4.3 Our Place in the Universe Flashcards
Name the planets of our solar system, in order.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
What are comets made of? Describe their orbit.
Rock, ice and dust. Elliptical.
Explain how you would use radar to measure large distances from the Earth.
Send a short pulse of radio waves to be reflected back to Earth. Measure the time between emission and detection, t and use the equation 2d = c t to find d.
How can you measure the average speed of distant objects using radar?
Send two pulses repeated by a time interval. Find the difference in distance between the intervals and use it to calculate average speed.
State two assumptions made when using radar to measure large distances.
The radio waves are always travelling at c and the time taken to reach the object is equal to the time taken to return. (Also no relativistic effects)
Name two factors that affect the brightness of a star.
Its luminosity (energy given out in a given time) and its distance from us.
Give two factors that affect how bright a star appears to us.
Absolute magnitude and how far away it is.
What is apparent magnitude?
How bright a star appears from Earth.
Give the name and an example of objects that you can calculate the brightness of directly.
Standard candles, for example Cepheid variable stars.
Why are Cepheid variable stars standard candles?
Because their brightness changes in a predictable pattern.
What is the definition of an astronomical unit, AU?
The mean distance between the Earth and the Sun.
How many metres are there in an astronomical unit?
1.50 x 10^11
What is the definition of a light-year?
The distance that electromagnetic waves travel though a vacuum in one year.
How many AU in one light-year?
63000
How many metres are there in one light-year?
9.46 x 10^15
What is the distance between the Sun and the nearest star, Proxima Centauri in light-years?
4.2ly
What is the width of the Milky Way in light-years?
100,000ly
How can you calculate the size of the observable universe?
Multiply the age of the universe by the speed of light.
When a car is moving away from you, what happens to the sound waves and therefore the frequency of the sound heard from the car?
They are stretched out, giving a longer wavelength and there a lower frequency when they reach you.
How does speed of the emitter change the sound wave being observed?
The greater the speed, the greater the change in wavelength.
Explain the principle that allows us to use the Doppler effect to measure the speed of distant objects.
Atoms will emit and absorb radiation with same characteristic spectrum wherever they are. You can measure how much it has been shifted to find the object’s speed.
When is an object’s emission spectrum redshifted?
When it is moving away from the observer.
When is an object’s emission spectrum blueshifted?
When it is moving towards the observer.
Give the equation used to find the velocity of an object from the radiation it emits.
v / c = ∆λ / λ
