Section 8 - Astrophysics P2 Flashcards
What does a star’s brightness depend on?
-its size
-its temperature
the bigger and hotter a star is, the brighter it is
What are the flaws of classifying stars by brightness?
- can be difficult, since the brightness that they appear an also be affected by the distance that they are from earth
- the closer the star the brighter it appears
How do we overcome the flaws with classifying stars by brightness?
Absolute magnitude
-it is a measure of how bright a star would appear if it was a set distance away from the Earth (allows us to compare the brightness without the affect of their relative distances from earth)
What does a lower absolute magnitude mean?
The lower the absolute magnitude, the brighter the star
-negative absolute magnitudes are the brightest stars
What is a diagram which you can see different types of stars on?
Hertzsprung-Russel Diagram
What is the Hertzsprung-Russel Diagram?
a graph of absolute magnitude against temperature for many stars
What are the clear groups on a Hertzsprung-Russel Diagram?
Red Giants and Red Supergiants are in the top-right (they are cool but very large, so are very bright)
White Dwarfs are in the bottom-left (they are hot but small, so are dim)
Main Sequence Stars span the whole range of the graph diagonally, top-left to bottom-right (roughly the same size, the brighter the star, the higher the temperature)
What is the Doppler effect?
When a source of waves is moving relative to the observer, the waves will undergo an apparent change in frequency and wavelength when they are observed, compared to when they are emitted
What types of waves does the Doppler effect occur with?
All types of waves, including light
What is a red-shift?
When a light source is moving away from you, the light it emits will appear to be shifted towards the red end(lower frequency end) of the visible part of the EM spectrum
What do astronomers use red shift for?
They determine if stars are moving away from earth if distant star are emitting more red light (lower frequency) from them than we would expect
What is the evidence for why most galaxies seem to be moving away from each other?
- different elements absorb different frequencies of light
- when light is passed through an element, a pattern of dark lines appear, each line shows the frequencies in the EM spectrum that the element absorbs
- when we look at light from distant galaxies the same pattern occurs but lower frequencies - the patterns have undergone red-shift
How do you calculate red-shift?
change in wavelength / reference wavelength = velocity of a galaxy / speed of light
Δλ / λ₀ = v / c
What is the speed of light?
3.00 x 10⁸ m/s
What do measurements of red-shift suggest?
All the distant galaxies are moving away from us quickly - it’s the same wherever you look
