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Venus Through the Telescope

The Venus Evening Apparition of 2011-2012

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Star map showing the path of Venus through the zodiac during the 2012-13 morning apparition (Copyright Martin J Powell, 2012)

The path of Venus through the zodiac constellations during the planet's morning apparition in 2012-13 (move your cursor over the image - or click on the image - to reveal the constellation names in their abbreviated three-letter form - the full names are listed here). Zodiac constellations are labelled in green and non-zodiac constellations in grey. The numbers along the sides of the chart (Right Ascension and Declination) are co-ordinates of celestial longitude and latitude which astronomers use to locate the position of a celestial body in the night sky. A print-friendly version is available here.

The Venus Morning Apparition of 2012-2013

by Martin J. Powell

Having passed through inferior conjunction on June 6th 2012 (when it was positioned directly between the Earth and the Sun) and its much-publicised transit, Venus swiftly entered the dawn sky as a 'Morning Star' in mid-June. Equatorial and Southern latitudes were the first to see it, low down in the East-North-East shortly before sunrise. Northern latitudes began to detect the planet from around mid-June (at 30° North), late June (50° North) and early July (60° North). The planet was moving retrograde, in a South-westerly direction, within the 'V'-shaped Hyades star cluster (central Taurus) at this time.

Venus rising at dawn behind a city centre tower block (Copyright Martin J Powell, 2011)

Venus rising at dawn behind a city skyline (click for full-size picture) (Copyright Martin J Powell 2011)

During June the planet's solar elongation (angular distance from the Sun) increased rapidly from 10° West (on June 12th) to 20°W (on June 19th) to 31°W (by month's end). As it emerged from the dawn twilight, telescopes pointed towards the planet showed a large, slender, Eastward-facing crescent, its apparent diameter measuring 56" (56 arcseconds) and shining at an apparent magnitude of -3.9. The planet's apparent diameter continued to shrink throughout the morning apparition, as it slowly receded from the Earth in space (click here to see how Venus typically appears through a small telescope at various phases).

Venus passed 3°.5 North of Taurus' brightest star Aldebaran (Greek lower-case letter 'alpha' Tauri or Alpha Tauri, mag. +0.9) on June 15th, its daily apparent motion slowing until it reached its Western stationary point on June 27th. Thereafter, the planet resumed direct motion (West to East) passing Aldebaran once more (1° to the North of the star) on July 9th.

Whilst Venus was pulling away from the Sun, dedicated telescopic observers began their search for the elusive Ashen Light, which is a faint glowing of the night side of Venus through its thick clouds. The phenomenon is believed to be caused by the surface of the planet glowing red hot. Observers searching for the Light will normally use ultraviolet and/or infrared filters in order to help reveal it, an occulting bar often being used to block the bright, visually-intrusive crescent from view. Observers in Equatorial and Southern hemisphere latitudes were best placed to view the Light at this early stage of the 2012-13 apparition due to the higher altitude of Venus above the horizon before sunrise.

Venus attained its greatest brilliancy for this apparition (mag. -4.4) on July 10th 2012. The planet was now 25% illuminated (phase = 0.25), its apparent diameter was 38".2 and its solar elongation was 38°.

Around this time, observers at mid-Southern latitudes saw Venus attain its highest altitude in the sky before sunrise for the 2012-13 apparition. At 35° South latitude in mid-July, the planet was rising around 3 hours ahead of the Sun, reaching an altitude of around 26° high some 30 minutes before sunrise.

On August 4th, Venus entered the Northernmost section of Orion, the Hunter, occupying there for nine days before entering Gemini, the Twins, on August 13th. Observers in Equatorial latitudes now saw Venus attain its highest altitude above the local horizon for the 2012-13 apparition, the planet being some 37° high in the East-North-East at 30 minutes before sunrise. At these latitudes, the planet rose over 3 hours before sunup.

Venus reached its greatest elongation from the Sun for this apparition (45°.8 West) on August 15th 2012. Telescopes now showed Venus' disk half-illuminated (phase = 0.50 or 50%) with an apparent diameter of  23".5. Although the greatest elongation from the Sun occurred on August 15th, Venus was in fact positioned at precisely 45°.8 elongation for a whole week from August 12th through to August 19th. The planet's apparent magnitude at this time was -4.2.

