On June 5 (or 6, depending on where you live), you may have the opportunity to see the last transit of Venus in your lifetime!
A transit of Venus is when the planet Venus passes directly in front of the Sun, according to our view from Earth. It’s like a teeny, tiny eclipse of the Sun that you can only see with special solar-observation gear. (Proper eye protection is essential for watching a transit of Venus, else you risk blindness or permanent eye damage!) It’s a relatively rare alignment, but when it happens, viewers on Earth in the right place at the right time can see Venus as a small dot passing across the Sun. The next transit of Venus won’t happen again until December 11, 2117, so you’d have to live another 105.6 years (approximately) and still have your wits and eyesight about you in order to see another one.
Why are they rare?
If Venus’ orbit is inside Earth’s orbit of the Sun, shouldn’t we get a transit every time it passes between us and the Sun? No, because Venus’ orbital plane is inclined to Earth’s orbital plane by 3.4o–that means we are not traveling on the same plane–maybe you can think of it as Venus’ traveling a slightly higher road than the Earth does. While 3.4 degrees seems a small difference, it is enough so that Venus usually passes above or below the Sun (as seen from Earth) on most of its journeys between the Earth and the Sun, which happens five times every eight years, or one time in every 584 or so days. So they just don’t line up right all the time.
Why should we care?
Well, for one, it is one of the rarest of predictable astronomical phenomena, and it is fun to observe something that happens rarely and that humans have figured out how to predict. If you heard about the one in 2004, you might doubt its rarity; however, they occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of up to 121.5 years. Before 2004, the last pair of transits were in December 1874 and December 1882.
Two, it has historical value–this rare alignment is how we measured the size of our solar system. In the 18th century, scientists realized that by timing the event from different locations, the transits of 1761 and 1769 could be triangulated and give the distance between Earth and the Sun.
And third, scientists use transits of planets in front of distant stars to search search for other solar systems. For more information about this aspect, read about the Kepler Mission from NASA.
How can I see it?
You can use eclipse-viewing glasses (specialty glasses, NOT your normal sunglasses!) to view it, but without magnification, it will be very small. According to TransitofVenus,org: “At one minute of arc in size, Venus is near the visual limit of most people’s eyes. It’s tiny compared to the sun, which is about 32 arcminutes in diameter.” You can order glasses through Rainbow Symphony or Edmund Scientific. Rainbow Symphony is much less expensive, though, and they’re even cheaper per pair if you buy a large quantity. You can also make a pinhole viewer, like for viewing a solar eclipse through a projection of the Sun, or there are other methods of projection and magnification you can try. See the TransitofVenus.org page about viewing safety for complete details. You could also check out the live webcast from Mauna Kea, Hawaii, or look for a local astronomy club or university who may be offering a viewing. You can begin a search for astronomy club events with the NASA Night Sky Network.
Where/When can I see it?
From transitofvenus.org: “Much of the world can witness the 2012 transit of Venus. The date depends on what side of the International Dateline you will be observing. Observers in North America will see the transit in the evening on June 5, 2012, through sunset, so you want to have a clear western horizon.”
From an earthsky.org article: “Depending on where you live worldwide, the transit of Venus will happen on June 5 or 6, 2012. If you live in the world’s Western Hemisphere (North America, northwestern South America, Hawaii, Greenland or Iceland), the transit will start in the afternoon hours on June 5. In the world’s Eastern Hemisphere (Europe, Africa, Asia, Australia or New Zealand), the transit will first be seen at sunrise or in the morning hours on June 6.”
Basically, for everything you want to know about the transit (and more), you can go to http://www.transitofvenus.org. That site is devoted to the event and has information on the history of Venus transits, how and when to see it, lesson plans for educators, and much more.
For teachers and parents, there are many lesson plans available concerning the transit event, including those found here.