SP7: Astronomy Flashcards
SP7a
1) Describe the different bodies that make up the Solar System (satellite, asteroids, comets, galaxies, solar systems)
2) Recall the names and order of the planets in the Solar System.
3) Describe how ideas about the structure of the Solar System have changed over time.
1) - A satellite is anything that orbits a planet. The moon is a natural satellite, and orbit around planets in approximately circular orbits. Artificial satellites usually orbit around earth in approximately circular orbits.
- Asteroids are mainly made of rock and metal.
- Comets are made of ice, and travel around the sun in highly elliptical orbits.
- A galaxy is a collection of millions of stars.
- The solar system is made up of planets orbiting the sun
2) The planets in order from the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
3) One of the early models of the Solar System was the geocentric model. This showed that the earth was in the middle and the planets and sun were orbiting around it.
The currently accepted model of the Solar System is called the heliocentric model. The planets (including the earth) orbit the sun in elliptical or roughly circular orbits.
People used to believe that the earth was flat, but now they are aware that the earth is spherical.
The definition of a planet has changed, so Pluto is no longer a planet.
SP7a
1) Describe how methods of observing the Universe have changed over time.
2) State what is meant by the aperture of a telescope
3) Explain why moving a telescope to a location that is higher up and away from sources of light will improve the images.
4) Briefly explain why telescopes other than optical telescopes were invented and why computers are now more commonly used to help observe the universe
1) Photography enables astronomers to make detailed observations and measurements. Computers and computer modelling are used for analysis. Telescopes in orbit around the earth give much clearer images than ground based telescopes. Telescopic evidence supported the heliocentric model, and discovered new planets.
2) The aperture of a telescope is the diameter of the objective lens.
3) Earth’s atmosphere absorbs light from space, so placing a telescope in a higher location reduces the amount of atmosphere between the telescope and the distant object and improves the visible image. Light pollution from nearby sources of light makes it hard to see dim objects in the sky, so moving the telescope to a darker place will improve the image that is visible.
4) Optical telescopes detect visible lights but after the 1940s, telescopes were built to detect a range of electromagnetic radiation which allows other parts of the Universe to be seen. Using telescopes alongside computers creates clearer and sharper images and allows astronomers to capture pictures and store lots of data, making it quicker and easier to analyse.
SP7b
1) Recall the factors that affect the strength of the gravitational field.
2) Explain why g has different values on different bodies in the Solar System.
3) Describe the orbits of moons, planets, comets and artificial satellites.
1)The factors that affect the gravitational field strength are the mass of the object and the radius of the object.
2)The gravitational field strength (g) has different values on different bodies in the solar system. This is because the different bodies have a different mass, so their pull of gravity is different. The bigger the mass the bigger the gravitational field strength.
3) Moons orbit around planets in approximately circular orbits. The orbit of a planet is almost circular. Comets travel in elliptical orbits. The orbit of an artificial satellite depends on its use, but orbits of artificial satellites around earth are usually circular.
SP7b
1) Explain why the velocity of a planet changes even if orbiting at a steady speed.
2) Describe how changing the speed of an orbiting body affects the radius of its orbit.
3) Explain how the radius of a stable orbit is affected by the orbital speed.
4) Define orbit
1) The velocity of a planet changes because the planet that it is orbiting exerts a force on the orbiting object. The force is unable to pull the object in, but it causes it to change direction. The changing direction means that there is a changing velocity, and the orbiting object is accelerating.
2) An increase in speed decreases the radius of an orbiting body’s orbit. A decrease in speed increases the radius of its orbit.
3) In order to change orbital speed, an object must change the radius of its orbit at the same time, to maintain a stable orbit. The gravitational force on a satellite in a low orbit or smaller radius (closer to the object it is orbiting) is greater than on a satellite with a high orbit (further away from the object it is orbiting.) Therefore, the lower the orbit/smaller the radius, the stronger the gravitational field strength pulling on the object is. Therefore a larger velocity is needed for the planet to be in a stable orbit.
4) Orbit: the curved path of a celestial object around another celestial object.
SP7c
1) Describe the evolution of stars of similar mass to the Sun
2) Describe the forces acting on a star in terms of thermal expansion and gravity
1) - A nebula is a cloud of dust and gas. These materials are pulled together by a gravitational force in order to form a protostar.
- As more particles collide and join the protostar, it gets bigger, and its force of gravity gets stronger, allowing it to attract more dust and gas. Gravity also squeezes the protostar together, making it more dense, which means the particles inside it collide more often, raising its temperature.
- When the temperature gets high enough, hydrogen start fusing to form helium in nuclear fusion, which makes it a main sequence star.
- When the star runs out of hydrogen, it is not able to perform nuclear fusion, so the inward pressure from gravity contacts the star into a smaller ball. It then becomes so hot and dense that nuclear fusion can start again and it starts to expand, but instead of just forming helium, the nuclear fusion will form heavier elements.
