[Music] [Music] candidates are expected to have a thorough understanding of the syllabus details outlined in the accompanying figure the universe the universe contains many billions of galaxies there are three types of galaxies a spiral elliptical and irregular galaxies are made up of billions of stars our galaxy is called the Milky Way our Milky Way is a spiral there are many planetary systems in the Galaxy with planets orbiting a host star the Milky Way the Milky Way is one of galaxies in the universe its diameter is approximately 100,000 light years our planetary system is called solar system and it is located in an outer spiral arm of Milky Way galaxy the sun is one of billions of stars in the Milky Way other stars in the Milky Way galaxy are much further away from Earth than the sun is some of these Stars also have planets which orbit them the solar system our solar system consists of our star the sun and everything bound to it by gravity the sun lies at the center of the solar system it is a star that makes up over 99% of the mass of the solar system the eight planets in our solar system in ascending order of the distance from the Sun are Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune there are four rocky and small planets mer Mercury Venus Earth and Mars that are nearest to the sun these are small and dense and mainly made of rock and iron there are four gaseous and large planets Jupiter Saturn Uranus and Neptune that are the furthest from the Sun these are large mainly gas and have no solid surface although they do have a solid core the eight planets travel the sun in the same direction and in approximately the same plane the further a planet is from the Sun the lower its average surface temperature this is because the intensity of the sun's radiation weakens with increasing distance however as shown in the table Venus is an exception its average surface temperature is higher than Mercury's even though it is farther from the Sun this is because Venus has a thick atmosphere rich in greenhouse gases which trap heat and raise the temperature there are an unknown number of dwarf planets which orbit the sun such as Pluto ays horia Makemake siries and others there are dozens of moon that orbit the planets as near circular orbit moons are an example of natural satellites there are artificial satellites are man-made and can orbit any object in space there are millions of asteroids it is a small rocky object that orbits the Sun the asteroid belt lies between Mars and Jupiter there are millions of comets that orbits the Sun as highly eccentric elliptical orbits that extend beyond the planets into the Kyper belt comets are made of dust and ice and orbit the Sun in a different orbit to those of planets the ice melts when the comet approaches the Sun and forms the comet's tail there are millions of meteoroids that are rocky fragments of asteroids comets Moon and planetary collisions they are much smaller than asteroids ranging in size from Tiny grains up to a meters further from Neptune we have discovered Kyper belt and or Cloud gravitational force there is a gravitational attractive force between all objects with mass the gravitational law of Newton states that the attractive force between two masses is directly proportional to the product of their masses and inversely proportional to the Ware of the distance between them the greater the mass of each object the stronger the gravitational attraction between them the closer the objects are the stronger the gravitational attraction between them the further apart the objects are the weaker the gravitational attraction if the mass of one object is doubled the forces between them are doubled however doubling the mass of both objects together the forces between them increases fourfold this this is because the force is proportional to the product of their masses if the distance between two objects is doubled the forces between them are quartered this is because the force is inversely proportional to the square of the distance these forces obey Newton's third law of motion every action has an equal and opposite reaction this means that the gravitational forces between two objects are always equal in magnitude and opposite in direction even though they act on different objects gravitational field strength the gravitational field strength at a specific point is the gravitational force exerted per unit Mass on an object placed at that point it is measured in Neons per kilogram it is a vector quantity meaning it has both magnitude and Direction the direction is always towards the mass the gravitational field strength is directly proportional to to the mass of the object and inversely proportional to the square of the distance from the object's Center of mass the greater the mass of the object the stronger its gravitational field this is why Jupiter with its massive size has a much stronger gravitational field than Earth as shown in the table a clear relationship exists between the mass of a planet and its gravitational field strength heavier planets tend to have stronger gravitational field Fields Earth's gravitational field strength is roughly 10 Newtons per kilg while the moon's is about 1.6 Newtons per kilogram six times weaker the farther away you are from an object the weaker its gravitational field this is why the gravitational field strength decreases as you move further away from a planet's surface objects in orbit with no force acting on any any other object in the space so they will travel through space in a straight line gravitational forces exist between all masses providing the centripedal force that causes planets and other objects to orbit the Sun and moons to orbit planets Moon and their orbits moons are natural satellites that orbit planets because they are closer to their planets than the sun experiencing a stronger gravitational pull these orbits are often not per perfectly circular but they are generally elliptical