In theory, greatest elongation is the time at which the planet's terminator (the line seperating the light and dark sides of the planet) appears perfectly straight through telescopes, essentially dividing Venus into two perfect halves; this is known as the dichotomy. However, telescopic observers often report the straight terminator several days earlier or later than the greatest elongation date. Interestingly, the date of dichotomy is usually reported early in evening apparitions and late in morning apparitions. The precise reason for this phenomenon - which is referred to as Schröter's Effect - is not known, however it is possibly due to the fact that the precise moment of dichotomy cannot be determined by an observer to within an accuracy any better than a few days.

Venus passed 12°.3 South of Gemini's second-brightest star Castor (Greek lower-case letter 'alpha' Gem or Alpha Geminorum, mag. +1.6) on August 30th and then 8º.7 South of its brightest star Pollux (Greek lower-case letter 'beta' Gem or Beta Geminorum, mag. +1.1) on September 1st.

From late August into early September of 2012, observers at Northern latitudes saw the planet attain its highest altitude above the horizon for the 2012-13 morning apparition. At latitude 30° North, some 30 minutes before sunrise, the planet attained a significant 37° above the Eastern horizon. At higher latitudes the altitude attained was progressively less. From latitude 50° North, in early September 2012, the planet was placed 33° above the Eastern horizon at 30 minutes before sunrise. From latitude 60° North, in late August 2012, the planet was placed 31° above the East-South-Eastern horizon at 30 minutes before sunrise. Nearly coinciding with the date of greatest elongation, Northern latitudes now saw Venus rising 3½ hours before the Sun (at 30° North), 4 hours before the Sun (at 50° North) and 4½ hours before the Sun (at 60° North).

Venus entered Cancer, the Crab, on September 4th, passing 2°.3 South of the open cluster called Praesepe or The Beehive Cluster (Messier 44) from September 13th-14th (for a fuller description of this cluster, see the Zodiacal Sky: Cancer, Leo and Virgo page). Through telescopes, the planet now showed a 60% illuminated gibbous phase, the apparent diameter having reduced below 20" and shining at an apparent visual magnitude of -4.1.

The planet entered Leo, the Lion, on September 23rd, passing just 7' (7 arcminutes, or 0º.1) South of Regulus (Greek letter Alpha Leonis or Alpha Leonis, mag. +1.3) on October 3rd. With the planet now heading Southwards along the ecliptic, the position of Venus along the local horizon at dawn began to move noticeably further Southwards with each passing week.

Venus entered Virgo, the Virgin, on October 23rd. Over the next month the planet passed four bright stars and one planet, all of which lay within (or close to) the ecliptic plane (some of the more interesting bright stars in Virgo are described in the Zodiacal Sky page). Venus passed 0º.8 North of the star Zavijah or Zavijava (Greek lower-case letter 'beta' Vir or Beta Virginis, mag. +3.6) on October 26th, crossing the celestial equator (declination = 0°) a few days later on October 31st. It then passed 0º.3 North of the star Zaniah (Greek lower-case letter 'eta' Vir or Eta Virginis, mag. +3.9) on November 1st, 1º.1 South of the star Porrima (Greek lower-case letter 'gamma' Vir or Gamma Virginis, mag. +2.8) on November 6th and just 2' (2 arcminutes) North of Theta Virginis (Greek lower-case letter 'theta' Vir, mag. +4.4) on November 11th. Four days later (November 15th) Venus passed 4º.1 North of Virgo's brightest star Spica (Greek lower-case letter 'alpha' Vir or Alpha Virginis, mag. +1.0).

'Greetings of the Goddesses' sketched by Tamás Bognár (Image: Tamás Bognár/ASOD)

Venus and the crescent Moon at dawn, sketched by Tamás Bognár of Hungary in October 2009 (see the full picture and description at Astronomy Sketch of the Day)

Whilst in South-eastern Virgo, Venus encountered the planet Saturn (mag. +0.9), passing 0º.5 South of it on November 27th. Saturn was now just commencing its 2012-13 apparition on the Virgo-Libra border. This particular planetary conjunction favoured Northern hemisphere observers, the two planets being positioned 29º West of the Sun. The planetary pair rose in the East-South-East about 3 hours ahead of sunrise (at latitude 60º North), about 2½ hours before sunrise (at 50º North) and about 2 hours ahead of sunrise (at 30º North).

