Universe - Overall Study Flashcards
What are all stars born out of?
Stellar nebula; molecular cloud
State the life cycle of a massive star
Stellar nebula –> massive star –> red supergiant –> supernova –> black hole or neutron star
State the life cycle of an average star
Stellar nebula –> average star –> red giant –> planetary nebula –> white dwarf
Define luminosity in terms of a star’s energy.
The rate at which a star produces energy
Which spectrum shows the true colour of a star?
Emission spectrum
TRUE or FALSE
The lower the number in the B-V colour index, the bluer the star.
True
What is the blue and green filters used to find the colour of stars called?
B-V Colour Index
What is the colour of a star dependent on?
Temperature
When two hydrogen atoms fuse, what element is created?
Helium
What process does a star produce its energy from?
Nuclear fusion
Who proposed the heliocentric model?
Nicolaus Copernicus
Who proposed the geocentric model?
Claudius Ptolemy
How does a geocentric and heliocentric model differ?
Geocentric: Earth at the centre
Heliocentric: Sun at the centre
Where is the best place for an optical telescope to be placed?
At a high altitude with low light pollution.
TRUE or FALSE
The further away a star, the more it appears to move due to parallax.
False
It appears to move less.
What is the formula for calculating distance to a star in parsecs?
Distance to star (in pc) = 1
———————–
parallax angle in arcseconds
How do we know the universe is moving away from us?
Because when astronomers look at the spectra from distant galaxies, they find the emission lines are commonly shifted towards the red part of the spectrum
How are galaxies classified?
Their shape according to the Hubble galaxy classification scheme.
How do we know about other planets outside the Milky Way?
Because planets don’t emit light, they only reflect it from stars, they create miniature eclipses when passing in front of their stars
What is the limit (of distance) that parallax is used?
Around 100 light years
How fast does light travel?
300 million metres per second (3*10^8m/s)
Define Hubble’s Law.
The further away a galaxy is, the faster it is moving away from Earth.
Define recessional velocity.
The relative rate at which a star is moving away from Earth
Define dark energy
A theoretical force responsible for accelerating the expansion of the universe
Define dark matter
Matter that does not emit light and is responsible for unidentified gravity in the universe
Define observable universe
The spherical region of the universe that can be observed from Earth because light has had time to reach Earth.
Define epoch of recombination.
The part in time where electrons and ions could combine to form atoms.
Define cosmic microwave background
Electromagnetic radiation left over from the early stages of the universe.
Define singularity.
A point at which an infinitely dense matter occupies an infinitely small space.
Define big bang
The large explosion that scientists believe created the universe.
Define goldilocks zone.
The habitable zone around a star where the temperature is not too hot and not too cold.
Define exoplanet
A planet orbiting a star that is outside the solar system.
Define red shift
A spectrum shifted towards the longer wavelengths
Define blue shift
A spectrum shifted towards the shorter wavelengths.
Define Doppler effect
A change in the frequency of sound or light waves emitted from an object when it moves towards or away from an observer.
Define arcsecond
1/3600th of a degree.
Define parsec
The distance at which a star appears to move one arcsecond in six months (equal to 3.26 light years or 30 trillion km)
Define baseline
A line between the two viewpoints used to calculate parallax angle (1AU is the baseline used for calculating star parallax)
Define astronomical unit (AU)
The distance between Earth and the sun
Define parallax
The effect by which the position of an object seems to change when it is observed from different locations
Define light year
The distance that light travels in one year (about 10 trillion km)
Define H-R diagram
A graph where the star luminosity is plotted against spectral type/temperature; Hertzsprung - Russel diagram
Define galaxy
An independent groups of stars that are held together by gravity
Define black hole
The extremely dense remnant of a massive star; a region in space where gravity is so strong that nothing, not even light, can escape.
