What is a Transit?

A Transit is when a planet crosses between the Sun and the Earth, causing what might be called a little eclipse. Unlike eclipses, Transits have no real effect on the sun’s light to the earth. Mercury’s Transit across the path of the sun is virtually invisible to the naked eye, and telescopes using projection onto screens, or fitted with special safety filters, are required. Don’t try and look at the sun to see this Transit. You will definitely harm your eyes.

In an eclipse the sun is often almost obliterated for a short time and the earth goes dark. But because we view Mercury as being about 200 times smaller than the diameter of the sun, its Transit is like a spider crawling over a large football.

How often do Transits happen?

Transits of Mercury happen, on average, thirteen times in each century. In the 21 st century, the Transits will always happen either in May or November. In May the appearances will be between the 7 th and the 10 th . In November they will be between the 7 th and the 14 th .

There are also Transits of Venus, but these are much rarer. There have only been seven of these since the telescope was invented in the early 17 th century, and though they usually happen twice in a century, there were none at all in the 20 th .

Who can see it?

People living in North and South America, and the Caribbean, will see the beginning of the Transit. Australians, Indonesians and Eastern Asians will only be able to see the end of it.

But people living in the Pacific Basin, including those in New Zealand, will be able to see the entire Transit, which takes just under five hours. As a result many observatories are opening their doors to the public to give them a chance to see something that for most people will be a relatively rare occurrence. The next Transit to be fully visible to New Zealanders will not occur until 2052.

On this occasion, the Transit will ‘ascend’ across the sun. When the Transit occurred in May 2003, Mercury went the other way and ‘descended.’

When will it happen?

The transit commences at about 19:12 Universal Time (close to Greenwich Mean Time) on November 8th and ends at about 00:10 Universal Time on November 9th. Those who will be fortunate enough to see the Transit should check with a local observatory to find out when the Transit will take place in their local time.