The Sun, Radio Propagation and the Brasilia Planetarium


In recent years it is common for any radio listener or radio amateur to have become a specialist in reading data such as: A-INDEX, K-INDEX, X-RAY, MUF, among others…

But without a doubt, the one we pay most attention to is the famous “SFI” of the acronym in English (Solar Flux Index).

Which is very easy to interpret, the higher the number of sunspots, the higher the SFI value. It is taken as a good reference that the value remains above 100, in this way we ensure a good propagation in HF bands.

So, used to this, the first thing we do is check the SFI number on our computer and if the index is low, we don’t even turn on our transmitters or receivers, which I consider a serious mistake.

Ham radio penguins, and other radio enthusiasts, often monitor radio propagation during special events, such as total solar eclipses, as part of the HamSCI project. HamSCI QSL © Chris Mackerell Collection, Radio Heritage Foundation

That’s why when forecasting propagation conditions I decide instead of relying on data readings, to start from the very origin.

If the propagation depends on the SFI, it means that we are talking about the Sun but: How much do we really know about the Sun?

To answer this and other questions, I went to the planetarium in Brasilia (Brazilian capital), to interview Marcelo Domingues, an astrophotographer and member responsible for the CAsB (Clube de Astronomia de Brasília). Marcelo Domingues is also a member of BRAMON (Brazilian Meteor Monitoring Network) and is passionate about the Sun, he has been studying its activity for more than 30 years.

Let’s start!!

Marcelo Domingues and Martin Butera, in the planetarium of Brasilia DF

Martín Butera:  How could you define me What is the Sun?

Marcelo Domingues: The sun is a star, which is the center of our Solar System

The electromagnetic radiation emitted by the Sun generates heat and is transformed into solar energy that feeds plants through photosynthesis, determines the climate, allows human beings to carry out their daily activities, among many other functions.

Martín Butera: What is the sun made of?

Marcelo Domingues: The Sun is made mostly of hydrogen which at high temperatures converts to helium. This process causes a high concentration of energy to be maintained, which allows the star to continue to live. Quantities of nickel, iron, gold, oxygen, and many other elements that we know of can also be found on Earth.

Martín Butera: What are the parts of the Sun?

Marcelo Domingues: The Sun is divided into two zones, the internal zone and the external zone. The first is the center of the Sun, that is where the energy is created and it is made up of a nucleus, a radiant zone and the convective zone. Then follows the external part that is known as the solar surface, which is made up of the photosphere, the chromosphere and the corona, the latter is what we can see.

Martín Butera: How is energy produced inside the Sun?

Marcelo Domíngues and Martín Butera, talking about the sun, in the planetarium of the city of Brasilia

Marcelo Domingues:  In the innermost part of the Sun is where the magic happens. Hydrogen, which is in the nucleus, is transformed into helium produced by temperature reactions. This creates particles that carry electromagnetic radiation. Each particle then travels from the core to the last layer of the solar surface with the movement of boiling gasses. The process from the creation of energy to its arrival at the solar corona lasts more than 1 million years. It’s impressive, isn’t it?

Martín Butera: Does the sun move?

Marcelo Domingues: Yes, in fact everything in the universe is in constant motion and the Sun is no exception. Although we cannot perceive it with our senses, the Sun rotates on its own axis and it takes approximately 27 days to carry out this process. In addition, the Sun moves with the Solar System within the Milky Way, since it also rotates on itself.

Martín Butera: What are sunspots?

Marcelo Domingues: Sunspots are areas of intense magnetic activity. The magnetic fields in these areas are enormous, and as a result the surface of the sun is disturbed. This causes the surface temperature to drop in these areas, causing a darker area to be perceived, which we call sunspots.

Martín Butera: In addition to sunspots, are there any other phenomena produced by the sun that may be relevant to our communications?

Marcelo Domingues and Martín Butera outside the planetarium in Brasilia.

Marcelo Domingues: If of course an important one is the CME or Coronal Mass Ejection, this is an emission of plasma ejected from the Sun, which when hitting the earth’s atmosphere affects the terrestrial magnetism.

We also have solar flares, where the main effect on the earth is the increase in solar radiation received, this radiation covers the entire spectrum of electromagnetism.

Other elements are X-rays and ultraviolet rays, which generate some kind of effect on radio communications because it affects the ionization levels of the atmosphere, specifically the friend of all radio listeners and radio amateurs, the ionosphere (laughs…)

Martín Butera: How could you briefly explain to us, what is a solar cycle?

Marcelo Domingues: A solar cycle is the 11-year period in which the polarity of our star’s magnetic field changes.

In this cycle, the sun reaches a peak of activity for two to three years in that period and slowly returns to a dormant process for 3 to 4 years, slowly reactivating for 3 to 4 years again until it reaches its peak again.

These multi-year observations help astronomers understand the signs that indicate the waning of one solar cycle and the start of the next. We are currently in solar cycle 25

Martín Butera: For us radio amateurs the previous cycle did not seem to be good, I ask you, would the sun be less active?