with the planet at the center therefore the orbit of moons are approximately circular with the planets at the center planets and their orbits the sun contains most of the solar systems Mass causing its gravity to pull planets comets and asteroids into orbits around it the sun's gravitational field strength decreases with distance from the Sun this causes the orbital speed of planets to to decrease farther from the Sun because the weaker gravitational attraction results in a lower centripedal Force requiring less speed to maintain the orbit this also leads to longer orbital duration these orbits are often not perfectly circular but they are generally elliptical with the planet at the center therefore the orbit of planets are approximately circular with the sun is the at the center comets and their orbit comets have high highly elliptical orbits meaning they are elongated compared to planets that is nearly circular orbits as a comet moves further from the Sun its speed decreases due to the weakening gravitational pull at this point some of its kinetic energy converts into potential energy as the comet approaches the Sun the gravitational pull increases causing the comet to speed up as it gains translational kinetic energy this happens because some of its potential energy converts back into kinetic energy the ice melts when the comet approaches the Sun and forms the comet's tail the comet's tail is always directed away from Sun at here Comet moves fastest longest tail and most easily seen at here Comet moves slowest shortest tail orbital speed when planets or moons orbit another object their paths are often nearly circular in one orbit the object travels a distance equal to the circumference of its orbit this distance is equal to 2 pi r where R is the average radius of the orbit time is the one period is the time that it take to complete one orbit therefore the average orbital speed can be calculated by dividing the total distance traveled in one orbit by the orbital period this relationship is expressed by the equation V = 2 piun R / T where V equals average orbital speed in m/s R equals average radius of the orbit in meters T equals orbital period in seconds the orbital period is the time it takes for the object to complete one full orbit the orbital radius is always measured from the center of the object being or ored to the object during the orbiting for example calculate the speed of a satellite that is orbiting 200 km above the Earth's surface and complete one orbit in 1 hour 24 minutes the radius of the Earth is 6,400 KM the radius of the orbit is measured from the center of the earth so the radius of the Earth plus the height of the orbit above the Earth's surface radius of orbit equals 2 200 + 6,400 is equal to 6,600 km or equals 6, 600,000 M orbital period equals 60 Minutes + 24 minutes * 60 seconds = 5,040 seconds orbital speed equals 2 piun R / T to substitute R = 6, 600,000 T = 5 ,40 its result is 88,200 m/s astronomical distance stars are so far apart that astronomers use special units to measure their distances an astronomical unit AU is the average distance between the Earth and the Sun it is approximately 1.5 * 10 the power of 8 km light year one light year is the distance that light travels in 1 year it is approximately 9.5 * 10 ^ of 12 km the speed of light is approximately 300,000 km/s one year has 365 days one day has 24 hours 1 hour has 60 minutes and 1 minute has 60 seconds using the formula distance equals speed multiply by the time one light year equals 300,000 * 365 * 24 * 60 * 60 is equal to 9.5 * 10 ^ of 12 [Music] kilm candidates are expected to have a thorough understanding of the syllabus details outlined in the accompanying figure the stars stars exist in a wide range of sizes and colors from yellow stars like our sun to Red dwarfs and from blue giants to red super Giants color classification is used for stars as the color they emit is related to their surface temperature red stars are the coolest with temperatures around 3,000 Kelvin while blue stars are the hottest with temperatures reaching around 30,000 Kelvin our sun is a medium-sized star composed primarily of hydrogen and helium it radiates most of its energy in the infrared visible and UltraViolet regions of the electromagnetic spectrum nuclear fusion in a star in the center of a stable star where immense pressure and temperature exist hydrogen nuclei fuse to form helium this nuclear fusion reaction can be represented by the following equation dyum and tricium both isotopes of hydrogen can be fused to form a helium nucleus and a neutron a huge amount of energy is released in this reaction this energy exerts a pressure that prevents the star from collapsing under its own gravity Stellar Evolution a star is formed by the interstellar clouds of hydrogen gas and dust called a nebula a protostar is an Interstellar Cloud collapsing causing an increase in temperature as a result of its internal gravitational attraction nuclear fusion reactions occur within the core of a protostar hydrogen nuclei fuse to form helium nuclei releasing heat energy and light energy which keeps the core hot a Proto star becomes a stable star when the inward force of gravitational attraction is balanced by an outward Force caused by the high temperature in the core of the star this stable star is main sequence star most less massive star expand to form red giants and more massive star expand to form red super Giants when most of the hydrogen in the core of the star has been converted to helium a red giant from a less massive star forms a planetary nebula with a white dwarf star at its core a red super giant from a more massive star explodes as a supernova forming a nebula containing hydrogen and new heavier elements leaving behind a neutron star or a black hole at its Center the nebula from a supernova may form new with orbiting planets the brightness of stars astronomers measure the brightness of stars at a standard distance