Review of Astronomers' Tools
http://edu-observatory.org/olli/tobbc/Week1.html#Spectra
o Photon Properties
o Atomic Structure
o Spectral Lines
o Doppler Shift
Modern Tests of General Relativity
https://en.wikipedia.org/wiki/Tests_of_general_relativity#Modern_tests
Gravitational lensing (Einstein Ring)
https://en.wikipedia.org/wiki/Einstein_ring
Recently, radio telescopes have measured the deflection of
radio waves by the Sun to extremely high precision,
confirming the amount of deflection predicted by general
relativity aspect to the 0.03% level.
Distances to the lensing object(s) and the more distant
light source are estimated by respective redshifts. The mass
of the lensing object(s) can be calculated given the
observed ring radius and redshifts.
Shapiro time delay
https://en.wikipedia.org/wiki/Shapiro_time_delay
The Shapiro time delay effect, or gravitational time delay
effect, is one of the four classic solar-system tests of
general relativity. Radar signals passing near a massive
object take slightly longer to travel to a target and longer
to return than they would if the mass of the object were not
present. The time delay is caused by spacetime dilation,
which increases the time it takes light to travel a given
distance from the perspective of an outside observer. In a
1964 article entitled Fourth Test of General Relativity,
astrophysicist Irwin Shapiro wrote.
Because, according to the general theory, the speed of a
light wave depends on the strength of the gravitational
potential along its path, these time delays should thereby
be increased by almost 0.0002 seconds when the radar pulses
pass near the sun. Such a change, equivalent to 60 km in
distance, could now be measured over the required path
length to within about 5-10 percent with presently
obtainable equipment.
Shapiro uses c as the speed of light and calculates the time
delay of the passage of light waves or rays over finite
coordinate distance according to a Schwarzschild solution to
the Einstein field equations.
The Equivalence Principle
https://en.wikipedia.org/wiki/Equivalence_principle
https://www.youtube.com/watch?v=gkFD9ZPM3Jg (12:56 to 23:30)
The equivalence principle, in its simplest form, asserts
that the trajectories of falling bodies in a gravitational
field should be independent of their mass and internal
structure, provided they are small enough not to disturb the
environment or be affected by tidal forces. This idea has
been tested to extremely high precision by Eˆtvˆs torsion
balance experiments, which look for a differential
acceleration between two test masses.
Relativity in the Global Positioning System
http://link.springer.com/article/10.12942/lrr-2003-1
lrr-2003-1Color.pdf
The Global Positioning System (GPS) uses accurate, stable
atomic clocks in satellites and on the ground to provide
world-wide position and time determination. These clocks
have gravitational and motional frequency shifts which are
so large that, without carefully accounting for numerous
relativistic effects, the system would not work. This paper
discusses the conceptual basis, founded on special and
general relativity, for navigation using GPS. Relativistic
principles and effects which must be considered include the
constancy of the speed of light, the equivalence principle,
the Sagnac effect, time dilation, gravitational frequency
shifts, and relativity of synchronization.
Frame-dragging tests
Lense-Thirring Precession
https://en.wikipedia.org/wiki/Lense-Thirring_precession
In general relativity, Lense-Thirring precession or the
Lense-Thirring effect (named after Josef Lense and Hans
Thirring) is a relativistic correction to the precession of
a gyroscope near a large rotating mass such as the Earth. It
is a gravitomagnetic frame-dragging effect. According to a
recent historical analysis by Pfister, the effect should be
renamed as Einstein-Thirring-Lense effect. It is a
prediction of general relativity consisting of secular
precessions of the longitude of the ascending node and the
argument of pericenter of a test particle freely orbiting a
central spinning mass endowed with angular momentum S.
The difference between de Sitter precession and the
Lense-Thirring effect is that the de Sitter effect is due
simply to the presence of a central mass, whereas the
Lense-Thirring effect is due to the rotation of the central
mass. The total precession is calculated by combining the de
Sitter precession with the Lense-Thirring precession.
Gravity Probe B
https://en.wikipedia.org/wiki/Gravity_Probe_B
Gravity Probe B (GP-B) was a satellite-based mission to
measure spacetime curvature near Earth, and thereby the
stress-energy tensor (which is related to the distribution
and the motion of matter in space) in and near Earth.
By August 2008, the frame-dragging effect had been confirmed
to within 15% of the expected result, and the December 2008
NASA report indicated that the geodetic effect was confirmed
to better than 0.5%.
Evidence found that spinning black holes drag spacetime
https://news.mit.edu/1997/blackholes
CAMBRIDGE, Mass.--Avid Star Trek fans--and physicists--have
known that spacetime gets distorted near certain galactic
objects, but now they have more precise information about
the way that distortion works near spinning black holes.
Researchers led by an MIT scientist recently obtained the
first observational evidence that massive, rotating black
holes in our galaxy drag space and time around with them as
they gather matter into their spiral, much as a twister
picks up objects in its path.
This phenomenon, known as frame-dragging, was first
predicted in 1918 as a natural consequence of Einstein's
general theory of relativity, which describes the effects of
gravity on space and time. But it had been unproved by
experiments or observation until recently, when Italian
researchers suggested the effect might be present near
spinning neutron stars. The MIT team then applied a similar
idea to several black holes in our galaxy.
sam.wormley@gmail.com