Be safe. A fraction of a second of magnified, unfiltered sunlight will sear your eye's retina irreparably. Observing the Sun directly without appropriate protection can damage or destroy retinal cells, causing temporary or permanent blindness.

The safest way to watch a transit is to observe an image of the Sun projected onto a screen through a telescope, binoculars, pinhole or reflected pinhole.

If you can get hold of them, welder's goggles rated at 14 or higher will protect your vision.

The event can be viewed without magnification using filters specifically designed for this purpose, such as an astronomical solar filter or eclipse viewing glasses coated with a vacuum-deposited layer of chromium.

However, the disk of Venus is tiny compared to the sun and not much will be seen. The once-recommended method of using exposed black-and-white film as a filter is now not considered safe, as small imperfections or gaps in the film may permit harmful UV rays to pass through.

A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and Earth, becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun.

The duration of such transits is usually measured in hours. A transit is similar to a solar eclipse by the Moon. While the diameter of Venus is more than 3 times that of the Moon, Venus appears smaller, and travels more slowly across the face of the Sun, because it is much farther away from Earth.

Wikipedia | NASA