ASTRONOMY ENTHUSIASTS are in for a treat tonight: the planet Venus will be travelling across the face of the Sun in a rare event not due to be repeated until 2117.

Known as the ‘Transit of Venus’, the event happens in two pairs every 243 years. It last occurred in 2004.

According to NASA, the Transit of Venus has helped astronomers gauge the distance between the Earth and the Sun, as well as to calculate the size of the solar system.

The best time for anyone in Ireland (weather permitting) to watch the Transit is very early tomorrow morning, at sunrise.

However, be careful not to look at the rising Sun with the naked eye. NASA has a list of recommended safety techniques outlining the proper use of solar filters, while Astronomy Ireland is holding an event at Skerries Harbour from 5am tomorrow where telescopes fitted with safety equipment will be available for public use.

NASA is carrying a live webcast of the event throughout today, with link-ups from different parts of the world to track the planet’s movements. The schedule is available online here tonight (note the times are based on Hawaiian time) and the NASA webcasts can be watched online here.

In the meantime, this NASA video explains the scientific importance of the Venus Transit:

(Video uploaded by SunEarthDay)

The planet Venus (the black spot above) crossing the Sun is photographed through a telescope at Planetarium Urania in Hove, Belgium, in this June 8, 2004 file photo. (AP Photo/Geert Vanden Wijngaert, PA File)