Can you observe the Sun with the naked eye? Is there any difference? Can we expect any results from the observations? The answer to all these questions is affirmative and we will try to explain the how and why.

Together with the Moon, the Sun is the celestial object easier to observe but also the most dangerous. Contrary to the rest of the astronomical observations, the diurnal observations are about reducing the amount of light received by our eyes to avoid damaging the retina. There are many absorbent materials that allow this to be done but it is preferable to distrust most of them. Among the recommendable are the glasses that are usually used to observe eclipses or welder filters. You have to choose the densest one that we find (preferably one of nº 14). If in the store they do not have that number, we can choose one more transparent although to use it we must avoid that the sunlight reaches perpendicularly to the glass: inclining it more or less we will graduate the luminosity of the image adapting it to the needs. Other materials, such as mylar, are more expensive and difficult to obtain (a welder filter can be found in any hardware store for around € 3).

When we look at the Sun, already properly protected, we will see the shiny disk and possibly nothing else. If so, let's pay more attention or try another day. With a little patience we will perceive the first spots. While with a telescope you can see all kinds of structures, at first glance we will only see tiny black dots. The observation with the naked eye has the advantage that it is very easy to do (2 or 3 minutes are enough with a filter that fits in your pocket), but the drawback is that the number of spots we can see is much smaller than with the telescope. During a maximum of activity the probabilities play in our favor but, even so, we find ourselves with many days without spots, although there are also possible situations in which we observe several spots simultaneously.

At this point we may think that, next to a telescopic image, observation with the naked eye is worthless. Nothing is further from reality. The number of Wolf (R) that we obtain with the telescope is a count made from the number of groups and focuses. An increase in R may be due to the presence of many small groups with few spots, the appearance of some very large and massive groups with numerous spots, or both at the same time. When we observe the naked eye we are filtering all the small groups staying only with the larger ones, that is, we are selecting a very specific type of activity that does not exactly match what we observe with the telescope. This is where the true value of observation resides: the behavior of the activity associated with the large groups may differ from that shown by the rest of the groups.

In order to obtain a result, it is necessary to use a certain method that will simply consist in making a daily count of the visible spots with the naked eye (henceforth we will call this value SV). Unlike Wolf's number, we will not take into account if the spots are associated in groups or are isolated so that work, if possible, is simpler. In the end, every month we will calculate the average (SV). Many times SV will be less than 1 because, during the month, it is common to find at least one day without spots.

Click here to see the data of the last years.