Editing Venus (section)

== Observability ==
[[File:Venus-pacific-levelled.jpg|thumb|alt=A photograph of the night sky taken from the seashore. A glimmer of sunlight is on the horizon. There are many stars visible. Venus is at the centre, much brighter than any of the stars, and its light can be seen reflected in the ocean.|Venus, pictured centre-right, is always brighter than all other planets or stars at their maximal brightness, as seen from Earth. Jupiter is visible at the top of the image.]]

To the [[naked eye]], Venus appears as a white point of light brighter than any other planet or star (apart from the Sun).<ref name=Dickinson_1998/> The planet's mean [[apparent magnitude]] is −4.14 with a standard deviation of 0.31.<ref name="Mallama_and_Hilton" /> The brightest magnitude occurs during the crescent phase about one month before or after an inferior conjunction. Venus fades to about magnitude −3 when it is backlit by the Sun, although the exact value depends on the [[Phase angle (astronomy)|phase angle]].<ref name="n850">{{cite web | title=Start watching for Venus brightest in the morning sky | website=[[Earth & Sky]] | date=15 April 2025 | url=https://earthsky.org/astronomy-essentials/venus-brightest-greatest-brilliancy-greatest-illuminated-extent-2/ | access-date=21 April 2025}}</ref> The planet is bright enough to be seen in broad daylight,<ref name=Flanders_2011/> but is more easily visible when the Sun is low on the horizon or setting. As an [[inferior planet]], it always lies within about 47° of the [[Sun]].<ref name="ephemeris"/>

Venus "overtakes" Earth every 584 days as it orbits the Sun.<ref name="fact" /> As it does so, it changes from the "Evening Star", visible after sunset, to the "Morning Star", visible before sunrise. Although Mercury, the other inferior planet, reaches a maximum elongation of only 28° and is often difficult to discern in twilight, Venus is hard to miss when it is at its brightest. Its greater maximum elongation means it is visible in dark skies long after sunset. As the brightest point-like object in the sky, Venus is a commonly misreported "[[unidentified flying object]]".<ref name=ASP_2021/>

Because Venus comes close to the earth at [[inferior conjunction]] and has an orbit inclined to the plane of the earth's orbit, it can appear more than 8° north or south of the [[ecliptic]], more than any other planet or the moon. Every eight years around March it appears this far north of the ecliptic, in [[Pisces (constellation)|Pisces]] (such as in mid-March 2025), and every eight years it appears this far south of the ecliptic in August or September in [[Virgo (constellation)|Virgo]] (as in late August 2023). Venus can thus be north of the sun and appear as a morning star and an evening star on the same day, in the northern hemisphere. The timing of these north or south excursions  gets slowly earlier in the year, and over 30 cycles (240 years) the cycle is gradually replaced by another cycle offset by three years, so the situation returns close to the original situation after 243 orbits of Earth, 395 of Venus.<ref>See [https://ssd.jpl.nasa.gov/api/horizons.api?format=text&COMMAND=299&START_TIME=%272000-1-21%2015:51:57%27&STOP_TIME=%272104-4-15%2013:23:31%27&STEP_SIZE=2798&QUANTITIES=31 this JPL Horizons ephemeris calculation].</ref>

[[Lunar occultation of Venus|Lunar occultations of Venus]], in which the moon blocks the view of Venus for observers in certain parts of the earth, occur on average about twice a year, sometimes several times in a year (though rarely).

=== Phases ===
{{Main|Phases of Venus}}
[[File:Phases Venus.jpg|thumb|The phases of Venus and evolution of its apparent diameter|alt=Diagram illustrating the phases of Venus]]

As it orbits the Sun, Venus displays [[phases of Venus|phases]] like those of the [[Moon]] in a [[optical telescope|telescopic]] view. The planet appears as a small and "full" disc when it is on the opposite side of the Sun (at superior [[conjunction (astronomy)|conjunction]]). Venus shows a larger disc and "quarter phase" at its maximum [[Elongation (astronomy)|elongation]]s from the Sun, and appears at its brightest in the night sky. The planet presents a much larger thin "crescent" in telescopic views as it passes along the near side between Earth and the Sun. Venus displays its largest size and "new phase" when it is between Earth and the Sun (at inferior conjunction). Its atmosphere is visible through telescopes by the halo of sunlight refracted around it.<ref name="ephemeris" /> The phases are clearly visible in a 4" telescope.<ref>{{Cite web |last=Lavender |first=Gemma |date=26 March 2023 |title=What equipment do you need to see and photograph the planets |url=https://www.space.com/what-equipment-do-you-need-to-see-and-photograph-the-planets |access-date=5 June 2024 |website=Space.com |language=en}}</ref> Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent.<ref name="Goines_1995" />

