Universe Solar System

The limitless expanse of space around us consisting of solar system, stars galaxies etc is called universe.

Solar system the sun the planets revolving about the sun in elliptical orbits and the satellites moving around the planets is our solar system. It also includes asteroids comets and meteors. The above table gives the radius, distance, time of revolution time of rotation and number of satellites of the planets of the solar system.

Moon the natural satellite of earth, is 3.84 x 10⁵ km always, its mean diameter is 3480 km, and mass 7.35 x 10²² kg.

The gravity of moon = g / 6 = 1.66 ms². The temperature during the day is 1000˚ C and during the night is 150˚C, no atmosphere or water exists, hence no possibility of life. 

Asteroids group of more than 1600 tiny rock ices moving around the sun between mars and Jupiter. The largest amongst these is cares with a radius of 350 km. the smallest one has radius 50m. It is believed that asteroids are pieces of a planet which broke up due to gravitational pull of Jupiter.

Comets are composed of rock like materials surrounded by large masses of easily vaporized substances like ice, water, NH, and CH_4they revolve around the sun in highly elliptical orbits. The time period of revolutionist very large. For example, Halley comet has a time period of 76 years. They appear to have a bright head and a long tail while passing close to the sun.

Meteors are the smaller pieces of stones and metals which may be produced due to the breaking up of comets while approaching the sun. Then they reach reach’s atmosphere due to friction they start bring. 

Keller’s law can be used to find distance

T²₁ / T²₂ = R³₁ / R³₂ 

Distance can also be determined using specter - scope method I₁ / I₂ = r²₂ / r²₁

Inferior planets mercury and venues are closer to the sum than earth.

To find 

The mass of the sun 

GMs M_E/ R²_SE = M_ER_SEω²

Or Ms = (R_SE)³ / G (2π / T)²

Where R_SE distance of the earth from the sun M_E = mass of the earth, MS mass of the sun ω --> angular velocity of the earth. 

Mass of a planet = 4 π² R³PM / GT

Where RpM is the distance of its moon, T time period of revolution of the moon about the planet.

Surface temperature can be determined using Stefan’s law or wein’s displacement law. 

Stefan’s law I = σT⁴ or power P = AσT⁴

A is area receiving radiation 

Wein’s displacement law λ_m T = (b) constant where, b = 2.89 x 10^-3 m^{– K}.

Acceleration due to gravity g = GM/R²,

Orbital velocity = GM/R = gR

Escape velocity 2 (GM/R) = 2gR 

Surface temperature of the sun = 5800 K.

Solar constant (S) is the amount of solar energy received per second by a unit area of a perfectly black body surface held at right angles to the direction of sun rays at the mean distance of the earth from the sun. The value of solar constant is 1388 wm^-2 or 2 cal cm^-2 min^-1

Solar luminosity = 4πr²S

Where r = distance of earth from the sun 

S = solar constant 

T =( r²S / R²σ)1/4 where , R = radius of the sun

Solar flare during solar flare a rich emission of protons is found

Sun spots many dark spots visible on its disc are called solar spots.

1 AU (astronomical unit) = 1.5 x 10¹¹m,

L parsecs = 3.26 light year.

Closest star (after sun) is alpha century, 4.3 light years from the earth. One can see 2500 to 5000 stars with naked eye on a clear night. Star is a self luminous body emitting radiations due to nuclear fusion reaction going on in. it 

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