Editing Venus (section)

==Observation and exploration history==
{{Main|Observations and explorations of Venus}}

===Early observation===
Venus is in Earth's sky bright enough to be visible [[Naked eye|without aid]], making it one of the [[classical planets]] that human cultures have known and identified throughout history, particularly for being the third brightest object in Earth's sky after the Sun and the Moon. Because the movements of Venus appear to be discontinuous (it disappears due to its proximity to the sun, for many days at a time, and then reappears on the other horizon), some cultures did not recognize Venus as a single entity;<ref name="Cooley"/> instead, they assumed it to be two separate stars on each horizon: the morning and evening star.<ref name=Cooley/> Nonetheless, a [[cylinder seal]] from the [[Jemdet Nasr period]] and the [[Venus tablet of Ammisaduqa]] from the [[First Babylonian dynasty]] indicate that the ancient Sumerians already knew that the morning and evening stars were the same celestial object.<ref name=Sachs_1974/><ref name=Cooley/><ref name=Hobson_2009/>

[[File:Venus Tablet of Ammisaduqa.jpg|thumb|upright=0.75|Oldest known recording of Venus positions, on the [[Babylonia]]n ''[[Venus tablet of Ammisaduqa]]'' (1600 BC)]]

In the Old [[Babylonia]]n period, the planet Venus was known as Ninsi'anna, and later as Dilbat.<ref>Enn Kasak, Raul Veede. Understanding Planets in Ancient Mesopotamia. Folklore Vol. 16. Mare Kõiva & Andres Kuperjanov, Eds. ISSN 1406-0957</ref> The name "Ninsi'anna" translates to "divine lady, illumination of heaven", which refers to Venus as the brightest visible "star". Earlier spellings of the name were written with the [[cuneiform]] sign si4 (= SU, meaning "to be red"), and the original meaning may have been "divine lady of the redness of heaven", in reference to the colour of the morning and evening sky.<ref name=Heimpel_1982/>

The Chinese historically referred to the morning Venus as "the Great White" ({{transliteration|zh|Tàibái}} {{lang|zh|太白}}) or "the Opener (Starter) of Brightness" ({{transliteration|zh|Qǐmíng}} {{lang|zh|啟明}}), and the evening Venus as "the Excellent West One" ({{transliteration|zh|Chánggēng}} {{lang|zh|長庚}}).<ref name=Needham_1959/>

The ancient Greeks initially believed Venus to be two separate stars: [[Phosphorus (morning star)|Phosphorus]], the morning star, and [[Hesperus]], the evening star. [[Pliny the Elder]] credited the realization that they were a single object to [[Pythagoras]] in the sixth century BC,<ref name=Pliny_1991/> while [[Diogenes Laërtius]] argued that [[Parmenides]] (early fifth century) was probably responsible for this discovery.<ref name=Berkert_1972/> Though they recognized Venus as a single object, the ancient Romans continued to designate the morning aspect of Venus as [[Lucifer]], literally "Light-Bringer", and the evening aspect as [[Hesperus|Vesper]],<ref name=Dobbin_2002/> both of which are literal translations of their traditional Greek names.

In the second century, in his astronomical treatise ''[[Almagest]]'', [[Ptolemy]] theorized that both Mercury and Venus were located between the Sun and the Earth. The 11th-century [[Samanid Empire|Persian]] astronomer [[Avicenna]] claimed to have observed a [[transit of Venus]] (although there is some doubt about it),<ref name="Goldstein"/> which later astronomers took as confirmation of Ptolemy's theory.<ref name=Enc_Irnica/> In the 12th century, the [[Al-Andalus|Andalusian]] astronomer [[Ibn Bajjah]] observed "two planets as black spots on the face of the Sun"; these were thought to be the transits of Venus and Mercury by 13th-century [[Maragheh observatory|Maragha]] astronomer [[Qotb al-Din Shirazi]], though this cannot be true as there were no Venus transits in Ibn Bajjah's lifetime.<ref name=Ansari_2002/>{{refn|group=note
|Several claims of transit observations made by mediaeval Islamic astronomers have been shown to be sunspots.<ref name="VaqueroVázquez2009"/> Avicenna did not record the date of his observation. There was a transit of Venus within his lifetime, on 24 May 1032, although it is questionable whether it would have been visible from his location.<ref name="Kennard"/>}}

