Umbra, penumbra and antumbra: Difference between revisions
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{{Short description|Distinct parts of a shadow}} | {{Short description|Distinct parts of a shadow}} | ||
{{refimprove|date=December 2012}} | {{refimprove|date=December 2012}} | ||
[[File:Diagram of umbra, penumbra & antumbra.png|thumb|275px|right|Umbra, penumbra and antumbra of Earth and images that could be seen at some points in these areas (Note: the relative size and distance of the bodies shown are not to scale.) | [[File:Diagram of umbra, penumbra & antumbra.png|thumb|275px|right|Umbra, penumbra and antumbra of Earth and images that could be seen at some points in these areas (Note: the relative size and distance of the bodies shown are not to scale.)]] | ||
[[File:Kernschatten und Halbschatten.svg|thumb|Umbra (A) and penumbra (B)]] | [[File:Kernschatten und Halbschatten.svg|thumb|Umbra (A) and penumbra (B)]] | ||
The '''umbra''', '''penumbra''' and '''antumbra''' are three distinct parts of a [[shadow]], created by any light source after impinging on an [[Opacity (optics)|opaque]] object of lesser size. In cases of equal or smaller impinging objects, only an umbra and penumbra are generated. Assuming no [[diffraction]], for a [[collimated beam]] (such as a point source) of light, only the umbra is cast. | |||
These phenomena are generally observed within solar systems, as the size of the stars within the system are larger than the orbiting satellites, hence these terms are most often used for the shadows cast by [[celestial body|celestial bodies]], though they are sometimes used to describe levels of darkness, such as in [[sunspots]]. | |||
==Umbra== | ==Umbra== | ||
{{Redirect|Umbra}} | {{Redirect|Umbra}} | ||
[[File:Antumbra.jpg|thumb|200px|right|Umbra, penumbra | [[File:Antumbra.jpg|thumb|200px|right|Umbra, penumbra and antumbra formed through windows and shutters]] | ||
The '''umbra''' ({{langnf|la||shadow}}) is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body. An observer within the umbra experiences a total [[occultation]]. The umbra of a round body occluding a round light source forms a [[cone|right circular cone]]. When viewed from the cone's [[apex (geometry)|apex]], the two bodies [[angular diameter|appear the same size]]. | The '''umbra''' ({{langnf|la||shadow}}) is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body.<ref>{{cite web |url=https://www.merriam-webster.com/dictionary/umbra |title=umbra |website=Merriam-Webster |access-date=August 4, 2025 |archive-url=https://web.archive.org/web/20250608074031/https://www.merriam-webster.com/dictionary/umbra |archive-date=June 8, 2025 |url-status=live}}</ref> An observer within the umbra experiences a total [[occultation]]. The umbra of a round body occluding a round light source forms a [[cone|right circular cone]]. When viewed from the cone's [[apex (geometry)|apex]], the two bodies [[angular diameter|appear the same size]]. | ||
The [[lunar distance (astronomy)|distance]] from the [[Moon]] to the apex of its umbra is roughly equal to that between the Moon and [[Earth]]: {{cvt|384402|km|mi}}. Since [[Earth's diameter]] is 3.7 times the Moon's, its umbra extends correspondingly farther: roughly {{convert|1.4|e6km|mi|abbr=unit}}.<ref>{{cite web |url=http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit2/eclipses.html |title=Lecture 9: Eclipses of the Sun & Moon |work=Astronomy 161: An Introduction to Solar System Astronomy |first=Richard |last=Pogge |publisher=[[Ohio State University]] |access-date=July 16, 2015}}</ref> | The [[lunar distance (astronomy)|distance]] from the [[Moon]] to the apex of its umbra is roughly equal to that between the Moon and [[Earth]]: {{cvt|384402|km|mi}}. Since [[Earth's diameter]] is 3.7 times the Moon's, its umbra extends correspondingly farther: roughly {{convert|1.4|e6km|mi|abbr=unit}}.<ref>{{cite web |url=http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit2/eclipses.html |title=Lecture 9: Eclipses of the Sun & Moon |work=Astronomy 161: An Introduction to Solar System Astronomy |first=Richard |last=Pogge |publisher=[[Ohio State University]] |access-date=July 16, 2015}}</ref> | ||
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{{redirect|Penumbra}} | {{redirect|Penumbra}} | ||
