June 5, 2012 marks the last opportunity for viewers now living, anywhere in the world, to see a transit of Venus. After this one, the next visible anywhere on the planet will be in 2117, 105 years from now. For us in North America, the wait is even longer, as the next widely visible transit doesn’t even happen until 2125 (a very small portion of the 2117 transit will be observable from the West Coast).
The transit image here is from a glass plate of the 1882 tranist, courtesy of the United States Naval Observatory., with Venus appearing a distinct black dome. Interestingly,Tony Misch and William Sheehan have produced a Video of 1882 Venus transit (from EarthSky.org)
Obviously, since this is the last transit for more than 100 years, you will not have another chance to see such an event in your lifetime.
Many websites have described the coming transit in detail, so I will not go through it all again. Basically, transits occur when a planet (Mercury or Venus) pass directly in front of the Sun in a situation analogous to a solar eclipse (substituting Venus or Mercury for the Moon). Then we see planet as a small black dot, sihouetted agaisnt the brilliant Sun. This does not happen every time the planet passes between the Earth and the Sun simply because the slight difference in orbital inclination between the Earth and the other planet. As a result, the other planet usually passes above or below the Sun, and cannot be seen. Only when the conditions are just right do we see a transit (and even then the exact timing determines on which hemisphere of the Earth it will be observed).
For Mercury, which is much closer to the Sun, transits are visible somewhere on Earth every 7-8 years. The next visible from North America will be May 9, 2016.
For Venus, however, the time is much longer. Although transits come in pairs separated by 8 years (the last was in 2004, and not visible from North America), the pairings are more than 100 years apart. (Prior to the 2004 transit, the most previous one was in 1882, and the next after 2012 will be in 2117, which I have already said is essentially not visible in North America).
The transit image here is from a glass plate of the 1882 eclipse, courtesy of the United States Naval Observatory.
Depending of course on the weather in your area, you have several options for observing this “last of your lifetime” event. If you do not have the proper equipment yourself, the first and best option is to find an observing opportunity in your area, usually sponsored by colleges, museums or astronomical societies. Check locally, and if you cannot find anything, check the NASA Night Sky Network website.
In the Denver area, the Denver Astronomical Society, the Denver Museum of Nature & Science Gates Planetarium, Metro State College Physics Dept. and the Community College of Aurora Observatory are all planning observing events open to the public. Please see the DAS website for info at the Museum as well. For information on the Metro and CCA events, please check on June 5 for more specifics.
If you still can’t find anything in your area, email me and I let you know if I know anything in or near your city.
The transit begins (Contact I) at approximately 22:10 UT, which is 6:10 p.m. EDT, 5:10 p.m. CDT, 4:10 p.m. MDT & 3:10 p.m. PDT. The midpoint of the transit occurs at about 1:30 UT (6/6), which is 9:30 p.m. EDT, 8:30 p.m. CDT, 7:30 p.m. MDT & 6:30 p.m. PDT. The mid-point will be after sunset in the Eastern Time Zone, and for most in the Central Time Zone. The transit ends at roughly 4:50 UT (6/6), which is 12:50 a.m. EDT and 9:50 p.m PDT…. meaning that it is after sunset for all locations in North America except for portions of Alaska. Observers in Hawaii will be able to observe (cautiously) the entire event. (Note that these times are “geocentric”, meaning that they are calculated for an hypothetical (and impossible!) observer at the center of the Earth. The exact time will vary by up to a minute or two, depending on the exact geographic location of the observer on the surface of the Earth. You can get the exact times based on your location, here: http://goo.gl/lHrZi.)
If there simply are no organized observing opportunities in your area, you can observe the transit with very little equipment. However…. you must be careful. I think that most folks are smart enough not to ruin their eyesight by looking directly at the Sun, but in consideration of the horror stories I have heard, it is obligatory to caution everyone. Do not under any circumstances ever look directly at the Sun with your eyes, even if “protected” by sunglasses, photographic negatives (?) or welder’s glasses. And NEVER, EVER look at the Sun through a telescope or binoculars even if you have a so-called eyepiece filter. Just don’t do it. And if you use one of the projection methods below, be sure that no one, especially not a child or animal, looks at the Sun directly either through the telescope or binocular projection
You can use a pair of bincoculars or a small telescope to image the transit, but I must warn you on several points.
- First, as already stated, do not look through the binculars or telescope with your eyes. This should go without saying, but I am saying it again. Just don’t do it.
- Second, do not leave the projection on the Sun for too long. I suggest that you make a couple of minutes of observations, then turn the rig away from the Sun. After a few minutes, do it again. The reason is that the hot rays of the Sun are concentrated on the eyepiece of the telescope or binoculars and its gets very hot. Too much of this can shatter the glass and ruin the instrument.
- Third, aiming this device is not always easy. Use the shadows as a guide, since of course you cannot look through the scope or binoculars. You might want to mount the whole device on a camera tripod or other mount, and I also suggest that you do a practice run the day before the transit.
All that said, you can make a decent observation instrument with binoculars (or a small telescope) and a couple of pieces of stiff, white cardboard:
The basic idea is that you focus the image of the Sun through the binoculars (or telescope) onto a white card a foot or two away. You need to make a mask out of something like thick card stock or cardboard ot help block the sunlight from falling directly onto the projection card, which will make it much easier to see. This is all much easier as well if you can mount it on a tripod or other adjustable mount. You will have to readjust it every few minutes because the Sun appears to move in the sky.
Ordinary pinhole projection may be used as well,but probably will not work well because the dot of Venus is small. Instead, you could try what I call “pinhole reflection,” substituting a small mirror for the pinhole and projecting it about 20 feet to form a reasonably large image (~2 inches). Tiny mirrors for this are not easy to come by, so you can take a normal flat mirror and create a paper or cardboard mask for it with a small (1/8 to 1/4 inch) hole in it. The sunlight is then reflected from the hole onto some darkened wall nearby.
I have used this for years with students, and while a bit tricky, can form a pretty good image of the Sun that is big enough to show Venus. Just be short that the hole (cut-out) is no more than 1/4 inch across, and that the reflection (projection) distance is about 20 feet. Too far and the image is too faint, too close and while it is bright, it is not properly focussed. (The graphic is just a suggestion of one way to do this.)
Again, I suggest that if all possible, find a local museum, planetarium or educational institution that is providing observational opportunities. But if you can’t do that, and don’t like my particular ideas or graphics here, there are are number of other websites with excellent ideas for this transit. First off, try this page from EarthSky.org:
Then check out this page from the Exploratorium in San Francisco:
You also should visit the Exploratorium’s main transit page, which features a live video feed if it is cloudy in your area:
Still need more information? Please check out these sites:
And there is much more observing information on the Transit of Venus website.
And if that is not enough for you, NASA also has more here: The 2012 Transit of Venus.
(But wait, there is a partial lunar eclipse before dawn on June 4. Read about it here: Lunar Eclipse)