Venus entered Libra, the Balance, on November 28th, passing 1º.3 North of the star Zuben Elgenubi (Greek lower-case letter alpha Lib or Alpha Librae, mag. +2.8) on December 4th. Telescopically Venus now appeared 89% illuminated with an apparent size of 11".6. With the solar elongation having reduced below 30º, Venus appeared much lower in the sky than it had been a few months previous. At mid-Northern latitudes, half an hour before sunrise, the planet appeared just 15º above the horizon, less than half the altitude it had been in late August. At mid-Southern latitudes, some 30 minutes before sunrise, the planet was even lower (ca. 11º high) over the East-South-Eastern horizon. In the Northern hemisphere, the month of December saw Venus' altitude above the horizon fall off rapidly day-by-day as it headed in towards the Sun.

Venus entered Scorpius, the Scorpion, on December 18th and four days later (December 22nd) it entered the non-zodiac constellation of Ophiuchus, the Serpent-Bearer. On December 23rd the planet passed 5º.7 North of the orange-red star Antares (Greek lower-case letter alpha Sco or Alpha Scorpii, mag. +1.0v), the Scorpion's brightest star which is named after its visual similarity to the planet Mars.

Venus passed 6º.4 South of  Ophiuchus' second-brightest star Sabik (Greek lower-case letter eta Oph or Eta Ophiuchi, mag. +2.4) on December 31st and entered Sagittarius, the Archer, on January 6th 2013. With the arrival of the new year, observers at high-Northern latitudes began to have difficulty detecting Venus, which was now rising in twilight just 1½ hours ahead of sunrise, the planet's solar elongation having reduced to 20°. Whilst in Sagittarius - the most Southerly constellation of the zodiac - Venus attained its most Southerly declination for this apparition (-23°.16) on January 12th. Across the world, the planet now rose at its most Southerly point along the local horizon.

Observers at mid-Northern latitudes began to have difficulty detecting the planet from around mid-January 2013. From 50° North latitude, Venus was now rising in the South-east just 1 hour ahead of the Sun, barely reaching an altitude of 5° above the horizon before disappearing into the brightening twilight. In the Southern hemisphere, the planet's altitude above the horizon at any given duration before sunrise began to fall away quickly during January.

Now starting to ascend the ecliptic once more, Venus entered Capricornus, the Sea Goat, on February 1st. Observers at Northern Tropical latitudes saw Venus rising just 40 minutes before sunrise, the planet appearing lower above the East-South-Eastern horizon with each passing day. By mid-February Equatorial and Southern latitudes saw Venus rising in the East some 50 minutes ahead of the Sun, the planet rapidly losing altitude above the horizon as its solar elongation fell below 10°. The planet ended the 2012-13 apparition shining at nearly the same apparent magnitude (-3.8) as when it had entered the morning sky in the previous June, the telescopic view now showing a 98% illuminated disk measuring just 10" across.

Venus became lost from view in the dawn twilight as it approached the boundary with Aquarius, the Water-Bearer, which it entered on February 23rd. The planet reached superior conjunction (passing behind the Sun as seen from the Earth) in the constellation of Pisces, the Fishes, on March 28th 2013.

Having passed from the morning to the evening sky, Venus remained out of view - lost in the solar glare - for over a month, as it made its slow passage on the far side of its orbit from the Earth. The planet became visible once again from around early May 2013, when it was seen shortly after sunset as an 'Evening Star' in the Western sky, heralding a new evening apparition (2013-14) which lasted through to January 2014.

 [Terms in yellow italics are explained in greater detail in an associated article describing planetary movements in the night sky.]

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Naked-eye Venus: Apparitions, Conjunctions and Elongations

The Naked-eye appearance of Venus

Naked Eye Planet Index

Planetary Movements through the Zodiac

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Copyright  Martin J Powell  June 2012


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