Star Formation and Stellar Distance

• The Universe is 13.8 billion years old.
• A light year is the distance light travels in a year, used to measure very large distances.
• The diameter of the observable universe is 93 light years.
• One light year can be calculated by multiplying the number of seconds in a year (with 86400 seconds in a day) by the speed of light.
• Pluto orbits around 40 AU from the Sun.
• The Sun blows a constant wind of charged gas into interstellar space, called the solar wind.
• Boundary between the Solar Wind and interstellar space (the Heliosphere) is around 100 AU from the Sun (200 AU diameter).
• The solar neighborhood is the region of the Galaxy within about 20 light-years of the Sun (40 light-years diameter).
• The neighborhood stars generally move with the Sun in its orbit around the center of the Galaxy.
• The Milky Way Galaxy is a giant disk of stars, 100,000 light-years across and 1,000 light-years thick.
• The Sun is located at the edge of a spiral arm, 30,000 light-years from the center of the Milky Way Galaxy.
• The Sun takes about 250 million years to complete one orbit.
• There are 200 billion stars in the Milky Way.
• The local group contains 3 large spiral galaxies: Milky Way, Andromeda(M31), and Triangulum(M33), plus a few dozen dwarf galaxies with elliptical or irregular shapes.
• The local supercluster is a huge cluster of thousands upon thousands of galaxies, the largest being the Virgo cluster containing well over a thousand galaxies.
• The local supercluster is 130 million light-years across.
• Clusters and groups of galaxies are gravitationally bound together, however the clusters and groups spread away from each other as the Universe expands.
• The observable Universe has great walls and filaments of galaxy clusters surrounding voids containing no galaxies.
• The Universe is estimated to contain between 200 billion to 2 trillion galaxies.
• The closest star is Proxima Centauri.
• One Astronomical Unit (AU) is the average distance between the Earth and the Sun.
• The speed of light is 3 x 10 to the power of 8 meters per second.
• A light year is the distance light travels in one Earth year.
• Parallax is a method used by astronomers to measure distances to nearby stars.
• Astronomers take pictures of a star at two different times of the year to measure its parallax.
• A star will appear to move slightly compared to the background stars because of parallax.
• Closer stars have a bigger parallax angle.
• Farther stars have a smaller parallax angle.
• Stars form from pockets of dust and gas floating around in empty space.
• These pockets are often massive and stretched out over light years of space.
• Dust particles condense when they have a density of 100 atoms per cubic centimeter.
• Gravity forces cause the entire pocket to undergo gravitational collapse, creating a cloud of gas called a nebula.
• A nebula can be hundreds of light years across and is denser than the space around it.
• The densest parts of nebulae continue to grow as gravity pulls the particles closer together.
• Dense clouds of hydrogen gas are called protostars.
• Nuclear fusion is a radioactive process where two particles fuse to form a larger particle requiring temperatures in the millions of degrees Celsius.
• A protostar becomes a star once nuclear fusion starts, mostly hydrogen atoms fusing to form helium.
• Dust not used to form the star slowly combines to form planets, moons, asteroids etc.
• An average sized star dies when the hydrogen runs out, causing gravity to bring matter from the outer area towards the core which will expand and cool becoming a Red Giant.
• A medium star becomes a Red Giant where fusion happens at lower temperature, using helium as fuel making the core heavy, which will run out after 100 million years.
• A medium star dies when helium runs out, outer layers escape gravity creating a cloud of gas around the star, thus a planetary nebula.
• A medium star dies when no nuclear fusion occurs anymore, thus it dims into a white dwarf star, which cools down over billions of years into a black dwarf star
• Large stars burn through their hydrogen more quickly due to their size and gravity.
• Large stars exist for millions of years instead of billions.
• Supergiant stars use helium as fuel after hydrogen runs out, becoming a red supergiant and cooling down as it uses other elements, eventually fusing all matter into iron.
• A giant star dies to a supernova when energy stops being produced by the core, gravity causes all the matter to collapse to the centre, which rebounds and causes a massive explosion called a supernova.
• Supernova leads to a Neutron star where electrons and protons all become neutrons and the size of the star shrinks to only 20 km across.
• A neutron star dies into a black hole if the star left after a supernova is more than three times the mass of the Sun, gravity will cause it to shrink down further.
• Gravity is the force that pulls you to the center of the largest mass.
• The bigger the mass, the bigger the force of gravity.
• Scientists theorize gravity is caused by a particle called a graviton.
• Bigger mass means larger gravitational force.
• Blackholes consists of massive stars.
• Nebulae are made of dense clouds of hydrogen.
• Gravity causes particles or dust to move towards each other, contributing to the birth of a star.
• A star enters the main sequence stage after it is fully formed.
• Stars shine because the energy from fusion creates the light and heat that stars emit.
• Elements besides hydrogen and helium come from stars going supernova and spreading all the elements in the star everywhere.
• When a star explodes in a supernova, it smashes atoms together with a lot of energy, creating new elements like gold, silver, and iron which spread out into space, mixing with gas and dust to form new stars, planets, and even life.
• Nuclear fusion begins when dust moves so close it is squished together and the pressure gets so high that nuclear fusion begins and the star ignites and turns into a main sequence star.
• The size of a star determines how long it will burn and what will happen when it runs out of hydrogen.
• A red super giant leads to a super nova because it pulls matter outside to the inside causing the outside to lose energy and fuel so outside cools down, when it cools the articles move further away from each other and the sun becomes larger.
• A blue super giant is a star 10 times larger then other stars.
• AU is typically used for distances within our Solar System, while light-years are used for much greater distances beyond it.
• Gravity keeps planets in our Solar System in their orbits and maintains the order and movement of celestial bodies within the Solar System.
