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](#References) * [ 6 External links ](#External_links) Toggle the table of contents # Angular diameter 44 languages * [Afrikaans](https://af.wikipedia.org/wiki/Skynbare_grootte "Skynbare grootte – Afrikaans") * [العربية](https://ar.wikipedia.org/wiki/%D9%82%D8%B7%D8%B1_%D8%B2%D8%A7%D9%88%D9%8A "قطر زاوي – Arabic") * [Asturianu](https://ast.wikipedia.org/wiki/Di%C3%A1metru_angular "Diámetru angular – Asturian") * [Català](https://ca.wikipedia.org/wiki/Di%C3%A0metre_angular "Diàmetre angular – Catalan") * [Čeština](https://cs.wikipedia.org/wiki/%C3%9Ahlov%C3%A1_velikost "Úhlová velikost – Czech") * [Dansk](https://da.wikipedia.org/wiki/Vinkeldiameter "Vinkeldiameter – Danish") * [Deutsch](https://de.wikipedia.org/wiki/Scheinbare_Gr%C3%B6%C3%9Fe "Scheinbare Größe – German") * [Ελληνικά](https://el.wikipedia.org/wiki/%CE%A6%CE%B1%CE%B9%CE%BD%CF%8C%CE%BC%CE%B5%CE%BD%CE%B7_%CE%B4%CE%B9%CE%AC%CE%BC%CE%B5%CF%84%CF%81%CE%BF%CF%82 "Φαινόμενη διάμετρος – Greek") * [Español](https://es.wikipedia.org/wiki/Di%C3%A1metro_angular "Diámetro angular – Spanish") * [Esperanto](https://eo.wikipedia.org/wiki/Angula_diametro "Angula diametro – Esperanto") * [Euskara](https://eu.wikipedia.org/wiki/Diametro_angeluar "Diametro angeluar – Basque") * [فارسی](https://fa.wikipedia.org/wiki/%D9%82%D8%B7%D8%B1_%D8%B2%D8%A7%D9%88%DB%8C%D9%87%E2%80%8C%D8%A7%DB%8C "قطر زاویه‌ای – Persian") * [Français](https://fr.wikipedia.org/wiki/Taille_apparente "Taille apparente – French") * [한국어](https://ko.wikipedia.org/wiki/%EC%8B%9C%EC%A7%81%EA%B2%BD "시직경 – Korean") * [Հայերեն](https://hy.wikipedia.org/wiki/%D4%B1%D5%B6%D5%AF%D5%B5%D5%B8%D6%82%D5%B6%D5%A1%D5%B5%D5%AB%D5%B6_%D5%B9%D5%A1%D6%83%D5%BD "Անկյունային չափս – Armenian") * [हिन्दी](https://hi.wikipedia.org/wiki/%E0%A4%95%E0%A5%8B%E0%A4%A3%E0%A5%80%E0%A4%AF_%E0%A4%B5%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%B8 "कोणीय व्यास – Hindi") * [Hrvatski](https://hr.wikipedia.org/wiki/Kutni_promjer "Kutni promjer – Croatian") * [Bahasa Indonesia](https://id.wikipedia.org/wiki/Diameter_sudut "Diameter sudut – Indonesian") * [Italiano](https://it.wikipedia.org/wiki/Diametro_angolare "Diametro angolare – Italian") * [עברית](https://he.wikipedia.org/wiki/%D7%A7%D7%95%D7%98%D7%A8_%D7%96%D7%95%D7%95%D7%99%D7%AA%D7%99 "קוטר זוויתי – Hebrew") * [Lëtzebuergesch](https://lb.wikipedia.org/wiki/W%C3%A9nkelduerchmiesser "Wénkelduerchmiesser – Luxembourgish") * [Magyar](https://hu.wikipedia.org/wiki/Sz%C3%B6g%C3%A1tm%C3%A9r%C5%91 "Szögátmérő – Hungarian") * [Македонски](https://mk.wikipedia.org/wiki/%D0%90%D0%B3%D0%BE%D0%BB%D0%BD%D0%B0_%D0%B3%D0%BE%D0%BB%D0%B5%D0%BC%D0%B8%D0%BD%D0%B0 "Аголна големина – Macedonian") * [Bahasa Melayu](https://ms.wikipedia.org/wiki/Diameter_sudut "Diameter sudut – Malay") * [日本語](https://ja.wikipedia.org/wiki/%E8%A7%92%E7%9B%B4%E5%BE%84 "角直径 – Japanese") * [Norsk bokmål](https://no.wikipedia.org/wiki/Vinkeldiameter "Vinkeldiameter – Norwegian Bokmål") * [Polski](https://pl.wikipedia.org/wiki/Rozmiar_k%C4%85towy "Rozmiar kątowy – Polish") * [Português](https://pt.wikipedia.org/wiki/Di%C3%A2metro_angular "Diâmetro angular – Portuguese") * [Română](https://ro.wikipedia.org/wiki/Diametru_unghiular "Diametru unghiular – Romanian") * [Русский](https://ru.wikipedia.org/wiki/%D0%A3%D0%B3%D0%BB%D0%BE%D0%B2%D0%BE%D0%B9_%D1%80%D0%B0%D0%B7%D0%BC%D0%B5%D1%80 "Угловой размер – Russian") * [Simple English](https://simple.wikipedia.org/wiki/Angular_size "Angular size – Simple English") * [Slovenščina](https://sl.wikipedia.org/wiki/Kotna_velikost "Kotna velikost – Slovenian") * [کوردی](https://ckb.wikipedia.org/wiki/%D8%AA%DB%8C%D8%B1%DB%95%DB%8C_%DA%AF%DB%86%D8%B4%DB%95%DB%8C%DB%8C "تیرەی گۆشەیی – Central Kurdish") * [Srpskohrvatski / српскохрватски](https://sh.wikipedia.org/wiki/Kutni_promjer "Kutni promjer – Serbo-Croatian") * [Suomi](https://fi.wikipedia.org/wiki/Kulmal%C3%A4pimitta "Kulmaläpimitta – Finnish") * [Svenska](https://sv.wikipedia.org/wiki/Vinkeldiameter "Vinkeldiameter – Swedish") * [Taqbaylit](https://kab.wikipedia.org/wiki/Akdu_u%C9%A3mir "Akdu uɣmir – Kabyle") * [ไทย](https://th.wikipedia.org/wiki/%E0%B8%82%E0%B8%99%E0%B8%B2%E0%B8%94%E0%B9%80%E0%B8%8A%E0%B8%B4%E0%B8%87%E0%B8%A1%E0%B8%B8%E0%B8%A1 "ขนาดเชิงมุม – Thai") * [Türkçe](https://tr.wikipedia.org/wiki/A%C3%A7%C4%B1sal_%C3%A7ap "Açısal çap – Turkish") * [Українська](https://uk.wikipedia.org/wiki/%D0%9A%D1%83%D1%82%D0%BE%D0%B2%D0%B8%D0%B9_%D1%80%D0%BE%D0%B7%D0%BC%D1%96%D1%80 "Кутовий розмір – Ukrainian") * [Tiếng Việt](https://vi.wikipedia.org/wiki/%C4%90%C6%B0%E1%BB%9Dng_k%C3%ADnh_g%C3%B3c "Đường kính góc – Vietnamese") * [吴语](https://wuu.wikipedia.org/wiki/%E8%A7%92%E7%9B%B4%E5%BE%91 "角直徑 – Wu") * [粵語](https://zh-yue.wikipedia.org/wiki/%E8%A7%92%E7%9B%B4%E5%BE%91 "角直徑 – Cantonese") * [中文](https://zh.wikipedia.org/wiki/%E8%A7%92%E7%9B%B4%E5%BE%91 "角直徑 – Chinese") [Edit 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"Edit interlanguage links") Print/export * [Download as PDF](/w/index.php?title=Special:DownloadAsPdf&page=Angular_diameter&action=show-download-screen "Download this page as a PDF file") * [Printable version](/w/index.php?title=Angular_diameter&printable=yes "Printable version of this page \[alt-shift-p\]") In other projects * [Wikidata item](https://www.wikidata.org/wiki/Special:EntityPage/Q718647 "Structured data on this page hosted by Wikidata \[alt-shift-g\]") Appearance move to sidebar hide From Wikipedia, the free encyclopedia How large a sphere or circle appears [![](//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png)](/wiki/File:Question_book-new.svg)| This article **needs additional citations for[verification](/wiki/Wikipedia:Verifiability "Wikipedia:Verifiability")**. Please help [improve this article](/wiki/Special:EditPage/Angular_diameter "Special:EditPage/Angular diameter") by [adding citations to reliable sources](/wiki/Help:Referencing_for_beginners "Help:Referencing for beginners"). Unsourced material may be challenged and removed._Find sources:_ ["Angular diameter"](https://www.google.com/search?as_eq=wikipedia&q=%22Angular+diameter%22) – [news](https://www.google.com/search?tbm=nws&q=%22Angular+diameter%22+-wikipedia&tbs=ar:1) **·** [newspapers](https://www.google.com/search?