Space (Chapter 16) Flashcards
What are the main objects in our solar system?
- Sun
- (8) planets
- dwarf planets
- moons
- asteroid (belt)
- comets
What kind of object is the sun?
Star
Which galaxy is our Solar System in?
The milky way
What do all stars start of as?
huge cloud of gas and dust called a nebula
Which force is responsible for forming a protostar from a nebula?
gravity
What kind of reaction causes the expansion of a star?
nuclear fusion
How does a main sequence star remain stable?
fusion reactions produce outwards forces which balance the gravitational forces pulling it inwards
What determines the life cycle of a star?
mass
What is the life cycle of a star with about the same mass as the Sun?
protostar→main sequence star→red giant→white dwarf→black dwarf
What is the life cycle of a star with much more mass than the Sun?
protostar→main sequence star→red supergiant→supernova→neutron star or black hole (if mass big enough)
How are naturally occurring elements formed?
From nuclear fusion during the life cycle of stars
What element are only produced in a supernova?
elements heavier than iron
How are the elements distributed throughout the universe?
supernovas scatter them
How does the force of gravity make objects in orbit change their velocity but not their speed?
gravity provides a centripetal force which keeps orbiting objects moving in a circle - they are constantly changing direction
to change the speed of an object in a stable orbit what factor must change
radius of the orbit
what is red shift
wavelengths of light get longer if the light source is moving away from the observer
what evidence suggests that the universe is expanding
light from more distant galaxies is more red-shifted so more galaxies are moving away faster
what is the big bang theory
the scientific theory that the universe started of as an extremely small, hot, and dense region
what are the eight planets in order
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune (NOT Pluto)
How was our Sun formed?
- The Sun formed about 4.5 billion years ago when a cloud of gas and dust (a nebula) was pulled together by gravitational attraction.
- The particles in the cloud got faster and collided more.
- The gas warmed up and eventually became hot enough to glow. This was a protostar.
- As the protostar gets more dense, more collisions take place and it gets hotter. Eventually the cloud gets hot enough for hydrogen atoms to fuse, forming helium. We call a star in this state a main sequence star.
Why does the Sun remain in the main sequence stage?
In the main sequence stage, the gravitational attraction still pulling on the gas (actually a plasma) is balanced by the outward force of the radiation from the nuclear fusion in the core. We say the forces are in equilibrium
Why do we have uranium
Uranium and other such heavy elements naturally present on Earth can only be formed in a supernova explosion so the Sun must have formed from the remnants of a supernova.
What is going to happen to our Sun
eventually?
- When a star starts to run out of hydrogen to fuse, its core collapses and the outer layers swell, cool down and the star will become a red giant.
- Here, helium and other light elements in the core fuse to form heavier elements.
- When there are no more light elements in the core, fusion stops and no more radiation is released. The star collapses, and as it does it turns from red to yellow to white becoming a white dwarf (much smaller than it was before). Such stars eventually fade out becoming black dwarfs.
What would happen eventually if our
Sun was much bigger?
- Stars much bigger than ours become red supergiants then they collapse. Because there is more mass the collapse is more violent and a supernova explosion occurs. This is where elements heavier than iron can form from fusion.
- The explosion compresses the core into a neutron star, an extremely dense object made only of neutrons.
- If the original star was massive enough, it becomes a black hole instead of a neutron star. The gravitational field of a black hole is so strong nothing can escape from it, not even light.
What is a planet
A planet orbits a star, enough gravity to make it spherical and sweeps out its own orbital path of other smaller objects.
what is a moon
A moon orbits a planet.
what is a satillite
A satellite is something that orbits something else. The Moon is a natural satellite. There are many artificial (man-made) satellites.
What provides the force that allows planets and satellites (natural and artificial) to maintain their circular orbit?
Gravity. It is an example of a centripetal force because it is acting towards the centre of a circle.
Describe a circular orbit.
An object orbits another at a constant speed. Its direction is constantly changing so its velocity is changing (speed in a given direction). Therefore we say the object is accelerating towards the centre of the circle. The acceleration is a change of velocity per second.
What happens to the orbit of an object if
its speed changes?
- If an object in orbit slows down, it will fall into a lower orbit (closer to the Earth). If it gets too slow, it will crash to the surface.
- If an object in orbit speeds up, it will move to a higher orbit (further from the Earth). If it gets sufficiently fast it will escape the gravitational pull of the object it is orbiting and fly off into space.
- At the correct speed an object will orbit at a constant height and speed.
What evidence is there for the Big Bang theory?
(Red-shift and) In 1965 scientists discovered microwaves coming from every direction in space. This microwave radiation had been red-shifted suggesting that 13.5 (ish) billion years ago there must have been a massively energetic event in one place to still have evidence of it today. This radiation was called the Cosmic Microwave Background Radiation (CMBR).
Were there any other theories (not the big ban) for the origin of the universe?
- The Steady State theory suggested that the universe was expanding, but it had always been there and matter was created into the spaces that the universe expanded into.
- More evidence was present for the Big Bang theory so that is why it is widely accepted today as being the most probable origin story for the universe.
What will happen to our universe?
Depending on the total mass of matter in the universe (unknown because we still have not observed dark matter, a strange substance that is needed for galaxies to maintain their shape) the universe could:
1. [If the universe is less dense than a certain amount] Expand forever, the stars will gradually die out and the universe will cool (Big Yawn)
2. [If the universe is more dense than a certain amount] Stop expanding and collapse (Big Crunch) - Some scientists currently think the universe has gone through cycles of this.
