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Milagro (experiment)

Milagro (experiment)

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Milagro, was a ground based water Čerenkov radiation telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 situated in the Jemez Mountains
Jemez Mountains
The Jemez Mountains are a volcanic group of mountains in New Mexico, United States. The highest point in the range is Chicoma Mountain at an elevation of 11,561 feet . The town of Los Alamos and Los Alamos National Laboratory adjoin the eastern side of the range while the town of Jemez Springs...

 near Los Alamos, New Mexico
Los Alamos, New Mexico
Los Alamos is a townsite and census-designated place in Los Alamos County, New Mexico, United States, built upon four mesas of the Pajarito Plateau and the adjoining White Rock Canyon. The population of the CDP was 12,019 at the 2010 Census. The townsite or "the hill" is one part of town while...

 at the Fenton Hill Observatory
Fenton Hill Observatory
Fenton Hill Observatory is an astronomical research facility operated by Los Alamos National Laboratory in the Jemez Mountains of New Mexico, about west of Los Alamos. The site is home to several astronomical experiments and observatories spanning . It is also known as Technical Area 57 and is...

 site. It was primarily designed to detect gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

s but also detected large numbers of cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...

s. It operated in the TeV
TEV may refer to:* TeV, or teraelectronvolt, a measure of energy* Total Enterprise Value, a financial measure* Total Economic Value, an economic measure* Tobacco etch virus, a plant pathogenic virus of the family Potyviridae....

 region of the spectrum at an altitude of 2530 m. Like conventional telescopes, Milagro was sensitive to light but the similarities ended there. Whereas "normal" astronomical telescopes view the universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

 in visible light, Milagro saw the universe at very high energies. The light that Milagro saw was about 1 trillion times more energetic than visible light. While these particles of light, known as photons, are the same as the photons that make up visible light, they behave quite differently, simply because they are much more energetic.

A cosmic ray or high-energy gamma ray striking an atom in the upper atmosphere generates a cascade of particles known as an air shower
Air shower (physics)
An air shower is an extensive cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray enters the atmosphere...

. This cascade of particles are traveling near the speed of light and generate Čerenkov radiation as they pass through the atmosphere and the water in the Milagro experiment. The photons of Čerenkov radiation are detected by an array of detectors or photomultiplier tubes which send a signal to a recorder. The data from the recorder can then be used to determine the energy and direction of the cosmic or gamma ray. The Milagro experiment used 700 sensitive light detectors submerged in the pond plus another 200 detectors arrayed around the pond.

The Milagro Experiment stopped taking data in April 2008 after seven years of operation. There is a proposed follow up experiment called the High Altitude Water Cherenkov Experiment HAWC to be located near the Large Millimeter Telescope
Large Millimeter Telescope
The Large Millimeter Telescope was inaugurated in Mexico on 22 November 2006. It is the world's largest and most sensitive single-aperture telescope in its frequency range, built for observing radio waves in the wave lengths from approximately 0.85 to 4 mm...

 at the Sierra Negra
Sierra Negra
Sierra Negra is an extinct volcanic companion peak of Mexico's highest mountain, the Pico de Orizaba . At up to 4,640 m above sea level it is one of Mexico's highest peaks, perhaps even the fourth highest, though it is usually listed fifth...

 volcano, Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

, which is expected to be 15 times more sensitive.
In November 2008 Milagro published the surprising result of observing cosmic ray anisotropy.

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