&q=%22Angular+diameter%22&tbs=bkt:s&tbm=bks) **·** [books](https://www.google.com/search?tbs=bks:1&q=%22Angular+diameter%22+-wikipedia) **·** [scholar](https://scholar.google.com/scholar?q=%22Angular+diameter%22) **·** [JSTOR](https://www.jstor.org/action/doBasicSearch?Query=%22Angular+diameter%22&acc=on&wc=on) _( September 2009)__([Learn how and when to remove this message](/wiki/Help:Maintenance_template_removal "Help:Maintenance template removal"))_ ---|--- [![](//upload.wikimedia.org/wikipedia/commons/thumb/e/ed/Angular_diameter.jpg/300px-Angular_diameter.jpg)](/wiki/File:Angular_diameter.jpg)Angular diameter: the angle subtended by an object The **angular diameter** , **angular size** , **apparent diameter** , or **apparent size** is an [angular distance](/wiki/Angular_distance "Angular distance") describing how large a [sphere](/wiki/Sphere "Sphere") or [circle](/wiki/Circle "Circle") appears from a given point of view. In the [vision sciences](/wiki/Vision_sciences "Vision sciences"), it is called the [visual angle](/wiki/Visual_angle "Visual angle"), and in [optics](/wiki/Optics "Optics"), it is the [angular aperture](/wiki/Angular_aperture "Angular aperture") (of a [lens](/wiki/Lens_\(optics\) "Lens \(optics\)")). The angular diameter can alternatively be thought of as the [angular displacement](/wiki/Angular_displacement "Angular displacement") through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side. Humans can [resolve](/wiki/Angular_resolution "Angular resolution") with their [naked eyes](/wiki/Naked_eye "Naked eye") diameters down to about 1 [arcminute](/wiki/Arcminute "Arcminute") (approximately 0.017° or 0.0003 radians).[[1]](#cite_note-Yanoff2009-1) This corresponds to 0.3 m at a 1 km distance, or to perceiving [Venus](/wiki/Venus "Venus") as a disk under optimal conditions. ## Formula [[edit](/w/index.php?title=Angular_diameter&action=edit§ion=1 "Edit section: Formula")] [![](//upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Angular_diameter_formula.svg/400px-Angular_diameter_formula.svg.png)](/wiki/File:Angular_diameter_formula.svg)Diagram for the formula of the angular diameter The angular diameter of a [circle](/wiki/Circle "Circle") whose plane is perpendicular to the displacement vector between the point of view and the center of said circle can be calculated using the formula[[2]](#cite_note-2)[[3]](#cite_note-3) δ = 2 arctan ⁡ ( d 2 D ) , {\displaystyle \delta =2\arctan \left({\frac {d}{2D}}\right),} ![{\\displaystyle \\delta =2\\arctan \\left\({\\frac {d}{2D}}\\right\),}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0b1fe8761cc49e8bae4b4825b916681d2d60d317) in which δ {\displaystyle \delta } ![{\\displaystyle \\delta }](https://wikimedia.org/api/rest_v1/media/math/render/svg/c5321cfa797202b3e1f8620663ff43c4660ea03a) is the angular diameter in _degrees_ , and d {\displaystyle d} ![{\\displaystyle d}](https://wikimedia.org/api/rest_v1/media/math/render/svg/e85ff03cbe0c7341af6b982e47e9f90d235c66ab) is the actual diameter of the object, and D {\displaystyle D} ![{\\displaystyle D}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f34a0c600395e5d4345287e21fb26efd386990e6) is the distance to the object. When D ≫ d {\displaystyle D\gg d} ![{\\displaystyle D\\gg d}](https://wikimedia.org/api/rest_v1/media/math/render/svg/c880bab4ac0296be74e58f613c3f12da63425e15), we have δ ≈ d / D {\displaystyle \delta \approx d/D} ![{\\displaystyle \\delta \\approx d/D}](https://wikimedia.org/api/rest_v1/media/math/render/svg/811098732e268b2bf5867d9fb7d95d417f66bb64),[[4]](#cite_note-4) and the result obtained is in [radians](/wiki/Radians "Radians"). For a spherical object whose _actual_ diameter equals d a c t , {\displaystyle d_{\mathrm {act} },} ![{\\displaystyle d_{\\mathrm {act} },}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f2299ee5579c51001f5083f15ae6c274b8dcfcac) and where D {\displaystyle D} ![{\\displaystyle D}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f34a0c600395e5d4345287e21fb26efd386990e6) is the distance to the _center_ of the sphere, the angular diameter can be found by the following modified formula[_[citation needed](/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")_] δ = 2 arcsin ⁡ ( d a c t 2 D ) {\displaystyle \delta =2\arcsin \left({\frac {d_{\mathrm {act} }}{2D}}\right)} ![{\\displaystyle \\delta =2\\arcsin \\left\({\\frac {d_{\\mathrm {act} }}{2D}}\\right\)}](https://wikimedia.org/api/rest_v1/media/math/render/svg/3c4ca27d1b7593a19ca7dc0075e5ecd8cc82b95c) The difference is due to the fact that the apparent edges of a sphere are its tangent points, which are closer to the observer than the center of the sphere, and have a distance between them which is smaller than the actual diameter. The above formula can be found by understanding that in the case of a spherical object, a right triangle can be constructed such that its three vertices are the observer, the center of the sphere, and one of the sphere's tangent points, with D {\displaystyle D} ![{\\displaystyle D}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f34a0c600395e5d4345287e21fb26efd386990e6) as the hypotenuse and d a c t 2 D {\displaystyle {\frac {d_{\mathrm {act} }}{2D}}} ![{\\displaystyle {\\frac {d_{\\mathrm {act} }}{2D}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a92695ab65a1a665213f9e92bd24178ade24d4a1) as the sine.