International Year of Astronomy IYA2009

This is the first of a series of articles written by Christine (Coutts) Clement for the Thamesville Herald in honour of IYA2009.

It was published on January 14, 2009.


Since 1959 the United Nations has designated International Years in order to call attention to topics of global importance. For example, 1959/1960 was World Refugee year, 1985 was International Youth Year and 1986 was International Year of Peace. Initially, not every year was designated and there was only one topic per year, but this has changed. The year 2008 was the year of Languages, Sanitation, Planet Earth and the Potato!

In 2009, we are celebrating the International Year of Astronomy. IYA2009 commemorates the 400th anniversary of the first astronomical use of the telescope, by Galileo in 1609.

More than 130 countries are participating and an IYA web site has been set up at

Canada has its own site at

The vision of IYA2009 is "to help the citizens of the world rediscover their place in the Universe through the day and night time sky - and thereby engage a personal sense of wonder and discovery".

As 2009 begins, our neighbouring planet Venus shines brightly in the southwest sky in the early evening and will continue to do so until the end of March. One of Galileo's most important discoveries was what he saw when he pointed his telescope at Venus: he observed that it exhibited phases similar to those of our Moon.

We can readily see how the Moon's phases progress from night to night over the course of a month: new Moon, waxing crescent, waxing gibbous, full, waning gibbous, waning crescent and back to new Moon.

The phases of Venus are harder to detect because its apparent size in the sky is much smaller. However with his telescope, Galileo saw that Venus sometimes appeared as a crescent and sometimes gibbous. The accepted wisdom in the early 1600s was that both Venus and the Sun moved in orbits around Earth and that Venus should always be closer to Earth and appear as a crescent. The appearance of the gibbous phase indicated that Venus sometimes moves behind the Sun in the sky and thus must orbit the Sun. This observation played an important role in the acceptance of the heliocentric hypothesis that the Earth and other planets revolve about the Sun.

Since June 9, 2008, Venus has appeared in the evening sky but on March 27, 2009, it will pass between us and the Sun and switch to the morning sky. If you are not an early riser, enjoy Venus this winter. It will not appear again in the evening sky until mid-January 2010 after it passes behind the Sun.

In honour of IYA2009, I plan to write articles for the Herald from time to time so that readers can learn more about our place in the Universe. Stay tuned.

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