Today is your last chance to see Venus cross the sun for this lifetime.
For those with an astronomical interest, or for those who just like to see something that doesn’t happen every day, today is a good day. This evening will witness the transit of Venus, an event that has only happened six times since the invention of the telescope, and will not happen again for another 105 years.
The transit of Venus is, simply, when the planet Venus travels directly between Earth and the sun. It is similar to a solar eclipse, except that Venus’s distance from Earth and the sun’s relative size mean that, instead of blocking either all or a significant portion of the sun, it will appear only as a small dot moving across the face of the sun. Mercury and Venus are the only planets capable of this phenomenon, because they are the only two closer to the sun than Earth. Transits of Mercury are much more common that transits of Venus, but due to its greater distance from Earth and its much smaller size (less than half the diameter of Venus), they are also much more difficult to view.
The transit of Venus carries historical significance as it allowed early scientists to make much more accurate measurements of the distance from Earth to the sun than had previously been available. And it continues to be of scientific value. Scientists will be observing this transit to gather data on subjects ranging from how Venus’s atmosphere polarizes sunlight to the search for exoplanets.
To help determine when the transit will be visible where you live, the US Naval Oberservatory has developed an online transit computer here: http://www.usno.navy.mil/USNO/astronomical-applications/data-services/transit-us
For more information about how to safely view the transit of Venus, click here.