[_[citation needed](/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")_] The difference is significant only for spherical objects of large angular diameter, since the following [small-angle approximations](/wiki/Small-angle_approximation "Small-angle approximation") hold for small values of x {\displaystyle x} ![{\\displaystyle x}](https://wikimedia.org/api/rest_v1/media/math/render/svg/87f9e315fd7e2ba406057a97300593c4802b53e4):[[5]](#cite_note-5) arcsin ⁡ x ≈ arctan ⁡ x ≈ x . {\displaystyle \arcsin x\approx \arctan x\approx x.} ![{\\displaystyle \\arcsin x\\approx \\arctan x\\approx x.}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0fb8d2d65ea72bdf894f70d4302d59ca849e5204) ## Estimating angular diameter using the hand [[edit](/w/index.php?title=Angular_diameter&action=edit§ion=2 "Edit section: Estimating angular diameter using the hand")] [![](//upload.wikimedia.org/wikipedia/commons/thumb/7/79/Estimating_angular_size_with_hand.gif/220px-Estimating_angular_size_with_hand.gif)](/wiki/File:Estimating_angular_size_with_hand.gif)Approximate angles of 10°, 20°, 5°, and 1° for the hand outstretched at arm's length Estimates of angular diameter may be obtained by holding the hand at right angles to a [fully extended arm](/wiki/Angular_mil#Use "Angular mil"), as shown in the figure.[[6]](#cite_note-6)[[7]](#cite_note-7)[[8]](#cite_note-8) ## Use in astronomy [[edit](/w/index.php?title=Angular_diameter&action=edit§ion=3 "Edit section: Use in astronomy")] [![](//upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Elements_of_astronomy-_accompanied_with_numerous_illustrations%2C_a_colored_representation_of_the_solar%2C_stellar%2C_and_nebular_spectra%2C_and_celestial_charts_of_the_northern_and_the_southern_hemisphere_%2814804687203%29.jpg/220px-thumbnail.jpg)](/wiki/File:Elements_of_astronomy-_accompanied_with_numerous_illustrations,_a_colored_representation_of_the_solar,_stellar,_and_nebular_spectra,_and_celestial_charts_of_the_northern_and_the_southern_hemisphere_\(14804687203\).jpg)A 19th century depiction of the apparent size of the Sun as seen from the Solar System's planets (incl. [72 Feronia](/wiki/72_Feronia "72 Feronia") and the then most outlying known asteroid, here called _Maximiliana_). In [astronomy](/wiki/Astronomy "Astronomy"), the sizes of [celestial objects](/wiki/Celestial_object "Celestial object") are often given in terms of their angular diameter as seen from [Earth](/wiki/Earth "Earth"), rather than their actual sizes. Since these angular diameters are typically small, it is common to present them in [arcseconds](/wiki/Arcsecond "Arcsecond") (″). An arcsecond is 1/3600th of one [degree](/wiki/Degree_\(angle\) "Degree \(angle\)") (1°) and a radian is 180/_π_ degrees. So one radian equals 3,600 × 180/ π {\displaystyle \pi } ![{\\displaystyle \\pi }](https://wikimedia.org/api/rest_v1/media/math/render/svg/9be4ba0bb8df3af72e90a0535fabcc17431e540a) arcseconds, which is about 206,265 arcseconds (1 rad ≈ 206,264.806247"). Therefore, the angular diameter of an object with physical diameter _d_ at a distance _D_ , expressed in arcseconds, is given by:[[9]](#cite_note-9) δ = 206 , 265 ( d / D ) a r c s e c o n d s {\displaystyle \delta =206,265~(d/D)~\mathrm {arcseconds} } ![{\\displaystyle \\delta =206,265~\(d/D\)~\\mathrm {arcseconds} }](https://wikimedia.org/api/rest_v1/media/math/render/svg/a0d1126723c5efba1603f62315aac539d135925b). These objects have an angular diameter of 1″: * an object of diameter 1 cm at a distance of 2.06 km * an object of diameter 725.27 km at a distance of 1 [astronomical unit](/wiki/Astronomical_unit "Astronomical unit") (AU) * an object of diameter 45 866 916 km at 1 [light-year](/wiki/Light-year "Light-year") * an object of diameter 1 AU (149 597 871 km) at a distance of 1 [parsec](/wiki/Parsec "Parsec") (pc) Thus, the angular diameter of [Earth's orbit](/wiki/Earth%27s_orbit "Earth's orbit") around the [Sun](/wiki/Sun "Sun") as viewed from a distance of 1 pc is 2″, as 1 AU is the mean radius of Earth's orbit. The angular diameter of the Sun, from a distance of one [light-year](/wiki/Light-year "Light-year"), is 0.03″, and that of [Earth](/wiki/Earth "Earth") 0.0003″. The angular diameter 0.03″ of the Sun given above is approximately the same as that of a human body at a distance of the diameter of Earth. This table shows the angular sizes of noteworthy [celestial bodies](/wiki/Astronomical_object "Astronomical object") as seen from Earth: Celestial object | Angular diameter or size | Relative size ---|---|--- [Magellanic Stream](/wiki/Magellanic_Stream "Magellanic Stream") | over 100° [Gum Nebula](/wiki/Gum_Nebula "Gum Nebula") | 36° [Milky Way](/wiki/Milky_Way "Milky Way") | 30° (by 360°) Width of spread out hand with arm stretched out | 20° | 353 meter at 1 km distance [Serpens-Aquila Rift](/wiki/Serpens-Aquila_Rift "Serpens-Aquila