Topic 10 Flashcards
What is the Astronomical Unit
The astronomical unit is the mean distance between the Earth and the Sun.
1AU = 1.5 x 10^11 m
What is the unit of a light year a measure of
Distance
What is a light year
The distance through space that a light photon travels in the space of a year
1ly = 9,46 x 10^15 m
What can parallax be used for
Parallax can be used to calculate distances in space, using observations and trigonometry
What is a parsec
A parsec is an astronomical unit of distance. A star is one parsec (pc) away from the Earth if the parallax angle is 1 arcsecond
What is a Hertzsprung-Russell diagram
A Hertzsprung-Russel diagram is a plot of a star’s stellar luminosity against its surface temperature
What category of star is represented by the main diagonal on a HR diagram
The main sequence stars
What category of stars lie below the main sequence diagonal on a HR diagram
White dwarfs
What categories of stars lie above the main sequence diagonal on a HR diagram
Red giants and red supergiants
State the equation linking the intensity, luminosity and distance of a star
I = L / (4πd^2)
What is the doppler effect
The doppler effect is the apparent change of wavelength as result of relative movement between a receiver and source
What happens to the observed wavelength of a wave source moving away from the observer
The observed wavelength will increase
What happens to the observed wavelength of a wave source moving towards an observer
The observed wavelength will decrease
What happens to the observed frequency of a wave source moving towards an observer
The observed frequency will increase
What is red-shift
Red-shift is the apparent shift of the wavelength of light emitted by a star towards the red end of the light spectrum, as a result of it receding
What equations are used to calculate red-shift
z = Δλ/λ = Δf/f = v/c
Describe how the relative speed value inputted into the equation differs depending on whether the source and receiver are nearing or receding
If the source and receiver are approaching each other, the value should be negative, otherwise the value is positive
What is the difference between a positive and negative ‘z’ value
A positive ‘z’ value represents red shift, whereas a negative value represents blue shift
What are the two main conclusions that can be drawn from observations of red shift from distant galaxies
- All galaxies show red shift and so all galaxies are moving away
- The more distant a galaxy is, the greater its red shift and so the faster it is receding
What does the red-shift of distant galaxies provide evidence for
Red-shift of distant galaxies suggests that they are moving away from us. This supports the concept that the universe is expaning, which supports the Big Bang theory
What does CMBR stand for
Cosmic Mircowave Background Radiation
What is cosmic microwave background radiation
Radiation in the microwave region of the EM spectrum that is present in very small quantities all around us
How does the existance of CMBR support the Big Bang theory
In the big bang, lots of high energy radiation was produced. As the universe has expanded over time, the wavelength of this radiation has been ‘stretched’ so that it is now in the microwave region. Other theories of the universe can’t account for the existance of CMBR
What is the Big Bang theory
The Big Bang thery is a theory for the formation of the universe. It proposes that the universe began from a very small, hot and dense region, and expanded from this point
What two quantities does Hubble’s law relate
The distance of a galaxy to the speed at which it is moving away
Express Hubble’s law in words
The speed at which a galaxy is moving away, is directly proportional to the distance it is at
State the defining equation for Hubble’s law
v = Hod
Where Ho is Hubble’s constant
Describe what was observed when observations of galaxies’ brightnesses were compared to the predictions made by Hubble’s law
- THe actual and predicted brightnesses of distant galaxies don’t always agree with each other
- Distant galaxies aren’t as bright as predicted by Hubble’s law, suggesting that they are more distant that predicted
State the conculsion that can be made from Hubble’s law and observations
The rate of expansion of the universe is accelerating, since galaxies are further away than predicted
Give one possible explanation for the acceleration of the universe’s expansion
The existence of dark energy. This would explain where the energy required for the expansion rate to cnstantly accelerate comes from
Why is the existence of dark energy still only a hypothesis
Dark matter and energy can’t easily be observed
