Astronomy

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Astronomy

the study of stars

the two ways stars differ

brightness (magnitude) and colour

lightyear

one lightyear is the distance that light will travel in one earth year

parsec

a unit of length used in astronomy, equal to >30 million km

how far can light travel in a lightyear

9.5 milllion km

one parsec equals

3.26 lightyears

how is parallax is used to measure how far a star is from earth

by observing its shift against distant, fixed background stars from two opposite points in Earth's orbit

absolute magnitude

a star’s actual brightness, as if it was 10 parsecs from earth

the relationship of the electromagnetic spectrum and colour of stars

a star’s colour is based from its temperature. different temperatures have different wavelengths

Hertzsprung-Russell diagram

a diagram showing different stars categorised into their spectral class, absolute magnitude and temperature (OBAFGKM)

main elements found in stars

Hydrogen and Helium

nuclear fusion

the process where two hydrogen atoms combine to form a heavier element (helium), releasing an immense amount of energy

Our sun’s temperature, spectral class and magnitude

5,500 celcius, G, 4.83

the two opposing forces that determine the structure of a star

gravity - causes the material within the star to fall in towards the center of the star

radiation pressure - produced by the heat generated in nuclear fusion

they balance each other out, giving the star a constant radius and brightness

how are red giants formed

when the hydrogen in the core of a medium and large star runs out, fusion and outward radiation pressure stops, causing the star to collapse inwards then expand and cool

how is a planetary nebula formed

when a red giant’s fuel runs out, the outer layers escape to become a cloud of gas, known as a planetary nebula

how does a white dwarf become a black dwarf

nuclear fusion has ceased on a white dwarf so the star will fade to become a cold, dark ball of inert matter known as a black dwarf

how are supergiant stars different

they have a different life cycle. they start as blue supergiants and consume their hydrogen much quicker. once the helium is used it fuses into heavier elements. once those run out, a supernova occurs

the relationship between supergiant stars and supernovae

a supernova happens when a supergiant can’t fuse any furthur and it stops producing energy. If there’s nothing opposing gravity, the outer layers collapse inwards. When it reaches the cure it has a massive explosion (supernova).

a neutron star

a small dense star made from the material left over from a supernova if gravity pulls it together

how are black holes formed

when the supernova remnants are >3x the mass of our sun, the immense gravitational forces cause the star to shrink even furthur into a black hole

small star lifecycle

small star > hydrogen burns > white dwarf > heat is lost > black dwarf

medium star lifecycle

medium star > hydrogen burns > red giant > helium burns and runs out > white dwarf

large star lifecycle

large star > hydrogen burns > red giant > helium burns > heavier elements are burnt > core implodes > supernova > white dwarf/neutron star/blackhole

gravity definition

the force of attraction between two objects in the universe

Galaxies

a collection of solar systems held together by gravitational forces, contains nebulae, dust clouds, comets, asteroids

spiral galaxy

wide, flat disks of rotating gas and dust in a spiraling shape

elliptical galaxy

oblong shape, lack of structure, may be the result of galactic collisions

peculiar galaxy

almost always the result of a galactical collision, odd shape, make up 5-10% of all known galaxies

irregular galaxy

small, dwarf galaxies that lack a distinguishable shape, companions to larger galaxies

what really are stars

a luminous ball of gas held together by its own gravity, nuclear fusion reactions in its core to support it

main sequence stars

spectrum of stars where gravity and pressure balances

the Big Bang Theory

current theory for the origin of the universe, 13.8 billion years ago there was nothing, then a singularity started to expand

evidence of big bang theory

1. galaxies appear to be moving away from us at a speed proportional to their distance

2. the discovery of cosmic microwaves carry the remnants of the original heat from the big bang

3. the abundance of light elements H and He in the universe; would be expected

deuterium

a stable isotope of hydrogen containing one proton and one neutron in the nucleus