The highly anticipated transit of Venus on June 5, 2012 is the second transit since 2004, but we won't be around next time. Transits of Venus occur in pairs, and the next one won't occur until December 2117.
The transit of Venus is a rare planetary alignment during which viewers on Earth can watch as Venus passes across the sun over a 6-hour period.
Astronomers through the centuries have observed the transit of Venus for the purpose of refining the astronomical unit -- the approximate distance between the earth and the sun -- which is used to measure distances within the solar system.
Scroll Down For A Brief History Of The Transit Of Venus
By observing the differences in movement of Venus and the Sun, astronomers on Earth were able to calculate our own distance from the Sun. The search for precise measurements of the transit of Venus spurred epic expeditions in the 18th and 19th centuries, as explorers searched the globe for viewing locations.
Today, advanced radio technologies and space probe measurements have led to more accurate readings of this distance, so we don't have to look to Venus to find out.
But the transit of Venus remains important to scientists, particularly those searching for planets outside the solar system: The 2012 Venus transit will help scientists calibrate instruments that can aid in the search for solar planets outside our solar system that may have life-giving atmospheres.
The Kepler observatory, for one, scans the cosmos for these planets by looking for light fluctuations on distant stars. If a star gets dimmer at regular intervals, that may mean there's a planet orbiting it that blocks some of its light.
The June 2012 transit of Venus also marks the first time that the occurrence will be photographed from space. These photos will be transmitted to the Internet so that non-astronomers can experience a crystal-clear view of the celestial event.
According to a NASA-produced video, astronaut Don Pettit brought a solar filter and a high-end Nikon camera aboard the International Space Station for the specific purpose of taking pictures of the rare transit from the station's specially designed cupola.
If you're an amateur astronomer who plans on bringing out the telescope for some skywatching this Tuesday, send us pics of your rig and the transit! We'll be collecting user photos from all over, and yours may be featured. Upload your photos to our Facebook page, tweet them to @HuffPostScience, or email them to us at email@example.com.
LOOK: The Transit Of Venus - Past, Present And Future:
Jeremiah Horrocks - 1639
In November 1639, a young English astronomer named Jeremiah Horrocks predicted and observed the transit of Venus through a simple helioscope. He projected the image of the sun onto a piece of paper, and saw Venus as a small speck moving across the diagram for about half an hour. Based on his observations, Horrocks was able to more accurately calculate the size of Venus, and its distance from earth.
Edmund Halley - 18th Century
In the 18th century, astronomer Edmund Halley proposed that observing the transit of Venus might hold the key to determining the size of the solar system. Based on his calculations, which were refinements of earlier work by James Gregeory, global expeditions were launched to observe and accurately time the transits of 1761 and 1769. Perhaps the most celebrated voyage to observe the transit of Venus was that of James Cook, who sailed to Tahiti in order to view the transit from the southern Pacific in 1769.
19th Century Transits
Expeditions continued in the 19th century, with expeditions spanning the globe from Cairo, to New Zealand to the southern Indian Ocean. Some teams, including those sent by the United States Naval Observatory, <a href="http://www.skyandtelescope.com/observing/objects/daylightphenomena/3308756.html" target="_hplink">photographed the transits</a>. These expeditions refined the value of the astronomical unit.
Transits In The Digital Age
The first of the most recent pair of Venus transits occurred in June 2004. For the first time in history, digital imaging allowed detailed looks at the transit of Venus. Although astronauts were aboard the International Space Station in 2004, they did not have the right equipment to photograph the transit of Venus from orbit.
Photographing The 2012 Venus Transit From Space
Because the sun's light is so bright and Venus only covers a fraction of the solar disc, a special filter is required to capture images of the transit. Astronaut Don Pettit brought a solar filter and a high-end Nikon camera aboard the International Space Station for the specific purpose of taking pictures of the 2012 transit. Here, an astronaut on board the ISS peeks his head into a special observation cupola, from which Pettit will take pictures.
Planetary Transits In The Age Of Space Exploration
By the digital age, new technology, like radio telemetry and space probes, superseded the need for parallax calculations to refine the astronomical unit. But planetary transits remain relevant as <a href="http://www.space.com/15713-venus-transit-sun-alien-planets.html" target="_hplink">a way to detect planets outside our solar system</a>. The Kepler observatory, depicted here, reads the cosmos for light fluctuations that occur when faraway planets pass in front of their stars. Additionally, data from the <a href="http://www.huffingtonpost.com/2012/06/01/venus-transit-polarized-alien-exoplanet_n_1561949.html" target="_hplink">transit of Venus can be used to calibrate instruments</a> that search for other worlds.
WATCH: Astronaut Don Pettit To Photograph 2012 Venus Transit From Space: