Solar system

Galaxy

• Gravitational bound system of star, stellar remnants, interstellar gas, dust, and dark matter. Ex: Milky way.
• A galaxy is a huge system of billions of stars.
• Our solar system is a part of the milky way galaxy.
• Our Milky way galaxy was named “Akash ganga”.
• There are millions of galaxies that make the Universe.
• Distance galaxy: GN-z11 (March 2016)
• Hubble classification
• Eliptical (E)
• Spiral (S): Andromeda & Sombrero (unbarred)
• Lenticular

Celestial bodies: Sun, Moon.

• Two types: Emit light (Star), Don’t Emit Light (Planets)
• North Star – Pole Star – Indicates north Direction

Constellations (Group of star) – 88 Official

• Ursa Major – Big Dipper
• Tail – Alioth – Brightest in Ursa Major
• Saptarishi Mandal
• Polaris – Brightest in Ursa Minor

The Sun

• Made up of extremely hot gases.
• The sun is about 150 million km away from the earth.
• 30 times greater than Earth.
• Black hole – It absorb light but does not emit due to high gravitational force.
• Corona – Outer surface of the sun (About 6000 k)
• Solar flaws/solar wind – Sudden outpour of wind/stone. Comprising of electrical charged gases.

Evolution of the Earth

Theories

• Early Theories
• Nebular Hypothesis
• Binary theories
• Modern Theories
• Big Bang Theory (Expanding universe hypothesis.) – Edwin Hubble, in 1920

Expansion of universe - Hoyle’s concept of steady state.

The Star Formation

• Galaxy starts to form by accumulation of hydrogen gas in the form of a very large cloud called nebula.
• Growing nebula develops localised clumps of gas.
• Clumps continue to grow into even denser gaseous bodies.
• Giving rise to formation of stars

Formation of Planets

• Stars are localised lumps of gas within a nebula.
• Gas cloud starts getting condensed – (Planetesimals) are a large number of smaller bodies.
• large number of small planetesimals accrete to form a fewer large bodies (Planets).

Planets

• Planets move around the sun in a fixed path – Elliptical orbit.

Terrestrial Planets	Jovian Planets
Inner/ Solid Planets Earth like mostly silicate Mercury (0), Venus (Earth’s twin) (0), Earth (1), Mars (2) Denser planet Less moons or no moon. Ring system is absent Solar wind blew off lots of gas. (terrestrial planets are smaller and their lower gravity could not hold the escaping gases) Close vicinity of the parent star where it was too warm for gases to condense to solid particles	Outer/ gaseous planet Jupiter like (Giant planet) Jupiter & Saturn (Gas), Uranus & Neptune (Ice) Less dense planets Large no of moons Presence of ring system (But Saturn is visible). Solar winds were not all that intense Jovian planets are quite a distant location.

 Mercury

• Small and absence of moon & atmosphere
• N₂, H₂, O₂ & CO₂
• No water
• 88 days to complete rotation.
• Except Mercury All Planets have Atmosphere, Earth Atmosphere Contain habitable condition

Venus

• Hottest – Presence of atmosphere
• Earth twin
• No moon

Earth

• Blue planet & 1 Moon
• Geoid (Geographical) or Obiate Spheroid (Geometrical). It is the 3^rd nearest planet to the sun and 5^th largest planet.
• Age: 4.8 billion years ago. (between the 4,600 million years and the present – Evolution of Life)
• Chemical composition in Crust – Silica, Aluminum & Lime.
• Earth’s mass – Iron (32%), Oxygen (30%), Silicon (15%).
• Earth crust contain 47% oxygen
• Rotation (Day & Night) – 24 hrs & Revolution (Seasons) – 365.26 days.
• Bulged at Equator & flattened at poles (12756 km – Equatorial diameter, 12714 – Polar Diameter).
• Earths perihelion (closest to sun) around 3 January & aphelion around 4 July.
• Circle of Illumination 
• Divide the earth into two equal halves (Earth rotate on its axis, stay same in normal position).
• Dependent on the different season.
• Sphericity of the Earth - possible circum navigation of the earth without a steep fall, different times of sunrise & sunset, During lunar eclipse, the shadow cast by the earth on the moon is always circular

Mars

• 2^nd smallest
• Red planet – Iron rich red soil.
• Dark patches on its Surface. Possibility of some plant life.
• 2 Moons – Phobos, Deimos.
• Tallest volcanic Mt – Olympus mons
• 2^nd largest Mt in solar system – Active volcano

Jupiter

• Largest planet. 200°F (-130°C)
• Made up of hydrogen, helium & Methane.
• Circular light and dark bands. 12 Satellites circular around it.
• Ganymede (Lo, Europa) - largest moon in solar system.
• 53 (Named) + 23 (Unnamed) moons.

