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VIDEO: See a vizualization of the entire event!
What Will Happen
Earth, Venus and the Sun will all be in a direct line in space. Venus will make contact with the outer portion of the Sun early in the morning in Europe (and before dawn U.S. time). It will appear as a small black spot about 1/32 the diameter of the Sun.
The black drop effect.
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Safe viewing techniques must be employed.
One of the curious aspects, called the "black drop," will occur just as Venus gets fully in front of the Sun's disk at ingress, and again just before it egresses about six hours later from the other side. Venus' black disk will appear to remain linked to the edge of the Sun for a moment, stretching into an apparent pear shape.
There are two causes for the black drop: The Sun is less bright at its visible edge, and there is a natural blurring effect in telescopes.
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| A visualization of the transit from New York; only the final moments are visible. Still / Video | The solar system from above on the day of the transit. | A world map shows who sees what during the transit. |
Where and When It's Visible
The transit will be visible in all of Europe and most of Asia and Africa. It begins shortly after 0500 Universal Time (1 a.m. EDT) and ends in midday for European locations. Times for world cities are available from NASA here. Reading the NASA timetable.
A gallery of Venus images taken prior to the transit.
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In the United States, the final moments of the event will be visible only in Eastern parts of the country just after sunrise, providing viewer's have an unobstructed view of the horizon.
In Boston, New York and Philadelphia, for example, the Sun will be more than 15 degrees above the horizon at around 7:05 a.m. ET when Venus begins its 20-minute exit from the Sun's disk. (Your fist on an outstretched arm covers about 10 degrees of sky.)
Times for U.S. cities are available from NASA here. Reading the NASA timetable.
Reading the NASA Time Table: The event is discussed in Universal Time and must be adjusted for local timekeeping. (Example: 11:05 UTC minus 4 hours equals 7:05 EDT). The times are listed in hours:minutes:seconds format (example: 11:05:54). The table shows two ingress times (when Venus touches the Sun's limb and then is fully in front of the Sun) and two egress times (when it begins and finishes leaving the disk). Alt=Altitude, in degrees above the horizon (10 degrees is about the width of your fist on an outstretched arm).
How to Watch Safely
Never look directly at the Sun with your naked eye or through a telescope or binoculars. Severe eye damage can result.
With proper viewing filters, the transit will be visible without telescopes or binoculars. Viewers should use special, approved filters that can be purchased from reputable dealers of astronomy products.
The Sun's image and the shadow of Venus can also be projected through binoculars or a telescope onto a white screen, sheet of paper or wall.
Webcasts [Tell us about other webcasts]
For many observers, the best view will come over the Internet. Several observatories plan live video streams or the posting of photos as the six-hour event unfolds. Some observatories may be clouded out, so here are more than a dozen to pick from:
Other expected webcasts, some using smaller telescopes and some planned by amateur astronomers:
The University of Central Lancashire has a list of other worldwide events associated with the transit.
Education Opportunities
The Venus transit is a great way to introduce young people to astronomy. It can be used as a launch point to teach about Venus, the Sun, and orbital mechanics.
Some institutions have put together teacher's guides for the event:
History of Transits
Summary: Venus regularly passes between Earth and the Sun, but usually it is slightly above or below our line of site. Not for 122 years has Venus transited the Sun. And because the first Venusian transit was only predicted in the 1600s, by Johannes Kepler, only five have been recorded, in 1639, 1761, 1769 and 1874 and 1882.
Harper's Weekly ran this illustration of a man and a woman observing the transit of Venus in 1769. Viewing the Sun without proper safety gear will cause severe eye damage.
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Early astronomers hoped the transits would allow them to pin down distances from Earth to Venus and to the Sun, but efforts proved disappointing. This year's event will be watched mostly for the sake of curiosity.
Some astronomers are interested in the transit as a way to hone skills for using the related celestial alignments for detecting planets passing in front of other stars and probing the atmospheres of those planets.
There is some strange mathematical sense to the years between Venusian transits. The circumstances repeat in this manner: 8 years, 121 years, 8 years, 105 years.
The next transit is on June 6, 2012 and will be visible from northwestern North America, northern Asia, Japan, Korea, eastern China, Philippines, eastern Australia, and New Zealand, according to NASA. Portions of the 2012 event will be visible in parts of North America, Asia, the Middle East, Europe and Africa.
Mercury crossed in front of the Sun last year. See photos.
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Related Links
Strange Venus
Venus and Earth are similar in size, mass and composition. Comparisons stop right there. Venus is hotter than an oven, and that's not just a saying. Astronomers once speculated whether it was a desert world or perhaps an oasis. We know now:
Any astronaut who landed on Venus would be simultaneously crushed, roasted, choked and dissolved, scientists say.
Venus has no oceans and no moons. It is covered by thick clouds of sulfur and droplets of sulfuric acid. The dense cloud cover acts as a blanket to trap heat. Atmospheric pressure is 90 times what you are used to. The atmosphere consists mainly of carbon dioxide, which is called a greenhouse gas on Earth.
On Venus, a day is longer than a year and the rotation on its axis is backward. Some fine points:
- Mean Distance from Sun: 67.2 million miles (108.2 million km)
- Orbital Period: 224.695 days
- Rotational Period: 243 days (it backward compared to its orbit and to the rotation of other planets)
- Diameter: 7,520 miles (12,100 km)
- Mass: 82 percent of Earth
- Gravity: 91 percent as of Earth
- Atmosphere: 96 percent carbon dioxide
- Mean Surface Temperature: 855 degrees Fahrenheit (457 Celsius)
On the Record: The composer John Philip Sousa (1854-1932), interested in the 1882 transit of Venus, wrote the "Venus Transit March." Learn more.
SOURCES for this page: NASA's GSFC; Fred Espenak; RAS; ESO; SPACE.com reporting
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