The '''penumbra''' ({{etymology|la|{{wikt-lang|la|paene}}|almost, nearly||{{wikt-lang|la|umbra}}|shadow}}) is the region in which only a portion of the light source is obscured by the occluding body | The '''penumbra''' ({{etymology|la|{{wikt-lang|la|paene}}|almost, nearly||{{wikt-lang|la|umbra}}|shadow}}) is the region in which only a portion of the light source is obscured by the occluding body, and an observer in the penumbra experiences a [[partial eclipse]]. | ||
An alternative definition is that the penumbra is the region where ''some or all'' of the light source is obscured (i.e., the umbra is a subset of the penumbra). For example, [[NASA]]'s [[Navigation and Ancillary Information Facility]] defines that a body in the umbra is also within the penumbra.<ref>[http://naif.jpl.nasa.gov/pub/naif/misc/toolkit_docs_N0061/Tutorials/pdf/individual_docs/45_event_finding_preview.pdf ''Event Finding Subsystem Preview''] Navigation and Ancillary Information Facility.</ref> | An alternative definition is that the penumbra is the region where ''some or all'' of the light source is obscured (i.e., the umbra is a subset of the penumbra). For example, [[NASA]]'s [[Navigation and Ancillary Information Facility]] defines that a body in the umbra is also within the penumbra.<ref>[http://naif.jpl.nasa.gov/pub/naif/misc/toolkit_docs_N0061/Tutorials/pdf/individual_docs/45_event_finding_preview.pdf ''Event Finding Subsystem Preview''] Navigation and Ancillary Information Facility.</ref> | ||
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== See also == | == See also == | ||
* [[Antisolar point]] | * [[Antisolar point]] | ||
* [[Earth's shadow]] | * [[Earth's shadow]] | ||
* [[Umbrella]] | |||
==References== | ==References== | ||
Latest revision as of 22:14, 16 October 2025
Template:Short description Template:Refimprove
The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object of lesser size. In cases of equal or smaller impinging objects, only an umbra and penumbra are generated. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast.
These phenomena are generally observed within solar systems, as the size of the stars within the system are larger than the orbiting satellites, hence these terms are most often used for the shadows cast by celestial bodies, though they are sometimes used to describe levels of darkness, such as in sunspots.
Umbra
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The umbra (Template:Langnf) is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body.[1] An observer within the umbra experiences a total occultation. The umbra of a round body occluding a round light source forms a right circular cone. When viewed from the cone's apex, the two bodies appear the same size.
The distance from the Moon to the apex of its umbra is roughly equal to that between the Moon and Earth: Template:Cvt. Since Earth's diameter is 3.7 times the Moon's, its umbra extends correspondingly farther: roughly Template:Convert.[2]
Penumbra
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The penumbra (Template:Etymology) is the region in which only a portion of the light source is obscured by the occluding body, and an observer in the penumbra experiences a partial eclipse.
An alternative definition is that the penumbra is the region where some or all of the light source is obscured (i.e., the umbra is a subset of the penumbra). For example, NASA's Navigation and Ancillary Information Facility defines that a body in the umbra is also within the penumbra.[3]
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Antumbra
The antumbra (Template:Etymology) is the region from which the occluding body appears entirely within the disc of the light source. An observer in this region experiences an annular eclipse, in which a bright ring is visible around the eclipsing body. If the observer moves closer to the light source, the apparent size of the occluding body increases until it causes a full umbra.[4]
See also
References
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- ↑ Script error: No such module "citation/CS1".
- ↑ Event Finding Subsystem Preview Navigation and Ancillary Information Facility.
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