What is the importance of transits to astronomers?

Question

That's the main question up there and ...

-what knowledge have they gained from studying the transits of Venus and Mercury.

-why did Captian. Cook come to New Zealand?

And if you could add any interesting facts then that would be great.

I am looking for quality not quantity (although that would be alright as well.)

Answer 1

Simple answer:

Transits aided in our ability to identify our "place" in the solar system.  Edmund Halley purposed that transits of Venus, when viewed from various locations on earth, could help us determine the distance of earth from the sun.  (The inconsistencies of the eclipses of the Gallilean satellites of Jupiter  helped us determine we were 8 light minutes fomr the sun, however, the amount of space that light could travel in those 8 minutes was undetermined, for we had not found an agreeable distance of the earth from the sun).  The 1761 transit of Venus helped calculate our distance from the sun.  

As far as modern day goes, I don't think anything new can be learnd from transists of Venus and Mercury.  We are looking at the transists of planets over distant stars, or at least, that is the hope... The NASA Kepler mission will look at nearly 100,000  stars and try to detect earthlike planets orbiting them.  Hopefully, this will help us to continue to figure out where we fit in the universe...

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I suppose it is possible that Cook's voyage was in part to get to a point of the earth more distant from most observers of the 1761 transit.

"In 1766, the Royal Society hired Cook to travel to the Pacific Ocean to observe and record the transit of Venus across the Sun.[1]" (from wikipedia)

Answer 2

Cook went to New Zealand as part of the search for a southern continent.

While he was on on Tahiti he had to prevent his crew from removing iron nails from the ship's hull - they were being traded for sexual favours, metals being in short supply there.  

Answer 3

Transits have almost no scientific importance nowadays. They were considered important in earlier days as a way of measuring the size of the solar system and the speed of light, but we now have far more accurate ways of measuring these. Still neat to look at, though!