Rift") | 20° by 10° [Canis Major Overdensity](/wiki/Canis_Major_Overdensity "Canis Major Overdensity") | 12° by 12° [Smith's Cloud](/wiki/Smith%27s_Cloud "Smith's Cloud") | 11° [Large Magellanic Cloud](/wiki/Large_Magellanic_Cloud "Large Magellanic Cloud") | 10.75° by 9.17° | Note: brightest [galaxy](/wiki/Galaxy "Galaxy"), other than the Milky Way, in the [night sky](/wiki/Night_sky "Night sky") (0.9 [apparent magnitude](/wiki/Apparent_magnitude "Apparent magnitude") (V)) [Barnard's loop](/wiki/Barnard%27s_loop "Barnard's loop") | 10° [Zeta Ophiuchi](/wiki/Zeta_Ophiuchi "Zeta Ophiuchi") Sh2-27 nebula | 10° Width of fist with arm stretched out | 10° | 175 meter at 1 km distance [Sagittarius Dwarf Spheroidal Galaxy](/wiki/Sagittarius_Dwarf_Spheroidal_Galaxy "Sagittarius Dwarf Spheroidal Galaxy") | 7.5° by 3.6° [Northern Coalsack Nebula](/wiki/Northern_Coalsack_Nebula "Northern Coalsack Nebula") | 7° by 5°[[10]](#cite_note-OMeara_2019-10) [Coalsack nebula](/wiki/Coalsack_nebula "Coalsack nebula") | 7° by 5° [Cygnus OB7](/wiki/Cygnus_OB7 "Cygnus OB7") | 4° by 7°[[11]](#cite_note-Dobashi_Matsumoto_Shimoikura_Saito_2014_p=58-11) [Rho Ophiuchi cloud complex](/wiki/Rho_Ophiuchi_cloud_complex "Rho Ophiuchi cloud complex") | 4.5° by 6.5° [Hyades](/wiki/Hyades_\(star_cluster\) "Hyades \(star cluster\)") | 5°30′ | Note: brightest [star cluster](/wiki/Star_cluster "Star cluster") in the night sky, 0.5 apparent magnitude (V) [Small Magellanic Cloud](/wiki/Small_Magellanic_Cloud "Small Magellanic Cloud") | 5°20′ by 3°5′ [Andromeda Galaxy](/wiki/Andromeda_Galaxy "Andromeda Galaxy") | 3°10′ by 1° | About six times the size of the Sun or the Moon. Only the much smaller core is visible without [long-exposure photography](/wiki/Long-exposure_photography "Long-exposure photography"). [Charon](/wiki/Charon_\(moon\) "Charon \(moon\)") (from the surface of [Pluto](/wiki/Pluto "Pluto")) | 3°9’ [Veil Nebula](/wiki/Veil_Nebula "Veil Nebula") | 3° [Heart Nebula](/wiki/Heart_Nebula "Heart Nebula") | 2.5° by 2.5° [Westerhout 5](/wiki/Westerhout_5 "Westerhout 5") | 2.3° by 1.25° [Sh2-54](/wiki/Sh2-54 "Sh2-54") | 2.3° [Carina Nebula](/wiki/Carina_Nebula "Carina Nebula") | 2° by 2° | Note: brightest [nebula](/wiki/Nebula "Nebula") in the night sky, 1.0 apparent magnitude (V) [North America Nebula](/wiki/North_America_Nebula "North America Nebula") | 2° by 100′ Earth in the [Moon's sky](/wiki/Extraterrestrial_sky#The_Moon "Extraterrestrial sky") | 2° - 1°48′[[12]](#cite_note-Gorkavyi_Krotkov_Marshak_2023_pp._1527–1537-12) | Appearing about three to four times larger than the Moon in Earth's sky The [Sun](/wiki/Sun "Sun") in the sky of [Mercury](/wiki/Mercury_\(planet\) "Mercury \(planet\)") | 1.15° - 1.76° | [[13]](#cite_note-o116-13) [Orion Nebula](/wiki/Orion_Nebula "Orion Nebula") | 1°5′ by 1° Width of little finger with arm stretched out | 1° | 17.5 meter at 1 km distance The Sun in the sky of [Venus](/wiki/Venus_\(planet\) "Venus \(planet\)") | 0.7° | [[13]](#cite_note-o116-13)[[14]](#cite_note-k092-14) [Io](/wiki/Io_\(moon\) "Io \(moon\)") (as seen from the “surface” of Jupiter) | 35’ 35” [Moon](/wiki/Moon "Moon") | 34′6″ – 29′20″ | 32.5–28 times the maximum value for Venus (orange bar below) / 2046–1760″ the Moon has a diameter of 3,474 km [Sun](/wiki/Sun "Sun") | 32′32″ – 31′27″ | 31–30 times the maximum value for Venus (orange bar below) / 1952–1887″ the Sun has a diameter of 1,391,400 km [Triton](/wiki/Triton_\(moon\) "Triton \(moon\)") (from the “surface” of Neptune) | 28’ 11” Angular size of the distance between Earth and the Moon as viewed from [Mars](/wiki/Mars "Mars"), at [inferior conjunction](/wiki/Inferior_conjunction "Inferior conjunction") | about 25′ [Ariel](/wiki/Ariel_\(moon\) "Ariel \(moon\)") (from the “surface” of Uranus) | 24’ 11” [Ganymede](/wiki/Ganymede_\(moon\) "Ganymede \(moon\)") (from the “surface” of Jupiter) | 18’ 6” [Europa](/wiki/Europa_\(moon\) "Europa \(moon\)") (from the “surface” of Jupiter) | 17’ 51” [Umbriel](/wiki/Umbriel "Umbriel") (from the “surface” of Uranus) | 16’ 42” [Helix Nebula](/wiki/Helix_Nebula "Helix Nebula") | about 16′ by 28′ [Jupiter](/wiki/Jupiter "Jupiter") if it were as close to Earth as [Mars](/wiki/Mars "Mars") | 9.0′ – 1.2′ Spire in [Eagle Nebula](/wiki/Eagle_Nebula "Eagle Nebula") | 4′40″ | length is 280″ [Phobos](/wiki/Phobos_\(moon\) "Phobos \(moon\)") as seen from [Mars](/wiki/Mars "Mars") | 4.1′ [Venus](/wiki/Venus "Venus") | 1′6″ – 0′9.7″ [International Space Station](/wiki/International_Space_Station "International Space Station") (ISS) | 1′3″ | [[15]](#cite_note-Angular_size-15) the ISS has a width of about 108 m Minimum resolvable diameter by the [human eye](/wiki/Human_eye "Human eye") | 1′ | [[16]](#cite_note-Wong_2016-16) 0.3 meter at 1 km distance[[17]](#cite_note-Science_in_School_–_scienceinschool.org_2016-17) For visibility of objects with smaller apparent sizes see [the necessary apparent magnitudes](/wiki/Apparent_magnitude#List_of_apparent_magnitudes "Apparent magnitude"). About 100 km on the surface of the [Moon](/wiki/Moon "Moon") | 1′ | Comparable to the size of features like large lunar craters, such as the [Copernicus crater](/wiki/Copernicus_\(lunar_crater\) "Copernicus \(lunar crater\)"), a prominent bright spot in the eastern part of [Oceanus Procellarum](/wiki/Oceanus_Procellarum "Oceanus Procellarum") on the waning side, or the [Tycho crater](/wiki/Tycho_\(lunar_crater\) "Tycho \(lunar crater\)") within a bright area in the south, of