Physics Notes Part 6

  1 light year = 9.5 x 10¹² km

v Rotation – day and night. Revolution and tilt (23.5°) – season

v Sunlight is spread out in poles due to the larger surface area. Sunlight is less spread out in the equator due to less surface area, and more concentrated. A large amount of energy is needed to maintain high temperatures on Earth.

v Mercury and Mars have ellipse orbits, while the rest of them have circular orbit.

v The first 4 inner planets are rocky and small. Outer planets are large gas giants and large.

v In the middle, there is an asteroid, which consists of gravity elements and disk formation.

v Asteroid – between Mars and Jupiter, and is a rocky material.

v Comet – Icy lump heated by gas and dust particles.

v Meteriods – Tiny grains of material heated up at Earth’s surface.

v Satellites: Any object in orbit around a massive one.

v Communication – signals (TV, mobiles); Geostationary – motion matching to Earth; Monitoring – weather. Polar – located at poles; Navigation(GPS) – used to locate positions by boats or vehicles. Astronomical – used for observing distant stars and galaxies.

v Nebula: Rotating cloud of gas and dust due to gravity. It collapsed inwards.

v Protostar: A massive clump forms at circle. GPE converted to thermal energy. Gas gets hotter and compressed.

v Main sequence star: Nuclear fusion takes place. Star becomes stable because inward pressure due to gravity equals outward pressure due to the release of energy.

v Accretion disk: Remaining gas and dust particles are pulled by gravity or slowed down by collisions. These clumps become planets and moons. Note: Accretion means gradual growth by the addition of material.

v The sun is a huge, glowing ball of gas called a star. It radiates infrared, visible and ultraviolet regions of the electromagnetic spectrum.

v Earth moves around the Sun in a near-circular path, orbit. Moon moves around Earth for 27.3 days. Orbital speed is 2πr/T.

v The Sun, planets and other objects orbit together known as the solar system.

v The Sun is a member of a huge star system called a galaxy. Our galaxy is the Milky Way. It is one of many billions of galaxies in the Universe. Between stars, there’s thinly spread gas and dust called interstellar matter.

v In the Sun’s core, thermal activity prevents gravity from pulling material further inwards. When all hydrogen is converted to helium, the core collapses. Sun’s outer layer expands and cools to a red glow, forming a red giant. The outer layer drifts into space, exposing a hot, dense core called a white dwarf.

v Supernovae: Stars become red supergiants and blow up in a gigantic nuclear explosion, supernova. This leaves the core compressed causing protons and electrons to form neutrons, in a neutron star.

v When most massive stars explode, the core can’t resist gravity's pull and collapses. The result is a black hole.

v When objects move away from Earth at high speed, light waves are stretched, known as the Doppler effect. It means wavelengths are shifted towards the red end of the visible spectrum, called the redshift.

v The universe began many billions of years ago when a single, hot ‘superatom’ erupted in a burst of energy called the Big Bang.

v Radio telescopes have picked up microwave radiation of a particular frequency coming from every direction in space. This may be heavily red-shifted remnants of radiation from the Big Bang. It’s Cosmic microwave background radiation. (CMBR)

v Using redshift, scientists have measured the rate at which galaxies appear to move apart. It is represented using the Hubble constant, H_o.

H_o = (Speed at which galaxy is moving away from Earth) / (Distance of galaxy from earth)