Editing Umbra, penumbra and antumbra

{{Short description|Distinct parts of a shadow}}
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[[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.)“… The Earth’s shadow has two distinct parts,… the UMBRA is the part of the shadow where all direct sunlight is blocked by the Earth; the PENUMBRA of the shadow is where the Earth only blocks some of the sunlight.”  ]]
[[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. Assuming no [[diffraction]], for a [[collimated beam]] (such as a point source) of light, only the umbra is cast.

These names are most often used for the shadows cast by [[celestial body|celestial bodies]], though they are sometimes used to describe levels, such as in [[sunspots]].

==Umbra==
{{Redirect|Umbra}}
[[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 [[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>

== 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. 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>

[[File:Earth umbral cone (partial).png|thumb|center|upright=3|Scale diagram of [[Earth's shadow]], showing how the umbral cone extends beyond the [[orbit of the Moon]] (The Moon is indicated by the yellow dot.)]] 
[[File:Partial Lunar Eclipse 2019-07-16.jpg|thumb|upright=3|center|Earth's umbra, as seen during a partial lunar eclipse]]
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== Antumbra ==
[[File: Transit Of Mercury, May 9th, 2016.png|thumb|[[Transit of Mercury]] in front of the Sun, an extreme version of an annular eclipse. Mercury is visible as a black dot below and to the left of the center. The dark area above the center of the solar disk is a [[sunspot]].]]

The '''antumbra''' ({{etymology|la|{{wikt-lang|la|ante}}|before||{{wikt-lang|la|umbra}}|shadow}}) 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.<ref name=TandD>{{cite web|url=https://www.timeanddate.com/eclipse/antumbra-shadow.html |title=Eclipses: What Is the Antumbra?  |work=timeanddate.com |access-date=26 May 2019 }}</ref>

== See also ==
* [[Antisolar point]]
* [[Earth's shadow]]

==References==
{{reflist}}

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[[Category:Optical phenomena]]
[[Category:Shadows]]