the [lunar near side](/wiki/Near_side_of_the_Moon "Near side of the Moon"). [Jupiter](/wiki/Jupiter "Jupiter") | 50.1″ – 29.8″ Earth as seen from Mars | 48.2″[[13]](#cite_note-o116-13) – 6.6″ Minimum resolvable gap between two lines by the human eye | 40″ | a gap of 0.026 mm as viewed from 15 cm away[[16]](#cite_note-Wong_2016-16)[[17]](#cite_note-Science_in_School_–_scienceinschool.org_2016-17) [Mars](/wiki/Mars "Mars") | 25.1″ – 3.5″ Apparent size of Sun, seen from [90377 Sedna](/wiki/90377_Sedna "90377 Sedna") at aphelion | 20.4" [Saturn](/wiki/Saturn "Saturn") | 20.1″ – 14.5″ [Mercury](/wiki/Mercury_\(planet\) "Mercury \(planet\)") | 13.0″ – 4.5″ Earth's Moon as seen from Mars | 13.27″ – 1.79″ [Uranus](/wiki/Uranus "Uranus") | 4.1″ – 3.3″ [Neptune](/wiki/Neptune "Neptune") | 2.4″ – 2.2″ [Ganymede](/wiki/Ganymede_\(moon\) "Ganymede \(moon\)") | 1.8″ – 1.2″ | Ganymede has a diameter of 5,268 km An [astronaut](/wiki/Astronaut "Astronaut") (~1.7 m) at a distance of 350 km, the average altitude of the ISS | 1″ Minimum resolvable diameter by [Galileo Galilei](/wiki/Galileo_Galilei "Galileo Galilei")'s largest [38mm refracting telescopes](/wiki/Galileo%27s_objective_lens "Galileo's objective lens") | ~1″ | [[18]](#cite_note-Graney_2006-18) Note: 30x[[19]](#cite_note-Esposizioni_on-line_-_Istituto_e_Museo_di_Storia_della_Scienza-19) magnification, comparable to very strong contemporary terrestrial [binoculars](/wiki/Binoculars "Binoculars") [Ceres](/wiki/Ceres_\(dwarf_planet\) "Ceres \(dwarf planet\)") | 0.84″ – 0.33″ [Vesta](/wiki/4_Vesta "4 Vesta") | 0.64″ – 0.20″ [Pluto](/wiki/Pluto "Pluto") | 0.11″ – 0.06″ [Eris](/wiki/Eris_\(dwarf_planet\) "Eris \(dwarf planet\)") | 0.089″ – 0.034″ [R Doradus](/wiki/R_Doradus "R Doradus") | 0.062″ – 0.052″ | Note: R Doradus is thought to be the extrasolar star with the largest apparent size as viewed from Earth [Betelgeuse](/wiki/Betelgeuse "Betelgeuse") | 0.060″ – 0.049″ [Alphard](/wiki/Alphard "Alphard") | 0.00909″ [Alpha Centauri A](/wiki/Alpha_Centauri_A "Alpha Centauri A") | 0.007″ [Canopus](/wiki/Canopus "Canopus") | 0.006″ [Sirius](/wiki/Sirius "Sirius") | 0.005936″ [Altair](/wiki/Altair "Altair") | 0.003″ [Rho Cassiopeiae](/wiki/Rho_Cassiopeiae "Rho Cassiopeiae") | 0.0021″[[20]](#cite_note-20) [Deneb](/wiki/Deneb "Deneb") | 0.002″ [Proxima Centauri](/wiki/Proxima_Centauri "Proxima Centauri") | 0.001″ [Alnitak](/wiki/Alnitak "Alnitak") | 0.0005″ [Proxima Centauri b](/wiki/Proxima_Centauri_b "Proxima Centauri b") | 0.00008″ Event horizon of black hole [M87*](/wiki/M87* "M87*") at center of the M87 galaxy, imaged by the [Event Horizon Telescope](/wiki/Event_Horizon_Telescope "Event Horizon Telescope") in 2019. | 0.000025″ (2.5×10−5) | Comparable to a tennis ball on the Moon A star like [Alnitak](/wiki/Alnitak "Alnitak") at a distance where the [Hubble Space Telescope](/wiki/Hubble_Space_Telescope "Hubble Space Telescope") would just be able to see it[[21]](#cite_note-21) | 6×10−10 arcsec [![](//upload.wikimedia.org/wikipedia/commons/thumb/3/38/Diffraction_limit_diameter_vs_angular_resolution.svg/220px-Diffraction_limit_diameter_vs_angular_resolution.svg.png)](/wiki/File:Diffraction_limit_diameter_vs_angular_resolution.svg)Log-log plot of [aperture](/wiki/Aperture "Aperture") diameter vs [angular resolution](/wiki/Angular_resolution "Angular resolution") at the diffraction limit for various light wavelengths compared with various astronomical instruments. For example, the blue star shows that the [Hubble Space Telescope](/wiki/Hubble_Space_Telescope "Hubble Space Telescope") is almost diffraction-limited in the visible spectrum at 0.1 arcsecs, whereas the red circle shows that the human eye should have a resolving power of 20 arcsecs in theory, though normally only 60 arcsecs. [![](//upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Comparison_angular_diameter_solar_system.svg/300px-Comparison_angular_diameter_solar_system.svg.png)](/wiki/File:Comparison_angular_diameter_solar_system.svg)Comparison of angular diameter of the Sun, Moon and planets. To get a true representation of the sizes, view the image at a distance of 103 times the width of the "Moon: max." circle. For example, if this circle is 5 cm wide on your monitor, view it from 5.15 m away. [![](//upload.wikimedia.org/wikipedia/commons/thumb/2/20/Jupiter.mit.Io.Ganymed.Europa.Calisto.Vollmond.10.4.2017.jpg/250px-Jupiter.mit.Io.Ganymed.Europa.Calisto.Vollmond.10.4.2017.jpg)](/wiki/File:Jupiter.mit.Io.Ganymed.Europa.Calisto.Vollmond.10.4.2017.jpg)This photo compares the apparent sizes of [Jupiter](/wiki/Jupiter "Jupiter") and its four [Galilean moons](/wiki/Galilean_moons "Galilean moons") ([Callisto](/wiki/Callisto_\(moon\) "Callisto \(moon\)") at maximum [elongation](/wiki/Elongation_\(astronomy\) "Elongation \(astronomy\)")) with the apparent diameter of the [full Moon](/wiki/Full_moon "Full moon") during their [conjunction](/wiki/Conjunction_\(astronomy\) "Conjunction \(astronomy\)") on 10 April 2017. The angular diameter of the Sun, as seen from Earth, is about 250,000 times that of [Sirius](/wiki/Sirius "Sirius"). (Sirius has twice the diameter and its distance is 500,000 times as much; the Sun is 1010 times as bright, corresponding to an angular diameter ratio of 105, so Sirius is roughly 6 times as bright per unit [solid angle](/wiki/Solid_angle "Solid angle").) The angular diameter of the Sun is also about 250,000 times that of [Alpha Centauri A](/wiki/Alpha_Centauri_A "Alpha Centauri