• AU denotes the distance between the earth and the sun.
• A light year is the distance light will travel over the space of a year.
• The Geocentric model says that the centre of the universe is earth with everything orbiting around it.
• A solar system is a system where planets revolve around a star.
• Seven other planets including Earth and one dwarf planet are orbiting the sun.
• A Heliocentric system says that: the sun is the centre of the solar system.
• The milky way galaxy contains: Stars, Nebulae, Black holes, Asteorids.
• The order and names of the planets: (MVEM JSUNP) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto (Dwarf planet).
• Moons are smaller celestial bodies that orbit around the moon.
• Jupiter has 79 moons.
• The Kuiper Belt is a belt of asteroids beyond Neptune and Pluto.
• Comets whiz through the solar system in large paths.
• An arcsecound is a special unit of measurement for very small angles in space.
• An arcminute is 1/60 of a degree.
• Parralax is a way to calculate distance to a star
• A parsec is the distance separating us and a star, if the star's parallax angle is one arcsecound (useful for large distances)
• One million parsecsis a megaparsec.
• Planets orbit stars.
• A moon is not planet, it orbits earth not a star.
• Pluto isn't a planet because it is too small to clear its orbit.
• Stars are several hundreds or thousands of times bigger than planets.
• Planets orbit around stars.
• Stars are giant ball fo hot gas that generates heat by fusion.
• Nebulae are large cloud of dust and gas particles held together by gravity to eventually form stars and planets, with a size of several light years across.
• Galaxies are gravitationally bound collections of stars, planets, nebulae, dark matter and other features, most containing billions of stars & forming clusters that then form superclusters.
• The our universe contains up to trillions of galaxies.
• What type of stars in Milky Way galaxy: Main sequence star, red dwarfs, blue supergiant, red supergaint, white dwarfs, neutran star.
• A neutron Star: massive star exhausts its nuclear fuel and undergoes a supernova explosion, the core collapses under gravity compressing protons and electrons into neutrons.
• Dark mater does not emit, absorb or reflect light making it invisible and detectable only through its gravatational effects on visible matter, it plays a crucial role in formation of structure of galaxies
• Comets originate from outer regions of the solar system, asteroids orbit the sun mainly found in the asteroid belt between Mars and Jupiter, they do not have tails like comets.
• Dark energy makes up 68 percent of the universe and is responsible for the accelerated explansion of the universe.
• The Main Sequence star: is formed when nuclear fusion begins in the core of a protostar
• When a protostar transforms into a Mains sequence star: :he protostar gravity increasing force and temp increase causes nuclear fusion to begin converting hydrogen into helium and releasing energy
• The different death of a star scenarios are: Red giant, white dwarf, black dwarf. The colour of a star refers to its temperature.
• Classified stars by colour: blue, red, yellow, orange and white.
• At a higher temperature stars will emit radiation at a higher frequency and have a colour on the blue side of the spectrum.
• Stars are classified by distance using the parallax angle (allows us to map out how far these stars are).
• Stars are classified by their brightness of a star and measure of how much energy they give off.
• Stars luminosity is how its distance from us combined with Brightness to give the stars Luminosity.
• Classifying stars through spectral class refers to each class being assigned a letter and has a temperature range and a colour associated with it An stars
• Brightness: An apparent measurement where we judge how intense the light of a star is.
• Luminosity refers to how much light a star gives off and not just how we see.
• The Heart sprung Russell diagramClassifies stars according to their luminosity, spectral class, colour, temperature and evolutionary stage.
• White dwarfs on hertz have high temperatures are located on the left side of the graph. meaning they have high temperatures.
• Giants are cool and located toward the right of hertz.
• Luminiscity: the higher the star the more luminocity
• Supergiants are generally cooler than the hottest main sequence stars.
• The Main Sequence spans a wide range of temperatures, from hot blue stars (left) to cool red stars (right).
• Yaxis: on the on the Hertzsprung- Russell diagram refers to luminocity.
• Xaxis: on the on the Hertzsprung- Russell diagram refers to temperature..
• The 3 main characteristics of the main sequence location on the Hertzsprung- Russell diagram: 1. show stars at their most stable stages of life 2. organised by colour which indicates temperature 3. stars on top left of HR are heavier, larger more luminous and have a higher surface temperature
• A theory is a though or assumption of what happened or what might happen.
• A Scientific theory has: 1. explanation for observation 2. Evidence for explanation 3. Allows predictions to be made
• In Steady-state cosmology matter is constantly created as the universe expands.
• In the beginning of the Universe the mass of universe was compressed into a small ball (like an atom) its basically a small amount of energy.
• Planck Era 1: the universe mass was a ball of energy
• Inflationary Era 2: energy becomes mass called singularity.s
• Quark Era 3: universe if full of dense plasma
• Hadron Era 4: universe gets bigger and reaches one trillion trillion km across and protons and neutrons are formed from the quarks
• Quarks: are the building blocks of protons and neutrons
• Era of Nucleos synthesis 5: neutrons and protons get attracted to eachother through gravitation to form nuclei and Elements like hydrogen and helium are created.
• Photon Era 6: a sooupy mixture of hydrogen, helium and nuclei and electrons and photons bound off these particles filling the universe with light.
• During Dark Era 7: nebula forms, but no stars or planets, then after 300 million years galaxies are born.
• during the Stary era: stars and dust gather to create milky way galaxy which the sun will take. 4 billion years to create its first form.

Understanding star formation involves parallax for distance, nebula to protostar evolution, and nuclear fusion's role. The parallax effect helps determine the distance to nearby stars by measuring the observable shift against distant background stars. Nebulae are considered 'birthing points' due to their role in supplying raw material that forms stars.