Why don't we see it often?
Although Mercury sits between the earth and the sun about three times a year traffic does not occur every time it is because the planets do not orbit the sun on the same plane, its orbits have a some slope with respect to the earth (taken as a reference). For example, the Mercury orbit has a slope of of 7º with respect to the Earth's.
It is through this slope that the times that Mercury passes between our planet and the sun ( above or below the solar disk ) no traffic occurs. So that it can be seen from Earth, the earth adaptation to the Mercury node is necessary. This means that the sun, mercury and the earth are aligned at the time of the planet's lower conjunction. This happens on average about 13 times every 100 years so it becomes a special astronomical phenomenon.
How to see it
To observe this phenomenon, you need yes or yes special eye protection, because directly looking at the sun causes serious damage to your vision irreversibly it can even cause injuries resulting in blindness . Therefore, it is very important that you follow the recommendations of the letter to enjoy this view of nature correctly. You CANNOT use: X-rays, smoked glasses, sunglasses of any kind, photo negatives, etc. No home method for direct observation is safe.
Because of the apparent size of Mercury seen from the earth, the use of instrumental is crucial Optical to see traffic. Even if you have special lenses that are approved to see the solar eclipses, you could not understand anything, as it is a very small black dot that parades in front of the solar disk. The ideal is to have a telescope or binoculars with a special sunscreen film for these cases. If you have either of these two elements but you do not have the special filter, DO NOT use them as you would seriously damage your eyesight. Don't take the risk!
indirect methods are a good option you can project the image of the sun onto a cardboard or paper, as long as you do not look directly at the sun it is safe.
And if I don't have a telescope with a filter?
Since most people do not have binoculars and telescopes with special filters to see this event on their own, we say that you can, for example, approach Planetarium Galileo Galilei in Buenos Aires, which will install telescopes and a "solar box" during the phenomenon of five and a half hours (free events).
Another alternative is to approach the Faculty of Exact Sciences and Naturales (Ciudad Universitaria, UBA), in front of the IAFE Building (Institute of Astronomy and Physics of Space), where a (free) dissemination activity for the observation of the transit of Mercury comes to take place from 9 to 15
You can also follow NASA's live broadcast from any device by clicking on this link. We are already in the countdown Get ready!