Caltech in the context of "George Ellery Hale"

Ultraviolet astronomy is the observation of electromagnetic radiation at ultraviolet wavelengths between approximately 10 and 320 nanometres; shorter wavelengths—higher energy photons—are studied by X-ray astronomy and gamma-ray astronomy. Ultraviolet light is not visible to the human eye. Most of the light at these wavelengths is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space.

Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was an American experimental physicist who received the Nobel Prize in Physics in 1923 "for his work on the elementary charge of electricity and on the photoelectric effect."

As Chairman of the Executive Council of Caltech (the school's governing body at the time) from 1921 to 1945, Millikan helped to turn the school into one of the leading research institutions in the United States. He also served on the board of trustees for Science Service, now known as Society for Science & the Public, from 1921 to 1953.

The BFH paper was a landmark scientific paper on the origin of the chemical elements. The paper's title is Synthesis of the Elements in Stars, but it became known as BFH from the initials of its authors: Margaret Burbidge, Geoffrey Burbidge, William A. Fowler, and Fred Hoyle. It was written from 1955 to 1956 at the University of Cambridge and Caltech and published in Reviews of Modern Physics in 1957.

The BFH paper reviewed stellar nucleosynthesis theory and supported it with astronomical and laboratory data. It identified nucleosynthesis processes that are responsible for producing the elements heavier than iron and explained their relative abundances. The paper became highly influential in both astronomy and nuclear physics.

A traveling-wave tube (TWT, pronounced "twit") or traveling-wave tube amplifier (TWTA, pronounced "tweeta") is a specialized vacuum tube that is used in electronics to amplify radio frequency (RF) signals in the microwave range. It was invented by Andrei Haeff around 1933 as a graduate student at Caltech, and its present form was invented by Rudolf Kompfner in 1942–43. The TWT belongs to a category of "linear beam" tubes, such as the klystron, in which the radio wave is amplified by absorbing power from a beam of electrons as it passes down the tube. Although there are various types of TWT, two major categories are:

• Helix TWT - in which the radio waves interact with the electron beam while traveling down a wire helix which surrounds the beam. These have wide bandwidth, but output power is limited to a few hundred watts.
• Coupled cavity TWT - in which the radio wave interacts with the beam in a series of cavity resonators through which the beam passes. These function as narrowband power amplifiers.

A major advantage of the TWT over some other microwave tubes is its ability to amplify a wide range of frequencies i.e. a large bandwidth. The bandwidth of the helix TWT can be as high as two octaves, while the cavity versions have bandwidths of 10–20%. Operating frequencies range from 300 MHz to 50 GHz. The power gain of the tube is on the order of 40 to 70 decibels, and output power ranges from a few watts to megawatts.

Robert A. Schommer (December 9, 1946 – December 12, 2001) was an American observational astronomer. He was a professor at Rutgers University and later a project scientist for the U.S. office of the Gemini Observatory Project at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. He was known for his wide range of research interests, from stellar populations to cosmology.

Schommer was born in Chicago, Illinois to Harvey and Bea Schommer. He received a B.A. in Physics from the University of Chicago in 1970 and a Ph.D. in Astronomy from the University of Washington in 1977, where he continued for one year as instructor. Following two years in seminary college in Chicago, he held postdoctoral positions at Caltech (as Chaim Weizmann Fellow), the Hale Observatories, the University of Chicago, and Cambridge University (as NATO Postdoctoral Fellow) before joining the Department of Physics at the State University of New Jersey. He became increasingly unhappy with the department's unwillingness to support astronomy, and in 1990 he moved to CTIO in Chile where he remained until his death in 2001.

The Wide Field/Planetary Camera (WFPC, pronounced as "wiffpick") was a camera installed on the Hubble Space Telescope launched in April 1990 and operated until December 1993. It was one of the instruments on Hubble at launch, but its functionality was severely impaired by the defects of the main mirror optics which afflicted the telescope. However, it produced uniquely valuable high resolution images of relatively bright astronomical objects, allowing for a number of discoveries to be made by HST even in its aberrated condition.

WFPC was proposed by James A. Westphal, a professor of planetary science at Caltech, and was designed, constructed, and managed by JPL. At the time it was proposed, 1976, CCDs had barely been used for astronomical imaging, though the first KH-11 KENNEN reconnaissance satellite equipped with CCDs for imaging was launched in December 1976. The high sensitivity offered such promise that many astronomers strongly argued that CCDs should be considered for Hubble Space Telescope instrumentation.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Prior to LIGO, all data about the universe has come in the form of light and other forms of electromagnetic radiation, from limited direct exploration on relatively nearby Solar System objects such as the Moon, Mars, Venus, Jupiter and their moons, asteroids etc, and from high energy cosmic particles. Initially, two large observatories were built in the United States with the aim of detecting gravitational waves by laser interferometry. Two additional, smaller gravitational wave observatories are now operational in Japan (KAGRA) and Italy (Virgo). The two LIGO observatories use mirrors spaced 4 km apart to measure changes in length—over an effective span of 1120 km—of less than one ten-thousandth the charge diameter of a proton.

The initial LIGO observatories were funded by the United States National Science Foundation (NSF). They were conceived, built, and are operated by Caltech and MIT. They collected data from 2002 to 2010, but no gravitational waves were detected during that period.

The Palomar Testbed Interferometer (PTI) was a near infrared, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County, California, United States. It was built by Caltech and the Jet Propulsion Laboratory and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer. It began operations in 1995 and achieved routine operations in 1998, producing more than 50 refereed papers in a variety of scientific journals covering topics from high precision astrometry to stellar masses, stellar diameters and shapes. PTI concluded operations in 2008 and has since been dismantled.

PTI was notable for being equipped with a "dual-star" system, making it possible to simultaneously observe pairs of stars; this cancels some of the atmospheric effects of astronomical seeing and makes very high precision measurements possible.