Week 6 Flashcards
Telescope Collecting area
Bigger area = can collect more photons
Focusing device
- depends on wavelength
visible = curved mirror
x-ray = nested mirror
Detector
records photons, visible
Einstein’s Theory of Special Relativity relies on what 2 principles
- The laws of physics are the same for everyone
2. The speed of light is measured by everyone to be the same
Lunar eclipse
Earth passes between the Sun and the Moon, so that Earth’s shadow passes across the Moon
solar eclipse
Moon passes between Earth and Sun blocking out the Sun
what kind of telescopes are used on earth?
optical and radio (some infrared)
Effects of Earth’s Atmosphere
most wavelengths of light are filtered out, optics can alter image (effect of seeing)
What affects telescope resolution?
Size of the collecting area, Wavelength of light, atmosphere/ionosphere
Special relativity
describes the motion of one object relative to another, when both are moving with constant velocity
General relativity
Acceleration feels like gravity
consequences of special relativity
- Time dilation (fast clocks tick slower)
- Relativity of simultaneity (order of events)
- Length contraction (fast objects appear to shrink)
- Mass increase (fast objects gain mass)
Reference frames
Measured velocity depends on frame of reference, There is no such thing as a stationary frame of reference
inertial frame of reference
moving at constant velocity
Accelerated frame of reference
accelerating or in a gravitational field
Why can’t we reach the speed of light?
- All observers must see light travelling a c, and you moving more slowly
- Thus you cannot accelerate to a velocity greater than or equal to the speed of light
Time dialation
Time appears to pass more slowly as you move faster
Consequences of general relativity
- Space and Time are linked as spacetime
- Time Dilation due to gravity
- Gravity is curved spacetime
- Black Holes
- Tests: GPS, Orbits and Gravitational Lenses
Curved spacetime
Spacetime in the presence of masses is curved
Equivalence principle
-gravitational acceleration and acceleration due to a
force produce the same effect
-You cannot tell the difference between being in a
closed room on Earth, and in a closed room in space accelerating
Gravitational Lensing
Matter capable of bending the light from the source as the light travels towards the observer due to curved space time
Gravitational waves
‘ripples’ moving at the speed of light in the fabric of space-time, Generated by lopsided, moving masses
In 2030, the Australian Space Agency launches a spaceship to our nearest neighbour Alpha Centauri (4 lightyears away).
How long will the journey take according to a clock on the spaceship if it travels at v=0.999 c=299482km/s (where ‘c’ is the speed of light equal to 299782km/s).
Just over 2 months.
If the Sun was shrunk to fit the same mass into a smaller volume what would happen to the curvature of spacetime near the surface of the Sun?
decrease volume + same mass = density increases,
which causes spacetime curvature to increase
Would would happen to Spacetime at the surface of the Sun if you kept the volume the same but increased the mass?
increase mass + same volume = density increases,
which causes spacetime curvature to increase
Einstein’s Theory of General Relativity is based around the principle that gravity is indistinguishable from what?
acceleration
light and intense gravitational field
A light ray is bent more by an intense gravitational field.
GR tell us that clocks run slower in a gravitational field. If you take two clocks, one on the surface of Earth, and one orbiting 100km above, and check what time they say a year later what would you see?
The clock on earth will run slower, as clocks run slower in intense gravitational fields, and the stength of gravity increases as you get closer to the surface on the Earth,
Curvature Near Black Hole
radius keeps reducing
