material to the surface (photosphere) of the Sun. Once the material cools off at the surface, it plunges back downward to the base of the convection zone, to receive more heat from the top of the radiative zone. There is a bit of convective overshoot at the base of the convection zone, carrying turbulent downflows into the top layers of the radiative zone.

The thermal columns in the convection zone form an imprint on the surface of the Sun, in the form of the solar granulation and supergranulation. The turbulent convection of this outer part of the solar interior gives rise to a 'small-scale' dynamo that produces magnetic north and south poles all over the surface of the Sun.

ફોટોસ્ફીયર

The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light. Above the photosphere, sunlight is free to propagate into space and its energy escapes the Sun entirely. Sunlight has a black-body spectrum that is characteristic of about 6,000 kelvins, interspersed with atomic absorption lines from the tenuous layers above the photosphere. The photosphere has a particle density of about 1023/m3 (this is about 1% of the particle density of Earth's atmosphere at sea level). The parts of the Sun above the photosphere are referred to collectively as the solar atmosphere. They can be viewed with telescopes operating across the electromagnetic spectrum, from radio through visible light to gamma rays.

તાપમાન લધુત્તમ

The coolest layer of the Sun is the temperature minimum region about 500km above the photosphere. It is about 4,000 kelvins. It is the only part of the Sun cool enough to support simple molecules such as carbon monoxide and water; all other parts of the Sun are hot enough to break chemical bonds.

ક્રોમાસ્ફીયર

Above the visible surface of the Sun is a thin layer, about 2,000 km thick, that is dominated by a spectrum of emission and absorption lines. It is called the chromosphere from the Greek root chromos, meaning color, because the chromosphere is visible as a colored flash at the beginning and end of total eclipses of the Sun.

કોરોના

The corona is the extended outer atmosphere of the Sun, which is much larger than the Sun itself. The corona merges smoothly with the solar wind that fills the solar system and heliosphere. The low corona, near the surface of the Sun, has a particle density of 1011/m3.

Solar neutrino problem

For some time it was thought that the number of neutrinos produced by the nuclear reactions in the Sun was only one third of the number predicted by theory, a result that was termed the solar neutrino problem. Several neutrino observatories were created including the Sudbury Neutrino Observatory to try and measure the amount of neutrinos given off by the Sun. From these observatories and experiments it was recently found that neutrinos had rest mass, and could therefore transform into harder-to-detect varieties of neutrinos while en route from the Sun to Earth; thus measurement and theory were reconciled.


ચુંબકીય ક્ષેત્ર

All matter in the Sun is in the form of plasma due to its extreme temperature. This makes it possible for the Sun to rotate faster at its equator (about 25 days) than it does at higher latitudes (28 days near its poles). The differential rotation of the Sun's latitudes causes its magnetic field lines to become twisted together over time, causing magnetic field loops to erupt from the Sun's surface and trigger the formation of the Sun's dramatic sunspots and solar prominences. (See magnetic reconnection) The solar activity cycle includes old magnetic fields being stripped off the Sun's surface starting from one pole and ending at the other. The magnetic field of the sun reverses once for each 11-year sunspot cycle.

Calculating the position of the Sun

Since the path of the sun across the sky varies throughout the year, a completely automatic heliostat, or sun tracker, must be guided by continuous calculations. The National Renewable Energy Laboratory has released its Solar Position Algorithm (SPA) with complete documentation. Another resource is the libnova Celestial Mechanics and Astronomical Calculation Library, which also calculates variables such as apparent position and rise, set and transit times among many others of astronomical objects.

Solar space missions

To obtain an uninterrupted view of the Sun, the European Space Agency and NASA cooperatively launched the Solar and Heliospheric Observatory (SOHO) on December 2, 1995.

Elemental abundances in the photosphere are well known from spectroscopic studies, but the composition of the interior of the Sun is much less well known. A solar wind sample return mission, Genesis, was designed to allow astronomers to directly measure the composition of solar material. It returned to Earth in 2004 and is undergoing analysis, but it was damaged by crash-landing when its parachute failed to deploy on reentry to Earth's atmosphere.


History and future of the Sun

The Sun is thought to be a second-generation star, perhaps formed from some of the remains of a previous supernova. The evidence is mainly a high abundance of heavy elements such as iron, gold, and even uranium in the solar system: the most plausible ways that these elements could be produced is by nucleosynthesis inside a large, hot star.

Our Sun does not have enough mass to explode as a supernova. Instead, in 4-5 billion years it will enter its red giant phase, expanding as the hydrogen fuel in the core is consumed. Then it will start to fuse helium and the core temperature will rise to 3×108 K. While it is likely that the expansion of the outer layers of the Sun will reach the current position of Earth's orbit, recent research suggests that mass lost from the Sun earlier in its red giant phase will cause the Earth's orbit to move further out, preventing it from being engulfed. Following the red giant phase, giant thermal pulsations will cause the Sun to throw off its outer layers forming a planetary nebula. The Sun will then become a white dwarf, slowly cooling over eons. This scenario is typical of small stars: our Sun appears to be a fairly run-of-the-mill star.

Human understanding of the Sun

In many prehistoric and ancient cultures, the Sun was thought to be a deity or other supernatural phenomenon. One of the first people in the Western world to offer a scientific explanation for the sun was the Greek philosopher Anaxagoras, who reasoned that it was a giant flaming ball of rock or metal, and not the chariot of Apollo. For teaching this heresy he was imprisoned by the authorities and sentenced to death.

Sun and eye damage

Sunlight is quite bright and looking directly at the Sun is painful to the eyes. Looking directly at the Sun when it is high in the sky causes temporary bleaching of the photosensitive pigments in the retina, which makes phosphene visual artifacts and temporary partial blindness. Direct viewing of the Sun with the naked eye delivers about 4 milliwatts of sunlight to the retina that is in the solar image, heating it up and potentially (though not normally) damaging it. Brief viewing of the direct Sun with the naked eye is unpleasant but generally safe. Long-term exposure of the eyes to direct sunlight contributes to the normal UV-induced yellowing of the lens and cornea over periods of decades, and could play a part in the formation of cataracts.

Viewing the Sun through light-concentrating optics such as binoculars is hazardous without an attenuating filter to dim the sunlight. Suitable filters are available at welding supply shops and camera stores. Viewing the Sun through unfiltered 7x50mm binoculars can deliver as much as 2.5 watts of sunlight into each eye, over 300 times more power than naked eye viewing. Even brief glances at the Sun through binoculars can cause permanent blindness.

During partial eclipses of the Sun, another hazardous condition exists because of the way that the eye responds to bright light. The pupil is controlled by the total amount of light in the visual field, not by the brightest object in the field. During partial eclipses, most sunlight is blocked by the Moon passing directly in front of the Sun, but the uncovered parts of the photosphere have the same surface brightness as during a normal day. In the dim overall light, the pupil tends to dilate from ~2mm to perhaps 6mm diameter, increasing the eye's collecting area by a factor of nearly 10. Each retinal cell that is exposed to the partially-eclipsed solar image thus receives about ten times as much light as it would looking at the normal, non-eclipsed Sun. This can cause permanent localized damage to the retina, resulting in small, permanent blind spots for the viewer. This is an especially insidious hazard for inexperienced observers and for children, because there is no immediate perception of pain and it is tempting to stare at the spectacle of the eclipsing Sun.

See also

See related

સંદર્ભ

  • en:Sun - સૂર્ય ઉપર અંગ્રેજી વિકિપીડિયાનો લેખ

બાહ્ય કડીઓ

ઢાંચો:Footer SolarSystem

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