Venus passes between the Earth and the Sun tomorrow, October 29th. We usually don't see this phenomena as Venus is up during the day. However, Venus does not pass directly between the Earth and Sun. From our perspective, it passes slightly below the Sun. The Solar and Heliospheric Observatory (SOHO) has a camera with a coronagragph (a little disk the blocks the Sun) and gives us a nice view. Here is a pic from today.
Venus is the bright guy at the bottom. The streak is due to the fact that Venus is so bright, it bleeds over into neighboring pixels.
Now the main reason I mention this is that next time Venus undergoes inferior conjunction, it will pass directly between the Earth and the Sun. This is called a transit and will happen on June 5th/6th 2010 2012 (and I am telling you now, so no crazy people get to say in 2012 that no one predicted this before!) With proper solar filters or a solar telescope, you can see the disk of Venus on the face of the Sun. For most of North America, the transit will be in progress at Sunset (you can find more info about what you can see from your location here). We will see the first part but not the entire transit. The last time this happened was in 2004 and the transit was in progress at Sunrise. If you put the two together, I will have seen a whole transit!
Mark you calendars, because these are much more rare than you think. They occur in pairs separated by 8 years. After the 2012 transit, you have to wait until 2117 for the next one!
Reprinted with permission from the Half-Astrophysicist Blog.