- Then, if the star was the same size as the sun or smaller, it will form a red giant. After a relatively short time, the red giant expels its outer layers, leaving behind a hot dense, solid core that does not do any nuclear fusion. This is called a white dwarf. It gives off a lot of light, and is relatively small.
- Over time, the white dwarf gets cooler and darker as it emits all of its energy until it finally transitions to a black dwarf, as it no longer has enough energy to emit light, so it appears dark.
2) A star remains a fairly constant size during the main sequence phase. This is because the gravitational collapse of the star and the thermal expansion outwards due to nuclear fusion are in equilibrium.
SP7c
1) Explain how the balance of thermal expansion and gravity affects the life cycle of stars.
2) Describe the evolution of stars with a mass larger than the Sun.
1) Hydrogen performs nuclear fusion which causes the thermal expansion of the main sequence star, while gravity acts to pull the star in on itself. When the star runs out of hydrogen nuclei to fuse together in its core, then it reaches the end of its main sequence stage. The thermal expansion and gravity are out of balance, causing the core to collapse and its outer layers to swell out.
2) Red supergiants shine brightly as they undergo nuclear fusion. When a star with a mass greater than the Sun stops being a red supergiant, it expands and contracts several times until it finally explodes in a supernova. The supernova forms element heavier than iron that are ejected across the universe. This leaves behind a very dense core, called a neutron star, or if the star was large enough, it collapses in on itself, and forms a black hole.
SP7d
1) Define the Doppler effect
2) Define red shift
3) Describe how the movement of a wave source affects the observed frequency and wavelength.
1) The Doppler effect: the change in pitch when the source of sound is moving relative to the observer.
2) Red-shift: waves emitted by something moving away from an observer have their wavelength increased and frequency decreased compared to waves from a stationary object.
3) When the observed frequency changes, so does the wavelength. If the observer and source are moving toward each other, then the frequency increases and the wavelength decreases.
SP7d
1) Describe the amount of red-shift observed in galaxies at different distances from Earth.
2) Explain why the red-shift of galaxies provides evidence that the Universe is expanding.
3) Explain how the visible light spectrum illustrates red shift
1) The most distant galaxies are moving away from us the fastest. The faster a galaxy is moving away from us, the more red-shifted the light from the galaxy is. This relationship is interpreted to earn that the universe is expanding.
2) Measurements of red-shift show all the distant galaxies, (whichever direction you look in) are moving away from us. The more distant a galaxy is, the faster its moving away, which shows the universe is expanding. This expansion started from a single point, which is the point at which the Big Bang is said to have originated from.
3) The visible spectrum of light from stars contains patterns of dark lines. These dark lines are caused by atoms in the atmosphere absorbing the light rays. If these are red shifted (moved towards the red end of the spectrum), the star is moving away from us.
SP7e
1) Describe the Steady State and Big Bang theories.
2) Compare the Steady State and Big Bang theories.
3) Describe the evidence supporting the Big Bang theory.
1) The Big Bang theory states that all the matter in the universe was in a small space of concentrated energy. This space was very hot and dense. This space then ‘exploded’ and began expanding.
The Steady State theory states that the universe is expanding but new matter is continually being created, so the universe will always appear the same.
2) The Big Bang theory states that the universe started from one tiny point, while the Steady State theory states that the Universe has always existed, and that the Universe is expanding and constantly creating matter as the Universe expands.
3) Cosmic microwave background radiation is a piece of evidence that only supports the Big Bang theory, and not the Steady State theory. Cosmic microwave background (CMB) radiation is microwave radiation receives from all over the sky, originating at the Big Bang.
SP7e
1) Explain which model is the currently accepted model and why
2) Explain how both theories of the origin of the Universe account for red-shift.
3) Explain how the discovery of the CMB radiation led to the Big Bang theory becoming the currently accepted model.
1) The Big Bang theory is the currently accepted model. This is because there is more supporting evidence for the Big Bang theory (for example CMB radiation) than the Steady State theory.
2) Both models (Big Bang and Steady State) accept the universe is expanding, so they both allow for the observation of red-shift, and that all observable galaxies are moving away from us.
3) The Big Bang theory states that huge amounts of radiation were released at the beginning of the universe. Because the universe is expanding, the wavelength of this radiation has increased so now it is only detectable as microwave radiation. It is called Cosmic Microwave Background (CMB) radiation.
1) Why did scientists originally believe in the geocentric model of the solar system?
2) How can you improve the images taken by a telescope?
1) At the time, there was only naked-eye evidence, which indicated the sun, moon and planets move across the sky in the dame direction and the same motion each day.
2) - Use a wider aperture telescope or camera
- Better quality objective lens
- Use a longer exposure time while telescope is locked onto star
- Move telescope to better seeing conditions, eg. higher up a mountain