[[File:Dresden Codex p09.jpg|thumb|left|upright=0.7|The [[Pre-Columbian era|Pre-Columbian]] Mayan ''[[Dresden Codex]]'', which calculates appearances of Venus]]

===Venus and early modern astronomy===
{{multiple image
|footer=In 1610 [[Galileo Galilei]] observed with his telescope that [[Phases of Venus|Venus showed phases]], despite remaining near the Sun in Earth's sky (first image). This proved that it orbits the [[Sun]] and not Earth, as predicted by [[Copernicus]]'s [[heliocentric model]] and disproved Ptolemy's [[geocentric model]] (second image).
|width=220
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|image1 = Phases-of-Venus2.svg|
|image2 = Phases-of-Venus-Geocentric.svg|}}

When the Italian physicist [[Galileo Galilei]] first observed the planet with a telescope in the early 17th century, he found it showed [[planetary phase|phases]] like the Moon, varying from crescent to gibbous to full and vice versa. When Venus is furthest from the Sun in the sky, it shows a [[Elongation (astronomy)|half-lit phase]], and when it is closest to the Sun in the sky, it shows as a crescent or full phase. This could be possible only if Venus orbited the Sun, and this was among the first observations to clearly contradict the Ptolemaic [[geocentric model]] that the Solar System was concentric and centred on Earth.<ref name="palmieri"/><ref name="Fegley"/>

The 1631 [[transit of Venus]], while not recorded, was the first one successfully predicted, by [[Johannes Kepler]] and his calculations, which he published in 1629. The following [[1639 transit of Venus]] was accurately predicted by [[Jeremiah Horrocks]] and observed by him and his friend, [[William Crabtree]], at each of their respective homes, on 4{{spaces}}December 1639 (24 November under the [[Julian calendar]] in use at that time).<ref name="Kollerstrom"/>

[[File:Lavender - Jeremiah Horrocks (1618–1641).jpg|thumb|Twentieth century painting of [[Jeremiah Horrocks]] observing the [[1639 transit of Venus]].]]

The [[atmosphere of Venus]] was discovered in 1761 by Russian polymath [[Mikhail Lomonosov]].<ref name="Marov2004"/><ref name=Britannica/> Venus's atmosphere was observed in 1790 by German astronomer [[Johann Schröter]]. Schröter found when the planet was a thin crescent, the cusps extended through more than 180°. He correctly surmised this was due to [[scattering]] of sunlight in a dense atmosphere. Later, American astronomer [[Chester Smith Lyman]] observed a complete ring around the dark side of the planet when it was at [[inferior conjunction]], providing further evidence for an atmosphere.<ref name=Russell_1899/> The atmosphere complicated efforts to determine a rotation period for the planet, and observers such as Italian-born astronomer [[Giovanni Cassini]] and Schröter incorrectly estimated periods of about {{val|24|u=hours}} from the motions of markings on the planet's apparent surface.<ref name=Hussey_1832/>

[[File:Venus Drawing.jpg|thumb|left|upright=0.9|The "[[black drop effect]]" as recorded during the 1769 transit|alt=A hand-drawn sequence of images showing Venus passing over the edge of the Sun's disk, leaving an illusory drop of shadow behind]]

===Early 20th century advances===
Little more was discovered about Venus until the 20th century. Its almost featureless disc gave no hint what its surface might be like, and it was only with the development of [[astronomical spectroscopy|spectroscopic]] and [[ultraviolet]] observations that more of its secrets were revealed.