Marcelo Domingues: Cycle 24 was actually very inactive as well as very long, it is considered one of the worst in the entire tracking number.

If the sun were less active, it is something that we cannot determine, so easily if we take the last cycle 24 as a reference.

It’s just a trend, showing that the number of sunspots was lower, but this number is only a rough guide, because there is a considerable amount of variation in this.

The sun does not always look the same. There are cycles in which its activity is greater and in other cycles like the previous one its activity was very low, producing what we call “valleys”.

Marcelo Domingues and Martín Butera. (in the background we can see the great planetarium of the city of Brasilia)

So far twenty-four have been studied and we are at the beginning of twenty-five.

Martín Butera: According to your experience, what will be the propagation predictions for us radio amateurs, during cycle 25?

Marcelo Domingues: It is expected that propagation in the amateur bands will improve in the coming years.

I think the predictions can be good, a sign that the sun has already begun to “wake up” is the reversal of the polarity of the sunspots.

As I already mentioned, we are currently in solar cycle 25, the maximum of which, according to experts, could occur in 2024 and is expected to end in 2030.

Martín Butera: Finally I am curious to ask you the following, how many years of life does the sun have and how many does it have left?

Marcelo Domingues: The Sun, like all living things, will die at some point. It is estimated that our Sun has a life of approximately 10 billion years from its formation to the moment of its death. He currently has half the years of life. That is, it is 5 billion years old and it still has 5 billion more years to shine. Don’t worry, Martin, we have had the Sun for a long time (laughs…)

Final Conclusion

As we were able to read in the interview with Marcelo Domingues, the sun is complex, it is not enough just to interpret the propagation forecast charts.

Marcelo Domingues, Martín Butera and Lígia (Martín’s wife and photographer in this article), say goodbye

In recent years, many radio amateurs have complained that there are not good propagation conditions, which Marcelo Domingues confirmed, it was one of the worst cycles reported.

However, it was demonstrated that during the famous “Stay home”, in the first massive confinements of the Covid-19 pandemic, the radio bands were at full throttle, radio amateurs could be heard everywhere, the most popular radio contests beat Participation records and the new cycle 25, had only started a few months before the pandemic with almost no sunspots.

All that participation of active radio amateurs gradually diminished.

Perhaps the problem is not that we went through a frustrating solar minimum with the previous cycle and the Sun hasn’t woken up yet, but rather that I think we are at an all-time low for activity.

If we will have good conditions this year, we cannot know for sure, but the only way to find out is to turn on our equipment.

About CAsB

The Brasilia Astronomy Club (CAsB) is an association that encourages and brings together astronomy lovers. The CAsB is not for profit and is dedicated to the study, research, teaching and dissemination of astronomical science. The entity is basically made up of amateur astronomers, some with extensive courses in astronomy, and a group of consultants made up of professionals in the area, with a name recognized in the Brazilian scientific community.

About the Brasilia Planetarium

The Planetarium was inaugurated in 1974, and today it is linked to the Department of Science, Technology and Innovation of the Federal District, forming part of the ABP – Brazilian Association of Planetariums

We had access to the “SpaceMaster” star projector, according to legend, which arrived at the Planetarium in 1970, as part of a debt.

Brazil had sold coffee to East Germany and since they could not pay them in money, they sent these projectors as payment instead.

Together with the “SpaceMaster”, the projection of the Rio de Janeiro Planetarium and the telescope of the University of Brasilia (UnB) also came.

The projector is analog and is still active.

The “SpaceMaster” star projector, from the Brasilia planetarium
Martin Butera, Marcelo Domingues and the director of the Planetarium, in the dome together with the “SpaceMaster” projector

Excerpts of the video interview with Marcelo Domingues

Welcome sign to the Brasilia Planetarium

Tour of the Planetarium of the City of Brasilia

We take advantage of the visit of our friend Martin Butera to take you on a tour of the Planetarium of the City of Brasilia.

Located in the Monumental Axis, just below the convention center and in front of the Mané Garrincha Stadium, the Brasilia Luiz Cruls Planetarium – a tribute to the Belgian astronomer and geodesics based in Brazil and responsible for mapping the Central Plateau – is a haven of fun and know.

Science receives the visitor immediately, in the external area of the site, with a model of a suborbital rocket used by the Brazilian Space Agency. Very close on the floor, in a beautiful ceramic, there is a rose of the winds, a symbolic instrument of orientation.

In another exhibition, in the basement of the planetarium, the visitor can learn a little more about the Brazilian Space Agency (AEB), founded in 1994. Anyone who wants to play at being an astronaut and feel in the world of the moon, just take a photo next to the spacesuit of Marcos Pontes, the only Brazilian cosmonaut.

Take a Photographic Tour of some of the displays

We say goodbye to this fascinating article, from our friend and collaborator Martin Butera, carried out in an environment conducive to awakening curiosity, knowledge, disseminating science and reconnecting people with the sky, the universe, in short, the cosmos, something that goes hand in hand with our passion for radio.

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