13- Our place in the universe Flashcards
Define parallax.
The apparent shift of near objects against the background of further objects when the observer moves.
Define absolute luminosity.
The brightness a star would have at a standard distance of 10 parsec.
Define standard candle.
A star of known absolute luminosity which can be used as a comparative measure for other stars.
Define doppler shift.
A change in the observed wavelength due to the relative motion of the observer and source.
Define red shift.
The shift of spectral lines towards the red (long wavelength) end of the spectrum.
What is Hubble’s Law?
In plot of speed of recession of galaxies against their distance, distant galaxies seem to be moving away from us at a speed proportional to their distance.
Equation for red shift, z.
z = Δλ/λ
Equation for “stretch of space”
1+ z
What is Cosmic Microwave Background Radiation?
Microwave radiation that permeates the entire universe, being red shifted radiation left over from an early hot stage of the universe.
Define special relativity.
Einstein’s theory of motion based on his postulates.
Einstein’s first postulate:
Physical behaviour cant depend on any “absolute velocity”. Physical laws must take the same form for all observers, no matter their state of uniform motion in a straight line.
Einstein’s second postulate:
The speed of light is a universal constant. It has the same value, regardless of the motion of the platform from which it is observed. The translation between distance and time units is the same for everybody.
What are the axis for space-time diagrams?
Distance on x, units being x/c (light-seconds)
Time on y.
Describe the motion of a light pulse on a space-time diagram.
Travels at 1 light second per second, 45 degrees angle.
What is a light clock?
A pair of mirrors between which pulses of light bounce back and fourth.