Saturn

• Concentric ring circle (due to unique mineral composition)
• Which has three rings.
• 2^nd largest planet.
• Titan – 2^nd largest moon in solar system.
• Speed, Jupiter > Saturn

Uranus

• Venus & Uranus Rotate opposite direction than other planets (East to West).
• 50 times larger than Earth. 15 times as heavy.
• Nearly 20 Moons, largest moons - Miranda, Aricl, titamia

Neptune

• Coldest planet
• 14 moons – Triton (largest)
• Except Uranus and Neptune all other planets are visible by naked eye.
• Uranus & Neptune are Ice twin of solar system; both are appearing in bluish green.

Dwarf Planets

• Pluto – smaller size, Offbeat orbit, Beyond Kuiper belt, Now Planetoid. (Planet need more than 27% mass of Pluto is considering as planet). No Ring system.
• Till august 2006, Pluto consider as planet.
• Ceres – Largest object in asteroid between Mars & Jupiter (only dwarf planet located in the inner solar system).
• Eirs – 2003 UB₃₁₃ (or Xena) – 10^th Planets & largest draft discovered.
• Oort Cloud Are Composed of Ice like ammonia, methane & water
• Kuiper belt – Ice belt beyond Neptune
• Planet nine in Kuiper belt is 10 times the mass of earth and 5000 times the mass of pluto
• Kuiper similar to asteroid belt between Mars & Jupiter
• Perihelion – When it is closest to the sun.
• Aphelion – When it is farthest from the sun.
• Dawm – Period between sunrise and full daylight.
• Twilight – Period between sunset and complete darkness.

Natural Satellite - The Moon

• 5^th largest Natural satellite of the earth. – ¼ of Earth - dumb-bell-shaped.
• Tides: Gravitational attraction between moon and earth.
• Distance about 3.84,400 km (239,900 miles) away.
• It is now generally believed that the formation of moon, as a satellite of the earth, is an outcome of ‘giant impact’ or what is described as “the big splat”.
• Sideral month 1 revolution take 27.32 days.
• Synodic month, Similar alignment of Earth, the sun and the Moon – 29.53 days
• Moon mission: Chandrayaan - I & II, Teamindus.

Asteroids

• They are numerous tiny bodies which move around the sun between the orbits of Mars and Jupiter.
• Small rocky celestial body.
• There is a “belt” of such objects, called the “Asteroid belt”
• Planetoids – largest asteroid.
• Ceres, vesta, psyche – Important astroid.
• Apophis - Near earth astroid.

Meteoroids, Meteors, Meteorites

• The small pieces of rocks/dust particle which move around the sun or dust particle apart from asteroid belt - Meteoroids.
• The dust particle enters into earth atmosphere, due to friction it is completely burn off – Meteors (Shooting star)
• The Meteors hit the earth called Meteorites.

Crater

• When asteroid hits earth the place in the earth form hole
• After some time, the hole is filled with water is called crater lake
• E.g. India, Lonar Lake (Maharashtra)
• Jazero Crater - Mars
• Aitken Basin, Mitra Crater, Bhabha Crater - Moon

Comets or dirty snowball

• Revolve around the sun only in long elliptical orbits, develop tail when close to the sun (Tail formation (due to ice) – If it come near sun ice melt).
• Dust/Rock covered with Ice move to solar radiation, No fixed path. 
• Do not have light of their own
• Short-Period comets (Halley comet visible every 76 years) – last observed in 1986, next in 2062.
• 3,650 comets as of now.

Pulsars

• Highly magnetized Rotating body/ rotating neutron star emit beam of electro magnetic radiation