Spectroscopic observations in the 1900s gave the first clues about the Venusian rotation. [[Vesto Slipher]] tried to measure the [[Doppler shift]] of light from Venus, but found he could not detect any rotation. He surmised the planet must have a much longer [[rotation period]] than had previously been thought.<ref name=Slipher_1903/>

The first ultraviolet observations were carried out in the 1920s, when [[Frank E. Ross]] found that [[Ultraviolet photography|ultraviolet photographs]] revealed considerable detail that was absent in visible and [[infrared]] radiation. He suggested this was due to a dense, yellow lower atmosphere with high [[cirrus cloud]]s above it.<ref name=Ross_1928/>

It had been noted that Venus had no discernible [[oblate spheroid|oblateness]] in its disk, suggesting a slow rotation, and some astronomers concluded based on this that it was [[tidally locked]] like Mercury was believed to be at the time; but other researchers had detected a significant quantity of heat coming from the planet's nightside, suggesting a quick rotation (a high surface temperature was not suspected at the time), confusing the issue.<ref name=Martz_1934/> Later work in the 1950s showed the rotation was retrograde.

===Space age===
{{Further|List of missions to Venus}}
[[File:11214 2023 956 Fig3 HTML.webp|thumb|upright=2|Venus imaged in different wavelengths by spacecraft]]

The first [[interplanetary spaceflight]] attempt was in 1961 when the [[Uncrewed spacecraft|robotic space probe]] ''[[Venera 1]]'' of the Soviet [[Venera]] programme flew to Venus. It lost contact en route.<ref name="mitchell_1"/>

The first successful interplanetary mission, also to Venus, was ''[[Mariner 2]]'' of the United States' [[Mariner program]]me, passing on 14 December 1962 at {{convert|34833|km|mi|abbr=on}} above the surface of Venus and gathering data on the planet's atmosphere.<ref name=Mayer_et_al_1958/><ref name=NASA_1962/>

Additionally [[Radar astronomy|radar observations]] of Venus were first carried out in the 1960s, and provided the first measurements of the rotation period, which were close to the actual value.<ref name=Goldstein_Carpenter_1963/>

''[[Venera 3]]'', launched in 1966, became humanity's first probe and lander to reach and impact another celestial body other than the Moon, but could not return data as it crashed into the surface of Venus. In 1967, ''[[Venera 4]]'' was launched and successfully deployed science experiments in the Venusian atmosphere before impacting. ''Venera 4'' showed the surface temperature was hotter than ''Mariner 2'' had calculated, at almost {{cvt|500|C|||}}, determined that the atmosphere was 95% carbon dioxide ({{chem|C|O|2}}), and discovered that Venus's atmosphere was considerably denser than ''Venera 4''{{'s}} designers had anticipated.<ref name="mitchell_2"/><ref name=Harvey115>{{cite book |last=Harvey |first=Brian |date=2007 |title=Russian Planetary Exploration History, Development, Legacy and Prospects  |publisher=Springer-Praxis |pages=115–118 |isbn=9780387463438 }}</ref>

In an early example of space cooperation the data of ''Venera 4'' was joined with the 1967 ''[[Mariner 5]]'' data, analysed by a combined Soviet–American science team in a series of colloquia over the following year.<ref name=COSPAR_Group_VII_1969/>

On 15 December 1970, ''[[Venera 7]]'' became the first spacecraft to [[Landings on other planets|soft land on another planet]] and the first to transmit data from there back to Earth.<ref name=Time_1971/>

In 1974, ''[[Mariner 10]]'' swung by Venus to bend its path towards Mercury and took ultraviolet photographs of the clouds, revealing the extraordinarily high wind speeds in the Venusian atmosphere. This was the first interplanetary [[gravity assist]] ever used, a technique which would be used by later probes.

