James Gregory

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Introduction References & Edit History Quick Facts & Related Topics

Images

Gregorian telescopeJames Gregory's telescope design (1663) uses two concave mirrors—a primary parabolic-shaped mirror and a secondary elliptic-shaped mirror—to focus images in a short telescope tube. As indicated by the yellow rays in the figure: (1) light enters the open end of the telescope; (2) light rays travel to the primary mirror, where they are reflected and concentrated at the prime focus; (3) a secondary mirror slightly beyond the prime focus reflects and concentrates the rays near a small aperture in the primary mirror; and (4) the image is viewed through an eyepiece.

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Galaxy clusters like Abell 2744 can act as a natural cosmic lens, magnifying light from more distant, background objects through gravity. NASA's James Webb Space Telescope may be able to detect light from the first stars in the universe if they are gravitationally lensed by such clusters. (astronomy, space exploration, galaxies)

How Fast Is the Universe Expanding?

Planet Earth and lunar moon from space

Where Did the Moon Come From?

solar eclipse, sun, moon, astronomy, space

How Do You Tell the Difference Between Total, Annular, Solar, and Lunar Eclipses?

Arrangement of the phases of the moon in total eclipse with Blood Moon

9 Celestial Omens

bunch of numbers

Unusual Counting Systems

Discover

illustration of the walking titanosaurus, Patagotitan mayorum

Titanosaurs: 8 of the World's Biggest Dinosaurs

Easter Procession of Maria Santisima del Sacromonte in Granada, Spain. This statue is known as Virgen de los Gitanos or The Virgin of the Gypsies.

What is Holy Week?

Lusitania sinking, illustration from The War of the Nations (New York), December 31, 1919. World War I, WWI. This image is one of three on the page. (See source file for the other two.)

7 of the World’s Deadliest Shipwrecks

African Americans demonstrating for voting rights in front of the White House as police and others watch, March 12, 1965. One sign reads, "We demand the right to vote everywhere." Voting Rights Act, civil rights.

Timeline of the American Civil Rights Movement

Fish. Lionfish. Lion-fish. Turkey fish. Fire-fish. Red lionfish. Pterois volitans. Venomous fin spines. Coral reefs. Underwater. Ocean. Red lionfish swims by seaweed.

10 of the World’s Most Dangerous Fish

Rural Irish landscape, Sligo, Ireland.

Why Is Ireland Two Countries?

Illustration for Demystified "How Dangerous is Quicksand"

How Deadly Is Quicksand?

James Gregory: Facts & Related Content

Written and fact-checked by The Information Architects of Encyclopaedia Britannica

Facts

Also Known As	James Gregorie
Born	November 1638 • Scotland
Died	October 1675 (aged 36) • Edinburgh • Scotland
Subjects Of Study	area • convergence • curve • divergence • fundamental theorem of calculus • infinite series • photometry • reflection • refraction • squaring the circle • telescope • trigonometry

Photos

Gregorian telescopeJames Gregory's telescope design (1663) uses two concave mirrors—a primary parabolic-shaped mirror and a secondary elliptic-shaped mirror—to focus images in a short telescope tube. As indicated by the yellow rays in the figure: (1) light enters the open end of the telescope; (2) light rays travel to the primary mirror, where they are reflected and concentrated at the prime focus; (3) a secondary mirror slightly beyond the prime focus reflects and concentrates the rays near a small aperture in the primary mirror; and (4) the image is viewed through an eyepiece.

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How did Ptolemy explain retrograde motion?

Ptolemy

Egyptian astronomer, mathematician, and geographer

Understanding Newton's theory of universal gravitation

Isaac Newton

English physicist and mathematician

Galileo

Galileo

Italian philosopher, astronomer and mathematician

Six astronomers, after Gerard Hoet (1692)

Hipparchus

Greek astronomer

Fermat, portrait by Roland Lefèvre; in the Narbonne City Museums, France

Pierre de Fermat

French mathematician

Eudoxus of Cnidus

Greek mathematician and astronomer

Leonhard Euler

Leonhard Euler

Swiss mathematician

Ibn al-Haytham

Arab astronomer and mathematician

Regiomontanus

German mathematician

Heron of Alexandria

Greek mathematician

Minggantu

Chinese astronomer and mathematician

Abū al-Wafāʾ

Persian mathematician

Boscovich, detail of a portrait by an unknown artist; in Dubrovnik Cloister, Croatia

Ruggero Giuseppe Boscovich

Italian astronomer and mathematician

Gilles Personne de Roberval

French mathematician

Willebrord Snell

Dutch astronomer and mathematician

James Stirling

British mathematician

Colin Maclaurin, engraving by S. Freeman; in the British Museum.

Colin Maclaurin

Scottish mathematician

Playfair, John

John Playfair

Scottish geologist and mathematician

Blaise Pascal

Blaise Pascal

French philosopher and scientist

Giordano Bruno

Giordano Bruno

Italian philosopher

Quiz

Equations written on blackboard

Numbers and Mathematics

Nicolaus Copernicus. Nicolas Copernicus (1473-1543) Polish astronomer. In 1543 he published, forward proof of a Heliocentric (sun centered) universe. Coloured stipple engraving published London 1802. De revolutionibus orbium coelestium libri vi.

All About Astronomy

View of the Andromeda Galaxy (Messier 31, M31).

Astronomy and Space Quiz

Michael Faraday (L) English physicist and chemist (electromagnetism) and John Frederic Daniell (R) British chemist and meteorologist who invented the Daniell cell.

Faces of Science