A") (it has about the same diameter and the distance is 250,000 times as much; the Sun is 4×1010 times as bright, corresponding to an angular diameter ratio of 200,000, so Alpha Centauri A is a little brighter per unit solid angle). The angular diameter of the Sun is about the same as that of the [Moon](/wiki/Moon "Moon"). (The Sun's diameter is 400 times as large and its distance also; the Sun is 200,000 to 500,000 times as bright as the full Moon (figures vary), corresponding to an angular diameter ratio of 450 to 700, so a celestial body with a diameter of 2.5–4″ and the same brightness per unit solid angle would have the same brightness as the full Moon.) Even though Pluto is physically larger than Ceres, when viewed from Earth (e.g., through the [Hubble Space Telescope](/wiki/Hubble_Space_Telescope "Hubble Space Telescope")) Ceres has a much larger apparent size. Angular sizes measured in degrees are useful for larger patches of sky. (For example, the three stars of [the Belt](/wiki/Orion%27s_Belt "Orion's Belt") cover about 4.5° of angular size.) However, much finer units are needed to measure the angular sizes of galaxies, nebulae, or other objects of the [night sky](/wiki/Night_sky "Night sky"). Degrees, therefore, are subdivided as follows: * 360 [degrees](/wiki/Degree_\(angle\) "Degree \(angle\)") (°) in a full circle * 60 [arc-minutes](/wiki/Arc-minute "Arc-minute") (′) in one degree * 60 [arc-seconds](/wiki/Arc-second "Arc-second") (″) in one arc-minute To put this in perspective, the [full Moon](/wiki/Full_moon "Full moon") as viewed from Earth is about 1⁄2°, or 30′ (or 1800″). The Moon's motion across the sky can be measured in angular size: approximately 15° every hour, or 15″ per second. A one-mile-long line painted on the face of the Moon would appear from Earth to be about 1″ in length. [![](//upload.wikimedia.org/wikipedia/commons/thumb/5/56/Moon_distance_range_to_scale.svg/800px-Moon_distance_range_to_scale.svg.png)](/wiki/File:Moon_distance_range_to_scale.svg "Minimum, mean and maximum distances of the Moon from Earth with its angular diameter as seen from Earth's surface, to scale") [ ](/wiki/File:Moon_distance_range_to_scale.svg "File:Moon distance range to scale.svg") Minimum, mean and maximum distances of the Moon from Earth with its angular diameter as seen from Earth's surface, to scale In astronomy, it is typically difficult to directly measure the distance to an object, yet the object may have a known physical size (perhaps it is similar to a closer object with known distance) and a measurable angular diameter. In that case, the angular diameter formula can be inverted to yield the [angular diameter distance](/wiki/Angular_diameter_distance "Angular diameter distance") to distant objects as d ≡ 2 D tan ⁡ ( δ 2 ) . {\displaystyle d\equiv 2D\tan \left({\frac {\delta }{2}}\right).} ![{\\displaystyle d\\equiv 2D\\tan \\left\({\\frac {\\delta }{2}}\\right\).}](https://wikimedia.org/api/rest_v1/media/math/render/svg/b653c14259ded79aa63a29fd330ab24e1dcac106) In non-Euclidean space, such as our expanding universe, the angular diameter distance is only one of several definitions of distance, so that there can be different "distances" to the same object. See [Distance measures (cosmology)](/wiki/Distance_measures_\(cosmology\) "Distance measures \(cosmology\)"). ### Non-circular objects [[edit](/w/index.php?title=Angular_diameter&action=edit§ion=4 "Edit section: Non-circular objects")] Many [deep-sky objects](/wiki/Deep-sky_object "Deep-sky object") such as [galaxies](/wiki/Galaxies "Galaxies") and [nebulae](/wiki/Nebula "Nebula") appear non-circular and are thus typically given two measures of diameter: major axis and minor axis. For example, the [Small Magellanic Cloud](/wiki/Small_Magellanic_Cloud "Small Magellanic Cloud") has a visual apparent diameter of 5° 20′ × 3° 5′. ### Defect of illumination [[edit](/w/index.php?title=Angular_diameter&action=edit§ion=5 "Edit section: Defect of illumination")] Defect of illumination is the maximum angular width of the unilluminated part of a celestial body seen by a given observer. For example, if an object is 40″ of arc across and is 75% illuminated, the defect of illumination is 10″. ## See also [[edit](/w/index.php?title=Angular_diameter&action=edit§ion=6 "Edit section: See also")] * [Angular diameter distance](/wiki/Angular_diameter_distance "Angular diameter distance") * [Angular resolution](/wiki/Angular_resolution "Angular resolution") * [Solid angle](/wiki/Solid_angle "Solid angle") * [Visual acuity](/wiki/Visual_acuity "Visual acuity") * [Visual angle](/wiki/Visual_angle "Visual angle") * [Perceived visual angle](/wiki/Perceived_visual_angle "Perceived visual angle") * [List of stars with resolved images](/wiki/List_of_stars_with_resolved_images "List of stars with resolved images") * [Apparent magnitude](/wiki/Apparent_magnitude "Apparent magnitude") ## References [[edit](/w/index.php?title=Angular_diameter&action=edit§ion=7 "Edit section: References")] 1. **[^](#cite_ref-Yanoff2009_1-0 "Jump up")** Yanoff, Myron; Duker, Jay S. (2009). [_Ophthalmology 3rd Edition_](https://books.google.com/books?id=u43MTFr7-m8C&pg=PA54). MOSBY Elsevier. p. 54. [ISBN](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [978-0444511416](/wiki/Special:BookSources/978-0444511416 "Special:BookSources/978-0444511416"). 