Thursday, June 7, 2012

2012: The Transit of Venus

On June 5 and 6, 2012 the planet Venus will pass in front of the Sun for the last time this century. Millions around the world will witness this rare astronomical phenomenon.


Venus appeared as a small dark dot crossing sun's face


What is a Transit of Venus?

A transit of Venus is the observed passage of the planet across the disk of the sun.  The planet Venus, orbiting the sun “on the inside track,” catches up to and passes the slower earth.  Venus, appearing as a small dot in the foreground, will move from left to right across the sun.  The word “transit” means passage or movement—in this case, across the face of the sun. 


What a transit of Venus looks like

Venus is about the same size as the Earth, but even though the planet is nearest to Earth at the time of a transit, it still looks very small at that distance. During the transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun. It takes about 6 hours for the planet to move from the left side of the Sun (ingress) to the right side (egress).


Venus will travel from left to right


When the transit is about to commence, the planet comes into contact with the disc of the Sun. The planet then enters slowly upon the disc of the Sun until it touches the solar limb on the inside. From this point Venus advances across the Sun’s disc and when the planet’s black silhouette reaches the other side it touches the limb of the Sun on the inside first. Then the planet begins to pass off the Sun’s disc and finally comes into contact with the solar limb for the last time and the transit is at an end.


Where and when to be to observe the transit of Venus

The transit of Venus lasts for about 6 hours and occurs on Tuesday June 5 and Wednesday June 6. When you’re living in North America, you will see the first part of the transit before sunset on June 5. European observers will see the last part of the transit after sunrise on June 6. When you’re in the Pacific, East Asia and above the Arctic Circle, you can see the transit in its entirety. The following map shows the world visibility of the transit:


Map of where June 5-6, 2012 transit of Venus will be seen


Frequency of Transits
Transits of Venus have a strange pattern of frequency.  A transit will not have happened for about 121 ½ years (prior to 2004, the last one was 1882).  Then there will be one transit (such as the one in 2004) followed by another transit of Venus eight years later (in the year 2012).  Then there will be a span of about 105 ½ years before the next pair of transits occurs, again separated by eight years.  Then the pattern repeats (121 ½, 8, 105 ½, 8).

 

Venus transit pattern of frequency

Transit of Venus timeline


If Venus and the earth orbited the sun in the same plane as the sun, transits would happen frequently.  However, the orbit of Venus is inclined to the orbit of earth, so when Venus passes between the sun and the earth every 1.6 years, Venus usually is a little bit above or a little bit below the sun, invisible in the sun’s glare.

A similar thing happens with our moon.  Every month the moon passes between the sun and the earth, yet we do not see a solar eclipse every month.  That’s because the moon’s orbit is also slightly inclined to earth’s orbit, so the new moon is usually a little above or a little below the sun.  The transit of Venus is essentially an annular eclipse of the sun by Venus.


The 2004 and 2012 transits form a contemporary pair separated by 8 years. More than a century will elapse before the next pair of transits in 2117 and 2125. During the 6,000-year period from 2000 BC to AD 4000, a total of 81 transits of Venus occur.


Observing the Transit of Venus
You can observe the transit in two ways: either by direct viewing (unaided eye or through a pair of binoculars or a telescope), or by indirect viewing (projecting the Sun’s image). Either way, you should be cautious not to look at the Sun without proper protection: the Sun’s light is so intense; it blinds you instantly if you do.


Viewing the transit of Venus through a telescope



Direct viewing can already be done with special eclipse shades. Venus will be just large enough to discern its silhouette on the Sun. If you are planning to use binoculars or a telescope to watch the event, you should apply a special solar filter to the front end. These devices will provide a magnified image of the Sun, so you can follow the transit up close.


Last sun show this century. Last transit of Venus in our lifetimes!






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