Solar stuff Flashcards
How does radar work?
A short pulse of radio waves are sent from a radio telescope towards a distant object. When the pulse hits the surface of object , it’s reflected back to Earth. The telescope picks up the reflected radio waves and records the time,t, taken for them to return. The distance of the planet can then be worked out using speed = distance/ time .
Explain how radar can be used to find the average speed of an object relative to Earth.
You send two pulses separated by a certain time interval, to give two separate measurements of the object’s distance. The difference between the distances shows how far the object has moved in the time interval.
What are the assumptions are made when using radar to measure planet distances?
1) The speed of the radio waves is the same on the way to the object and the way back to the telescope.2) The time taken for the radio waves to reach the object is the same as the time taken to return.
What is a more accurate method of measuring planet distances?
Using Doppler shifts
Why are there no relativistic effects when measuring planet distances with radar?
Even though the observer and object are both moving and the object’s speed must be much less than the speed of light, so that there are no relativistic effects.
What two things does the brightness of a star depend on?
1) Luminosity ( how much light energy it gives out in a given time.)2) Distance from Earth (if we ignore light pollution.)
Define apparent magnitude
How bright a star looks when seen from Earth.
What does the apparent magnitude of a star depend on?
Depends on absolute magnitude(how bright it really is.) and how far away it is.
How can you find the distance of the star?
1) You measure how bright it looks (apparent magnitude)2) You calculate how bright it really is (absolute magnitude)3) And then you put these two variables into an equation.
Give an example of the type of stars that can have their distance calculated using apparent magnitude and absolute magnitude.
This method works for objects that you can calculate the brightness of directly - called standard candles.Cepheid variable stars are examples of standard candles because their brightness changes in a certain pattern.
Define astronomical unit (AU)
One astronomical unit (AU) is defined as the mean distance between the Earth and the Sun.
Define light-year (ly)
The distance that electromagnetic waves travel through a vacuum in one year is called a light-year (ly).
One light-year is equivalent to what AU?
63000 AU
What is the approximate length in metres of an astronomical unit?
1.50 x 10^11 m
What is the approximate length in metres of a light-year?
9.46 x 10^15 m
How many light years is Sun to the next nearest star, observable universe and the Milky Way galaxy?
1) 4.2ly2) 14 billion ly3) 100 000 ly
How far can we look back in time? why?
When we look at the stars we’re looking back in time, and we can only see as far back as the beginning of the Universe.