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John C. Mather developed and led the scientific use of the COBE FIRAS instrument to test the radiation spectrum of the cosmic microwave background. Comparing the sky signal against a controlled reference blackbody made the measurement a stringent test of spectral shape.

The measured spectrum closely followed Planck's law at a temperature near 2.7 kelvin, strongly supporting a thermal origin in the early Universe. This result addresses a different observable from angular anisotropy: a nearly perfect blackbody spectrum concerns the distribution over frequency, while a sky map concerns changes with direction.^[ref]

Charles L. Bennett led the final nine-year WMAP analysis of cosmic microwave background maps. The work combined sky temperature and polarization measurements while modeling Galactic foreground emission and the response of the observing beams.

The angular patterns constrain cosmological parameters through a physical model of the early Universe. The paper compared the resulting Lambda-CDM model with independent observations, including baryon acoustic oscillations. Its quoted cosmic age and expansion rate are fitted consequences of those combined data and assumptions, rather than direct readings from a single sky image.^[ref]

Saul Perlmutter led the Supernova Cosmology Project's measurement of cosmic expansion using 42 distant Type Ia supernovae. Their peak brightnesses were standardized through a relation between light curve width and luminosity, then compared with a nearby sample.

Fitting the magnitude–cosmological redshift relation constrained the matter and cosmological constant contributions together. The paper reported a joint parameter distribution and distinguished statistical errors from identified systematic effects. Its result favored a substantial cosmological constant contribution within the tested models, independently supporting the accelerating-expansion picture.^[ref]

Brian Schmidt coauthored the High-Z Supernova Search Team's 1998 evidence for accelerating cosmic expansion. The analysis joined nearby Type Ia supernovae to a more distant sample to test the relation between luminosity distance and cosmological redshift.

Comparing multiple light curve fitting procedures helped test whether the inferred faintness depended on one calibration method. The combined observations favored an accelerating cosmological model with a positive cosmological constant.^[ref]

Adam Riess led the 1998 analysis of Type Ia supernovae that provided evidence for accelerating cosmic expansion. His team compared distant and nearby supernovae, using their light curves to estimate distances and their cosmological redshifts to test the expansion history.

The distant events were farther away than expected in the cited low-mass density model without a cosmological constant. Different fitting methods and sample selections favored a positive cosmological constant and present acceleration. The evidence came from a distance–redshift relation interpreted within cosmological models.^[ref]

Michel Mayor develops precise stellar radial velocity measurements and their use in searches for unseen companions. With Didier Queloz, he reported a planetary companion to 51 Pegasi in 1995.

The host star's regularly changing Doppler shift revealed its reflex motion around a shared center of mass. The approximately four-day orbital period showed that a giant planet could exist much closer to its host star than the giant planets of the Solar system. The discovery made this previously unexpected orbital arrangement an observational constraint on planet formation.^[ref]

Didier Queloz and Michel Mayor detected a planetary companion to the solar-type star 51 Pegasi through periodic changes in its radial velocity. Their 1995 observations used the ELODIE spectrograph to measure the stellar Doppler shift.

The signal repeated in about four days, implying a close companion rather than a distant analogue of Jupiter. The inferred minimum companion mass was planetary. Because radial velocity measures only the line-of-sight component of the reflex motion, the orbital inclination remains part of the mass inference.^[ref]

Reinhard Genzel investigates the central mass of the Milky Way using the motion of nearby stars. He coauthored the 2002 report led by Rainer Schödel that followed a close stellar orbit around Sagittarius A*.

An orbital path tests more than a high stellar speed: its curvature, timing and closest approach constrain how tightly the attracting mass is concentrated. The measured short-period orbit required several million solar masses in a compact central region, providing strong dynamical evidence for a supermassive black hole.^[ref]

Andrea M. Ghez measures stellar orbits around the supermassive black hole at the center of the Milky Way. Her team's Keck observations combined astrometry with radial velocities for the short-period star S0-2.

An angular orbit alone leaves a mass-distance degeneracy of an angular stellar orbit. Adding Doppler spectroscopy supplies a physical velocity scale, allowing central mass and Euclidean distance to be fitted together. Their 2008 analysis inferred roughly four million solar masses at a Euclidean distance of eight kiloparsecs, and examined how source confusion and assumptions about central motion affected the result.^[ref]

Rainer Schödel led a study that traced a short-period star around Sagittarius A* at the center of the Milky Way. Ten years of high-resolution astrometry captured both the nearest and farthest parts of the star's highly eccentric orbit.

