Mercury and Venus, whose orbits lie inside that of the Earth, usually pass north or south of the Sun at inferior conjunction (when the Earth and the planet are on the same side of the Sun). However, on rare occasions, if conjunction occurs when the orbit of the inferior planet crosses the ecliptic, the planet may make a transit in front of the Sun.

Planetary transits are actually a type of partial solar eclipse. Mercury and Venus are too small to eclipse the Sun when they move in front of it, and we see them cross the Sun’s surface as slowly moving black dots. Fortunately, unlike the narrow path of visibility for a total solar eclipse, planetary transits last for many hours and can be seen from more than half of the Earth’s surface.

Transit of Venus
The picture above, consisting of nine combined exposures, shows the complete sequence from the transit of Venus in June 2004. Igor Partiskovshi

This June, on the afternoon of the 5th (for those in North and Central America) or the morning of the 6th (for people in the Eastern Hemisphere), Venus will cross the face of the Sun. It is Venus’ second transit in the past eight years but the last one until 2117. Do not miss the chance to see the event!

Observers nearly everywhere in the world will get to watch at least part of this rare astronomical event. Those in North America will see at least a portion of it on the afternoon of June 5, while observers from Europe, northeast Africa, west and central Asia, and western Australia will see the transit after sunrise on June 6. South America will miss out.

No matter where you are in the world, the transit will start at 22:10 Universal Time (6:10 P.M. EDT, 5:10 P.M. CDT, 4:10 P.M. MDT, 3:10 P.M. PDT) on June 5. The event lasts for about six and a half hours. Click on the links for local times in an extensive selection of cities in the United States, Canada, and elsewhere in the world.

There are four phases during the transit: two at the start (ingress) and two at the finish (egress). “First exterior contact” occurs when Venus first appears to touch the Sun’s edge; “first internal contact” is the point at which the planet is fully upon the Sun’s disk but still contiguous with its edge; “second internal contact” occurs when Venus touches the opposite edge of the Sun, having crossed its disk; and “second external contact” is the moment when the planet’s trailing edge finally clears the Sun’s disk.

People with keen eyesight will be able to pick up Venus’ black silhouette across the face of the Sun with their eyes alone. However, you must use special “eclipse glasses” (not regular sunglasses) or some other safe solar viewing method during the transit. If you plan to use a telescope, do attach solar filters or project the Sun’s image onto a white flat surface. Under no circumstances should an observer look directly at the Sun without using an approved, safe filter!

You can also watch the transit online! Check out the live feeds below:

NASA TV – Live from Mauna Kea, Hawaii

Kwasan Observatory – Live from Japan