=== Daylight apparitions ===
[[File:Lunar Occultation of Venus (NHQ201512070001).jpg|alt=venus next to a crescent moon in the blue daytime sky|thumb|Venus is often visible to the naked eye in daytime, as seen just prior to the lunar occultation of 7 December 2015.]]
When Venus is sufficiently bright with enough angular distance from the sun, it is easily observed in a clear daytime sky with the naked eye, though most people do not know to look for it.<ref>{{Cite web |title=Viewing Venus in Broad Daylight |url=https://www.fourmilab.ch/images/venus_daytime/ |access-date=17 July 2023 |website=www.fourmilab.ch |archive-date=15 November 2021 |archive-url=https://web.archive.org/web/20211115012816/https://www.fourmilab.ch/images/venus_daytime/ |url-status=live }}</ref> Astronomer [[Edmund Halley]] calculated its maximum naked eye brightness in 1716, when many Londoners were alarmed by its appearance in the daytime. French emperor [[Napoleon Bonaparte]] once witnessed a daytime apparition of the planet while at a reception in [[Luxembourg]].<ref name="Chatfield_2015" /> Another historical daytime observation of the planet took place during the inauguration of the American president [[Abraham Lincoln]] in Washington, D.C., on 4{{spaces}}March 1865.<ref name="Gaherty_2012" />

=== Transits ===
{{Main|Transit of Venus}}
[[File:Transit of Venus viewed in Wagga Wagga (2).jpg|alt=White disk with a small black dot projected on a screen|left|thumb|upright=0.75|[[2012 transit of Venus]], projected by a [[telescope]] onto a white card]]

A [[transit (astronomy)|transit]] of Venus is the appearance of Venus in front of the Sun, during [[inferior conjunction]]. Since the orbit of Venus is slightly inclined relative to Earth's orbit, most inferior conjunctions with Earth, which occur every [[synodic period]] of 1.6 years, do not produce a transit of Venus. Consequently, Venus transits only occur when an inferior conjunction takes place during some days of June or December, when the orbits of Venus and Earth cross a straight line with the Sun.<ref name="NASA 2004">{{cite web | title=2004 and 2012 Transits of Venus | website=NASA | date=8 June 2004 | url=https://eclipse.gsfc.nasa.gov/transit/venus0412.html#:~:text=Transits%20of%20Venus%20are%20only,121.5%2C%208%20and%20105.5%20years. | access-date=2 May 2023 | archive-date=2 May 2023 | archive-url=https://web.archive.org/web/20230502134029/https://eclipse.gsfc.nasa.gov/transit/venus0412.html#:~:text=Transits%20of%20Venus%20are%20only,121.5%2C%208%20and%20105.5%20years. | url-status=live }}</ref> This results in Venus transiting above Earth in a sequence currently of {{val|8|u=years}}, {{val|105.5|u=years}}, {{val|8|u=years}} and {{val|121.5|u=years}}, forming cycles of {{val|243|u=years}}.

Historically, transits of Venus were important, because they allowed astronomers to determine the size of the [[astronomical unit]], and hence the size of the Solar System as shown by [[Jeremiah Horrocks]] in [[Transit of Venus, 1639|1639 with the first known observation]] of a Venus transit (after history's first observed planetary [[Transit of Mercury|transit in 1631, of Mercury]]).<ref name=Kollerstrom_1998/>

Only seven Venus transits have been observed so far, since their occurrences were calculated in the 1621 by [[Johannes Kepler]]. [[Captain Cook]] sailed to [[Tahiti]] in 1768 to record the third observed transit of Venus, which subsequently resulted in the exploration of the east coast of Australia.<ref name=Hornsby_1771/><ref name=Woolley_1969/>

The latest pair was [[Transit of Venus, 2004|June 8, 2004]] and [[Transit of Venus, 2012|June 5–6, 2012]]. The transit could be watched live from many online outlets or observed locally with the right equipment and conditions.<ref name=Boyle_2016/> The preceding pair of transits occurred in [[Transit of Venus, 1874|December 1874]] and [[Transit of Venus, 1882|December 1882]].

The next transit will occur in December 2117 and December 2125.<ref name=Espenak_2004/>

=== Ashen light ===
[[File:Venus-ParkerSolarProbe-July2020.jpg|thumb|[[Nightglow]] is since 2022 considered the most likely candidate for the ashen light, visible as bright line along the limb of Venus in this visible light near-infrared image.<ref name="e367">{{cite web | last=Dobbins | first=Thomas A. | title=The Parker Solar Probe Captures Surprising Images of Venus Nightside | website=Sky & Telescope | date=2022-02-22 | url=https://skyandtelescope.org/astronomy-news/the-parker-solar-probe-captures-surprising-images-of-venus-nightside/ | access-date=2025-03-14}}</ref> The surface and its features, like the visible [[Ovda Regio]] plateau of [[Aphrodite Terra]] as the dark patch, is much less discernable by the human eye, though some people reporting ashen light might be seeing the surface due to higher sensitive in the spectrum that the surface glows.<ref name="n420">{{cite web | title=Nightside observations by the Parker Solar Probe: implications for the reality of the Ashen Light – British Astronomical Association | website=British Astronomical Association – Supporting amateur astronomers since 1890 | date=2024-05-21 | url=https://britastro.org/journal_contents_ite/nightside-observations-by-the-parker-solar-probe-implications-for-the-reality-of-the-ashen-light | access-date=2025-03-14}}</ref>]]

A long-standing mystery of Venus observations is the so-called [[ashen light]]—an apparent weak illumination of its dark side, seen when the planet is in the crescent phase. The first claimed observation of ashen light was made in 1643, but the existence of the illumination has never been reliably confirmed. Observers have speculated it may result from electrical activity in the Venusian atmosphere, but it could be illusory, resulting from the physiological effect of observing a bright, crescent-shaped object.<ref name=Baum_2000/><ref name="Russell, Philips" /> The ashen light has often been sighted when Venus is in the evening sky, when the evening terminator of the planet is towards Earth.