Chicago-area sky gazers preparing for the transit of Venus are in luck: All signs point to the Midwest having a good view of the rare celestial event Tuesday evening.
On Tuesday, Venus will cross will cross in front of the sun, a rare phenomenon that will not occur again for more than another century, in 2117. The event will appear in the form of a small black dot crossing the sun at sunset.
The Chicago Tribune reports that, in the Chicago area, about half of the planet's journey across the sun should be visible beginning around 5 p.m.
As is the case with solar eclipses, attempting to look directly into the sun during the Venus transit is dangerous, so NASA suggests using eclipse shades or a number 14 welder's glass. A telescope with a special type of solar filter can also be used.
For curious Chicagoans without such gear laying around the house, the Adler Planetarium is celebrating the occasion by offering up free admission to a viewing party between 4 and 9 p.m. Tuesday to Illinois residents with proof of residency. Adler staff and volunteers will be on hand to help visitors safely view the planet's cross-solar voyage using their special telescopes.
The Adler will also be screening the live NASA broadcast of the transit in addition to hosting a special exhibition on the history of the event.
Astronomers through the centuries have observed the transit of Venus for the purpose of refining the astronomical unit -- the approximate distance between the earth and the sun -- which is used to measure distances within the solar system.