The Universe Flashcards
define star, solar system and the galaxy
- Stars are gaseous objects that emit light and heat
- Solar system refers to a star and all the objects travelling in orbit around it
- Galaxies are groups of millions of stars held together by gravitational forces
Name + describe our galaxy
- The Milky Way
- spiral galaxy
Describe our solar system
- The sun
- 8 planets + their natural satellites (moons, dwarf planets, asteroids, comets)
Why are light years used as an astronomical measurement of distance
- a light year = distance travelled in one year
- space is too big so astronomers use light years to measure distances between stars
what is the formula for light years + conversion of m into km
- d = c x t d = distance c = speed of light (3 x 10^8) t = time - 1km = 10^3
what is nuclear fusion + how does it produce energy in star’s core
- two light nuclei join to form a larger nucleus
- hydrogen atoms in core fuse together to form helium
- produces energy in core of star
- nuclear potential energy converted into other forms of energy
What does E = mc^2 represent
- E = energy (J), m = loss of mass (kg), c = speed of light
- shows that energy and mass are interchangeable
- energy produced in star is result of loss of mass when hydrogen fuel undergoes fusion
what is the difference between apparent and absolute brightness?
- apparent brightness is a measure of star’s brightness as viewed from earth
- absolute brightness is total energy radiated per sec
- apparent brightness depends on absolute brightness + distance from earth
how is apparent brightness measured
- logarithmic scale from -10 to +10 (lower = brighter)
- closer to earth => brighter
how is absolute brightness related to mass of main sequence stars
- absolute brightness of main sequence star tells their MASS not size
- the more massive the star, the greater its absolute brightness
what is the surface temperature of stars acc. to colour
red stars are the COOLEST orange yellow white whitish blue blue stars are the HOTTEST
how can temperature of star be calculated
Wiens law - the peak wavelength is INVERSELY proportional to the absolute temperature of object
T (K)=(3×10^6)/(Peak Wavelength (nm))
life cycle of stars
including alternate life cycle acc. to mass
- star starts as a nebula
-forms a protostar due to gravity (even tho no reactions, becomes hot because pressure makes it denser; will become main sequence) - if massive enough, hydrogen fusion begins in core (turns into main sequence star)
- once hydrogen in core runs out, main sequence star turns into:
*red giant (stars mass up to 8 solar masses
*red supergiant (stars mass greater than 8 solar masses)
RED GIANT - once fusion stops: - gases in outer region ejected into space
- core collapses into small very dense object (white dwarf)
RED SUPERGIANT: once fusion stops: - tremendous outburst of energy
-seen as supernova
-remaining star after supernova turns into:
*neutron star (less than 3 solar masses)
*black hole (greater than 3 solar masses)
What does the Big Bang model of the universe mean?
-used to describe rapid EXPANSION of very early universe from a hot, dense concentration of matter
Describe the evolution of the universe as it expanded and cooled
- at beginning of universe, only energy present
- electrons, protons, neutrons formed from energy converted into mass as universe expanded/cooled
- remaining energy in form of EM radiation
- Small gaseous atoms formed (H, He) as universe further expanded
What are the advantages of using instruments on spacecraft to explore the universe
- allowed us to explore new parts of the EM spectrum (eg. gamma, x rays, some uv, Infra-red)
- allowed us to overcome the interference it causes?
- we can travel close to astronomical objects of interest
What is Newton’s third law?
“If object A exerts a force (action) on object B then object B will exert an EQUAL force (reaction) in the opposite direction on object A.”
What is the force and thrust developed in a rocket’s engine in terms of Newton’s third law
- Rockets burn fuel explosively in a combustion chamber, causing exhaust gases to be forced out of nozzle at high speeds
- Due to exhaust gases being pushed backwards by rocket (action), the gases will push the rocket forwards with an equal force (reaction).
- This reaction force is called the thrust
How can an unbalanced force be produced using rocket thrust
- rockets generate thrust which can create an unbalanced force on spacecraft and thus CHANGE its speed and/or direction
What are 2 types of rocket engine and the pros/cons of each
- Solid fuel engine: both fuel and oxidizer mixed tog.
- ignited by a spark + burns rapidly until fuel used up
- cannot be stopped once lit
- powerful for weight + simpler to construct
- cheaper - Liquid fuel engine: has fuel (ie. liquid hydrogen) and (liquid) oxygen in diff. tanks
- their flow can be regulated
- SO this engine can be throttled back + turned off when not required
- it can be controlled
how do rockets work
- Fuel burns in the combustion chamber.
- The explosion when the combustion takes place, causes the gas to move at very high speed.
- This gas is forced out the nozzle at high speed.
- By Newton’s 3rd Law; if the rocket forces the gas down, the gas exerts an equal force on the rocket up.
- If this force is greater than the weight of the rocket, then the rocket will accelerate upwards.
- This force is called the thrust.
in model:
balloon exerts a force on gases (action)
Gases exert a force on the balloon in opposite direction on object A (reaction)
- EQUAL FORCE
- Causes acceleration of rocket
If the rocket forces the gas down, gas exerts an equal force on rocket up
- If force is greater than weight of rocket, then the rocket will accelerate upwards (ie. THRUST)
The rocket exerts a force on the burning gases down and by Newton’s third law, the burning gases exert the same size force on the rocket in the opposite direction (up)