Radar observations in the 1970s revealed details of the Venusian surface for the first time. Pulses of radio waves were beamed at the planet using the {{convert|300|m|ft|sigfig=1|abbr=on}} radio telescope at [[Arecibo Observatory]], and the echoes revealed two highly reflective regions, designated the [[Alpha Regio|Alpha]] and [[Beta Regio|Beta]] regions. The observations revealed a bright region attributed to mountains, which was called [[Maxwell Montes]].<ref name=Campbell_et_al_1976/> These three features are now the only ones on Venus that do not have female names.<ref name="jpl-magellan"/>

[[File:Foto de Venera 9.png|thumb|First view and first clear 180-degree panorama of Venus's surface as well as any other planet than Earth (1975, Soviet ''[[Venera&nbsp;9]]'' lander). Black-and-white image of barren, black, slate-like rocks against a flat sky. The ground and the probe are the focus.|upright=2]]

In 1975, the Soviet ''[[Venera 9]]'' and ''[[Venera 10|10]]'' landers transmitted the first images from the surface of Venus, which were in black and white. NASA obtained additional data with the [[Pioneer Venus project]], consisting of two separate missions:<ref name=Colin_Hall_1977/> the [[Pioneer Venus Multiprobe]] and [[Pioneer Venus Orbiter]], orbiting Venus between 1978 and 1992.<ref name=Williams_2005/> In 1982 the first colour images of the surface were obtained with the Soviet ''[[Venera&nbsp;13]]'' and ''[[Venera 14|14]]'' landers. After ''[[Venera 15]]'' and ''[[Venera 16|16]]'' operated between 1983 and 1984 in orbit, conducting detailed mapping of 25% of Venus's terrain (from the north pole to 30°N latitude), the Soviet Venera programme came to a close.<ref name=Greeley_Batson_2007/>

[[File:Russian "Vega" balloon mission to Venus on display at the Udvar-Hazy museum.jpg|thumb|left|upright=0.8|[[Vega programme|Vega balloon probe]] on display at the [[Steven F. Udvar-Hazy Center|Udvar-Hazy Center]] of the [[Smithsonian Institution]]]]

In 1985 the Soviet [[Vega programme]] with its ''[[Vega 1]]'' and ''[[Vega 2]]'' missions carried the last entry probes and carried the first ever extraterrestrial [[aerobot]]s for the first time achieving atmospheric flight outside Earth by employing inflatable balloons.

Between 1990 and 1994, ''[[Magellan (spacecraft)|Magellan]]'' operated in orbit until deorbiting, mapping the surface of Venus. Furthermore, probes like ''[[Galileo (spacecraft)|Galileo]]'' (1990),<ref name="PDS Atmospheres Node 1989">{{cite web | title=Welcome to the Galileo Orbiter Archive Page | website=PDS Atmospheres Node | date=18 October 1989 | url=https://pds-atmospheres.nmsu.edu/data_and_services/atmospheres_data/Galileo/galileo_orbiter.html | access-date=11 April 2023 | archive-date=11 April 2023 | archive-url=https://web.archive.org/web/20230411212904/https://pds-atmospheres.nmsu.edu/data_and_services/atmospheres_data/Galileo/galileo_orbiter.html | url-status=live }}</ref> ''[[Cassini–Huygens]]'' (1998/1999), and ''[[MESSENGER]]'' (2006/2007) visited Venus with flybys en route to other destinations.
In April 2006, ''[[Venus Express]]'', the first dedicated Venus mission by the [[European Space Agency]] (ESA), entered orbit around Venus. ''Venus Express'' provided unprecedented observation of Venus's atmosphere. ESA concluded the ''Venus Express'' mission in December 2014 deorbiting it in January 2015.<ref name=Howell_2014/>

In 2010, the first successful interplanetary [[solar sail]] spacecraft [[IKAROS]] travelled to Venus for a flyby.

Between 2015 and 2024 Japan's ''[[Akatsuki (spacecraft)|Akatsuki]]'' probe was active in orbit around Venus and [[BepiColombo]] performed flybys in 2020/2021.

