AST201 Week 1

solar system

our solar system is made up of the sun, planets, and their moons, rockey asteriods and icy comets

galaxy clusters

groups of galaxies with many more large members

astronomical unit (AU)

earths average distance from the sun

light year (LY)

the distance that light can travel in 1 year, about 10 trillion km

age of the universe

14 billion years

big bang

where the expansion of the universe began, most galaxies including our own milky way formed within a few billion years after

star birth

when gravity compresses the material in a cloud to the point at which the centre becomes dense enough and hot enough to generate energy by nuclear fusion

star life cycle

it ‘lives’ as long as it can shine with energy from fusion, and ‘dies’ when it exhausts its useable fuel

supernova

when a massive star dies, it throws it energy back out into space

chemical elements in early universe

hydrogen and helium (trace of lithium)

earths orbit speed

average speed of 100,000 km/hr

axis tilt

almost directly at the North Star

constellation speed

incredibly slow speed, but over time will be unrecognizable and they previously have been shaped differently as well

dark matter

matter which is completely invisible to our telescopes

dark energy

the expansion of the universe is getting faster with time, this means there is some invisible energy that is a lot of the unvierse

galaxies

all smudges are galaxies

looking out is looking back

when you look up at the sky you are looking back in time

contents of the universe (1920s)

most (99.9%) is stars, galaxies, planets, gas, dust, etc

fritz zwicky (1898 - 1974)

started looking at clusters of galaxies, idea of “missing mass”

vera rubin (1928 - 2016)

measure how fast a galaxy spins

milky way galaxy spin

takes 100 million years to rotate once

original observation of galaxy rotation speed

the further from the center of the galaxy, the slower the orbital speed

vera rubin’s observation of galaxy rotation speed

the further from the center of the galaxy, the faster the orbital speed, mass is concentrated on the outside and is invisible

contents of the universe (1980s - 1990s)

most (95%) is invisible dark matter, little (5%) is stars, galaxies, planets, gas, dust etc

contents of the universe (2023)

normal matter = 4.9%, dark matter = 26.6%, dark energy = 68.5%

relativity

we can only measure motion RELATIVE to a given frame of reference

speed of light

use the constant c, 300,000 km/s

light around the earth

7.5 times per second

speed of light rules

light always travels at c, no object w/ mass can ever reach or exceed light speed

speed of light in experiment

no matter how the experiment is done, all observers measure the same speed of light, the speed of light is the same in all frames of reference

speed of the bowling ball

is different in different “frames of reference”

invariant

unchanging, the speed of light

different frames of reference

povs are different so they see time and lengths differently

foundations of special relativity

1. we can only measure speeds of objects relative to one another

2. the speed of light is invariant

time dilation

if someone is moving relative to you, their clock will appear to run slower to you

length contraction

if someone is moving relative to you, their lengths will all appear shorter to you