The 2002 analysis found an orbital period of about 15 years and a close approach of only about 17 light-hours. Concentrating several million solar masses inside that small region excluded plausible extended clusters as the source of the central gravitational field, strengthening the supermassive black hole interpretation.^[ref]

Aleksander Wolszczan and Dale Frail discovered a planetary system around the millisecond pulsar PSR1257+12 through precise radio timing. The regular pulses supplied a clock whose observed arrivals varied periodically.

Those variations trace the changing light-travel time as the pulsar moves in response to its companions. Fitting the timing signal constrains the companions' orbital periods and minimum masses. The discovery established that the search for exoplanets could extend beyond ordinary main-sequence host stars.^[ref]

Dale Frail and Aleksander Wolszczan reported planetary companions to a millisecond pulsar in 1992. Their evidence came from small periodic variations in the arrival times of its radio pulses.

An orbiting pulsar changes its Euclidean distance from the observer, changing the travel time of its radio waves. Timing residuals can therefore reveal a reflex orbit and constrain unseen companion masses. This method found a planetary system around a neutron star, a very different environment from the Solar system.^[ref]

André Baranne designed precision astronomical spectrographs, including the ELODIE spectrograph, which was used for Michel Mayor and Didier Queloz's discovery of the planetary companion to 51 Pegasi. The instrument combined broad spectral coverage with precise radial velocity measurements.

The scientific goal was to distinguish tiny stellar Doppler shifts from instrumental changes. Its design and calibration supported long-term velocity stability sufficient for detecting giant planetary companions. The original instrument paper reports the construction, data treatment and measured performance, making the observing hardware part of the explanation of the discovery.^[ref]

Jean-Pierre Rivet coauthored measurements of stellar spatial coherence using intensity interferometry. Two separated optical telescopes recorded photon arrivals, and fast electronics measured the correlation of their intensity fluctuations.

Unlike combining optical field amplitudes directly, the experiment estimated a statistical correlation from many detected events. Observations of three bright targets tested how the contrast changed with angular source structure. The work demonstrated that modern photon-counting detectors could recover useful stellar visibilities with metre-class telescopes.^[ref]

Farrokh Vakili coauthored a modern stellar intensity interferometry experiment using two one-metre optical telescopes separated by fifteen metres. The team correlated photon-counting signals from bright stars, reviving a technique historically associated with Robert Hanbury Brown.

The measured quantity was the zero-delay correlation between detected light intensities. Its contrast contains information about angular source structure. The team measured reliable visibilities for two marginally resolved stars and found reduced contrast for a binary star, consistent with its more extended apparent structure.^[ref]

Frank Watson Dyson coauthored the report of the 1919 eclipse observations with Arthur Eddington and Charles Rundle Davidson. The experiment tested the predicted bending of stellar light passing near the Sun.

Comparing stellar positions on eclipse and reference plates tested a small radial displacement. Changes in plate scale and focus could alter the signal, so the report assessed instrumental errors alongside its gravitational interpretation.^[ref]

Arthur Eddington helped carry out the 1919 eclipse test of general relativity, observing the apparent directions of stars near the eclipsed Sun. He coauthored the resulting report with Frank Watson Dyson and Charles Rundle Davidson.

Comparing stellar positions on eclipse and reference plates tested a small radial displacement. Changes in plate scale and focus could alter the signal, so the report assessed instrumental errors alongside its gravitational interpretation.^[ref]

A chosen boundary in a frequency response, commonly where the voltage amplitude gain falls to $1/\sqrt{2}$ of its pass-region value. The convention must specify the reference gain.

For a linear time-invariant system, a sinusoidal wanted signal at ${\omega }_s$ and an unwanted sinusoidal component at ${\omega }_n$ acquire their separate frequency response factors. The ratio of their output amplitudes, divided by their input amplitude ratio, is $\eta =|H({\omega }_n)|/|H({\omega }_s)|$. An amplitude attenuation factor of $F=1/\eta$ corresponds to a factor $F^2$ in squared-amplitude power ratios under a common impedance convention. The unwanted component's own absolute attenuation is $|H({\omega }_n)|$, which need not equal its attenuation relative to the wanted signal.

Cited experimental account: Figures 70–77.