Transit of Mercury
Published on Oct 25, 2006 at 2:24 pm.
4 Comments.
Filed under planets, skywatching.
In two weeks, November 8, 2006, the planet Mercury will pass between the Earth and the Sun. Actually, it does this every few months, but this time will be special because it will be almost exactly on the line between the Earth and the Sun, so it will appear to pass directly in front of the face of the Sun (as seen with a telescope). This near perfect alignment is called a transit.
Only two planets can transit the Sun: Mercury and Venus. While only two planets can transit, several asteroids have orbits that pass inside of Earth’s orbit, so they can also transit if the alignment is just right. While Venus transits are very rare, Mercury transits the Sun several times per century. Venus transits come in pairs, 8 years apart, seperated by spans of almost 120 years. The last Venus transit was 2004, and the next will be 2012. But the prior Venus transit was 1882, and the next one after 2012 will not be until the year 2117. The last transit by Mercury was in 2003, and there was one in 1999 prior to that. The next two Mercury transits (after the one this November) will be in 2016 and in 2019.
What can you expect to see when a planet transits the Sun? Well, the planet will appear as a small dot moving across the face of the Sun. Don’t expect rapid motion. It takes hours for the dot to cross the Sun’s disk. 
But, this is a rare enough occurance that it is worth your time to watch it. After all, how many people do you know who can say that they’ve watched a planet move across in front of the Sun? Well, OK, I know a lot of folk who’ve seen transits, but most people don’t! To get an idea of what a transit looks like, I found this photo on NASA’s Astronomy Photo of the Day site. It is a series of photos of Mercury passing in front of the Sun taken by Dominique Dierick during the last transit in 2003.
This year’s transit begins at about 19:12 UT on November 8, 2006. That is about 1:12pm here in Texas. The transit lasts about five hours until 00:10 UT (November 9), which is about 6:10pm here in Texas. Unfortunately, this will be just after sunset for us, so we’ll see the Sun setting with Mercury in Transit.
So, how do you see this great event? Well, first of all, don’t just go out and stare at the Sun! You can damage your eyes that way. Also, pointing any optical instrument at the Sun only intensifies the sunlight, so you can damage your eyes even faster with a telescope or binoculars, unless you have the right equipment. Here at my college, we have the proper equipment, so we’ll be watching the transit. There will be astronomy clubs, museums, observatories, and planetariums all over the place watching the event. So, find organizations like that in your area. For those of you who can’t find someone looking at the Sun, you can watch it near real time for yourself at the Solar and Heliospheric Observatory (SOHO) web site. There are ways to watch it yourself, though, if you are careful. Any safe way of looking at the Sun works. But, there are only a few safe ways of looking at the Sun.
Whenever there is an eclipse, I tell people about looking at the Sun. It isn’t any more dangerous during an eclipse or transit than any other time, of course, but it is more interesting. That is why more people look and get injured. The best way is to find someone who is an expert and has the right equipment. They sell solar filters for telescopes and binoculars. Any good astronomy supply dealer should have such equipment. Several good online ones exist, too, such as Orion or Astronomics, both of which I’ve used and been satisfied with their customer service. These filters block most of the sunlight, making it safe to look at the Sun. Also, there are inexpensive eclipse glasses that you can buy that allow you to look at the Sun. Number 14 welding glass (for arc welding) also is safe, but harder to find than the normal welding glass. Other methods commonly used to view the Sun, such as smoked glass or developed film really are not safe, and so should be avoided at all cost. All of these alternate methods are generally a bad idea. You are better off if you use a product specificaly designed to be safe for solar viewing.
Mercury will appear as a small dot on the face of the Sun. It might be hard to see without magnification, so a telescope (properly equiped with a solar filter) or a pair of binoculars with solar filters are your best bet.
An alternate approach, that does not use any filters, is solar projection. But, I don’t like to talk about it to people who are not familiar with telescopes, because it is too tempting for novices to forget and to look through their unfiltered telescope. I don’t consider this method safe unless you know what you are doing. For that matter, I don’t consider looking at the Sun at all to be safe unless you know what you are doing. So, if you are a novice, then go find someone who knows what they are doing (see my suggestions above).
But, if at all possible, try to see this transit, since they don’t really happen al that often.
-Astroprof
A Ler…-- Rastos de Luz on October 26, 2006 at 8:24 am: 1
[…] “Transit of Mercury“, no Astroprof’s Page. Ainda o trânsito de Mercúrio no dia 8 de Novembro, que não será visÃvel em Portugal; […]
Merc on November 4, 2006 at 6:57 am: 2
at work so I’m going to see it here
discoverychannel.ca/mercury
Astroprof’s Page » Watching the Mercury Transit on November 8, 2006 at 10:44 am: 3
[…] Don’t forget! Mercury will transit the Sun today. You can read my earlier post on the transit to find out more about it. While not a once in a lifetime opportunity, it is still rare enough that you should go take a look. […]
Astroprof’s Page » Photos of the Transit! on November 8, 2006 at 6:34 pm: 4
[…] Here are some photos of the transit for those of you who missed it. I was using a Nikon D70 at prime focus on an 8″ Schmidt-Cassegrain telescope (focal length 2000mm). Most of these were 1/1000 second exposures, effective ISO 200. […]