Define supernova
The explosion of a massive star
Define white dwarf
A small, dense, dim star that has lost its outer layers and is at the end of its lifetime
Define red giant
A very large, bright, cool star that has run out of hydrogen at its core
Define main sequence
Stars that convert hydrogen into helium at their cores
Define luminosity
The intrinsic brightness of a celestial object
Define emission spectrum
A spectrum showing bright lines at wavelengths specific to emission from a substance
Define absorption spectrum
A spectrum showing dark lines due to specific wavelengths that have been absorbed by a substance
Define continuous spectrum
Continuous range of colours / wavelengths
Define B-V Colour Index
The difference in brightness measured through blue and green filters, indicating the colour of a star
Define spectral class
A group into which stars are classified based on their spectra / colour
Define nuclear fusion
The process of joining two nuclei to produce energy
Define radio telescope
A device that receives radio waves emitted by stars and other celestial objects
Define optical telescope
A device that collects and focuses light from the visible spectrum to form an image
Define heliocentric
A model of the solar system with the sun at the centre
Define retrograde motion
Apparent backwards motion of a planet as seen from Earth
Define geocentric
A model of the solar system with earth at the centre
Define constellation
A group of stars as seen from Earth that appear to form a familiar shape
What two points does Hubble’s law demonstrate?
- The universe is expanding from everywhere, not just earth
2. Using D=0 we can find the age of the universe
What is the formula for Hubble’s law?
v = H0D
How does a star’s spectra relate to how far away a star is?
The further a star’s spectra is shifted to red, the further away the star is
How far away is the edge of the observable universe?
45 billion light years
How was the cosmic microwave background discovered?
Two astronomers notices a buzzing and thought it was interference. They then investigated further and found it was the cosmic microwave background
Why are the ‘dark ages’ called this?
All photons were scattered by plasma and so could not be observed
What are three main pieces of evidence that support the big bang theory?
- Almost all galaxies are red shifted (moving away)
- Smaller elements not created inside stars
- Radiation left over (cosmic microwave background)
How old is the universe?
13.7 billion years old
What are some of the requirements an exoplanet must possess for it to be habitable by humans?
- Made of rock
- Enough oxygen in the atmosphere but not too much
- In the ‘Goldilocks Zone’
How far is the sun from the earth?
8 light minutes (150,000,000km)
State the different shapes that galaxies can be
Elliptical, lenticular, spiral, barred spiral, irregular
What luminosity is our sun on a H-R diagram?
1
At what mass does a supernova have to be to become a black hole?
greater than 40 times the mass of our sun
At what mass does a supernova have to be to become a neutron star?
Less than 40 times the mass of our sun
TRUE or FALSE
The bigger a star, the longer its lifespan
False
The bigger a star, the quicker it burns through its fuel
How big does a star have to be to become a red supergiant?
10x the mass of our sun
Why do red giants increase in size?
The helium builds up in the core of the star and the region where fusion occurs becomes a shell around the core. This means the star will increase in size
How many stars are estimated to be in their main sequence?
Roughly 90% of known stars
Outline the main sequence within the life cycle of a star
Where stars spend majority of their life. Stage which they convert hydrogen into helium
Explain why an ambulance siren changes to a slightly lower pitch as it passes you
When an ambulance passes someone, the sound waves become more stretched out, resulting in a lower pitch
Explain why we cannot see photons emitted in the early stages of the universe
During the early stages of the universe all photons were scattered by plasma resulting in it being impossible for us to see photons before the epoch of recombination
How do scientists know black holes exist without being able to see them?
Even though people can’t directly see a black hole, scientists can see the effect they have on nearby gas and stars
Why can’t we see black holes?
Black holes have such a great amount of mass in a very small area, therefore, resulting in a gravitational force so strong that not even light can escape, making it impossible for the naked eye to see one
What are the advantages and disadvantages of using a telescope in space?
The advantages are that the Earth’s atmosphere won’t be in the way, allowing the telescope to see into space more clearly. However, it does cost a lot more to do and becomes more difficult to repair