distance using the absolute magnitude scale this is because a really bright star far away will look the same as a dim star nearby so it is difficult to measure the brightness directly the absolute magnitude scale as shown in a diagram the absolute magnitude of stars is a measure of how bright they would be if they were all the same distance away from Earth this scale runs Back to Front The Brighter the star the smaller the magnitude and the dimmer the star the larger the magnitude the brightness of a star depends on two main factors how much light the star emits how far away the star is this is because more distant stars are usually fainter than nearby Stars the Herz sprung Russell diagram stars are classified using the Herz sprung Russell diagram which is a plot of stars showing Luminosity or absolute magnitude on the y- AIS and temperature or spectral class on the xais the main features of the H sprung Russell diagram are most stars lie on the main sequence this is the band of stars going from top left to bottom right below the main sequence and slightly to the left are the white dwarfs above the main sequence on the right hand side are the red giants above those are the red super Giants this means the white dwarfs are dimmer and hotter than the red giants which are brighter and cooler remember this will still go from dimmest highest number at the bottom to Brightest lowest number at the [Music] top [Music] candidates are expected to have a thorough understanding of the syllabus details outlined in the accompanying figure Doppler effect when a stationary ambulance car emits sound waves the wave fronts spread out symmetrically forming circles around the source if the wave Source moves the waves can become compressed in front of it and stretched behind it this movement changes the wavelength and frequency of the waves in front of the source the wavelength decreases and the frequency increases behind the source the wavelength increases and the frequency decreases this effect is known as the Doppler effect the Doppler effect also affects light if an object moves away from an observer the wavelength of light it emits increases this is known as a red shift because the light appears to shift towards the red end of the electromagnetic spectrum red shift red shift is an increase in The observed wavelength of electromagnetic radiation emitted from receding stars and galaxies this means that the light reaching us from these galaxies has its wavelength stretched shifting it towards the red end of the electromagnetic spectrum compared to the light we observe on Earth this figure shows the Spectra from five different objects the First shows the electromagnetic spectrum from our sun or stationary Source in laboratory the second shows the electromagnetic spectrum from a nearby star here we can clearly see that the positions of the dark lines have moved towards the red part of the spectrum the third shows the electromagnetic spectrum from a nearby Galaxy the lines have moved even further towards the red the fourth is the Spectrum from From A Distant Galaxy the lines have moved even further towards the red the last Spectrum shows the greatest shift for the furthest Galaxy by measuring the amount of red shift in the light from distant galaxies astronomers can estimate their recession velocity and determine that the universe is indeed expanding therefore the speed at which a galaxy is moving away from the earth can be found from the change in wavelength of the Galaxy's Starlight due to red shift this equation shows us how to calculate the speed at which a star or Galaxy is moving relative us where Lambda 0 is the reference wavelength that measure from sun or stationary Source in laboratory Lambda is the wavelength that measure from the distant galaxies or Stars so Lambda minus Lambda 0 is the change in wavelength V is the velocity of a galaxy C is the speed speed of light in vacuum which is 3 * 10 ^ of 8 m/s red shift supports the Big Bang Theory which proposes that the Universe originated from a very hot dense State and has been expanding ever since Cosmic microwave background the discovery of the cosmic microwave background radiation led to the Big Bang Theory becoming the currently accepted model the Cosmic microwave background radiation was produced shortly after the universe was formed and that this radiation has been expanded into the microwave region of electromagnetic spectrum as the universe expanded the microwave radiation is observed at all points in space around us the cosmic microwave background radiation is represented by the following map The Cosmic microwave background radiation map with areas of higher and lower temp temperature Blue Area represents the lower temperature orange red area represents the higher temperature places with higher temperature have a higher concentration of galaxies Suns and planets places with cooler temperatures have a lower density of galaxies and stars The Big Bang Theory according to this Theory the universe began about 14 billion years ago when a single hot superatom erupted in burst of energy called The Big Bang all the matter in the universe came from this here are two evidence to support the theory all distant galaxies show a red shift and so they are all moving away from us this implies that the universe as a whole is expanding radio telescopes have picked up cosmic background microwave radiation from every direction in space this may be the heavily red shifted remnants of radiation from The Big Bang the Big Bang was not an explosion into existing space space itself started to expand the galaxies are separating because the space between them is increasing to think about this it helps to use a simplified model of an expanding Universe such as the shown on diagram I hope you found this video helped if you did I would be grateful if you would subscribe share like and leave a positive comment your 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