2. **[^](#cite_ref-2 "Jump up")** This can be derived using the formula for the length of a chord found at ["Circular Segment"](http://mathworld.wolfram.com/CircularSegment.html). [Archived](https://web.archive.org/web/20141221042937/http://mathworld.wolfram.com/CircularSegment.html) from the original on 2014-12-21. Retrieved 2015-01-23. 3. **[^](#cite_ref-3 "Jump up")** ["Angular Diameter | Wolfram Formula Repository"](https://resources.wolframcloud.com/FormulaRepository/resources/Angular-Diameter). _resources.wolframcloud.com_. Retrieved 2024-04-10. 4. **[^](#cite_ref-4 "Jump up")** ["7A Notes: Angular Size/Distance and Areas"](https://w.astro.berkeley.edu/~casey_lam/7A_Angular_Distance_and_Area.pdf) (PDF). 5. **[^](#cite_ref-5 "Jump up")** ["A Taylor series for the functionarctan"](https://web.archive.org/web/20150218190328/http://www.mathstat.concordia.ca/faculty/rhall/mc/arctan.pdf) (PDF). Archived from [the original](http://www.mathstat.concordia.ca/faculty/rhall/mc/arctan.pdf) (PDF) on 2015-02-18. Retrieved 2015-01-23. 6. **[^](#cite_ref-6 "Jump up")** ["Coordinate Systems"](https://web.archive.org/web/20150121044615/https://dept.astro.lsa.umich.edu/ugactivities/Labs/coords/index.html). Archived from [the original](https://dept.astro.lsa.umich.edu/ugactivities/Labs/coords/index.html) on 2015-01-21. Retrieved 2015-01-21. 7. **[^](#cite_ref-7 "Jump up")** ["Photographing Satellites"](https://www.bartbusschots.ie/s/2013/06/08/photographing-satellites/). 8 June 2013. [Archived](https://web.archive.org/web/20150121045706/https://www.bartbusschots.ie/s/2013/06/08/photographing-satellites/) from the original on 21 January 2015. 8. **[^](#cite_ref-8 "Jump up")** [Wikiversity: Physics and Astronomy Labs/Angular size](https://en.wikiversity.org/wiki/Physics_and_Astronomy_Labs/Angular_size "v:Physics and Astronomy Labs/Angular size") 9. **[^](#cite_ref-9 "Jump up")** Michael A. Seeds; Dana E. Backman (2010). _Stars and Galaxies_ (7 ed.). Brooks Cole. p. 39. [ISBN](/wiki/ISBN_\(identifier\) "ISBN \(identifier\)") [978-0-538-73317-5](/wiki/Special:BookSources/978-0-538-73317-5 "Special:BookSources/978-0-538-73317-5"). 10. **[^](#cite_ref-OMeara_2019_10-0 "Jump up")** O'Meara, Stephen James (2019-08-06). ["The coalsacks of Cygnus"](https://astronomy.com/magazine/stephen-omeara/2019/08/the-coalsacks-of-cygnus). _Astronomy.com_. Retrieved 2023-02-10. 11. **[^](#cite_ref-Dobashi_Matsumoto_Shimoikura_Saito_2014_p=58_11-0 "Jump up")** Dobashi, Kazuhito; Matsumoto, Tomoaki; Shimoikura, Tomomi; Saito, Hiro; Akisato, Ko; Ohashi, Kenjiro; Nakagomi, Keisuke (2014-11-24). "Colliding Filaments and a Massive Dense Core in the Cygnus Ob 7 Molecular Cloud". _The Astrophysical Journal_. **797** (1). American Astronomical Society: 58. [arXiv](/wiki/ArXiv_\(identifier\) "ArXiv \(identifier\)"):[1411.0942](https://arxiv.org/abs/1411.0942). [Bibcode](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)"):[2014ApJ...797...58D](https://ui.adsabs.harvard.edu/abs/2014ApJ...797...58D). [doi](/wiki/Doi_\(identifier\) "Doi \(identifier\)"):[10.1088/0004-637x/797/1/58](https://doi.org/10.1088%2F0004-637x%2F797%2F1%2F58). [ISSN](/wiki/ISSN_\(identifier\) "ISSN \(identifier\)") [1538-4357](https://search.worldcat.org/issn/1538-4357). [S2CID](/wiki/S2CID_\(identifier\) "S2CID \(identifier\)") [118369651](https://api.semanticscholar.org/CorpusID:118369651). 12. **[^](#cite_ref-Gorkavyi_Krotkov_Marshak_2023_pp._1527–1537_12-0 "Jump up")** Gorkavyi, Nick; Krotkov, Nickolay; Marshak, Alexander (2023-03-24). ["Earth observations from the Moon's surface: dependence on lunar libration"](https://doi.org/10.5194%2Famt-16-1527-2023). _Atmospheric Measurement Techniques_. **16** (6). Copernicus GmbH: 1527–1537. [Bibcode](/wiki/Bibcode_\(identifier\) "Bibcode \(identifier\)"):[2023AMT....16.1527G](https://ui.adsabs.harvard.edu/abs/2023AMT....16.1527G). [doi](/wiki/Doi_\(identifier\) "Doi \(identifier\)"):[10.5194/amt-16-1527-2023](https://doi.org/10.5194%2Famt-16-1527-2023). [ISSN](/wiki/ISSN_\(identifier\) "ISSN \(identifier\)") [1867-8548](https://search.worldcat.org/issn/1867-8548). 13. ^ [Jump up to: _**a**_](#cite_ref-o116_13-0) [_**b**_](#cite_ref-o116_13-1) [_**c**_](#cite_ref-o116_13-2) ["The Sun and Transits as Seen From the Planets"](https://calgary.rasc.ca/sun_and_transits.htm). _RASC Calgary Centre_. 2018-11-05. Retrieved 2024-08-23. 14. **[^](#cite_ref-k092_14-0 "Jump up")** ["How large does the Sun appear from Mercury and Venus, as compared to how we see it from Earth?"](https://www.astronomy.com/observing/how-large-does-the-sun-appear-from-mercury-and-venus-as-compared-to-how-we-see-it-from-earth/). _Astronomy Magazine_. 2018-05-31. Retrieved 2024-08-23. 15. **[^](#cite_ref-Angular_size_15-0 "Jump up")** ["Problem 346: The International Space Station and a Sunspot: Exploring angular scales"](https://spacemath.gsfc.nasa.gov/weekly/7Page1.pdf) (PDF). _Space Math @ NASA !_. 2018-08-19. Retrieved 2022-05-20. 16. ^ [Jump up to: _**a**_](#cite_ref-Wong_2016_16-0) [_**b**_](#cite_ref-Wong_2016_16-1) Wong, Yan (2016-01-24). ["How small can the naked eye see?"](https://www.sciencefocus.com/the-human-body/how-small-can-the-naked-eye-see/). _BBC Science Focus Magazine_. Retrieved 2022-05-23. 17. ^ [Jump up to: _**a**_](#cite_ref-Science_in_School_–_scienceinschool.org_2016_17-0) [_**b**_](#cite_ref-Science_in_School_–_scienceinschool.org_2016_17-1) ["Sharp eyes: how well can we really see?"](https://www.scienceinschool.org/article/2016/sharp-eyes-how-well-can-we-really-see/). _Science in School – scienceinschool.org_. 2016-09-07. Retrieved 2022-05-23. 