On June 5, 2012, the Earth will experience an astronomical phenomenon that has long delighted astronomers and astrologers alike. On this summer day, the final transit of Venus for this century will cross our skies. This occurs when Venus passes directly between the sun and the Earth while also crossing the Earth’s orbital plane.


The transit of Venus is so rare that it's visible only once every century or so, and will next to be seen by our descendents in 2117. It is a paired event with an eight-year interlude. The first part of this current transit was on June 6, 2004, and was met by much enthusiasm from NASA and the world. The fact that its follow-up transit lands in 2012 has the world of science — and end-of-the-world theorists — riled with anticipation.


Venus is the brightest natural object in our skies after the moon. Covered in clouds of dense sulfuric acid, the planet's smaller stature means that it generally appears close to the sun, often reflecting back at us during sunrise and sunset. Despite its ubiquity, NASA calls the transit of Venus “among the rarest of planetary alignments.”


The transit occurs with a peculiar frequency. After this transit completes in 2012, another will not happen for 105.5 years. At that time, another eight years will pass for that transit pair. Then after that, it will be 121.5 years until the next transit, after which the entire cycle will repeat again. This happens because Venus passes between the sun and the Earth every 1.6 years while it is inclined to the orbit of the Earth.


This rare celestial event is returning to our skies, starting in the west on June 5, 2012, and ending in the east on June 6, 2012. According to NASA, the start of the transit will be visible at sunset from much of North and Central America and parts of northern South America. However, the sun will set before the event completes. Then, during the sunrise of June 6, watchers in Europe, parts of western and central Asia, eastern Africa and western Australia will witness the end of the event.


While the transit of Venus has occurred for centuries, the most “recent” transits have contributed much to the understanding of space. Both modern and past experts have used the transit to determine key facts about how the universe works. NASA notes that the 1663 transit brought the first speculation from mathematician Rev. James Gregory that the distance from the Earth to the sun could be calculated during the transit of Venus.


On June 5, 1761, Russian astronomer Mikhail Lomonosov observed that Venus was displaying traits that suggested it contained an atmosphere. In 1769, Capt. James Cook studied the transit from a point in Tahiti, going on to discover New Zealand and explore Australia.


Then on Dec. 6, 1882, astronomer Simon Newcomb ended what Gregory started. In 1896, Newcomb used data from this transit to determine that the distance from Earth to the sun was 92,702,000 plus or minus 53,700 miles. 


What do experts have planned for the 2012 transit? NASA and others hopes to use the information gathered to further the exploration of exoplanets. Exoplanets, or planets outside of our solar system, are often located by observing the changes in light that occur as they transit across their home stars. These slight variations can reveal important details about the exoplanets' atmosphere and surface. As Dr. Suzanne Aigrain of Oxford University explained in an interview with The Guardian, “By studying Venus as if it was an exoplanet, we will know how good are our techniques and how much they need to be refined.”


It’s not just astronomers who are eager to see what happens. Some feel that the Mayan calendar predicts the “end of days” on Dec. 21, 2012. Because Venus is central to the Mayan calendar, some theorists say that its transit in the same year is unsurprising. As one blogger writes, it is “an important divinatory alignment factored into the Maya calendar.”


On the other side, some astrologers find the coincidence not a harbinger of doom, but a declaration of universal love. One astrologer notes that the 2012 transit is when Venus will cross the face of the sun in Gemini, calling it “a powerful opportunity for a global heart-opening, and astrologically could be the biggest event of the year in terms of human experience and spiritual awakening.”


Whether it's the end of the world, a global love fest, or the heralding of a new understanding of space, June 5-6 will be an exciting time for both our planet — and for Venus.


Are you excited for the transit of Venus? Let us know your thoughts in the comments below.


Also on MNN: 9 surreal images of Venus