[[File:Wispr 4thflyby.gif|thumb|[[WISPR]] of the [[Parker Solar Probe]] took this visible light footage of the nightside in 2021, showing the hot faintly glowing surface, and its [[Aphrodite Terra]] as large dark patch, through the clouds, which prohibit such observations on the dayside when they are illuminated.<ref>{{cite web |last1=Hatfield |first1=Miles |title=Parker Solar Probe Captures Visible Light Images of Venus' Surface |url=https://www.nasa.gov/feature/goddard/2022/sun/parker-solar-probe-captures-its-first-images-of-venus-surface-in-visible-light-confirmed |website=NASA |access-date=29 April 2022 |date=9 February 2022 |archive-date=14 April 2022 |archive-url=https://web.archive.org/web/20220414155959/https://www.nasa.gov/feature/goddard/2022/sun/parker-solar-probe-captures-its-first-images-of-venus-surface-in-visible-light-confirmed/ |url-status=live }}</ref><ref name="Geophysical Research Letters 2022">{{cite journal | journal=Geophysical Research Letters | last1=Wood | first1=B. E. | last2=Hess | first2=P. | last3=Lustig-Yaeger | first3=J. | last4=Gallagher | first4=B. | last5=Korwan | first5=D. | last6=Rich | first6=N. | last7=Stenborg | first7=G. | last8=Thernisien | first8=A. | last9=Qadri | first9=S. N. | last10=Santiago | first10=F. | last11=Peralta | first11=J. | last12=Arney | first12=G. N. | last13=Izenberg | first13=N. R. | last14=Vourlidas | first14=A. | last15=Linton | first15=M. G. | last16=Howard | first16=R. A. | last17= Raouafi | first17=N. E. | doi=10.1029/2021GL096302 | date=9 February 2022 | title=Parker Solar Probe Imaging of the Night Side of Venus | volume=49 | issue=3| pages=e2021GL096302 | pmid=35864851 | pmc=9286398 | bibcode=2022GeoRL..4996302W }}</ref>]]

===Active and planned missions===
{{Further|List of missions to Venus#Future missions}}
[[File:VenusLanderTopo.jpg|thumb|upright=1.5|[[Global]] topographic map of Venus, with all probe landing sites marked]]

{{As of|2025}} there are no active probes at Venus, with [[Parker Solar Probe]] scheduled to return repeatedly to Venus until 2030.

Several [[List of missions to Venus|probes are under development]] as well as multiple proposed missions still in their early conceptual stages. The next Venus mission scheduled is the [[Venus Life Finder]], expected to launch not earlier than summer 2026.

Indian ISRO is working on [[Venus Orbiter Mission]], aiming to launch it in 2028. UAE mission to asteroids, [[MBR Explorer]], will perform a flyby of the planet. NASA approved two missions to the planet, [[VERITAS (spacecraft)|VERITAS]] and [[DAVINCI]], planned to be launched not earlier then 2031. ESA plans to launch [[EnVision]] also in 2031.

====Objectives====
Venus has been identified for future research as an important case for understanding:
* the origins of the solar system and Earth, and if systems and planets like ours are common or rare in the universe.
* how planetary bodies evolve from their primordial states to today's diverse objects.
* the development of conditions leading to habitable environments and life.<ref name="O'Rourke Wilson Borrelli Byrne 2023 p.">{{cite journal | last1=O'Rourke | first1=Joseph G. | last2=Wilson | first2=Colin F. | last3=Borrelli | first3=Madison E. | last4=Byrne | first4=Paul K. | last5=Dumoulin | first5=Caroline | last6=Ghail | first6=Richard | last7=Gülcher | first7=Anna J. P. | last8=Jacobson | first8=Seth A. | last9=Korablev | first9=Oleg | last10=Spohn | first10=Tilman | last11=Way | first11=M. J. | last12=Weller | first12=Matt | last13=Westall | first13=Frances | title=Venus, the Planet: Introduction to the Evolution of Earth's Sister Planet | journal=Space Science Reviews | publisher=Springer Science and Business Media LLC | volume=219 | issue=1 | year=2023 | issn=0038-6308 | doi=10.1007/s11214-023-00956-0 | page=10| bibcode=2023SSRv..219...10O | s2cid=256599851 | hdl=20.500.11850/598198 | hdl-access=free }}</ref>

