For some 400 visitors to the York Observatory, Tuesday’s transit of Venus across the face of the Sun was worth the visit.
The transit of Venus is a rare astronomical event and astronomers worldwide watched the planet cross the Sun. Tuesday’s transit was one of a pair of crossings, the first occurring in 2004. The event will not be repeated until the year 2117.
As part of its public outreach, the York Observatory opened its doors on Tuesday evening and hosted a special information and viewing session. Led by Paul Delaney, a senior lecturer and astronomer in the Faculty of Science & Engineering, visitors were treated to an informative session and had a chance to view the transit in action, along with startling images of solar flares and sunspots.
An image captured by the York Observatory telescope of Venus in transit
Mother Nature cooperated and the skies cleared from 4:30 to 7:30pm, which was prime viewing time for the rare astronomical event. The telescopes in the York Observatory successfully transmitted clear images to visitors from around the world who tuned into the observatory’s interactive website. For three hours, the Observatory’s online chat room buzzed with commentary. Images in a variety of formats were collected by the gigabyte load for York scientists to examine in the coming days.
In the courtyard at the base of the Observatory tower, five observing stations were the focus of some 400 visitors’ attention. Four filtered telescopes, and one projected image by astronomy and physics Professor Emeritus Jim Laframboise, revealed an array of interesting phenomena, including clear images of sunspots that were visible prior to the commencement of the transit of Venus.
“Questions were flying about all aspects of solar astronomy at the outdoor viewing stations and in the Observatory,” said 
Delaney. “The ‘solar glasses’ were a huge hit and the more than 200 pairs we had on hand were quickly distributed. Everything took on a festive air as 6:04pm approached.”
Some of the viewing stations in the Chemistry-Life Sciences courtyard
Visitors observed the Sun, and one after another announced by 6:05pm that they could see the planet moving across the Sun’s face. The telescopes quickly confirmed first contact and everyone managed to get a view of Venus crossing the solar limb.
“It was easily seen with the telescopes and an inspiring image that everyone admired,” said Delaney. “My compliments to all members of the Observatory team assisting on the event, all undergraduate or graduate students of York. They fielded questions with patience, were accurate in their commentary and quick on their feet!”
Transits of Venus first gained worldwide attention in the 1700s, when the concept and size solar system was still a mystery. Astronomers knew what planets were in the solar system and had an idea of the relative spacing of the planets, but little was known about their “absolute” distances, or in other words, how long it would take to travel to reach each planet. The astronomer Edmund Halley realized the importance of the transit of Venus, and that by observing such 
events from locations around the world it would be possible to calculate or triangulate using angles the distance of Venus using the principles of parallax.
Quite a crowd gathered to watch the transit of Venus
The transits of Venus are used by modern astronomers to better understand the properties of planets outside the solar system. As Venus crosses the face of the Sun, there is a dip in light that can be detected and measured by very large telescopes, such as the Kepler space telescopes used by NASA, and there is a similar dip in light as planets in other galaxies transit their stars. The data collected is used to determine how many planets are orbiting stars and if any have atmospheres.
For more information, visit the York Observatory website.