VLBI, or Very Long Baseline Interferometry is a technique used to determine very precise distances between radio telescopes in order to study the earth, it's place in the universe and to monitor the changes in both. VLBI uses radio signals from deep space to measure how the continents are moving, how the spin rate of the earth is changing, the motion of the pole and even how the earth 'wobbles' in space.
How do we benefit from VLBI?
Much of what we know about the interior of the earth has been gained through indirect observations. The size of the earth, it's shape, the changing orientation of it's polar axis and varying spin rate have all been determined by observing the stars and have all played a major role in our present understanding of the earth's structure.
VLBI produces very precise distance measurements on the earth's surface and assists us in our understanding of its interior, atmosphere and oceans. For example, did you know that one of the effects of the 1997 El Nino weather system was to lengthen our day by 0.6 milliseconds? Major weather systems like El Nino can literally cause the earth to speed up or slow down. How about continental drift? Did you know that the continents are pretty much in constant motion? North America and Europe are drifting apart at a rate of about 1 cm per year. Just think for a moment what an enormous task it must be to figure those facts out!
Another benefit of VLBI is its capability to accurately determine just where we are in the Universe. Just as the earth rotates around the Sun, the Sun rotates around our Galaxy. Our Sun is one of 100 billion stars that make up the Milky Way Galaxy - and they're all moving around the Galaxy at different speeds. Despite all this motion, VLBI observations make it possible to fix our position in the universe. A pretty tough task, but a necessary one to properly study the Universe.