If there is an important day in our lives, it is the day on which we were born. We are told stories of that day, we have pictures and perhaps we can even be told if it was a sunny day or if it was raining. But, how was the sun on the day we were born, after all?
It is convenient to do a preamble about some characteristics of the Sun and its activity before we answer the question:
The Sun is constituted by several layers:
Two of the external layers are called photosphere and chromosphere. In the photosphere we can observe a phenomena called sunspots. They are darker regions due to the sinking of plasma caused by magnetic forces.
This is a sunspot example. As we can see, there is a black region, called umbra, surrounded by a dark region called penumbra.
Regarding the chromosphere: in this layer we can observe other solar activity phenomena like prominences, eruptions of plasma that extend outside the solar surface, in regions corresponding to the location of sunspots (in the photosphere).
When I refer to knowing how the Sun on the day I was born was, I mean to observe some phenomena of solar activity occurring in the photosphere and chromosphere.
How can we do that?
Using the archive of solar observations of the Astronomical Observatory of the University of Coimbra, available online here, where we can find over 30.000 images, dating from 1926 up to 2010.
To access the solar image on your birthday, we just need to use the search engine (left side in the below capture) of the referred astronomical archive.
Select the desired time interval (MM/AAAA a MM/AAAA) and filter by line type (“Tipo de Risca”).
The choice of the line type allows us to decide on the layer of the Sun we want to observe: K1-v line(of calcium) allows us to visualize the photosphere and K3 line (of calcium) and Alpha line (of the hydrogen) allows to observe the chromosphere. If we want to observe specifically prominences, we should select K3 line.
In case you want to understand what the lines are and why these allow us to visualize certain layers of the Sun, you can read about it here.
Sometimes it happens that, on some days, there is no solar image or, if there is, we see some stripes crossing it. These stripe, usually are due to clouds that cross over the instruments which collect the image during the process of taking the picture.
If there is no image on a specific day, that can be because of being a rainy day, that didn’t allow to take the picture, or due to bad image quality of the original photograph, among other reasons.
Even so, from now on, we can add the record of the observation of our star to the pictures and stories told about the day we were born. A day either of high or low activity, but always a record of a special day.