Mercury transit of the sun 


The planet Mercury will make a rare transit of the sun during the morning of Thursday 9 November 2006. From the Territory, the transit is visible from sunrise, at 6.12am until 9.40am. Territorians will not see another for 26 years.

Only the eastern states can witness the complete event. Others see only part of the event.

Mercury takes almost five hours to cross the sun’s face and will do so 14 times this century. Although crossing far more often than Venus, which is the only other planet that can be seen transiting the sun from Earth, not all locations on Earth will witness the event.

‘Of the 14 transits due this century, Territorians will see only eight and only one, in 2052, will be complete. Our next visible transit is due on 13 November 2032,’ said local astronomy enthusiast Geoff Carr.

Planet transits were once very special events for astronomers, and hold special significance for Australia. The primary reason for James Cook’s third expedition was to observe the 1769 Transit of Venus from Tahiti.

The first observed Mercury transit was made in 1631. Astronomers had hoped that its frequent crossings could be accurately timed in order to calculate the distance of the sun, thereby allowing the distances of the other planets to be obtained and ‘unlock’ the solar system.

Observations were undertaken, but frustratingly, Mercury proved too small for accurate data to be gathered. Astronomers realised that such calculations could only be done by observing a Venus transit - due in 1761, over a century away!

Mercury’s size makes it a challenging target even for modern day astronomers. The black disk is only 1/194th the size of the sun; five times smaller than Venus’ appearance. Being near to the horizon means telescopic images are prone to shimmering and distortion. Top End clouds may be another barrier.

Amateur astronomers from many countries will be keenly observing the event, hoping to see the if the mysterious ‘black drop’ effect will elongate the round disk as it enters and exits the sun’s face.

The event will only be visible with a telescope fitted with proper solar filters. Remember – NEVER look directly at the sun without proper sun filters.

An excellent fact sheet on the transit and safe observing tips are available from the Australian Astronomical Society website.

For further information or interviews contact Geoff Carr on 0407 793 250 or 8920 1155 (w) 8985 4855 (h).