ellipse

noun

el·​lipse i-ˈlips How to pronounce ellipse (audio)
e-
1
a
: oval
b
: a closed plane curve generated by a point moving in such a way that the sums of its distances from two fixed points is a constant : a plane section of a right circular cone that is a closed curve
2

Illustration of ellipse

Illustration of ellipse
  • F F' foci
  • P P' P'' any point on the curve
  • FP + PF' = FP'' + P''F' = FP' + P'F'

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The Property of an Ellipse

A closed curve consisting of points whose distances from each of two fixed points (foci) all add up to the same value is an ellipse. The midpoint between the foci is the center. One property of an ellipse is that the reflection off its boundary of a line from one focus will pass through the other. As a result, in an elliptical room, a person whispering at one focus is easily heard by someone at the other. An oval may or may not fit the definition of an ellipse.

Examples of ellipse in a Sentence

Recent Examples on the Web Right now Bennu is 89 percent as far from the sun as Earth is, but to rendezvous with Earth, the spacecraft will have to follow an ellipse that takes it 40 percent farther out—almost as far from the sun as Mars is. IEEE Spectrum, 7 May 2021 The spacecraft traced a long ellipse, reaching lunar distance but then falling back to Earth and burning up on reentry over the Pacific Ocean. IEEE Spectrum, 15 Feb. 2024 In 2010, astrophysicists including Sean Raymond at the University of Bordeaux in France simulated the evolution of planetary systems and found that when one gas giant planet punts a sibling from their home system, as sometimes happens, the expulsion stretches the survivor’s orbit into an ellipse. Charlie Wood, WIRED, 31 Dec. 2023 At around 125 miles in altitude, mission controllers would adjust the ISS’s trajectory, tweaking the rocket’s burn to reshape the station’s roughly circular orbit into an ellipse, with its closest earthward point, or perigee, perhaps 90 miles above the planet. Meghan Bartels, Scientific American, 21 Nov. 2023 Astronomers continue to take a page from Hubble’s playbook and scrutinize Andromeda, the faint ellipse in the northern sky. WIRED, 12 Nov. 2023 Comet Borisov arrived from deep space moving at 32 kilometers per second, and its orbit past the Sun looked more like a bent line than a tidy planetary ellipse. Corey S. Powell, Discover Magazine, 30 June 2020 Meanwhile, the closest point on the ellipse, the perigee, is an average distance of about 226,000 miles from Earth. Drew Dawson, Journal Sentinel, 28 Aug. 2023 The capsule’s drop area in Utah is an ellipse that measures 36 by 8.5 miles. Leonard David, Scientific American, 27 July 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'ellipse.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

Etymology

Greek elleipsis

First Known Use

circa 1753, in the meaning defined at sense 1a

Time Traveler
The first known use of ellipse was circa 1753

Dictionary Entries Near ellipse

Cite this Entry

“Ellipse.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/ellipse. Accessed 20 Apr. 2024.

Kids Definition

ellipse

noun
el·​lipse i-ˈlips How to pronounce ellipse (audio)
e-
: an oval shape that is a conic section

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