=== Crewed mission concepts ===
Venus has been considered since the 1960s as a waypoint for [[crewed missions to Mars]] through [[Opposition (astronomy)|opposition]] missions instead of direct [[Conjunction (astronomy)|conjunction]] missions with Venus [[gravity assist]] [[flyby (spaceflight)|flybys]], demonstrating that they should be quicker and safer missions to [[Mars]], with better return or abort flight windows, and less or the same amount of radiation exposure from the flight as direct Mars flights.<ref name="Rao 2020">{{cite web | last=Rao | first=Rahul | title=Astronauts bound for Mars should swing by Venus first, scientists say | website=Space.com | date=7 July 2020 | url=https://www.space.com/mars-astronauts-venus-flyby-idea.html | access-date=24 April 2023 | archive-date=24 April 2023 | archive-url=https://web.archive.org/web/20230424055519/https://www.space.com/mars-astronauts-venus-flyby-idea.html | url-status=live }}</ref><ref name="Izenberg McNutt Runyon Byrne 2021 pp. 100–104">{{cite journal | last1=Izenberg | first1=Noam R. | last2=McNutt | first2=Ralph L. | last3=Runyon | first3=Kirby D. | last4=Byrne | first4=Paul K. | last5=MacDonald | first5=Alexander | title=Venus Exploration in the New Human Spaceflight Age | journal=Acta Astronautica | publisher=Elsevier BV | volume=180 | year=2021 | issn=0094-5765 | doi=10.1016/j.actaastro.2020.12.020 | pages=100–104| bibcode=2021AcAau.180..100I | s2cid=219558707 | doi-access=free }}</ref>

==== Possible atmospheric habitation ====
{{See also|Floating cities and islands in fiction#Venus|Colonization of Venus}}
[[File:NASA Cloud City on Venus.jpg|thumb|upright=1.2|Artist's rendering of a NASA [[HAVOC|High Altitude Venus Operational Concept (HAVOC)]] crewed floating outpost on Venus]]

While the surface conditions of Venus are extremely hostile, the atmospheric pressure, temperature, and solar and cosmic radiation 50&nbsp;km above the surface are similar to those at Earth's surface ("clement conditions").<ref name="f997">{{cite journal | last1=Arredondo | first1=Anicia | last2=Hodges | first2=Amorée | last3=Abrahams | first3=Jacob N. H. | last4=Bedford | first4=Candice C. | last5=Boatwright | first5=Benjamin D. | last6=Buz | first6=Jennifer | last7=Cantrall | first7=Clayton | last8=Clark | first8=Joanna | last9=Erwin | first9=Andrew | last10=Krishnamoorthy | first10=Siddharth | last11=Magaña | first11=Lizeth | last12=McCabe | first12=Ryan M. | last13=McIntosh | first13=E. Carrie | last14=Noviello | first14=Jessica L. | last15=Pellegrino | first15=Marielle | last16=Ray | first16=Christine | last17=Styczinski | first17=Marshall J. | last18=Weigel | first18=Peter | title=VALENTInE: A Concept for a New Frontiers–Class Long-duration In Situ Balloon-based Aerobot Mission to Venus | journal=The Planetary Science Journal | volume=3 | issue=7 | date=2022-07-01 | issn=2632-3338 | doi=10.3847/PSJ/ac7324 | doi-access=free | page=152| bibcode=2022PSJ.....3..152A }}</ref><ref name="Herbst Banjac Atri Nordheim 2019 p=A15"/><ref name="Patel Mason Nordheim Dartnell 2022 p=114796"/><ref name="Taylor 2020"/> Among the many engineering challenges for any human presence in the atmosphere of Venus are the corrosive amounts of [[sulfuric acid]] in the atmosphere.<ref name="Landis2003"/> [[Aerostat]]s for crewed exploration and possibly for permanent "[[Floating cities and islands in fiction#Venus|floating cities]]" in the Venusian atmosphere have been proposed as an alternative to the popular idea of living on [[planetary surface]]s such as [[Mars]].<ref name="Landis2003" /><ref name="Архив фантастики"/><ref name="Inner Solar System 2015"/><ref name="Tickle 2015"/><ref name=Warmflash_2017/>  NASA's [[High Altitude Venus Operational Concept]] was a training concept to study a crewed aerostat design.