18. **[^](#cite_ref-Graney_2006_18-0 "Jump up")** Graney, Christopher M. (Dec 10, 2006). "The Accuracy of Galileo's Observations and the Early Search for Stellar Parallax". [arXiv](/wiki/ArXiv_\(identifier\) "ArXiv \(identifier\)"):[physics/0612086](https://arxiv.org/abs/physics/0612086). [doi](/wiki/Doi_\(identifier\) "Doi \(identifier\)"):[10.1007/3-540-50906-2_2](https://doi.org/10.1007%2F3-540-50906-2_2). `{{[cite journal](/wiki/Template:Cite_journal "Template:Cite journal")}}`: Cite journal requires `|journal=` ([help](/wiki/Help:CS1_errors#missing_periodical "Help:CS1 errors")) 19. **[^](#cite_ref-Esposizioni_on-line_-_Istituto_e_Museo_di_Storia_della_Scienza_19-0 "Jump up")** ["Galileo's telescope - How it works"](https://brunelleschi.imss.fi.it/esplora/cannocchiale/dswmedia/esplora/eesplora2.html). _Esposizioni on-line - Istituto e Museo di Storia della Scienza_ (in Italian). Retrieved May 21, 2022. 20. **[^](#cite_ref-20 "Jump up")** Anugu, Narsireddy; Baron, Fabien; Monnier, John D.; Gies, Douglas R.; Roettenbacher, Rachael M.; Schaefer, Gail H.; Montargès, Miguel; Kraus, Stefan; Bouquin, Jean-Baptiste Le (2024-08-05). ["CHARA Near-Infrared Imaging of the Yellow Hypergiant Star $\rho$ Cassiopeiae: Convection Cells and Circumstellar Envelope"](https://arxiv.org/abs/2408.02756v2). _arXiv.org_. Retrieved 2024-08-12. 21. **[^](#cite_ref-21 "Jump up")** 800 000 times smaller angular diameter than that of Alnitak as seen from Earth. Alnitak is a blue star so it gives off a lot of light for its size. If it were 800 000 times further away then it would be magnitude 31.5, at the limit of what Hubble can see. ## External links [[edit](/w/index.php?title=Angular_diameter&action=edit§ion=8 "Edit section: External links")] * [Small-Angle Formula](https://web.archive.org/web/19971007100829/http://ceres.hsc.edu/homepages/classes/astronomy/fall97/Mathematics/sec9.html) (archived 7 October 1997) * [Visual Aid to the Apparent Size of the Planets](http://www.astronomynotes.com/solarsys/s2.htm) [Portals](/wiki/Wikipedia:Contents/Portals "Wikipedia:Contents/Portals"): * [![icon](//upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Nuvola_apps_edu_mathematics_blue-p.svg/19px-Nuvola_apps_edu_mathematics_blue-p.svg.png)](/wiki/File:Nuvola_apps_edu_mathematics_blue-p.svg) [Mathematics](/wiki/Portal:Mathematics "Portal:Mathematics") * ![](//upload.wikimedia.org/wikipedia/commons/thumb/0/00/Crab_Nebula.jpg/19px-Crab_Nebula.jpg) [Astronomy](/wiki/Portal:Astronomy "Portal:Astronomy") * [![icon](//upload.wikimedia.org/wikipedia/commons/thumb/5/5f/He1523a.jpg/16px-He1523a.jpg)](/wiki/File:He1523a.jpg) [Stars](/wiki/Portal:Stars "Portal:Stars") * ![](//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/RocketSunIcon.svg/19px-RocketSunIcon.svg.png) [Spaceflight](/wiki/Portal:Spaceflight "Portal:Spaceflight") * ![](//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Earth-moon.jpg/21px-Earth-moon.jpg) [Outer space](/wiki/Portal:Outer_space "Portal:Outer space") * ![](//upload.wikimedia.org/wikipedia/commons/thumb/8/83/Solar_system.jpg/15px-Solar_system.jpg) [Solar System](/wiki/Portal:Solar_System "Portal:Solar System") * [![icon](//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Nuvola_apps_kalzium.svg/19px-Nuvola_apps_kalzium.svg.png)](/wiki/File:Nuvola_apps_kalzium.svg) [Science](/wiki/Portal:Science "Portal:Science") Retrieved from "[https://en.wikipedia.org/w/index.php?title=Angular_diameter&oldid=1258012787](https://en.wikipedia.org/w/index.php?title=Angular_diameter&oldid=1258012787)" [Categories](/wiki/Help:Category "Help:Category"): * [Elementary geometry](/wiki/Category:Elementary_geometry "Category:Elementary geometry") * [Astrometry](/wiki/Category:Astrometry "Category:Astrometry") * [Angle](/wiki/Category:Angle "Category:Angle") * [Equations of astronomy](/wiki/Category:Equations_of_astronomy "Category:Equations of astronomy") Hidden categories: * [CS1 errors: missing periodical](/wiki/Category:CS1_errors:_missing_periodical "Category:CS1 errors: missing periodical") * [CS1 Italian-language sources (it)](/wiki/Category:CS1_Italian-language_sources_\(it\) "Category:CS1 Italian-language sources \(it\)") * [Articles with short description](/wiki/Category:Articles_with_short_description "Category:Articles with short description") * [Short description is different from Wikidata](/wiki/Category:Short_description_is_different_from_Wikidata "Category:Short description is different from Wikidata") * [Articles needing additional references from September 2009](/wiki/Category:Articles_needing_additional_references_from_September_2009 "Category:Articles needing additional references from September 2009") * [All articles needing additional references](/wiki/Category:All_articles_needing_additional_references "Category:All articles needing additional references") * [All articles with unsourced statements](/wiki/Category:All_articles_with_unsourced_statements "Category:All articles with unsourced statements") * [Articles with unsourced statements from April 2024](/wiki/Category:Articles_with_unsourced_statements_from_April_2024 "Category:Articles with unsourced statements from April 2024") * This page was last edited on 17 November 2024, at 18:08 (UTC). * Text is available under the [Creative Commons Attribution-ShareAlike 4.0 License](/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License "Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License"); additional terms may apply. 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