13-Our Place in the Universe Flashcards
What is the current age scale for the universe?
13.8 billion years
What is a light-year?
The distance light travels through space in a year
What is the speed of light?
3 X 10^8 m/s
What is the modern way in the universe to measure distances in the solar system?
Radar
What does r.a.d.a.r stand for?
Radio detection and ranging
How does radar work?
A signal is sent out and reflected from an object in the solar system and then detected on Earth
How can you calculate the distance of an object from earth using radar?
The time there and back / 2 times the speed of light
Why can’t we use radar for distant objects in the solar system?
The returing signal is far too weak to be detected
What is lidar?
Light detection and ranging
How do you measure the relative velocity of an asteroid?
Measure the distance using radar, then measure it again after 100s. Calculate the change in distance to find the relative velocity of the asteroid
What are the main assumptions with radar?
- Speed of the signal is same both ways
- The moment of delay was half way through the time delay of the pulse as observed on earth
Is the speed of light constant?
Yes
What method do astronomers use to measure distance to nearby stars?
Parallax
How does parallax work?
We measure the parallax angle to a nearby star at 2 six month intervals, and then we use small angle approximations to find the distance to the nearby
What do atoms in a distant star absorb and emit?
Light at particular wavelengths
What are the spectral lines of a star?
When atoms from a distant star absorb and emit light at particular wavelengths
If a star is moving away, what happens to the wavelengths of its spectral lines?
The wavelengths of its sprectral lines increase
Why do receding stars show red-shift?
Because their spectral lines are shifted towards the red end of the spectrum
What is the doppler shift?
When the wavelengths of a distant stars spectral lines increase(redshift) as it is moving away from us
What did the use of the doppler effect lead to?
The discovery that most stars are moving away from us, first hint of the expanding universe
What does Hubble’s law state?
The further away a galaxy is, the faster it is receding from us
With the red shift interpreted as a recession velocity, what is the equation of recession velocity?
Recession velocity = hubbles constant X distance r
What is the Big Bang theory?
That the universe originated in a very hot, very dense state from which it has expanded and cooled
What does the larger the value of Hubble’s Constant mean?
The larger the value of Hubble’s constant, the faster that universe must be expanding
What does 1 parsec equal?
3.09 X 10^16
What does red shift z =?
Change in wavelength / Wavelength
What has space expanded by?
A factor of 1 + z
When we observe object of a redishift z=10, what does this mean?
We are looking at a time when the universe was a tenth of its present size
What does Hubble’s law present evidence of?
That the universe is expanding
What is cosmic background radiation?
Microwave radiation that came from the hot beginnings of the universe
How does cosmic background radiation provide evidence that the universe began in a hot, dense stae?
The microwaves have a wavelength of 1mm, as they were streched due to the heat
What does Einstein’s second postulate state?
That the speed of light c is constant everywhere in the universe
What do space-time diagrams represent?
Objects moving through space and time
What is the equation of the relativistic factor y?
1 / root (1 -v squared / c squared)
What is time dilation a consequence of?
The speed of light being constant for all observers
What does the relativistic value mean?
The factor by which time, length and relativistic mass change
What does y / t equal?
The wristwatch time
